circle_2
Nov 23 2006, 12:49 PM
What's the fastest disc in your throwing experience?
From an aerodynamics' standpoint, there are drag coefficient and frontal-area factors... Seems to me the disc with the lowest profile (akin to frontal area) would be fastest...like a Flick or 2nd run CE Valkyrie, for instance, but both of these discs are/were pretty doggone overstable! Taller, domier discs 'should' be slower... Perhaps some discs leave the hand/finger-tips faster as the inside-rim angles do vary from mold to mold?
I bring all this up cuz I'm inconsistent with the faster, wider/widest rimmed discs...Wraith, T-Rex, Venom, Flash, (Spectra?!) etc...all probably due to my smaller hands. I can get max D with a Wraith, but don't hit my lines consistent enough to make it a go~to D driver. I prefer an Orc/Crush-like rim width...
Happy Thanksgiving! :cool:
the_kid
Nov 23 2006, 02:43 PM
The Venom and Illusion were the fastest ones about 6 months ago but I think the Inferno is a lot faster(very subtle speed) and I have been tols that the new disc they are running is even faster and lover profile.
thatdirtykid
Nov 23 2006, 03:50 PM
I believe speed is usually defined by rim width (wider = faster) and pofile (lower profile = faster)
the_kid
Nov 23 2006, 04:02 PM
I believe speed is usually defined by rim width (wider = faster) and pofile (lower profile = faster)
This as well as the shape of the wing. A disc with a convexed wing will usually be faster then a disc with a concaved wing.
mikeP
Nov 24 2006, 10:02 AM
I hear Avery Jenkins can make a disc fast :D.
I'm not sure if convex is always faster than concave. I think that greater mass on the outer edge of a disc makes it fast, and this is a correlate of the convex rim. I think that the concave shape is faster given the same ratio of mass on the outer edge of the disc. A good example would be Millenium's two distance drivers, the Orion LS and LF. The LS is convex, the LF is concave. Looking at the disc's wings, the LF looks like the bottom part of the mold is bigger than the top. The LS bottom and top are much closer to the same size. The LS is thicker in the flight plate. So basically, they have similar weight ratios dispite the difference in wing types. The concave LF is clearly the faster of the two.
circle_2
Nov 24 2006, 10:18 AM
Good point about where the mass of the disc is situated reletive to the wing.
So...is 'fast' how fast the disc leaves the hand...or how well it maintains it's speed ~> as in how slowly the disc decelerates?
xterramatt
Nov 24 2006, 11:07 AM
how well it maintains it's speed ~> as in how slowly the disc decelerates?
Bingo, we have a winner. Give that man a cupie doll.
circle_2
Nov 24 2006, 11:24 AM
Do those inflate? :o:D
Discs like the QK and Inferno have a more rounded lower lip/edge...does this facilitate the disc ripping from one's grasp thus increasing potential launch speed? And, does this design work toward more glide?
I frequently fall into the trap that speed = distance...where glide may be a better predictor...though, slower discs tend to have more/better glide. What a fun conundrum!
the_kid
Nov 24 2006, 02:01 PM
Do those inflate? :o:D
Discs like the QK and Inferno have a more rounded lower lip/edge...does this facilitate the disc ripping from one's grasp thus increasing potential launch speed? And, does this design work toward more glide?
I frequently fall into the trap that speed = distance...where glide may be a better predictor...though, slower discs tend to have more/better glide. What a fun conundrum!
The bottom lip wasn't intended to give a faster release and I don't think it does but the rounded lip helps reduce drag. Most discs with squared lips catch a lot of air when flying but the rounded lip allows the air to pass over it without slowing the disc down.
Do those inflate? :o:D
Discs like the QK and Inferno have a more rounded lower lip/edge...does this facilitate the disc ripping from one's grasp thus increasing potential launch speed? And, does this design work toward more glide?
I frequently fall into the trap that speed = distance...where glide may be a better predictor...though, slower discs tend to have more/better glide. What a fun conundrum!
The bottom lip wasn't intended to give a faster release and I don't think it does but the rounded lip helps reduce drag. Most discs with squared lips catch a lot of air when flying but the rounded lip allows the air to pass over it without slowing the disc down.
Was that an S.A.T. question scooter???
DRIFT : whats this I hear about a course in Livingston @ some scout ranch?? Do you have any info on this?
the_kid
Nov 24 2006, 06:38 PM
Yeah there is a course at a summer camp but I heard it is really overgrown and super short. I talked to the main guy out there about cleaning it up but he never called me back.
alirette
Nov 24 2006, 08:36 PM
What's the fastest disc in your throwing experience?
Still the fastest I have thrown. STAR WRAITH !!! (http://www.innovadiscs.com/discs/starwraith.html)
Just gotta keep throwing it if you want to be more consistant. :D
the_kid
Nov 24 2006, 09:12 PM
What's the fastest disc in your throwing experience?
Still the fastest I have thrown. STAR WRAITH !!! (http://www.innovadiscs.com/discs/starwraith.html)
Just gotta keep throwing it if you want to be more consistant. :D
I love it when people say that. The wraith is Innova's fastest but not the fastest by far. I just received a little info on the new raging inferno protos and they are supposedly a good deal faster than the inferno which would make it the fastest disc out.
gdstour
Nov 25 2006, 12:55 AM
Boy do we need a plastic byron today!
What is a plastic Byron you ask?
Well it will be disc golfs version of the iron byron, which is now used to test golf balls and clubs head to head for performance and consistancy!!!
Circle 2 says some of the flatter longer winged discs are fast but he has trouble with consistency.
Let me take a guess at why;
There is something called Gyroscopic procession, which is the amount of rotation or RPM's needed to give the disc a stable flight.
If you cannot throw a big winged (really gyroscopic disc) with enough spin to match the speed it never reaches the Gyroscopic procession needed for a stable flight pattern.
In Laymens terms;
"That discs is too overstable for you",which would make you release it with the wrong angle and develop bad technique, especially for a golf shot that was supposed to be intended for distance.
This is called JERKY BOY for back handed throws. Most Sidearm throwers experience this as well because they cannot get anough rotation to meet their speed when trying to throw sidearm distance shots. This causes a natural progression for side arm throwers to throw more overstable discs, when it should be the opposite.
Players just keep trying to make up for it by turning the disc over more and more as the spin will never reach the Gyroscopic procession needed for the discs to fly flat.
Sidearm throwers should actually choose less over stable discs and slow the disc speed down to match their spin for better and more consistent results.
Very few side arm throwers rarely release a disc without off axis rotation which is why they ( the darksiders) usually migrate towards overstable discs.
Hopefully we will be developing a machine that can test velocity and rotation.
The future of choosing a set of golf discs will be developing a custom fit set of golf discs that will match up with the players velocity and Spin.
My answer to the question of what makes a disc fast and maintain its speed would be:
To find the most gyroscopic disc you can throw that will achieve the gyroscopic procession needed.
Having a disc that has the lowest profile and least amount of drag should do the trick FOR YOU!
Maintaining the speed and spin of a disc that has a lot of glide is a great equation for distance!!!
Golf ball dimples on discs will be the future, not just for speed and distance, but control, especially in cross wind coditions./
We have 2 models now and 10 more in the works.
Next year is going to be HUGE!!!!!! and so will your shots if your discs have dimples on them :cool::cool::cool:
Birdie
Nov 25 2006, 12:54 PM
I have played with the Dimple Tech Max.
And it is super flippy for me. But I flip Tee-Rex's and Wraiths over easily to. On the big shots that is, when I am trying to use my entier body to throw the disc. Sometimes paired with a loud audible snap, sometimes not. They flip.
But they do roll okay. But I can't get the DT Max to stay straight on a a roll for more than a few seconds. But I could see this disc working in the future, and I know Dave is determined to have the best plastic on the market, and I think he is well on his way.
How about that Brick Dave? I'll...uh...field test a few of those for you. :D
gdstour
Nov 26 2006, 04:15 AM
I have played with the Dimple Tech Max.
And it is super flippy for me. But I flip Tee-Rex's and Wraiths over easily to. On the big shots that is, when I am trying to use my entier body to throw the disc. Sometimes paired with a loud audible snap, sometimes not. They flip.
But they do roll okay. But I can't get the DT Max to stay straight on a a roll for more than a few seconds. But I could see this disc working in the future, and I know Dave is determined to have the best plastic on the market, and I think he is well on his way.
How about that Brick Dave? I'll...uh...field test a few of those for you. :D
The Scream DT max ( Ithink thats whats your talking about is more of a mid-range disc, I'm pretty sure we have concluded the dimples only work on the bottom of the wing for distance, but we may wind up trying to put some of the top 1st 1-2 inches and not in the middle.
the new dimple technology is closer to actuall golf ball dimples and not honey combed.
I love the regular scream DT but the Scream DT max is for slower armspeeds and roations than I have :D
gdstour
Nov 26 2006, 02:17 PM
It appears I used the term Gyrscopic procession a bit out of context.
The concept of the amount of rotation needed to match the speed is something that is very important to a stable long flight and I am researching the proper terminology.
http://www.boomerangs.com/gyroscope.htmlHere is alink to an example of gyroscopic procession,
This example can be related to the flight of a discs, but not exactly what I was referring to in my post above.
the_kid
Nov 26 2006, 03:30 PM
Dave was the Scream DT Max the one you let me throw on #15 at Endicott? The one with dimples on top and bottom right? If so that is a pretty good smooth stright flyer if you throw it like 60-70%.
circle_2
Nov 26 2006, 07:35 PM
Why does an Epic AND a boomerang strike the same chord? :D
nanook
Nov 26 2006, 10:19 PM
It appears I used the term Gyrscopic procession a bit out of context.
The concept of the amount of rotation needed to match the speed is something that is very important to a stable long flight and I am researching the proper terminology.
http://www.boomerangs.com/gyroscope.htmlHere is alink to an example of gyroscopic procession,
This example can be related to the flight of a discs, but not exactly what I was referring to in my post above.
As a physics teacher, I thought something sounded a bit funny. You did mean gyroscopic prEcession, right? As the boomerang link says, it is the tendency of the spin axis to change direction if a gyroscope is not perfectly balanced. With a top that is spinning but not perfectly vertical, gravity creates a torque that causes the stem of the top (spin axis) will rotate (wobble) around in circular path as the top spins. From what you described, I would think that for stable (straight) flight, a disc should have a small amount of precession. The rate of precession for a gyroscope is smallest if: the mass is large, the mass is located far from the spin axis (large moment of inertia), the angular velocity (RPM) is large, and the net external torque is small (or zero) .
Phun Physics Phact: The earth is a very good gyroscope. The rate of precession is very small. The earth's axis of rotation wobbles around just once in about 26,000 years. That means in a few thousand years Polaris won't be the "north star" any more!
nanook
gdstour
Nov 28 2006, 03:57 AM
We are trying to write a paper on the difffernece betwen Gyroscopic and centrifugal and the effect it has on gof discs.
We are also trying to get a hold of a chonograph(?) that can measure the speed of a disc( the radar gun doesnt seek like it is accurate enough) as well as the RPMs or Rotation.
does anybody have a way to measure the amount of spin they can put on a disc?
baldguy
Nov 28 2006, 09:08 AM
do it mythbuster-style. print a thick, visible line on the radius of the disc and a measuring bar set on the floor. set up a high-speed camera above the thrower, and record several throws. the high-speed should be able to accurately measure the number of revolutions per second as well as the speed of release.
superq16504
Nov 28 2006, 01:27 PM
I was thinking some kind of wall to throw along and use a high speed camera then afix some kind of light or even dark mark to the top of the disc (led taped to the edge pointing out) then filmed from the side you would be able to get RPM based on rev per second. plus if you set up the bar lines on the wall the high speed will also allow you to get MPH
On a related note I went and got fitted for clubs a few weeks ago the pro shop had a virtual range. basicly a tee set up in front of a net with cameras and what not hooked into a pc. there is a program they use so you hit balls into the net and the cameras pick up launch angle spin (top bottom and side) and relates it all to the pc where you get real time distance and shot shape. ( I was hitting baby draws to about 260) the machine was very close to what I would have thought based on my normal shots.
perhaps there could be a way to merge this tech to DG.
I have also seen PAR TEE (http://www.optronicsltd.com/) golf simulators not quite as tech (no spin angle) but I have still shelled out 10 bucks to play 18 simulated holes with my own clubs
27493
Nov 28 2006, 08:21 PM
I don't think there is anything "centrifugal" about a golf disc. Centrifugal indicates movement away from the center. Golf discs are solid, so nothing is moving from the center toward the edge. Also, discs with moving parts will not be PDGA approved. There may be something centrifugal in the act of throwing a disc, but not in the rotation of the disc itself. Check out the "Research" link on the Discwing web page for good flying disc science.
I don't think there is anything "centrifugal" about a golf disc. Centrifugal indicates movement away from the center. Golf discs are solid, so nothing is moving from the center toward the edge. Also, discs with moving parts will not be PDGA approved. There may be something centrifugal in the act of throwing a disc, but not in the rotation of the disc itself. Check out the "Research" link on the Discwing web page for good flying disc science.
Let the science pissing match begin in 3....2......1.......
circle_2
Nov 29 2006, 11:21 AM
...seems like an Epic should wobble...some. :eek: :p
Parkntwoputt
Nov 29 2006, 04:55 PM
...seems like an Epic should wobble...some. :eek: :p
Some is an understatement.
The only time I have thrown an Epic backhanded, it wobbled sided to side in a ridiculous manner. (At least from my view point, I am sure a top view would reveal the wobble in a circular pattern.)
DreaminTree
Nov 29 2006, 06:49 PM
I would guess that centrifugal force is part of what makes a disc turn over at the beginning of its flight. As the disc moves through the air, it forces some of the air particles to rotate through a semi-circular path around the outer profile of the disc. That motion causes a reactionary force toward the center of rotation (the disc). Use the position of the disc as a reference frame but ignore rotation- since the air is curving around the disc faster on the left side (for RHBH) than the right, the net reactionary force on the left side is greater than that on the right. This helps the disc to bank. I would assume the force due to lift is probably more significant here anyways, since the left side will likely have more lift that the right also. At the end of flight, the disc has slowed down enough for gyroscopic forces to become dominant over lift and reactionary centrifugal force.
Just a guess. :D
circle_2
Nov 29 2006, 07:03 PM
Yup, makes sense, but it's basically never corroborated (much) in this forum. I think we agree that a fast throw with less spin will cause/create/contribute to turnover...ie -> a sidearm throw can pack a lot of speed & less spin (relatively) and will turnover easier.
When you see a (dyed) disc launch, it appears to not be spinning much initially, but then it seems to hit a hyperspin/speed and the RPMS appear to dramatically increase 50-80' out. Is it during this freshly-launched time that the disc is more understable (less spin) and thusly flips up?
What really gets me are those long-arse hyzerflip throws that flip up and go and go and go WAY out there...and THEN turn over...? What gives here?
AviarX
Nov 29 2006, 07:33 PM
when i get a disc to hyzer flip, i am throwing with a lot of spin and hyzer. the spin seems to hold the hyzer as long as it can and then it's all over and the flipping takes over ...
gdstour
Nov 29 2006, 09:12 PM
I don't think there is anything "centrifugal" about a golf disc. Centrifugal indicates movement away from the center. Golf discs are solid, so nothing is moving from the center toward the edge. Also, discs with moving parts will not be PDGA approved. There may be something centrifugal in the act of throwing a disc, but not in the rotation of the disc itself. Check out the "Research" link on the Discwing web page for good flying disc science.
Let the science pissing match begin in 3....2......1.......
please read patent number 4568297.
the whole concept of the patent is that the energy moves away from the center of the fleiible object when thrown and towards the mass and makes the disc expand, lowering the profile and reduciong the dome.
as it decelerates the energy comes back to the ceneter and the flexible object "domes Up".
This is supposed to be the utilty function of the invetion.
It has nothing to do with a triangular rim, only mass at the rim causing this pheneomom.
This is straight terminolgy from the embodiment of the 1st claim of the 297 invetion.
Maybe Dave D can chime in hear he would most likely be the expert as it is his patent!
So unlees the patent IS BS( which could still be the case) I would say the at the minumum at least the energy moves.
I think it some law of physics where energy moves towards the mass or something like this.
A disc can have more gyrsocpic weight distribution or less which in return would make the wieght distribution more contrifugal or less in the object as it
Of course this is not a pissing match its a discussion.
NASA BOeing, macdonnell douglass and many others have been doing research on circular displacement for over 50 years, most of it is very secret and unpublished, when you do find information it is usually very ambiguous.
One of the only things I have been able to find was info on an anmanned aircraft that operated off of ball bearings that were spinning causing Gyroscopic effect that caused energy and that energy was hanressed causing somewhat of a perpulsion that was used for directing the flight of the craft.
pnkgtr
Nov 30 2006, 05:07 AM
What really gets me are those long-arse hyzerflip throws that flip up and go and go and go WAY out there...and THEN turn over...? What gives here?
If the nose is down the disc will pick up speed as it descends. Which in turn makes it less stable again.
circle_2
Nov 30 2006, 11:14 AM
Interesting postulate! Though I've seen this phenomenon occur w/o the decension (sp!). Heck, I've done it with Rocs and XLs... Back when George Smith threw DX Firebirds, this late-turnover flightpath was a common line for him when throwing for big distance... A common element is a beat-up disc...and, of course, wind direction.
citysmasher
Nov 30 2006, 05:45 PM
I would guess that centrifugal force is part of what makes a disc turn over at the beginning of its flight. As the disc moves through the air, it forces some of the air particles to rotate through a semi-circular path around the outer profile of the disc. That motion causes a reactionary force toward the center of rotation (the disc). Use the position of the disc as a reference frame but ignore rotation- since the air is curving around the disc faster on the left side (for RHBH) than the right, the net reactionary force on the left side is greater than that on the right.
Just a guess. :D
I am guessing also, I guess we all are...
This could be the force that leads to "bad" precession. If the drag force on left side of the disc is greater, then a precession of nose up would be created. If the disc has a higher moment of inertia this precession force would be greater.
gdstour
Nov 30 2006, 08:43 PM
I am doubting that a disc will pick up speed after it is released regardless if it nose down.
Are you thinking that if a disc hits the Apex of the flight it could in theory gain momentum as it is falling to the earth.( BTW Apex is also the name of our new tee-birdish golf disc coming out soon !!!)
It would be interesting to get a chronograph on a discs flight from start to finish.
I know we have several models that seem to barely declerate from releae to landing.
A disc is trabeling the fastes the monet it is released, I'm pretty sure it cannot gain any velocity, but more gyroscopic discs mantain their speed longer then this that are more centrifigal.
citysmasher
Nov 30 2006, 08:59 PM
I am doubting that a disc will pick up speed after it is released regardless if it nose down.
A disc is traveling the fastest the moment it is released, I'm pretty sure it cannot gain any velocity, but more gyroscopic discs mantain their speed longer then this that are more centrifigal.
Actually, it is impossible for the disc to accelerate once it leaves our hand. That would be like the disc gaining energy, which is impossible. The disc will start losing energy the second it leaves your hand, so it is decelerating immediately.
Actually, in terms of time, low gyroscopic discs maintain there flight much longer before falling out of the sky. If you could get an Inferno to have the hang time of a Wizard, you would have something.
pnkgtr
Nov 30 2006, 09:03 PM
If something is thrown straight up there is a point where it actually stops. As it drops it picks up speed again. The same is true when it is thrown a 45 degrees or 33 degrees. There is a point where it may increase in speed but still not be as fast as it was when it left your hand.
ck34
Nov 30 2006, 09:11 PM
I think a disc could potentially be thrown so it goes faster later than the release speed but it would have to be a steep downhill shot down a mountain perhaps. I'm guessing that the terminal velocity of a disc just tossed out an airplane is faster than the fastest throw a player can make. In which case, there are likely locations where a hole could be created that might produce enough disc acceleration during the time of a flight. But this is a highly specialized situation.
citysmasher
Nov 30 2006, 09:13 PM
If something is thrown straight up there is a point where it actually stops. As it drops it picks up speed again. The same is true when it is thrown a 45 degrees or 33 degrees. There is a point where it may increase in speed but still not be as fast as it was when it left your hand.
Gravity is always acting on all objects on the Earth, so I guess you could say that the disc has energy from gravity subtracted as it goes up and added back when it comes down. So, all energy from gravity is a sum gain.
All objects on the Earth will fall (accelerating) at the same rate if not impeded by some other force (as in the case of a parachute).
You would also DO NOT want any disc to accelerate toward the ground ever... NOT accelerating toward the ground is called "glide" or hang time.
Increase the hang time of any disc at a given speed and it goes further.
An interesting experiment would be to measure hangtime of a particular thrower with a range of discs. Maybe all discs have the same hang time for a given thrower (say given a reasonable trajectory range), that is why the difference in distance between a putter and a long range driver.
true increases in distance must come from making the disc "fly" not just shoot out like bullet.
citysmasher
Nov 30 2006, 09:17 PM
I think a disc could potentially be thrown so it goes faster later than the release speed but it would have to be a steep downhill shot down a mountain perhaps.
If you threw the disc straight down from a telephone pole it would leave your hand with the acceleration equal to the speed you supplied with the throw with the force of gravity added.
As you raise the trajectory up from straight downhill the acceleration due to gravity decreases in relation to the angle.
This is trajectory physics 101.
DNA_2
Nov 30 2006, 09:20 PM
If you threw a disc straight up the disc would not actually stop. Actually a disc at the top of its apex if you threw it straight up would reach a velocity of 0 but the acceleration is on the way up and way down would remain constant.
Just look in your physics book im sure this is correct
citysmasher
Nov 30 2006, 09:26 PM
If you threw a disc straight up the disc would not actually stop. Actually a disc at the top of its apex if you threw it straight up would reach a velocity of 0 but the acceleration is on the way up and way down would remain constant.
Just look in your physics book im sure this is correct
The velocity would be 0 at the apex, that would mean it is stopped.
The acceleration is the rate of CHANGE of velocity, and is constant due to gravity.
The potential energy of the disc goes up on the way up, and goes down on the way down.
ck34
Nov 30 2006, 09:32 PM
On a straight down throw, the disc has a specific velocity at the point of release. The question is whether the deceleration forces from air resistance are greater or less than the gravitational acceleration force. If gravity is greater, the disc will start to move faster. However, the deceleration force from air resistance depends on the attitude of the disc. The more the edge strays from the downward vector, the more resistance and deceleration which may become greater than gravity causing the disc to slow. Without knowing the dead drop terminal velocity for a disc, we're just guessing. Because the aerodynamics are so variable with a disc flopping around in a dead fall, it may be hard to determine. For people, I think the number is something like 120mph.
ck34
Nov 30 2006, 09:37 PM
The velocity would be 0 at the apex, that would mean it is stopped.
No, it just means its velocity is passing thru the zero value on the vertical vector. Since an unbalanced force is still working on it, the disc is just passing on a continuum from a positive upward speed to a negative upward speed.
the_kid
Nov 30 2006, 09:52 PM
If something is thrown straight up there is a point where it actually stops. As it drops it picks up speed again. The same is true when it is thrown a 45 degrees or 33 degrees. There is a point where it may increase in speed but still not be as fast as it was when it left your hand.
Gravity is always acting on all objects on the Earth, so I guess you could say that the disc has energy from gravity subtracted as it goes up and added back when it comes down. So, all energy from gravity is a sum gain.
All objects on the Earth will fall (accelerating) at the same rate if not impeded by some other force (as in the case of a parachute).
You would also DO NOT want any disc to accelerate toward the ground ever... NOT accelerating toward the ground is called "glide" or hang time.
Increase the hang time of any disc at a given speed and it goes further.
An interesting experiment would be to measure hangtime of a particular thrower with a range of discs. Maybe all discs have the same hang time for a given thrower (say given a reasonable trajectory range), that is why the difference in distance between a putter and a long range driver.
true increases in distance must come from making the disc "fly" not just shoot out like bullet.
sounds like a good experiment for my physics class since we are doing centrifugal forces. /msgboard/images/graemlins/smirk.gif
the_kid
Nov 30 2006, 09:55 PM
Actually a disc at the top of its apex if you threw it straight up would reach a velocity of 0 but the acceleration is on the way up and way down would remain constant.
Just look in your physics book im sure this is correct
Yup we all missed this question when we 1st saw it. Not sure about the stopping part. I can find out though.:D
citysmasher
Nov 30 2006, 10:06 PM
No, it just means its velocity is passing thru the zero value on the vertical vector.
If the object were simply moving up and down it would stop. That is the condition that I was referring too.
In the case of a disc, it does not stop because it is still moving horizontally....but that is what you said.
Let's examine this...
Does the disc actually pick up speed? No, not really.
Looking at the horizontal vector it is constantly slowing due to DRAG. The LIFT is constantly decreasing with speed, some discs worse than others.
In the vertical axis there is a force vector down due to gravity, and a lift vector up due to LIFT. This is until the disc hits it apex.
From the apex, you have the same forces but you have to add the force of DRAG up (.
So, going up to the apex drag is bad, down from the apex, drag is good.
So, if you add drag to a disc it will slow the descent but take away energy to the apex.
...but then do it too much and it stalls...
...disc flight is very, very complicated.
ck34
Nov 30 2006, 10:13 PM
If the object were simply moving up and down it would stop. That is the condition that I was referring too.
Nope. Just like Scooter posted above. Not even if there's no horizontal motion. It looks like that but not from a technical standpoint. It's just as I stated above. The object is just passing thru a velocity of zero on a continuum. Accelerating from 8 to 10 mph is no different from accelerating from -1 to +1 mph.
27493
Nov 30 2006, 10:16 PM
I stand corrected. Take a golf disc made out of the most elastic stuff you can find and spin the heck out of it. It will increase in diameter. No doubt about it. You have your centrifugal golf disc. Which disc are we going to use to test the hypothesis? Omega SS? Probably couldn't pull it off with my "S" Illusion ;)
Alacrity
Nov 30 2006, 10:31 PM
Force = Mass * Acceleration
Once the disc leaves your hand you have placed a certain amount of force to the disc by the acceleration from your follow through. If the disc was a sphere, then the disc would constantly decelerate due to the force applied by air friction, however a disc is not a sphere and air friction can vary as the disc changes it's movement through the air. I believe the phenomenon where a disc appears to speed up, is probably due to two factors. The first is that the force due to air friction changes as the disc direct surface area to the wind changes. Imagine an over stable disc is thrown on a slight ani, nose down back up. As the overstable disc moves into a flatter angle to the wind the force of air friction actually decreases and the speed of the disc appears to increase, not because it really speeds up, but because the rate of deceleration decreases. Kind of like a car taken to a certain speed and then removing the gas and allowing it to slow then hitting the cruise control and it maintains. To the watcher it appears the car sped up.
The second thing is the "Flexing" of the disc. That slight change in the spin on the disc, which is actually due to centripital force not centrifugal, once again changes the dynamics of the forces of air friction. I don't know this, but I am guessing the point where the disc structure changes coincides with the point an overstable disc comes out of the ani.
Now as for how a disc can go straight for some distance and then ani, once again this is just me guessing, but the more spin you put on a disc the more it will hold a line. Probably due to the extended flex of the disc, but I am not sure. Once the speed decreases the disc then flies as the structure of the disc dictates, hyzer for overstable and anhyzer for understable. However there is one more thing to consider. Once the spin reduces enough the air foil created by the disc will require the disc to fall back in the direction opposite to the spin. Imagine the disc is grabing the air and rolling across it, but since air is slippery that curl against the spin is slow. Ed Headrick wrote several small articles about this effect.
For those of you that have never seen a disc "speed up" after a release, grab a new Pro-Line Wraith and snap the crap out of it with a very slight ani. The point at which it turns back straight it will definitely appear to speed up. I am sure other discs do this, I have seen it in T-Rex's and other discs as well, it is just so obvious with a new Wraith.
DNA_2
Nov 30 2006, 11:34 PM
Like Chuck, scooter, and my self said the velocity is zero but it never actually stops,
Just to let you know, I minor in physics here at the University of South Carolina.
the_kid
Nov 30 2006, 11:40 PM
Like Chuck, scooter, and my self said the velocity is zero but it never actually stops,
Just to let you know, I minor in physics here at the University of South Carolina.
I plan on majoring in it at UT :D
ck34
Nov 30 2006, 11:44 PM
I plan on majoring in it at UT
Don't "stop" those plans...
the_kid
Nov 30 2006, 11:46 PM
I plan on majoring in it at UT
Don't "stop" those plans...
I may go into history or architechture though
DNA_2
Nov 30 2006, 11:50 PM
Scooter, if your gonna do it stay commited because it is by no means easy. Whatever you do, architecture or physics, it will be worth it. Good luck
the_kid
Dec 01 2006, 12:01 AM
Thanks man. I took the ASVAB test and basically got a perfect score(didn't socre perfect in auto mechanics) so the millitary is trying to talk me into possibly going to westpoint. :D
DNA_2
Dec 01 2006, 12:49 AM
Sorry for thread drifting but thats funny because my grandfather and my old roomate went to westpoint. Either way UT or Westpoint you cant go wrong.
pnkgtr
Dec 01 2006, 04:37 AM
The question I was answering was concerning a disc going neg at the end of it's flight. If I hadn't seen it I don't think it would have ever occured to me. There was a local player that threw a beat DX Valk. He had an unusual release. He'd release the disc high and hyzer with the nose down and throw it very high. Kind of lifting the disc into the air. So out of his hand the disc is going left, it then corrects itself and straightens to a hyzer. Then as it slows because the nose was down it picks up speed and goes neg again. Instead of an S turn it would do a flattened W. I've never seen anyone else throw a disc like that.
citysmasher
Dec 01 2006, 08:30 AM
For those of you that have never seen a disc "speed up" after a release, grab a new Pro-Line Wraith and snap the crap out of it with a very slight ani. The point at which it turns back straight it will definitely appear to speed up. I am sure other discs do this, I have seen it in T-Rex's and other discs as well, it is just so obvious with a new Wraith.
I do not see this happening in zero wind.
All of the "kicking into turns" and "accelerating into a flex" that you see are usually due to a wind component. In this case the disc could actually ACCELERATE due to an outside force once it has left your hand. All big distance throws have a wind component. Using the wind to boost the disc from the apex is one of the most important aspects throwing monster throws.
Oh, and there is always wind blowing. Especially when you get above 50' in the air.
Alacrity
Dec 01 2006, 09:10 AM
I have seen it happening in near zero wind conditions and with the wind coming from different directions. It is not just the wind, it is also the disc. Regardless of that it is still F=MA. Now I do believe that you could gain velocity from the wind by changing the angle of the disc to the wind. A very good example is a boat tacking into the wind. By changing the angle of the sail to the on coming wind the boat gains force as a component of the wind force is transferred to the boat on a tangent to the wind. In this case you are right the disc did accelerate due to an outside force. I was not referring to that and I am not sure on a line dirve following a typical S pattern that you can tell an increase in velocity, but I will admit that I don't know.
I do not see this happening in zero wind.
All of the "kicking into turns" and "accelerating into a flex" that you see are usually due to a wind component. In this case the disc could actually ACCELERATE due to an outside force once it has left your hand. All big distance throws have a wind component. Using the wind to boost the disc from the apex is one of the most important aspects throwing monster throws.
Oh, and there is always wind blowing. Especially when you get above 50' in the air.
citysmasher
Dec 01 2006, 10:18 AM
I have seen it happening in near zero wind conditions and with the wind coming from different directions. It is not just the wind, it is also the disc.
In this case you are right the disc did accelerate due to an outside force. I was not referring to that and I am not sure on a line dirve following a typical S pattern that you can tell an increase in velocity, but I will admit that I don't know.
I don't know either, but this is really getting the noodle into high gear!!!
Now, there is of course the acceleration due to gravity that the disc (due to lift and angle of attack) converts into forward motion. Like a plane that dives downward, picks up speed and then pulls out at some lesser angle and glides on the gain in velocity, or simple glides at a constant rate downward, picking up speed the whole way.
Balke on Discgolfreview.com talks about a disc coming out of a turn nose down. Some dics have to much more nose down than others to gain velocity out of the turn. More overstable discs require much more severe angles out of the turn to "drop" and gain speed. If the angle is severe enough to get the disc to drop and gain speed on the downhill, the disc THEN has to be overstable enough to RECOVER and glide out.
Kind of like watching a hand launch glider dive and recover, dive and recover, and kind of porpoise its way around without losing a lot of altitude.
My point of this is that there has to be SOMETHING acting on the disc for it to accelerate. The disc does not accelerate by itself, that is impossible. It is designed to make use of outside forces.
To answer the question of the thread, all disc are the same speed when they leave your hand if thrown with the same force. So, all discs own my Avery Jenkins are fast. :D
As for maintaining speed, the lowest drag discs must be the fastest, and the designs with the best aerodynamics to maintain slight nose down are the fastest.
Anything that adds drag or forces the nose up, ultimately slow the disc.
abee1010
Dec 01 2006, 11:47 AM
Like Chuck, scooter, and my self said the velocity is zero but it never actually stops,
Just to let you know, I minor in physics here at the University of South Carolina.
I'm getting in on this a little late, but let me ask a question to those that feel an object thrown straight up into gravity does not stop before coming down...
How long do you feel an object would have to be at 0 ft/s (or whatever velocity unit you prefer) before you would consider it to be "stopped?"
ck34
Dec 01 2006, 12:03 PM
It's not so much a time thing as a force thing. When something is at rest sitting on the ground, the force of gravity pulling down is exactly offset by the support "force" of the ground pushing up. In the case of something in motion in the air, the force of gravity is steadily pulling down such that the item will be considered in motion (not stopped) until it encounters a force that exactly balances gravity such as the ground. Even then, these are only the vertical forces acting on the object. There might be horizontal forces (or at any other angle) that cause the object to move in another direction from vertical (wind) even when on level ground where gravity and the support force are matched.
superq16504
Dec 01 2006, 12:22 PM
Like Chuck, scooter, and my self said the velocity is zero but it never actually stops,
Just to let you know, I minor in physics here at the University of South Carolina.
I'm getting in on this a little late, but let me ask a question to those that feel an object thrown straight up into gravity does not stop before coming down...
How long do you feel an object would have to be at 0 ft/s (or whatever velocity unit you prefer) before you would consider it to be "stopped?"
It may be me but if stopped is taken to mean no force is causing the disc to move than the answer is never. Gravity will always affect any object, even if it is also being suported by the ground. For that matter nothing anywhere is ever really "at rest" when you consider atomic vibration and the movement of electrons (vibrations of strings if that floats your boat)
But for this conversation I would say David Mac makes discs fast. :D:D:D
citysmasher
Dec 01 2006, 12:22 PM
How long do you feel an object would have to be at 0 ft/s (or whatever velocity unit you prefer) before you would consider it to be "stopped?"
<golf clap>
The only reason I sued the word "stopped" was that many people (who are not minoring in physics) get velocity effects and acceleration effects confused.
I define "stopped" as velocity equals zero.
In the case of the projectile going up in gravity, at some point velocity equals zero. The acceleration of the object is never zero, due to effects of gravity being constant, but this an acceleration.
...but please, continue...
ck34
Dec 01 2006, 12:41 PM
It may be me but if stopped is taken to mean no force is causing the disc to move than the answer is never. Gravity will always affect any object, even if it is also being suported by the ground.
Of course this is true. And since the Earth is spinning, everything is still in motion on a bigger scale even when apparently at rest.
superq16504
Dec 01 2006, 12:46 PM
but the question was what makes a disc fast?
the answer is another question.
So if the original question is what disc designs increase the maximum possible velocity of a disc, and what designs limit the effects of drag, drop, and stall.
Can anyone point to more literature about the effects of dimples in discs or balls for that matter?
citysmasher
Dec 01 2006, 01:53 PM
but the question was what makes a disc fast?
In a nutshell:
1. Least drag.
2. Least turbulence.
3. Beak design that seeks an ever so slight nose down disc angle.
Don't think that the flattest discs are the fastest. Airfoil design is not that obvious.
Dimples on a golf ball serve a specific purpose. In general, they create a pocket of turbulence in the back bottom of the ball, when the ball is struck with backspin. This pocket of turbulence creates lift.
This added lift is great when the spin is in the same plane of travel.
On a disc, I see dimples increasing the lift on the left side of the disc (for backhand throws), making the disc easier to flatten (less stable). In the low speed mode glide portion of the flight the dimples might help keep the air attached to the wing so the disc does not stall.
Dimples will increase drag in HS, but for low speed throwers, dimples might help.
superq16504
Dec 01 2006, 03:29 PM
My understanding is that without resistance a sphere would not create drag ie. air would flow around the sphere evenly with no wake.
In the real world a ball creates a low pressure or wake behind it as the air flowing over the surface curls on the backside. so if the dimples on a golf ball are designed to decrease friction and in turn create a smaller wake behind the ball.
Seems like disc aerodynamics is still a pretty new field and there are not a lot of folks doing this research. I did find some work by Sarah Hummell she is a student at UC Davis doing work on the frisbee and also disc wing has a lot of study and published work.
I think that when someone makes a reliable launching machine we will gain information in leaps and bounds. Test flying a disc is a little bit of a joke the way its done now, a machine that could be calibrated to change launch angle tilt nose angle spin and speed would be a nice next step
the_kid
Dec 01 2006, 08:15 PM
Like Chuck, scooter, and my self said the velocity is zero but it never actually stops,
Just to let you know, I minor in physics here at the University of South Carolina.
My techer said that the velocity at the highest point is a Point of inflection and thus it is the velocity is 0 and "stops". :confused:
ck34
Dec 01 2006, 08:22 PM
Unfortunately, potential teachers typically have some of the lowest average SAT scores going into college versus sciences and engineering majors. :eek:
the_kid
Dec 01 2006, 08:24 PM
Yeah that is true and she is actually our main calculas teacher so maybe she has too much of the math and not enough of the science aspect of physics.
ck34
Dec 01 2006, 08:33 PM
Ask her to imagine a graph with time on the horizontal axis and vertical velocity of a ball, thrown perfectly vertical in the air, plotted on the vertical axis. Take your finger and trace it at a steady speed along the graph starting at time zero until the ball returns to the ground (for the first time). Your finger passes thru the inflection point with a zero value on the graph but your finger doesn't stop moving, just like the ball.
citysmasher
Dec 01 2006, 08:42 PM
Unfortunately, potential teachers typically have some of the lowest average SAT scores going into college versus sciences and engineering majors. :eek:
Well... I was a mechanical engineering major,and I graduated 15 years ago... and I have been a design mechanical engineer in the auto and aerospace industries ever since...
...and I say that "stop" and "zero velocity" are pretty much the same thing.
Seems like dancing on the head of a pin. :confused:
My Dad was a college professor, I would say he was pretty f**king smart... I am not sure he ever took the SAT though.
ck34
Dec 01 2006, 08:52 PM
I did say these were averages. My Dad is a college prof (not sciences), Mom, grandparents sisters, brother-in-law are/were educators. I escaped the educational vortex into disc golf (j/k Chemical Engineering).
DNA_2
Dec 01 2006, 09:25 PM
Chucks right teachers are not always the smartest of the bunch, actually they are sometimes the opposite. Ive seen alot of people here at USC that didnt get into Med, or Pharmacy school and they dropped Medicine as there major and started majoring in education. Some people have it others dont.
nanook
Dec 01 2006, 10:58 PM
Ask her to imagine a graph with time on the horizontal axis and vertical velocity of a ball, thrown perfectly vertical in the air, plotted on the vertical axis. Take your finger and trace it at a steady speed along the graph starting at time zero until the ball returns to the ground (for the first time). Your finger passes thru the inflection point with a zero value on the graph but your finger doesn't stop moving, just like the ball.
I have to respectfully disagree with you here, Chuck. I think you are comparing apples and oranges with this example. You are comparing the change in position of your finger to the change in velocity of the ball in the graph. In fact, in the absence of air resistance and between the toss and the catch, the velocity vs. time graph is linear (constant grav. acceleration = contant slope in the velocity vs. time graph = no change in curvature = no inflection point). Furthermore the velocity graph crosses the time axis (velocity = 0) when the ball reaches the peak of it's flight. The position vs. time graph of your vertically tossed ball is actually a parabola. Tracing that parabolic position-time graph with your finger, there is definitely an inflection point (slope = zero => velocity = zero) where your finger ceases travel in one direction and begins traveling in the other direction. How long is the velocity zero? An infinitessimally small instant of time, but zero none-the-less.
nanook
ck34
Dec 02 2006, 12:07 AM
The point is that the object is still moving. Zero velocity for a "moving" object is no more in the state of "stopped" than a velocity of 1 mph or -1 mph. They are all numbers representing the current speed of this moving object at a certain point in time.
Matt's calculus teacher can find the derivative of the gravity acceleration equation (.5gt*t) to determine the velocity after each small passage of time (gt). The value g is the gravitational acceleration of about 32 ft/sec-sec. The second derivative indicates the change in velocity after each second and it will be a constant indicating that the motion never stops (32). This is in a vacuum.
On page 5 of this doc www.phy.mtu.edu/~suits/PH3110/ballwairresist.pdf (http://www.phy.mtu.edu/~suits/PH3110/ballwairresist.pdf) , you can see these functions. The arcing curve is the height of the ball over time. The straight line going down to the right is the velocity (derivative of ball position formula). The constant slope of the straight line is the rate of velocity change which is a constant change of 32 feet/sec. This is assuming no air friction which is acceptable at slow speeds when the ball changes direction. Drag from air friction increases as the square of the velocity. So low velocities have little air resistance and objects have almost the behavior as if in a vacuum.
DNA_2
Dec 02 2006, 01:33 AM
Well stated Chuck
Does anyone remember when I predicted a science pissing match waaaaaay back on the first page?
circle_2
Dec 02 2006, 01:38 PM
Yup! :p
the_kid
Dec 02 2006, 04:23 PM
Unfortunately, potential teachers typically have some of the lowest average SAT scores going into college versus sciences and engineering majors. :eek:
She got a 1598 though.
circle_2
Dec 02 2006, 04:31 PM
Doctors are supposed to be smart...
...yet 50% graduate in the bottom half of their class...EVERY YEAR! :p :D:eek: :o
Furthur
Dec 02 2006, 05:48 PM
Unfortunately, potential teachers typically have some of the lowest average SAT scores going into college versus sciences and engineering majors. :eek:
She got a 1598 though.
I don't think that's a possible SAT score. Didn't the old SAT (pre-2006) scoring system had 2 parts to the test, with scores incrementing by 10?
Anyway, your SAT or ACT really doesn't reflect how intelligent you are. It reflects how well you do in standardized testing.
mikeP
Dec 02 2006, 07:33 PM
Chucks right teachers are not always the smartest of the bunch, actually they are sometimes the opposite. Ive seen alot of people here at USC that didnt get into Med, or Pharmacy school and they dropped Medicine as there major and started majoring in education. Some people have it others dont.
You guys are generalizing big time here. There are all sorts of teachers at every end of the spectrum. Teaching K-12 takes a varied type of intelligence not generally known in people that end up in a highly skilled and specialized profession. I can't imagine an engineer trying to teach middle school. Different people have different skills and abilities, this does not make certain people better or more important than others. Teaching is one of the most underpaid, underappreciated, and invaluable of all occupations. To imply that it is some sort of easy way out for people too stupid or lazy to succeed elsewhere is absurd, and as an educator, somewhat offensive.
ck34
Dec 02 2006, 07:43 PM
Not surprising when you get your degree from a place called Kalamazoo... (gentle ribbing from a U of Toledo grad :D)
citysmasher
Dec 02 2006, 08:06 PM
Does anyone remember when I predicted a science pissing match waaaaaay back on the first page?
On e of the best engineers I ever knew told me once, "Brad, if you want to PICK #$*&$!, you can go PICK #$*&$! with the chickens".
Does anyone remember when I predicted a science pissing match waaaaaay back on the first page?
On e of the best engineers I ever knew told me once, "Brad, if you want to PICK #$*&$!, you can go PICK #$*&$! with the chickens".
I don't get it. But then again, I didn't get a 1598 on my SATs.
the_kid
Dec 02 2006, 09:27 PM
Maybe she said 1590 and I thought she said 1598. Well basicall she was one off perfect.
nanook
Dec 02 2006, 10:00 PM
The point is that the object is still moving. Zero velocity for a "moving" object is no more in the state of "stopped" than a velocity of 1 mph or -1 mph. They are all numbers representing the current speed of this moving object at a certain point in time.
Matt's calculus teacher can find the derivative of the gravity acceleration equation (.5gt*t) to determine the velocity after each small passage of time (gt). The value g is the gravitational acceleration of about 32 ft/sec-sec. The second derivative indicates the change in velocity after each second and it will be a constant indicating that the motion never stops (32). This is in a vacuum.
On page 5 of this doc www.phy.mtu.edu/~suits/PH3110/ballwairresist.pdf (http://www.phy.mtu.edu/~suits/PH3110/ballwairresist.pdf) , you can see these functions. The arcing curve is the height of the ball over time. The straight line going down to the right is the velocity (derivative of ball position formula). The constant slope of the straight line is the rate of velocity change which is a constant change of 32 feet/sec. This is assuming no air friction which is acceptable at slow speeds when the ball changes direction. Drag from air friction increases as the square of the velocity. So low velocities have little air resistance and objects have almost the behavior as if in a vacuum.
So now I think I know why Chuck and are disagreeing. Consider the following in regards to Chuck's vertically tossed ball (sans air resistance):
Definition 1: "Stopped" means that somewhere in the ball's motion, the instantaneous velocity has a value of zero.
Definition 2: "Stopped" means that somewhere in the ball's motion, the instantaneous velocity has a value of zero AND REMAINS zero for a finite time interval.
It seems to me that I am subscribing to #1, while Chuck holds to #2. What do you think Chuck? I definitely do not want to put words in your mouth!
Actually, if we agree to operate under definition #2, I completely agree with Chuck on all his points. So why do I prefer the first definition? Well I think the second one requires a bit of subjectivity. How long does the ball's velocity need to remain zero before it is considered "stopped"? A microsecond? A millisecond? Tenth of a second? A full second? A bit arbitrary, no? Refering to Chuck's velocity graph, the first definition could be restated as: "stopped" means the ball's velocity graph either touches or crosses the time axis. No ambiguity there, the velocity graph either does or does not.
Does this mean I think the second definition is baseless? Certainly not. In fact I probably use it in the real world every day. Every time I come to a stop sign in my car, I need to cease forward motion, pause for a certain amount of time, and then proceed or else I'm running the risk of a ticket for "failing to stop".
Long story short, I think Chuck and I agree on the mechanics but disagree on semantics...
Hey Chuck, do you want to add in observers in different reference frames and really muck things up??? :D
nanook
ck34
Dec 02 2006, 10:42 PM
If there was some vertical balancing force equal to gravity that quickly occurred during the time when the velocity passes thru zero, I would agree that a short period of 'stopped' happened and go with def 1. However, the only force (other than air friction) that is happening during this motion is gravity and it works uniformly and continuously thru the full up and down motion. Thus, the fact that 'stopped' doesn't occur. As a general definition, I believe 'stopped' implies some intervention of another force that's actually "stopping" the motion. But in this case, the object is uniformly being accelerated downward at all times even when moving upward.
citysmasher
Dec 03 2006, 06:58 AM
Does anyone remember when I predicted a science pissing match waaaaaay back on the first page?
On e of the best engineers I ever knew told me once, "Brad, if you want to PICK #$*&$!, you can go PICK #$*&$! with the chickens".
I don't get it. But then again, I didn't get a 1598 on my SATs.
It means the following:
Don't bog down the process with a bunch nit picking that does nothing to fix the problem at hand.
paerley
Dec 03 2006, 11:17 PM
If we only consider the VERTICAL travel of the disc/ball/spherical chicken, and the position verses time, there will be an instantaneous point at which the ball is changing directions and has a velocity of 0 distance units per time unit. Comparing this to the graph of the position function, it's the inflection point, or the point at which the derivative is 0.
That is basic calculus(which is just physics for people who suck at word problems). Now we need a reference frame, usually the throwers POV. I'd love to see someone throw an object such that it actually hits 0 velocity. no amount of gravity will ever prevent lateral motion on a disc, ball, or anything without a significant amount of drag. Also, the rotation of a disc rarely stops before it reaches the ground, and in some cases, the disc continues to rotate even after the disc's position becomes fixed. This is most common in snow, but I've witnessed it in mud and sand.
As far as talking about winds affect on a disc, the disc is ALWAYS experiencing wind, except maybe in that rare case that you're throwing with a tail wind of exactly the same speed at which the disc is traveling. When this happens, you can get some crazy drops in altitude. The easiest way to imagine how a disc is flying is to thing of the travel of a disc not as the disc moving, but rather a wind in the opposite of where the disc was moving (take the disc as the frame of refference). This has helped me a lot in visualizing shots in high wind.
abee1010
Dec 04 2006, 02:05 PM
If there was some vertical balancing force equal to gravity that quickly occurred during the time when the velocity passes thru zero, I would agree that a short period of 'stopped' happened and go with def 1. However, the only force (other than air friction) that is happening during this motion is gravity and it works uniformly and continuously thru the full up and down motion. Thus, the fact that 'stopped' doesn't occur. As a general definition, I believe 'stopped' implies some intervention of another force that's actually "stopping" the motion. But in this case, the object is uniformly being accelerated downward at all times even when moving upward.
I guess I consider the initial force of the upward throw to be the 'vertical balancing force' that prevents the disc from travelling down under the influence of gravity (at the apex).
When the object is on the way up, the remaining force from the initial throw is still greater than the force applied by gravity.
When the object is on the way down, there is no force remaining from the initial throw and gravity is the only force acting on the object.
But what about the APEX!!!!
As the object gets closer to the apex, the amount of force which still remains due to the initial throw gets smaller and smaller. The APEX (point of zero velocity) is the EXACT moment when the upward force from the initial throw has decreased to the point where it EQUALS the downward force of gravity.
Although this condition only occurs for a small period of time, you still have a situation where the object experiences 2 equal and opposite forces. This causes the object to briefly be stopped before the remaining force from the initial throw goes to zero, and the object begins free falling with gravity.
But what do I know, I'm just an electrical engineer... said the ME! :o
If this and the previous posts don't get us on the same page on this topic, I think it will be best for all of us just to agree to disagree and move on...
ck34
Dec 04 2006, 05:34 PM
There is no upward force or "remaining upward force" once the object is released upward. Gravity is the primary force acting (other than some air friction). It is constantly and uniformly accelerating the object in the downward direction with no stopping point when the object passes thru the 0 velocity value.
As an EE, you also know that electrons don't stop but just reverse direction in alternating current. Correct?
DreaminTree
Dec 04 2006, 07:16 PM
Chuck is right. Once the disc leaves your hand, the only outside forces acting on it are wind resistance, lift and gravity. It has upward momentum, but there is no such thing as residual force. I still see most of this thread as an argument in semantics. It just depends on your definition of "stopped". Zero velocity, or static equilibrium? I would say zero velocity = "stopped" in the conventional use of the word.
circle_2
Dec 04 2006, 07:33 PM
Talking about 'creating a monster'...
What causes turnover, a hyzerflip, etc...? Precession, wind-drag, power, discspeed, nose-angle, spin, etc...??
Yes, ALL of the above...& this is subject is multifaceted... I do know I would like to understand these disc dynamics/physics...better.
Here we go into Semantix-Land...again! :D
I read this topic with some interest as I have a fascination with the physics of disc flight. I also have a Ph.D. in Mechanical Engineering specializing in aerodynamics, and would like to help shed more light on the topic. First, let me refer readers to http://www.discwing.com (Discwing's website) where there are some excellent technical papers on disc flight by J.R. Potts and W.J. Crowther. These articles are fairly technical; I'll try to be a little more conventional in the explanations.
In terms of the topic "What makes a disc fast?", readers that indicate slower deceleration is the key to a 'faster' disc are correct (as was noted by xterramatt). As Chuck and Citysmasher indicated, once the disc leaves a throwers hand, the only significant forces acting on the disc (we can safely neglect forces like coriolis or electromagnetism) are gravity and air resistance. For simplification we can consider the case of no wind, as it won't change the logic of the discussion. As mentioned previously, gravity acts continuously on the disc during its flight, the direction of force being towards the mass center of the earth. Conservation of energy tells us that the disc can never go faster than it leaves the hand unless it can gain potential energy by finishing at a lower altitude than it started. An extreme example of this is dropping a disc from rest down cliff. To reiterate: On level ground, the disc can never exceed the speed of release (freak hurricane tailwinds aside). The rate at which a disc slows is proportional to the overall drag (drag is sometimes broken down into components such as form, skin, and induced drag). Drag can be reduced by making a more aerodynamic shape (reducing form drag) and by having very smooth or polished surfaces (reducing skin or 'friction' drag).
As an aside, dimples on a golf ball are used to promote turbulence that actually reduces drag. This is because air passing around a sphere, much like a driver going too fast around a sharp corner, cannot stay on the surface and detaches (termed 'flow separation') to form a drag inducing wake. Turbulent flow, with its rigorous eddies, can follow the surface of the sphere further before separating, reducing the wake size and consequently the drag. Ultimate discs, because of their blunt profile, have scoring lines on the top to promote turbulence for the same reason. Golf discs (especially drivers) have aerodynamic profiles and don't need to promote turbulence to avoid separation. In fact, part of what is making discs go further these days is the smoother finish on the discs. The cavity on the underside the of the disc is another story, some roughness on the underside rim may actually help to reduce drag (go Gateway!).
Besides drag, the movement of an aerodynamic object (like a disc) through the air causes another force on the disc is called lift. Lift is defined as acting perpendicular to the direction of travel of the object center of gravity. Lift is nothing more than the equal and opposite reaction of the object to the force the air exerts downward as it passes over and around the object. Many texts explain lift in terms of pressure differences (lower pressure on the top than the bottom) but this is just another way of explaining the same thing (i.e. the pressure difference is a result of the air movement).
Now for circle_2's big question: What causes turnover, a hyzerflip, etc.? Answering this question in detail requires as more typing than a Ph.D. thesis so to avoid a second brush with insanity I'll try to give you the Readers Digest version. Take a look at the figure below. The throw is a right-handed backhand traveling in the direction of the green arrow. The lift force on the disc acts through the center of pressure (CP) which is generally along the centerline of the direction of travel.
http://www3.telus.net/discgolf/disc.png
In the case shown here, the center of lift is ahead of the center of gravity (CG) causing a nose-up pitching moment (or torque or twist in layman terms). Through the weird and wacky laws of physics (specifically the conservation of angular momentum), the nose-up pitching moment together with the clockwize spin (viewed from above) of the disc imparts a counter-clockwize roll moment (viewed from the back of the disc) causing the disc to bank left. This gyroscopic precession effect can easily be demonstrated with a bicycle wheel. Take off the front wheel and hold it horizontally (like a flying disc) by the end of the axle. Next, spin the tire clockwize as rapidly as you can (better to get a friend to help). Now rotate the nose up as rapidly as you can. Notice that as you twist the nose up the wheel also banks to the left. Also notice how much harder it is to change the orientation of the wheel (nose up or down, bank left or right) when the wheel is spinning rapidly than when it is not. This is termed gyroscopic stability. Without the spin the disc would rapidly increase the angle of attack due to the pitching moment until it stalled (due to flow separation) at which point the flight would become chaotic (try a push pass with no spin to see the effect). This is why a disc has most of its weight near the rim, to increase the gyroscopic stability, and minimize the pitch and roll rates.
Why do some discs naturally turn right instead of left? That is because the pitching moment is negative or that the center of pressure is behind the center of gravity. The pitching moment is a function of the disc shape, but it is also a function of other factors such as the disc speed, angle of attack, and rate of spin relative to the forward speed (termed the advance ratio). These factors can change rate of roll and even its direction (even during a flight - the 'helix').
What disc manufactures call 'stable' (this is an incorrect use of the term from an engineering perspective) discs are those that have larger nose up pitching moments (for a RH backhand) causing a large roll rate (left bank). As a disc gets 'beat up' its surface geometry changes - these subtle changes can be enough to move the CP behind the CG and cause the disc to be 'understable'. I'm not sure why the CP always moves backwards, but this must be implied because the disc never becomes more stable as it gets beat up (at least I've never seen it).
Finally on the topic of 'stopped'. The definition of zero velocity from engineering as physics is v=dx/dt=0, where v is the 3-component velocity vector and x is the 3-component position vector. These definitions imply relativity in a fixed reference frame such as the surface of the earth (Einstein showed that your v=0 is not my v=0 if we are moving relative to each other). If v=0 is your definition of 'stopped' then and object can be 'stopped' with a non-zero acceleration (albeit for an infinitely short period of time). It doesn't matter what forces are in play or how quickly the object came to rest or for how long. The other definition of 'stopped', where the object is not moving and will not move until an unbalanced force causes an acceleration of the object is often termed 'at rest'.
I think this post is long enough so I'll leave it at that. I can try to answer other questions in further posts.
citysmasher
Dec 06 2006, 10:19 AM
Cool post Doc.
The discs become more understable due to the beak of the disc being angled down from collisions. If you were to watch a disc collision in slow motion you would see the disc nearly double over or "taco". The more you "taco" a disc (down) the more the back of the wing (the inner portion of the rim where your fingers are) is pushed up (you can see this on Star discs as a ring will form on the dome at the back of the wing). The more the beak is angled down (or the percentage of arifoil above the beak to below the beak is increased) the more understable the disc becomes.
You are saying this "understable" effect is simply moving the CL rearward? Hmmm... I will have to think on this some.
It is complicated, I think.
circle_2
Dec 06 2006, 03:14 PM
DrD, great post, thank you! I perused through all the Discwing stuff myself yesterday, and was overwhelmed to say the least... Will do some more digesting and post back. Very intriguing! :cool:
doc
rangel
Dec 06 2006, 04:04 PM
I too found your post to be most interesting. I have not (yet) been to your referenced materials, but would you answer me this question. Can velocity alone "flip" a disc....all other things being equal. Throw the same disc (or identical discs) the same way and increase the velocity each time until it starts moving right (RHBH) and then increase the velocity even more until it "snaps" over. If so, what is changing each time? Is it the center of pressure or is there something else?
circle_2
Dec 06 2006, 08:45 PM
Until we have a reliable/accurate way to measure disc RPMs - at a/any given point in time...I'm gonna guess that all this is conjecture. Bring on the mechanical arm/launcher...and a slow-mo camera with tricky measurement methods for (*)...
Just to reiterate (in my own words), it "appears" a freshly thrown disc leaves the hand and is turning more slowly RPM-wise...but somewhere downrange 50-80' ('more' or less?) - something catches up(??) and the appearance of a hyper-spin occurs. It is also during this span of time that initial highspeed-turnover is dramatically happening...especially with a hyzerflip-type throw. What is going on 'here'?
Some folks throw flat and can achieve the same net-distance...right? And IFF so, why? Different disc choice?
The "scientific method" (and our feeble human minds /msgboard/images/graemlins/smirk.gif) are best at analyzing/integrating 1 or 2 variables at a time with statistical validity/reliability...and 'life' just ain't like that. (*)Initial disc launch velocity, spin/RPMs, nose angle, wind direction, wind speed, off-axis torque, launch angle (hyzer/anhyzer), flight, distance traveled, disc CHOICE, etc...ALL play a role...EVERY time we throw. Broken record playing: A disc launching arm/machine should (ideally) help to remove many of these variables by keeping them constant or, at least more controlled. Comments? :D
For Citysmasher,
I did mention that the pitching moment is a function of many things such as disc shape, angle of attack (AoA), advance ratio (AR, a measure of spin rate vs the forward speed), and disc speed. All of these things can affect where the center of lift is located. Because the disc is basically a flying gyro, nose up pitching moments cause left roll (for RHBH). From the Discwing papers it can been seen that both the AR and AoA can have an effect of the direction and rate of roll. It could be that instead of moving the CL rearward that the lift could become negative in which case the pitching momentum and roll direction would reverse (this seems unlikely unless the nose is pointed down).
For ADiscand3Plates,
I think I see what you're getting at. It seems that the harder you throw a disc the more flippy it becomes. This is very tricky to analyze because, as circle_2 points out, humans are poor at producing/measuring data accurately with just our muscles and senses, instrumentation and the scientific method must be employed. I have had this discussion about flippiness before and it seems to me that the way we throw, speed and spin are not decoupled. The harder you throw a disc (I mean the faster the release velocity) the more spin you put on it. I personally think it is this higher spin, coupled with a tendency to put the nose down slightly, is what makes the disc turn right (for a RHBH) on a hard throw. Data from the graphs in the Discwing papers support this conjecture.
It would be really cool to have a "Chromium Climo" or a "Silicon Schultz" (or something equivalent to ball golfs "Iron Byron") or even a wind tunnel, so that we could study modern disc performance. I imagine Discwing is already doing this.
circle_2
Dec 07 2006, 11:33 AM
The harder you throw a disc (I mean the faster the release velocity) the more spin you put on it. I personally think it is this higher spin, coupled with a tendency to put the nose down slightly, is what makes the disc turn right (for a RHBH) on a hard throw.
NOT nit picking, just brain picking! :)
I 'think' we agree that a sidearm throw results in less spin put on the disc (relative to a BH throw)...and therefore the SA throw has a higher propensity to turnover...and nose angle would be critical here if not moreso. I believe there is a greater propensity to put off-axis torque on a hard SA throw which can contribute to & induce turnover. I think I see 'spin' as a stabilizer rather than a turnover'er. :confused: I know we can't look at these aspects completely independently, but it helps to gain understanding.
Nose-up release/orientation would cause/contribute to a gyroscopic precessional force to be translated 90 degrees in the direction of spin contributing to a hyzering-out/stall flightpath, right? So, is a hyzerflip throw benefiting from nose-up release to assist the disc in essentially correcting itself into a more horizontal orientation?
Forgive my likely & sloppy technical nomenclature as I'm relying on my physics from the 80s!
citysmasher
Dec 07 2006, 12:56 PM
The harder you throw a disc (I mean the faster the release velocity) the more spin you put on it. I personally think it is this higher spin, coupled with a tendency to put the nose down slightly, is what makes the disc turn right (for a RHBH) on a hard throw.
It would be really cool to have a "Chromium Climo" or a "Silicon Schultz" (or something equivalent to ball golfs "Iron Byron") or even a wind tunnel, so that we could study modern disc performance. I imagine Discwing is already doing this.
Absolutely disagree with the first part. More spin equals more stability, every single time...and more forward velocity DOES NOT equal more spin.
The faster you spin a disc relative to the forward velocity not only increases the gyroscopic stability, it also generates turbulence which keeps the air attached to the wing for more glide in low speed.
My forehand shots have HALF the spin of backhand shots at the same forward velocity. I found this out from throwing at night with a glow stick attached to my disc.
I can throw very understable plastic backhand because my release has a very "old school" amount of spin (from skipping from Aviar drivers to modern plastic). Backhand my drives nearly screw themselves into the ground upon landing.
My forehand throws barely rotate at all. I can flip a Z Predator forehand.
I am not sure of the exact outside force causes the precession effect that causes it, but more gyroscopic discs tend to hyser and go nose up simultaneously, and gyroscopic plastic can be used to counteract turning over in high speed.
Rolling right also creates nose down, which makes the disc roll even more, unless the nose is forced up from precession. Some discs have the low speed aerodynamics to recover from nose down right hand roll, some don't... some use gyroscopic precession to recover back to nose up.
This is why (I guess) there have ZERO distance records set with disc with huge wings. Too much tendency to go nose up.
I am not an aerodynamics engineer, what I am is a mechanical engineer and machine designer. I called both Innova and Discraft and offered to discuss a design I have in mind for a disc Byron that could launch discs while manipulating the variables separately. Neither ever called back. There is very little interest in type of research I suppose.
Dave from Gateway is itching to get a disc thrower. We have been talking some. At least Dave is interested... excited even.
Watch what happens when disc golf gets big enough for say, Nike to get into disc manufacturing...
circle_2
Dec 07 2006, 03:16 PM
Rolling right also creates nose down, which makes the disc roll even more, unless the nose is forced up from precession. Some discs have the low speed aerodynamics to recover from nose down right hand roll, some don't... some use gyroscopic precession to recover back to nose up.
Can you expand your explanation here? I'm not sure what/where your going here...
citysmasher
Dec 07 2006, 03:50 PM
[QUOTE]
Rolling right also creates nose down, which makes the disc roll even more, unless the nose is forced up from precession. Some discs have the low speed aerodynamics to recover from nose down right hand roll, some don't... some use gyroscopic precession to recover back to nose up.
Can you expand your explanation here? I'm not sure what/where your going here...
Roll right means a lifting force is on the left side of the disc. The precession result of this is a nose up force (same direction 90 degrees later).
So, large wing premium plastic discs with higher moments of inertia have more of a resultant precession force than a lower moment of inertia disc.
So, as a disc rolls to the right trying to gets its nose down a CFR Wraith is fighting the nose down turn more than a DX Teebird.
circle_2
Dec 07 2006, 04:39 PM
Could the lifting force on the left be a precession from the back being up as a result of nose down? In other words, if the nose is down then the back must be up...and there would be an air/dragforce pushing the back down...which would then precess in the direction of spin resulting in what? The other forces have been from below, and this one is seemingly form above...so would this precession result in a lift on the left side? If so, then this would explain those long-arse RHBH shots that lift and go right after they're quite a ways down range.
If one follows these precessions backwards where is the first one? I would guess that it's disc orientation at release...with angle of attack...oh yeah, and ALL those other variables. Hmmmmm?! :eek: :D
Citysmasher, DrD, and all, thanks for your expertise...keep it coming! :cool:
How about this: compare a flat thrower's throw for golf distance with a hyzerflipper's throw for golf distance... What does a discflight with more precessional events result in? More distance? Does a hyzerflip throw require noseup or nosedown at launch to induce these precessional events? (I'm guessing nose up...)
gnduke
Dec 07 2006, 05:26 PM
And what makes a hyzer-flip shot stop rotating when it reaches level flight ?
circle_2
Dec 07 2006, 06:05 PM
Perhaps there's a Mother Earth gravitational quotient...or perhaps it's muscle memory of the thrower, cuz won't some hyzerflips flip too much...like a standard Optimizer flight :D or a roller...then there's the dreaded beotch that didn't flip enuff?! :eek:
Absolutely disagree with the first part. More spin equals more stability, every single time...and more forward velocity DOES NOT equal more spin.
Citysmasher if you disagree and say that spin = stability then are you telling me disc's like the sidewinder,maximizer,and optimizer don't spin as fast because thier definitely not stabile.
gdstour
Dec 08 2006, 03:47 AM
I would say that there is a point where the spin must be somwhat equal to the veocity for it to produce a stable flight. if not it could cause turbulance.
Too much spin and a disc can turn over , too little and of course it hyzers early.
Have you ever heard of a guy that cant throw mid-ranges or a guy that can throw mid-ranges as far as most can thorw drivers???
We will be experimenting with sharp nosed drivers by distributing weight from wing to flight plate in order to match a players velocity and rotation to accomplish more straight stable flights!.
A players with 55 mph and medium amount of rotation cannot throw a disc far if they have a lot of off axis rotation. but,,,, a player who can only generate 45 mPH but with a ton of rotation and a silky smoooth clean release will probably be able to out drive him almost everytime!
Speed alone does not equeal distance!
spin must match speed and techique also plays a big factor.
Steve,,, You out there?????
citysmasher
Dec 08 2006, 07:07 AM
I would say that there is a point where the spin must be somwhat equal to the veocity for it to produce a stable flight. if not it could cause turbulance.
Too much spin and a disc can turn over , too little and of course it hyzers early.
Again, I do not think there is a thing as too much much spin. The exception would be that you put so much spin on a disc as to make an overstable disc even more overstable causing it to heyser even earlier.
Bent arm throwing produces this type of flight. Throwing with a ton of spin just allows the thrower to go to less stable plastic. Typically, for all of the reasons described in this thread, less stable plastic is much more forgiving to launch angles and speed, given the thrower is producing enough spin.
Shultz played most of the 2005 WC's with a Roc, and drove the same distances as the other players in his group. One drive was 435' on very slight downhill for example. People marvel at being able to throw slow plastic far.
I think this is rare, however. For some reason, I can throw putters and mids much further than most of guys I play with, and I assume it is due to spin. I was surprised to learn that many of the accomplished players in the area could not throw a putter 100' or 200' feet, while being able to driver 400+. Most of these players throw very overstable drivers.
Like I said earlier I was shocked to see how much spin I was putting on a disc (throwing at night with an LED attached to the disc so the rotation is very evident---not wholly scientific I know). In fact, I worked on taking a lot of bent arm out of my throwing because there seemed to be no advantage to having more spin. However, the only negative was that too much energy was being expended spinning the disc and not propelling the disc forward. Even after trying to ELIMINATE spin in my technique the disc seemed to spin more than ever. There may be a lot to learn here.
Again, upon switching to forehand it was evident that, while the launching forward velocity was the same, the spin was about HALF that of a backhand throw. The result???? The disc turns over into the dirt, or even if compensated for with heyser, has no distance or glide.
BTW, all of my night testing is with mids so far (Z Storms, FT Roc). The effects of spin and the like are much more evident on slow plastic.
In disc flight I think controlled turbulence is good. The undercambering seen on most modern disc wings causes turbulence. The deeper the undercambering (the dished part of the wing---like a Starfire X is much more dished than a Starfire L---which is nearly flat) the more turbulence, and also the more drag.
Some day I think we will all learn why some wing designs are very stable and others are not. All it will take is some wind tunnel time, right?
I think Mark at Gateway is on the right track BTW.
NO ONE has combined "old school" disc moment of inertia design (Roc, Cyclone, Teebird, etc) with todays large wings (Wraith, Surge, Inferno). By the nature of disc molding, the bigger the wing, the more plastic ends up in the rim of the disc, creating more gyroscopic discs with higher moment of inertias, which (I believe) due to precession, have more of a tendency to go "nose up" than a less gyroscopic disc, thus making them more nose sensitive, harder to throw, and reducing low speed glide and increasing low speed fade. This is why premium plastic discs are more overstable than the exact same disc in lower density plastic.
I really wonder if the speed ratings we see on the discs is more of a function of gyroscopics (moment of inertia) than aerodynamics (you must throw an 11 speed Wraith twice a fast a 4 speed Roc, etc). Until someone can a make Wraith with the weight distribution of a Roc, we will never know...
citysmasher
Dec 08 2006, 07:15 AM
Citysmasher if you disagree and say that spin = stability then are you telling me disc's like the sidewinder,maximizer,and optimizer don't spin as fast because thier definitely not stable.
[QUOTE]
No. A Sidewinder is AERODYNAMICALLY less stable (not necessarily GYROSCOPICALLY less stable). The wing is designed in such a way that it does not have the inherent AERODYNAMIC stability of say, a Teebird, with a notched wing.
The notched wing that we so commonly see is used (I think) to flatten the lift response of the wing. We use similar fixed flaps o helicopter horizontal stabilizers to do the same thing. This protrusion on the wing surface clips the lift curved and flattens it. So, the wing makes the same lift over a wide range of speeds.
So, discs with big notches will fly similarly no matter how much air is passed over the disc (Predator, Tsunami, Teebird, Starfire, etc). Discs like the Sidewinder are basically speed sensitive. The faster you throw them the more lift is generated, causing the disc to turn.
citysmasher
Dec 08 2006, 07:23 AM
And what makes a hyzer-flip shot stop rotating when it reaches level flight ?
Now THAT is a good question!!!!
I will take a crack at this.
Spin a disc on your finger. How does the disc sit when spinning? It sits flat right? No matter what you do, the disc wants to be flat.
Now, if the disc is designed to be TRUE STABLE (not overstable not understable) when thrown, it will tend to go to this balanced orientation with gravity.
This is why a TRUE STABLE disc like Roc, Aviar X, Cylcone, beat DX Teebird, etc will not over rotate past flat on a heyser flip.
I think...
circle_2
Dec 08 2006, 01:01 PM
What disc orientation (nose down or up) at release would contribute most to a hyzerflip flipping up?
citysmasher
Dec 08 2006, 01:14 PM
What disc orientation (nose down or up) at release would contribute most to a hyzerflip flipping up?
Nose up promotes more nose up. More nose up promotes more fade.
To turn the disc to the right, use more nose down.
citysmasher
Dec 08 2006, 01:43 PM
Could the lifting force on the left be a precession from the back being up as a result of nose down?
I am not sure practical experience tells me that large winged drivers in premium plastic will turn over to the right more than a cheap plastic disc with a small wing when both are thrown nose down.
Is "nose down" a force??? No, not in my opinion.
Rolling left or right are dynamic actions. Right roll is due to greater lift on the left side of the disc due to a higher relative air speed than the right side of the disc. That is why a headwind makes turnover worse.
To have a precession you have to have a force. Nose down is a launch condition.
circle_2
Dec 08 2006, 02:27 PM
ALL this is REAL interesting... :cool:
gnduke
Dec 08 2006, 02:53 PM
But launch angle has a real impact on flight path.
Take an air-bounce. While it is more difficult to perform with a golf disc versus a lid, it is still possible and is purely caused by the launch angle being extremely nose up as compared to line of flight.
Kenja
Dec 08 2006, 03:15 PM
Rolling left or right are dynamic actions. Right roll is due to greater lift on the left side of the disc due to a higher relative air speed than the right side of the disc. That is why a headwind makes turnover worse.
Sorry to butt in but this is a commonly accepted explanation that is basically incorrect. What you're describing (Magnus Effect (http://en.wikipedia.org/wiki/Magnus_effect)) only affects objects that have relatively tall surfaces that are perpendicular to the flight path (cylinders and spheres). A disc is, well, flat. The 'sidewall' height of a disc is rarely more than 5-10% of the diameter, which would impart only a minor Magnus effect on the flight path.
Turnover/fade is precession caused by the center of lift not being in line with the center of gravity. Here's a basic summation: A flying, spinning disc acts like a gyroscopic airfoil.
To demonstrate, spin a disc clockwise on your finger. Lightly tap the front rim of the disc. Note that the disc wobbles and turns to the right. Repeat, but this time tap the back rim. It should tilt left. You've just simulated a moving center of lift on a rotating airfoil and incidently the flight path of a disc. Why does it do this?
The center of lift on any wing tends to move dependant on the relative velocity of the wing. Generally speaking, the center of lift moves back at higher velocity and forward at lower. Airplanes compensate for this by using flaps to change the wing configuration, making it wider and taller at low speeds and narrower and shorter at high speeds. Unfortunately, flying discs don't have this option, so we get a variable center of lift.
This brings us to rotational dynamics (the gyroscope part)
The center of lift (c.o.l.) is not in line with the center of gravity (c.o.g.) This imbalance of forces, in combination with the principle of angular precession (what keeps you upright on a bicycle) causes the disc to turn. When the disc is at high speed, the center of lift is behind the center of gravity and the force is transferred 90 degrees in the direction of the spin (clockwise) to push the left side of the disc up and make the thing fly to the right. When the disc slows down a bit, the center of lift moves through the center of gravity and the disc flies straight. When the disc really slows down, the c.o.l is in front of the c.o.g. and the forces act to push the disc to the left.
There's a fairly lengthy discussion of this on this thread (http://www.pdga.com/msgboard/showflat.php?Board=Equipment&Number=180457&Searchpage=2&Main=179020&Search=true&#Post180457)
NB I just noticed that I perpetuated the "equal transit time" myth in that thread. Oh well!
citysmasher
Dec 08 2006, 04:01 PM
Kenja, what is your reference?
Kenja
Dec 08 2006, 04:50 PM
There's plenty of great stuff on the web!
http://mae.engr.ucdavis.edu/~biosport/frisbee/frisbee.html
http://www.lpl.arizona.edu/~rlorenz/frisbee.html
Here's some excerpts from a paper (5th MACS Frisbee Simulation PDF File (http://mae.engr.ucdavis.edu/~biosport/frisbee/5thMACS_Frisbee_Simulation.pdf)) that supports my hypothesis:
A main conclusion was that the effect of spin on the aerodynamic forces is small. Stilley hypothesized, but did not measure, a �Magnus rolling moment�, induced by the interaction of spin and velocity.
Later in the article:
The net aerodynamic force acts at the centre of pressure (cp) which, in general, does not coincide with the centre of mass. Thus it also exerts a moment about the cm [center of mass]. One of the components is a pitching moment about the d2 axis
EXPERIMENT: Just try spinning a disc (clockwise) on your finger and tapping the front rim. Force on a spinning object is translated 90 degrees in the direction of rotation. Therefore, a force that pushes the nose down will pitch the disc to the right. A force that pushes the nose up will pitch the disc to the left.
Kenja is correct. If you look back at page 10 you will see a diagram that depicts what is being said, and a repeat of essentially the same explanation.
As Kenja indicates, the center of lift (COL) position can be a function of relative speed (Reynolds number). I didn't find data to support this but the references from Discwing below did show that lift and drag are not significantly affected by speed or spin. The references do show, however, that lift, drag, and pitching moment are significant functions of the angle of attack (AoA. Again the AoA is the nose up/down orientation of the disc to the direction of motion of the center of gravity (COG) ).
What is also important is the rate of gyroscopic precession when discussing the stability (in Frisbee terms) of a disc. The equation for how the roll rate corresponds to the pitching moment is:
M_p = I_zz * RR * omega_z
where,
M_p is the pitching moment
I_zz is the moment of inertia about the spin axis (in general, the more mass concentrated near the rim the larger the moment of interia).
RR is the roll rate
omega_z is the spin rate.
From the above equation you can see that, for a given pitching moment, the more the spin (larger omega_z) the smaller the roll rate. This means that the disc rolls slower (remember, if the COL is ahead of the COG the disc will roll left so increasing the spin will decrease the roll rate and as a result the disc will not fade right as much - this agrees with common experience).
Kenja's references point to the fact that it is the changes in angle of attack (and the resulting effect on the pitching moment) that are causing changes in rolling motion of a disc in flight (i.e. for a hyzer flip � I am going to try simulating the equations of motion using the wind tunnel data for force and moment coefficients to see if I can replicate a hyzer flip � I�ll let you know what I find).
One caveat in all the referenced information is that the Frisbees analyzed were shaped like ultimate discs and not the modern low profile drivers. The same logic about pitching moments causing roll and roll moments causing pitch still apply, but obviously the variation of these moments with Reynolds number and angle of attack will change.
References from discwing's website are:
ref1 (http://www.discwing.com/pdf/ARCpaper.pdf) and ref2 (http://www.discwing.com/pdf/ARCpaper.pdf)
circle_2
Dec 08 2006, 06:34 PM
So, is a hyzerflip drive that flips-up, then flies straight for awhile, and THEN rolls right FAR downrange before hyzering-out - just a series of precessions ocurring as a result of the COL shifting/moving from the front to rear?
Does a hyzerflip-type drive require some kind of imbalanced force (angle of attack/nose angle) to get it started?
gnduke
Dec 08 2006, 06:41 PM
Hyzer-flips are discs that are thrown on a hyzer angle at release that fairly rapidly go from a hyzer angle to flat and fly falt for the majority of their flight. Depending on the disc and height, they may or may not tail at the end. They are normally thrown a lower trajectory than anhyzers or s-shots.
The shot you describe is thought not to exist by some.
Kenja
Dec 08 2006, 06:48 PM
Dr D that diagram is great! (I didn't read back far enough in the thread :o) I still think my experiment is easier to do and more realistic :D
You're right to point out that those papers only used lid-shaped discs for their testing. I think we've all found that golf discs fly better and farther nose-down.
Disc wobble is apparently a huge factor in drag coefficient. (Smooth throws fly farther/faster? Seems reasonable) See Lorenz's article in New Scientist (http://www.lpl.arizona.edu/~rlorenz/frisbeenewscientist.pdf) for more interesting stuff. He apparently rigged up an Ultrastar with a flight recorder (he did this to test something about planetary probes -- who cares :p ). He also found out that discs don't lose (much) spin while in flight.
If you're trying to simulate a hyzer flip, it may help to think of it as a reverse S-curve whose plane is not parallel to the ground. The turning phase of flight is translated into increased altitude rather than turning to the right, the straight flight portion lasts longer because A) the nose is still pointing down which should equal less drag and B) the flight path has more altitude.
Kenja
Dec 08 2006, 06:57 PM
So, is a hyzerflip drive that flips-up, then flies straight for awhile, and THEN rolls right FAR downrange before hyzering-out - just a series of precessions ocurring as a result of the COL shifting/moving from the front to rear?
I suppose its possible if someone really cranked one that flipped up really high and the disc somehow gained more speed going 'downhill' than it lost due to drag... It's more likely that wind conditions are different further 'downrange'.
citysmasher
Dec 08 2006, 07:36 PM
This brings us to rotational dynamics (the gyroscope part)
The center of lift (c.o.l.) is not in line with the center of gravity (c.o.g.) This imbalance of forces, in combination with the principle of angular precession (what keeps you upright on a bicycle) causes the disc to turn. When the disc is at high speed, the center of lift is behind the center of gravity and the force is transferred 90 degrees in the direction of the spin (clockwise) to push the left side of the disc up and make the thing fly to the right. When the disc slows down a bit, the center of lift moves through the center of gravity and the disc flies straight. When the disc really slows down, the c.o.l is in front of the c.o.g. and the forces act to push the disc to the left.
I can dig it.
This explains the basics of the S curve and I can digest this. So, the natural path of of disc in a perfect world is an S curve due the aerodynamic center of lift shifting and the resulting precession...OK.
...but, we all know disc designs can be manipulated that to create radically different flight paths than these. We also know that these flight paths do not necessarily follow just the speed of the disc.
I just think it is way more complicated than this.
Kind of like explaining the moon landing with F=ma as the explanation....
Good point Kenja. For circle_D, yes, rolling is caused by the pitching moment which is a function of the disc shape and angle of attack (AoA). That means if the disc is rolling it must be at an AoA where the pitching moment is non-zero. Conversely if there is no rolling then the disc must be at an angle of attack where the pitching moment is zero. Note that the pitching moment could be zero or negligble over a range of AoA for some discs (seems like a Roc might be one).
My recollection is that hyzerflip throwers use neutral or understable discs (in the disc manufacturer sense of the word understable). This means the the disc has a propensity to roll right unless at a high enough AoA (i.e. it probably has a negative pitching moment when thrown flat). Releasing hyzer on a subtantial trajectory angle upward with a low enough AoA to have a negative pitching moment will cause roll right, resulting in the ensuing turn becoming altitude gain (as Kenja pointed out). Once gravity exceeds lift the resulting convex trajectory will naturally increase the AoA which will reduce the negative pitching moment which will reduce the right roll rate. If the AoA gets high enough the pitching moment will be zero (straight flight) or even reverse sign to +ve and the disc will roll left (late hyzer). Note that AoA is measured from the trajectory tangent not the ground plane (i.e., an observer on the ground can observe a nose-down trajectory from his/her point of view but if the disc is coming down steeply enough it will have a +ve AoA). Note also that skin friction causes the spin rate to decay over time so that, from the previous post, we know that late in the flight the roll rates will be enhanced. I believe this is a reasonable explanation of the hyzer flip.
Kenja, sorry I missed your point about spin decay being small. It means that you can ignore the comment about spin decay in my last post. I should have guessed knowing that air has relatively low viscosity and flight times are relatively short.
AviarX
Dec 08 2006, 11:55 PM
So, is a hyzerflip drive that flips-up, then flies straight for awhile, and THEN rolls right FAR downrange before hyzering-out - just a series of precessions ocurring as a result of the COL shifting/moving from the front to rear?
my two cents: a hyzer flip is simply a disc released with hyzer that flips out of the hyzer -- either to flat, or to flat and then continues to flip over, though it may fade back at the end (or not). i like to use them on holes where i need to go through a narrow fairway or tunnel first and then turnover to the right later. i will throw a Roadrunner with a lot of hyzer and spin and speed on the drive below and the hyzer and spin will help keep the disc from wanting to flip up more than to flat for the first few hundred feet despite the power and speed i drive here with -- and then the turnover will take over and the disc will go to the right before either dying or fading back at the end.
Teeshot hole 13 Idlewild (http://www.cincinnatidiscgolf.com/courses/Idlewild.htm) , long pin (586 feet par 4: straight long and then to the right), short pin (234 ft par 3: straight and to the right (both pins are always in place)
http://www.cincinnatidiscgolf.com/images/CoursePics/Idlewild/Idlewild13.jpg
second shot:
http://www.cincinnatidiscgolf.com/images/CoursePics/Idlewild/Idlewild13b.jpg
other guys -- especially some old schooler's i know who throw almost all understable stuff will throw everything (almost every hole) with hyzer and let it flip up to flat and then go straight.
Does a hyzerflip-type drive require some kind of imbalanced force (angle of attack/nose angle) to get it started?
i don't find that a requirement though it might add to your shot's potential characteristics. it is easy to throw a hyzer- flip with a really flippy disc though it may flip out of hyzer too quickly. (more spin will help it hold the hyzer and fight the flip longer) a more stable disc requires more speed and torque to flip up out of hyzer. Dave D also suggested to me that you can throw an understable disc nose up with hyzer to help keep it from flipping and fly straight and i find this true and helpful on narrow wooded fairways...
circle_2
Dec 09 2006, 10:47 AM
Hyzer-flips are discs that are thrown on a hyzer angle at release that fairly rapidly go from a hyzer angle to flat and fly falt for the majority of their flight. Depending on the disc and height, they may or may not tail at the end. They are normally thrown a lower trajectory than anhyzers or s-shots.
The shot you describe is thought not to exist by some.
Yes sir, thank you. Due to seeing the type of shot I described and actually doing it myself (only a few times, and not recently) got me to pursuing an explanation. I've posted these types of inquiring aerodynamic~physics questions over the last 5 years with little feeling-of-satisfaction from the responses. Whether I was ready or not back then to understand these complicated issues...these responses are meshing with my way of thinking and a much better understanding has resulted.
circle_2
Dec 09 2006, 11:04 AM
other guys -- especially some old schooler's i know who throw almost all understable stuff will throw everything (almost every hole) with hyzer and let it flip up to flat and then go straight.
Does a hyzerflip-type drive require some kind of imbalanced force (angle of attack/nose angle) to get it started?
i don't find that a requirement though it might add to your shot's potential characteristics. it is easy to throw a hyzer- flip with a really flippy disc though it may flip out of hyzer too quickly. (more spin will help it hold the hyzer and fight the flip longer) a more stable disc requires more speed and torque to flip up out of hyzer. Dave D also suggested to me that you can throw an understable disc nose up with hyzer to help keep it from flipping and fly straight and i find this true and helpful on narrow wooded fairways...
Hmmm...this "nose up release" hyzerflip thang with understable discs makes sense (to me anyways).
Excessive off-axis-torque could 'drive' a disc released with hyzer into a hyzerflip flight, though it would inherently hyzer back much more quickly...
How to add more spin? Gripstrength? What technique~aspects add/result in more spin?
AviarX
Dec 09 2006, 11:12 PM
i would say wrist fling/spring action combined with the tendon bounce? i have a hard time thinking about what i do to throw with a lot of spin because i do it more with my body than with my brain or by thinking about it... if you throw understable discs far and with power (or into a wind) you have to use a lot of spin -- at least that's my story and i am sticking with it.
citysmasher
Dec 10 2006, 08:47 AM
if you throw understable discs far and with power (or into a wind) you have to use a lot of spin -- at least that's my story and i am sticking with it.
That is correct, I think also.
This thread has been very educational for me.
I have been trying to make my assumptions and formulate ideas without jumping straight to a reference because I knew there has been nearly ZERO scientific studies of flying discs actually in flight, and probably even less in a windtunnel. So, most of what you read will be very simplified.
I think the idea that the natural flight of a disc is an S is a valuable thing to know. If noting else, the thrower will be armed with the fact that maximum distance for any disc is not being attained unless the disc goes through this entire cycle.
gdstour
Dec 10 2006, 07:32 PM
I would disagree with the the above spin/stability theory.
We have a lot of gateway Team players that switch from power grip to fan grip as a way to decrease the amount of rotation on the launch.
Discs with less rotation will not flip from hyzer to flat or turnover as easily and they will also lose rotation sooner, causing them to fly flat or fade earlier or with a different style of fade,as opposed to faster spinning shots lauched with the power grip.
less gyroscopic discs need less rotation to match Speed in order to achieve stable flights straight, regardless of the deflection angles of the wing ( overstable or understable models)!
NOse up or nose down releases will change where the drag is at on the discs and can offset the stability of alomst any model.
I can throw a beat up S Element with a fan grip and lower velocity to achieve a flat straight flight of 300 feet and still get fade at the end as well as take a overstable Spirit and jerk in over nose down 5 feet off the ground and get a pretty straight flight of 300 feet into the ground with no fade at the end.
I rarely hear about trajectory when other manufactures discuss stability of discs.
each model of disc could have 12 different flight charts depending on the distance it is thrown as well as the hieght it is thorwn
Our new ebsite is going to show a trajectory chart for the prefeered use of the discs, but we may get into more than one chart which can be sued for playesr to evaulate the discs flight chracteristics based on their Max D.
A better way would be for it to be based on thier velocity and rotation, but we are a little ways away from the equipment needed for the testing.
citysmasher
Dec 10 2006, 08:02 PM
We have a lot of gateway Team players that switch from power grip to fan grip as a way to decrease the amount of rotation on the launch.
Discs with less rotation will not flip from hyzer to flat or turnover as easily and they will also lose rotation sooner, causing them to fly flat or fade earlier or with a different style of fade,as opposed to faster spinning shots lauched with the power grip.
I would say, how do you know they have less spin?
I agree we are all guessing, and launch equipment would open a whole new world for the science of disc design....
AviarX
Dec 10 2006, 08:45 PM
i use a modified FU grip for everything and can throw on a good day 500 ft. (Pro Orc). i can throw a Roadrunner with full power and use hyzer-oriented-spin to keep the disc from flipping for the first 200 feet. now off-axis spin would flip it faster, but that isnt the kind to use. i hear Stokely could throw a Stratus forehand 400ft and the way to do that -- it seems to me -- is with a ton of spin (not off-axis).
from what i have read the spin acts like a gyroscope -- when the spin is no longer sufficient to maintain the orientation given to the disc -- natural tendencies kick in.
when i played ultimate i learned the best way to throw through a headwind was with added spin. this helps keep the disc from flipping and falling like a wounded duck.
if i am wrong would appreciate an explanation that explains why added spin helps me throw understable discs straight and hold off the flip for a longer time & distance than would otherwise happen... i probably also add a little nose up too to counter the flip...
citysmasher, have you checked out this thread (http://www.discgolfreview.com/resources/articles/distancesecrets.shtml) on disc techniques?
circle_2
Dec 11 2006, 11:25 AM
Discs with less rotation will not flip from hyzer to flat or turnover as easily and they will also lose rotation sooner, causing them to fly flat or fade earlier or with a different style of fade,as opposed to faster spinning shots lauched with the power grip.
Compare this to the low-spin SA shots that flip quickly...are ya sure about this?
citysmasher
Dec 11 2006, 12:50 PM
Discs with less rotation will not flip from hyzer to flat or turnover as easily and they will also lose rotation sooner, causing them to fly flat or fade earlier or with a different style of fade,as opposed to faster spinning shots lauched with the power grip.
Compare this to the low-spin SA shots that flip quickly...are ya sure about this?
Exactly.
My sidearm puts about half the spin on the disc as my backhand. I cannot sidearm a mid hardly at all without flipping it.
AviarX, look back through this post and you will see that roll (flip) rate is inversely proportional to the spin rate. In other words, as you suggested, the higher the spin the slower the flip. Also, Kenja found some research that shows that the spin rate doesn't change signficantly over the duration of the flight (due to the relatively low viscosity of air), implying flight changes due to spindown are unlikely. Earlier posts also show that the more the nose is up the less likely the disc is to flip (i.e., roll right for a RHBH).
gdstour
Dec 12 2006, 03:06 AM
Discs with less rotation will not flip from hyzer to flat or turnover as easily and they will also lose rotation sooner, causing them to fly flat or fade earlier or with a different style of fade,as opposed to faster spinning shots lauched with the power grip.
Compare this to the low-spin SA shots that flip quickly...are ya sure about this?
Not enough spin to match speed will cause turbulance and most side arm throwers release with off axis rotations
Kenja
Dec 13 2006, 03:55 PM
Have you considered putting flight instruments on the disc itself? This page has some interesting stuff on it: http://www.lpl.arizona.edu/~rlorenz/frisbee.html
He also published an electronics schematic for the instrumentation:
http://www.lpl.arizona.edu/~rlorenz/nutsvoltsfrisbee.pdf
Kenja
Dec 13 2006, 04:37 PM
Another interesting aerodynamic force is wingtip vortices (http://en.wikipedia.org/wiki/Wingtip_vortices). According to the wiki "A wing which does not generate a vortex cannot produce any lift at all." (I'm not sure of this statement because I think downdraft induced by the angle of attack is what produces lift). Longer/more elliptical wings produce weaker vortices. Winglets (http://en.wikipedia.org/wiki/Winglet) are used to change the aspect ratio without having to lengthen the wing (which would add more weight). Apparently one of the most efficient wings ever designed is the elliptical Spitfire (http://en.wikipedia.org/wiki/Supermarine_Spitfire) wing.
Flying discs probably don't generate (much) vorticity from the outer wing tips; instead they probably generate strong vortexes from the inner rim (which would explain why wide winged/shallow rimmed/cambered discs fly faster/longer). Have you considered a design that incorporates a bottom 'winglet'? I'm envisioning a groove on the bottom wing running parallel to the rim. Kinda like Rings of Hedrick but on the bottom, where they'd actually do something to the disc's flight.
MDR_3000
Dec 13 2006, 04:52 PM
There's something like that on the bottom of the Raging Inferno.
the_kid
Dec 13 2006, 07:22 PM
There's something like that on the bottom of the Raging Inferno.
Mike Robinson makes discs fly fast.... :D
circle_2
Dec 13 2006, 07:45 PM
Wouldn't instrumentation on a disc skew the result(s) due to added mass and (virtually) causing some added imbalance?
Let's get that outerspace discer to rip a good drive...I'll bet it doesn't turn over...ever! /msgboard/images/graemlins/smirk.gif
Airfoil theory, in particular the Kutta-Joukowski theorem (http://en.wikipedia.org/wiki/Lift_(force)) says that the Lift force is proportional to the strength of the vorticity. That's why trailing vortices are more pronounced at higher angles of attack. Below are a couple of pics from the discwing website showing how vortices are formed and how they grow stronger with increased lift (the second pic is at AoA 0 deg, 5 deg, 10 deg, from left to right).
circle_2, you're right, without atmosphere or gravity in outer space the disc would just keep on flying with its initial conditions. Maybe I could finally throw 500ft /msgboard/images/graemlins/smirk.gif
http://www3.telus.net/discgolf/vortex.jpg
http://www3.telus.net/discgolf/vortex2.jpg
citysmasher
Dec 13 2006, 11:46 PM
Wow, those are cool pics.
What exactly are (a) (b) and (c)?
Everything makes sense. More lift more drag. Same as any wing.
This would also explain why nose down launches slow more than nose up launches.
Funny thing is that nose up is not necessarily bad for big distance, especially with putters and such. Some disc designs are certainly more forgiving to nose up launch.
So I suppose you may have answered the question of the thread. Discs that can maintain low launch angles with less drag are the fastest.
One thing I will add here. Fast discs do not seem to have the decided distance advantage for golf shots in higher density air (like in the winter). For me anyway, the real fast discs that can be bombed at low trajectories seem to lose a lot when they are slowed in the thicker air. A slower disc with a lot of glide seem to be more consistent from winter to summer.
So, in other words, the thinner the air, the more proportionately faster the fast discs become...where the slower discs stay more the same. For me, and my tests, a Wraith will be 50' longer in the summer over say, a Valkyrie on similar lines, whereas, right now with the density of the air significantly higher, they are about the same distance, or at least the gap has been shortened to only a few feet.
Fast discs seem to like to go even faster with as little resistance as possible, where slow discs use the air more for he total distance equation.
Just my observations, nothing provable.
One of the things that does not seem to absolute is the bigger wing being higher drag. This seems to be the trend in design. The SOLF is nearly the same performance as a Star Starfire, yet the wing of the SOLF is smaller. This is something to be applauded if you have small hands. I wish there was less emphasis put on making the wings longer and longer, and more on making the smaller wings faster.
(a) (b) and (c) are views from behind the disc of the trailing vortices at various angles of attack. They use a laser to illuminate a plane perpendicular to the direction of travel.
Not sure about the winter/summer distance phenomenon athough I do know what you mean. Lift and Drag are proportional to air density. At the same speed there is more lift in the winter but also more drag. Human muscles don't work as well in the cold so it's likely the launch speed is less. This will change the lift/drag ratio which may explain things. Maybe fast discs like the wraith are somewhat optimized for faster launch speeds.
My feeling is that most of drag is coming from the cavity underneath the disc. The sudden step from the rim into the cavity is a separation inducing, drag creating geometry. I am certain the if you can lessen the flow disturbance caused by the sharp drop into the cavity you would make large strides in reducing drag. Like you mentioned, I don't think the current sizes of the underside rim width (I think this is what you call the wing) matter too much, as it they are all small in comparision to the cavity diameter. That being said, there just may be some reduction in drag with larger wings (i.e., smaller cavity). You only have to look at the aerobie, which is basically an annular wing (i.e. no bottom cavity), to see what large reductions in drag can do. I'd like to see a wind tunnel comparion of a disc and it's twin with a smooth cover over the cavity to see the difference. Of course the latter would be difficult to throw...
citysmasher
Dec 14 2006, 12:20 PM
My feeling is that most of drag is coming from the cavity underneath the disc. The sudden step from the rim into the cavity is a separation inducing, drag creating geometry.
The wider the wing, the smaller the cavity under the disc.
circle_2
Dec 14 2006, 01:05 PM
My feeling is that most of drag is coming from the cavity underneath the disc. The sudden step from the rim into the cavity is a separation inducing, drag creating geometry.
The wider the wing, the smaller the cavity under the disc.
- The QK and Inferno have a much smoother/rounder transition from cavity to wing...
Intriguing stuff!! You done went and provoked some (more) thoughts!! :cool::D
These wind tunnel tests are using non-spinning discs, correct? These vortices would be altered to some degree with spin...and how much spin is imparted to a disc would further the equation?? :confused:
Also, how does an Epic fly when the center of gravity (and such) would seemingly be in a constant flux? This barrel-roll overhand shot that some can get 400-500' on...what up with that?!?
I bow before you's fizix gods!! :cool:
citysmasher
Dec 14 2006, 02:52 PM
I think there is a lot to be learned from the use of the Gurney flap. We use simple fences on helicopter rear horizontal stabilizers to make them less speed sensitive.
For example, I found this:
Flow Separation
As you can see from the freeway analogy flow separation is caused by a reverse pressure gradient due to air slowing next to a fixed boundary. You don't have separation when air is accelerating as on the front of a moving vehicle where the flow is still attached to the surface. It's on the back of the car, where you have the air slowing down, that you get separation and the drag that goes with it.
Racecar designers fight flow separation in three main ways-gradual transitions, spoilers, and creating turbulence. At the rear of the car after the maximum body cross section, body-panel angles are kept small, less than 10 degrees. This gives the familiar teardrop, streamlined shape.
http://insideracingtechnology.com/Resources/gurneyflap.gif
Separated flow
If a large transition is needed a lip can spoil the air into the low-pressure area lowering drag. Look again at these sketches illustrating what a Gurney does. Air flowing over the bottom of a wing at low angles of attack speeds up over the thick part of the wing and then slows down until, at the trailing edge, it's at the same speed as the air that went over the top of the wing. As the air slows down, its static pressure rises and the boundary layer thickens. At higher angles of attack, the boundary layer can develop well enough to generate eddies and flow separates from the surface. When you have separated flow, as in the top sketch, drag goes up and the wing can stall.
A Gurney flap allows a wing to operate at higher angles of attack than the same wing without a Gurney. Look at the streamlines on the Gurney sketch. You can see the air has to move up to go around the Gurney lip. That creates a lower pressure right behind the flap that translates around the corner to the bottom of the wing. This guarantees a high-to-low pressure gradient along the bottom of the wing and prevents separation. This is why you see a lip on the back of almost every shape on a racecar.
The third drag-lowering device is turbulence. If the air close to a fixed boundary is swirling, at any moment some of it is moving toward the boundary making separation more difficult. When you see vanes and barge boards on a racecar think about how the air sees this obstacle and tries to move from areas of high pressure in front toward lower pressure behind the feature. Often the result is a turbulent, swirling motion that sweeps along the body panel retarding separation.
I maintain that most modern drivers with any speed insensitivity (what we call STABLE) are basically using the Gurney flap idea (these are the notches or beads on the bottom of the disc) to equalize the airflow across the disc.
bschweberger
Dec 15 2006, 11:09 AM
TT Rex