Explanation of the physics of flying discs (FIXED)

[hugheshilton]

Are you sure?

I think you're replying to a post that's 2.5 years old so don't expect a response anytime soon.

 

[lyleoross]

Think of it like this. Three factors impart lift, or how air flows over the disc to give lift; wing and disc shape, forward speed, and spin. As the disc flies forward, there is lift on the wing, the faster, the more lift (again, the shape of the wing and disc impacts this). As the disc spins, one edge, the left side, is traveling faster relative to forward motion, and gets more lift; the other, the right side, is slower and gets less lift. Again, the wing and disc shape plays a large role role in this, some wings give more lift at slower speeds, i.e. under-stable discs; and of course, the more spin, the more lift on the left side, and the disc turns right. Beat in discs are less stable either because they increase lift on the left side, or decrease lift on the right side. If the disruptions, nicks and mars, in the disc increase pressure beneath the wing on the left side, then the disc flies less stable. If the disruptions in the disc decrease pressure on the right side, same result, it's just hard to know which it is without an accurate wind tunnel and some equipment.

 

[hugheshilton]

Think of it like this. Three factors impart lift, or how air flows over the disc to give lift; wing and disc shape, forward speed, and spin. As the disc flies forward, there is lift on the wing, the faster, the more lift (again, the shape of the wing and disc impacts this). As the disc spins, one edge, the left side, is traveling faster relative to forward motion, and gets more lift; the other, the right side, is slower and gets less lift. Again, the wing and disc shape plays a large role role in this, some wings give more lift at slower speeds, i.e. under-stable discs; and of course, the more spin, the more lift on the left side, and the disc turns right. Beat in discs are less stable either because they increase lift on the left side, or decrease lift on the right side. If the disruptions, nicks and mars, in the disc increase pressure beneath the wing on the left side, then the disc flies less stable. If the disruptions in the disc decrease pressure on the right side, same result, it's just hard to know which it is without an accurate wind tunnel and some equipment.

I have advanced this same theory about disc flight before (maybe even earlier in this thread) and gotten into long arguments with the gyroscopic precession-ists. I still think you're probably correct, but the precession theory has some vocal proponents here as well. It makes sense in my mind that the air is flowing faster over one side of the disc than the other due to the spin of the disc and that the side with faster airflow would get more lift, causing the disc to turn. However, I don't think it's worth getting into a long argument again where people put forward as evidence physics papers that none of us actually understand so ¯\_(ツ)_/¯.

 

[zmannz1984]

I wish I had recorded the time I talked to a friends dad about this. He was an aerodynamics engineer or something-or-other for many years working at various research centers. His explanation, in very simple terms, was to look at the disc like a glider airplane wing for aerodynamic purposes, with the proper amount of weight and spin to make that certain disc shape fly correctly acting as a substitute for a balanced, normal weight distribution of a glider design. When the disc is released it starts out flying straight and true, like a well-built paper airplane. Once the spin and the forward momentum die down enough though, the wing is no longer balanced and begins to stall out - and fade. Too little forward motion and too little lift. The same goes for it spinning too fast, it will also begin to stall out, but turn over instead. Too much weight (actually force) and too little lift. But I dunno, I just like it when they fly perty.

 

[sidewinder22]

I have been throwing with a couple of pro (MPO ) players lately. one in particular has been frustrated with the way his discs fly here because of major loss of distance. The explaination he postulated was that the thinner air creates less lift related to the reduced molecules flowing over the top which creates a shorter throw (less air, less lift, =decreased ability for the disc to remain aloft). I was just wondering about the mechanics/mathematics on this theory. I think I agree since I seem to have been able to throw farther in Spokane (2200ft elevation) vs. here in Salt Lake (4500ft elevation), although I was just chalking it up to getting older and having less than perfect timing on my distance throws.

Somewhat depends on how you are throwing them. If you rely on air bouncing(downward trajectory with disc nose up), then you will not get as much distance at higher altitude. If you throw with an upward trajectory and nose down like the distance throwers do, you should get more distance at higher elevation. Many of the top distance throwers have said they prefer higher elevations and produced their longest throws around 4000-5000' elevation.

 

[sidewinder22]

I have a hard time accepting the notion that the disc's spin decreases enough in flight to really affect anything. Anyone ever thrown in snow/ice and have their disc still spinning after getting to it?

 

[wolfmandragon]

I have advanced this same theory about disc flight before (maybe even earlier in this thread) and gotten into long arguments with the gyroscopic precession-ists. I still think you're probably correct, but the precession theory has some vocal proponents here as well. It makes sense in my mind that the air is flowing faster over one side of the disc than the other due to the spin of the disc and that the side with faster airflow would get more lift, causing the disc to turn. However, I don't think it's worth getting into a long argument again where people put forward as evidence physics papers that none of us actually understand so ¯\_(ツ)_/¯.

One of the problems is that different disc molds create lift in different ways. Some are producing all their lift on the nose, therefore gyroscopic procession 'turns' the disc 'right'. Some discs have lift at the tail, these discs turn 'left'. I am not taking about a disc stalling but of discs like the Spirit or the Rask.
Compare this to a disc that is creating lift at the center of the disc, and one does not see that turn. These discs are basically lifting body wings as opposed to glider wings.

Now having said that, I read up on one, for lack of better word, thesis, that the gentleman showed that certain discs created lift, not by the wing, but by a vortex effect. Yeah, well, gyroscopic procession might be out the door there.

The only way to know where the lift is being created, is to wind tunnel the certain disc model. I, for one, would love to see Comets, TeeBirds, Volts and Rasks all wind tunneled, just to see how close my guess on which way each disc creates lift.

Go research how a helicopter creates lift and the wind tunnel tests that have been done upon them.

CS degree here as well, btw.

 

[wolfmandragon]

I have a hard time accepting the notion that the disc's spin decreases enough in flight to really affect anything. Anyone ever thrown in snow/ice and have their disc still spinning after getting to it?

Yes I have, and the faster the disc is spinning on ice, the straighter the flight was.
The spin keeps the disc stable, the faster it spins, the less turn or fade it has. Turn and fade are created at a right angle to where the lift is greatest and when the lift overcomes the stabilizing force of the spin.

 

[sidewinder22]

Yes I have, and the faster the disc is spinning on ice, the straighter the flight was.
The spin keeps the disc stable, the faster it spins, the less turn or fade it has. Turn and fade are created at a right angle to where the lift is greatest and when the lift overcomes the stabilizing force of the spin.

That's not quite what I was talking about. In a properly executed throw, does the disc vary(lose) enough of it's RPMs to significantly change it's course? Does air friction/time slow the RPM/gyroscopicness significantly in flight?

 

[wolfmandragon]

That's not quite what I was talking about. In a properly exepd throw, does the disc vary(lose) enough of it's RPMs to significantly change it's course? Does air friction/time slow the RPM/gyroscopicness significantly in flight?

Somewhere, maybe an old thread at DGR, someone had measured the spin and speed of some pros. From what I remember, both speed and spin decrease during the flight significantly, but speed decreased at a higher rate. I think this may have been the same place where they discovered that forehand throws had amuch slower rate of spin.
I am sorry I do not remember the link, I would like to refresh my memory as well.

 

[sidewinder22]

Somewhere, maybe an old thread at DGR, someone had measured the spin and speed of some pros. From what I remember, both speed and spin decrease during the flight significantly, but speed decreased at a higher rate. I think this may have been the same place where they discovered that forehand throws had amuch slower rate of spin.
I am sorry I do not remember the link, I would like to refresh my memory as well.

IIRC it only measured peak speed and spin. Obviously speed decreases since the disc stops going forward. In a 10 second or so flight I just don't see how spin would slow down significantly.

 

[wolfmandragon]

IIRC it only measured peak speed and spin. Obviously speed decreases since the disc stops going forward. In a 10 second or so flight I just don't see how spin would slow down significantly.

Your argument agrees with the hypothesis that turn and fade are artifacts of gyroscopic procession, which I believe to be correct.... On most discs, I think you are correct.
How fast the disc decreases rate of spin will come down to:

• initial speed, rate of spin and pitch
• coefficient drag on the rotation of Disc at any given vector.
• weight distribution

MVP's marketing is based on the weight distribution. Not including overmolded discs, it seems to me that certain discs retain their rate of spin longer, of course it could be that I am simply throwing those cleaner.

I wonder if I could go to a ball golf pro and have them test this with one of the Doppler radars they use?

 

[KniceZ]

Are you sure?

I was going on the common use of the phrase "the air is "soupy" due to humidity". but after doing some quick research it appears this is wrong - water vapor is less dense than dry air. Still don't understand the optimal barometric pressure to reduce drag and still produce lift - but my bad on the humidity statement.

IIRC it only measured peak speed and spin.

I wonder if I could go to a ball golf pro and have them test this with one of the Doppler radars they use?

How did they measure spin? Did they use cameras? Most basic doppler radars (hand helds used in sports or police) measure the dominate doppler which is the forward velocity. You'd need a pretty sophisticated doppler radar to measure all the doppler components needed to determine spin rate.

Does anybody know the typical spin rate?

 

[sidewinder22]

I was going on the common use of the phrase "the air is "soupy" due to humidity". but after doing some quick research it appears this is wrong - water vapor is less dense than dry air. Still don't understand the optimal barometric pressure to reduce drag and still produce lift - but my bad on the humidity statement.

http://science.opposingviews.com/humidity-affect-speed-sound-22777.html
"The "rigidity" of air or its elastic modulus does not change with humidity. Density, however, does. As the humidity increases, so too does the percentage of air molecules that are water molecules. Water molecules are much less massive than oxygen, nitrogen or carbon dioxide molecules, and so the greater the fraction of air that is made up of water vapor, the less mass per unit volume, and the less dense the air becomes. Lower density translates into faster sound wave travel, so sound waves travel faster at high humidity."

How did they measure spin? Did they use cameras? Most basic doppler radars (hand helds used in sports or police) measure the dominate doppler which is the forward velocity. You'd need a pretty sophisticated doppler radar to measure all the doppler components needed to determine spin rate.

https://www.dgcoursereview.com/dgr/forums/viewtopic.php?p=97136

I have designed and tested a method for measuring the RPM's of a thrown disc. This design utilizes an on board LCD readout taken from a Powerball Gyroscope.

Does anybody know the typical spin rate?

Typical? Erin's typical seemed to be around 2000 RPM, max was 2300 RPM at 54mph, while 2000 RPM was 80mph. He also stated his friend who doesn't throw as far had a higher spin to speed ratio.

 

[Toro71]

http://www.dgcoursereview.com/forums/showthread.php?t=107491

 

[Toro71]

My number 1 question now is the same as yours--why does a disc turn right?

http://www.dgcoursereview.com/forums/showthread.php?t=107491

In this previous thread we came to the unofficial conclusion that HS turn (right for RHBH) is caused by a combination of the location of the moment of lift (determined by forward velocity and mold shape) and gyroscopic precession ("caused" by spin.)

If the moment of lift occurs to the rear of the center of the disc, precession will "cause" some of that lift to occur to the left/rear of the center of the disc, causing it to bank right and go a bit nose down.

I think in that thread the consensus also reached was that the single airplane wing analogy was closer to accurate than thinking of each side of the disc as a different wing.

 

[Toro71]

In this previous thread we came to the unofficial conclusion that HS turn (right for RHBH) is caused by a combination of the location of the moment of lift (determined by forward velocity and mold shape) and gyroscopic precession ("caused" by spin.)

If the moment of lift occurs to the rear of the center of the disc, precession will "cause" some of that lift to occur to the left/rear of the center of the disc, causing it to bank right and go a bit nose down.

I think in that thread the consensus also reached was that the single airplane wing analogy was closer to accurate than thinking of each side of the disc as a different wing.

LOL, just realized I'm responding to a post from '09

 

[sidewinder22]

LOL, just realized I'm responding to a post from '09

I was wondering where you were going with that.

 

[ToddL]

You're going to encounter quite a number of people on here who absolutely insist that it's all about gyroscopic precession. Personally, I don't think precession explains all of what you see. (For example, why do you get more turn when throwing into a headwind since the headwind doesn't produce any more spin and thus shouldn't produce any extra precession?) However, I no longer think it's really worth arguing with anyone about that.

I'll argue about it anyway.

Throwing into a headwind results in a higher airspeed for the disc, which will change the amount of lift and the location of the center of lift. It doesn't change the spin or precession; the force will precess 90deg around the axis of rotation with or without a headwind.

No headwind, 50 mph throw: The amount of lift created is .1 lbs of force with the center of lift located 1 inch behind the center of the disc. That force precesses 90deg in the direction of spin, ending up 1 inch to the left of the center of the disc, creating a rolling of 0.1 in-lb (moment = .1 lbs * 1 in)

10 mph headwind, 50 mph throw = same thing as no headwind, 60 mph throw: The disc creates .12 lbs of force with the center of lift 1.25 inches behind the center of the disc. The force precesses 90deg, ending up 1.25 inches to the left of the center of the disc, creating a larger rolling moment of 0.15 in-lb (moment = .12 lbs * 1.25 in)

(those numbers are completely made up)

Think of it like this. Three factors impart lift, or how air flows over the disc to give lift; wing and disc shape, forward speed, and spin. As the disc flies forward, there is lift on the wing, the faster, the more lift (again, the shape of the wing and disc impacts this). As the disc spins, one edge, the left side, is traveling faster relative to forward motion, and gets more lift; the other, the right side, is slower and gets less lift. Again, the wing and disc shape plays a large role role in this, some wings give more lift at slower speeds, i.e. under-stable discs; and of course, the more spin, the more lift on the left side, and the disc turns right. Beat in discs are less stable either because they increase lift on the left side, or decrease lift on the right side. If the disruptions, nicks and mars, in the disc increase pressure beneath the wing on the left side, then the disc flies less stable. If the disruptions in the disc decrease pressure on the right side, same result, it's just hard to know which it is without an accurate wind tunnel and some equipment.

A disc does not behave like a helicopter. The physics are different between a disc's monolithic wing and a helicopter's blades. The advancing vs retreating side of the disc do not create an imbalance in lift.

 

[wkelly42]

Is anybody else getting an ad for iTunes Gift Cards instead of the graphics in the original post?