Just got our dog a new frisbee (he goes thru 'em pretty fast if we're
careless and leave them within reach after a session).

This one has a large outer wire rim, small inner ring, and stretched
radially between these 8 or 10 tapered spandex wedges (i.e., these
wedges get wider as they go radially outward). There are gaps of
comparable width between each of these blades, and each wedge is twisted
by 180 degrees between inner and outer rings with most of the twist
occurring close to the inner ring, so that these wedges give a
reasonably convincing imitation of a multi-bladed propellor.

This thing seems to fly just about as well, however, whether you fly it
right side up or upside down, and whether you flip it to spin CW or CCW.
(Hurts my left arm when I try to spin it CCW, however.) In other words,
if there's any helicopter effect here, it's pretty weak.

So, how does a frisbee fly, anyway? Another of his favorites is just a
10" diameter weighted outer rim filled in with a slightly saggy "cloth
drumhead", which visibly bulges upward 1" or so at the center into a
fair imitation of an airfoil when you throw it. I've always figured the
heavy rim kept the thing spinning and thus semi-rigid, and the forward
motion of the airfoil shape gave the lift.

"AES" > wrote in message
...

<< some text deleted>>

> So, how does a frisbee fly, anyway? Another of his favorites is just a
> 10" diameter weighted outer rim filled in with a slightly saggy "cloth
> drumhead", which visibly bulges upward 1" or so at the center into a
> fair imitation of an airfoil when you throw it. I've always figured the
> heavy rim kept the thing spinning and thus semi-rigid, and the forward
> motion of the airfoil shape gave the lift.

I'm a proponent of the Bernoulli theory (Stand by with flame deflectors). I
agree with the metal mass providing fly wheel effect and the airfoil for
lift. I'll add to that my theory that gyroscopic precession makes it tilt so
the lift vector turns it. Try changing from backhand to forehand to change
the direction of rotation.

One small quibble with your post. Frisbee is a brand name and deserves
trademark recognition. That is to say, while Frisbee makes a flying disc,
not all flying discs are Frisbees. If it don't say Frisbee on the gizzie, it
ain't.

AES wrote:
>
> So, how does a frisbee fly, anyway? Another of his favorites is just a
> 10" diameter weighted outer rim filled in with a slightly saggy "cloth
> drumhead", which visibly bulges upward 1" or so at the center into a
> fair imitation of an airfoil when you throw it. I've always figured the
> heavy rim kept the thing spinning and thus semi-rigid, and the forward
> motion of the airfoil shape gave the lift.

That, and a positive angle of attack. The spin keeps it gyroscopically
stable. As the forward motion decreases the Frisbee begins to settle,
increasing the angle of attack until becomes a kind of parachute. But
not always. Throwing the Frisbee up will give it a positive angle of
attack as it climbs. Once the forward motion stops the angle of attack
can become negative, generating downward lift and causing the Frisbee
to accelerate downward and back toward you like a boomerang. It comes
down faster than it would simply fall and it accelerates the whole way.

AES wrote:
> Just got our dog a new frisbee (he goes thru 'em pretty fast if we're
> careless and leave them within reach after a session).
>
> This one has a large outer wire rim, small inner ring, and stretched
> radially between these 8 or 10 tapered spandex wedges (i.e., these
> wedges get wider as they go radially outward). There are gaps of
> comparable width between each of these blades, and each wedge is twisted
> by 180 degrees between inner and outer rings with most of the twist
> occurring close to the inner ring, so that these wedges give a
> reasonably convincing imitation of a multi-bladed propellor.
>
> This thing seems to fly just about as well, however, whether you fly it
> right side up or upside down, and whether you flip it to spin CW or CCW.
> (Hurts my left arm when I try to spin it CCW, however.) In other words,
> if there's any helicopter effect here, it's pretty weak.
>
> So, how does a frisbee fly, anyway? Another of his favorites is just a
> 10" diameter weighted outer rim filled in with a slightly saggy "cloth
> drumhead", which visibly bulges upward 1" or so at the center into a
> fair imitation of an airfoil when you throw it. I've always figured the
> heavy rim kept the thing spinning and thus semi-rigid, and the forward
> motion of the airfoil shape gave the lift.

I'm not 100% sure and I'm not aerodynamicist, but I think two things
help a frisbee fly, or any disk even one lacking an airfoil shape.

1. The gyroscopic stabilization provided by the spinning imparted when
thrown. Just try to throw a frisbee or any disk without spinning it.
It won't go anywhere.

2. A small AOA imparted also when thrown. This is the essential part
and (1) above is really only important to the extent that it allows the
angle of attack to be maintained during flight.

Almost any object will create lift if it has some AOA. You can verify
this by extending your hand out of the car window when driving, which
most of us did as kids. If you rotate your hand from horizontal to say
30 degrees relative to the wind, you can create a fair bit of lift. And
most of our hands aren't exactly an ideal airfoil.


Matt

Casey Wilson wrote:

> "AES" > wrote in message
> ...
>
> << some text deleted>>
>
>>So, how does a frisbee fly, anyway? Another of his favorites is just a
>>10" diameter weighted outer rim filled in with a slightly saggy "cloth
>>drumhead", which visibly bulges upward 1" or so at the center into a
>>fair imitation of an airfoil when you throw it. I've always figured the
>>heavy rim kept the thing spinning and thus semi-rigid, and the forward
>>motion of the airfoil shape gave the lift.
>
>
> I'm a proponent of the Bernoulli theory (Stand by with flame deflectors). I
> agree with the metal mass providing fly wheel effect and the airfoil for
> lift. I'll add to that my theory that gyroscopic precession makes it tilt so
> the lift vector turns it. Try changing from backhand to forehand to change
> the direction of rotation.

Then how do you explain how well a simple flat disk such as a CD will
fly? It certainly has no airfoil shape.


Matt

Matt Whiting wrote:
> Almost any object will create lift if it has some AOA. You can verify
> this by extending your hand out of the car window when driving, which
> most of us did as kids. If you rotate your hand from horizontal to say
> 30 degrees relative to the wind, you can create a fair bit of lift. And
> most of our hands aren't exactly an ideal airfoil.

The magic question though is that B or N? I found as a kid (I guess I
was bored) that curving my hand resulting in better "lift", which would
seem to implicate B.

-Robert

Robert M. Gary wrote:

> Matt Whiting wrote:
>
>>Almost any object will create lift if it has some AOA. You can verify
>>this by extending your hand out of the car window when driving, which
>>most of us did as kids. If you rotate your hand from horizontal to say
>>30 degrees relative to the wind, you can create a fair bit of lift. And
>>most of our hands aren't exactly an ideal airfoil.
>
>
> The magic question though is that B or N? I found as a kid (I guess I
> was bored) that curving my hand resulting in better "lift", which would
> seem to implicate B.

Neither, it is C.

Matt

Matt Whiting > wrote in news:Fj%ng.29$Pa.4943
@news1.epix.net:

<Snipola>
> Then how do you explain how well a simple flat disk such as a CD will
> fly? It certainly has no airfoil shape.

They don't. At least none of the CD's that I've ever thrown went
very far. They all roll immediately and change direction.

I used to work at a CD plant, so I had a few to throw around.

Brian
--
http://www.skywise711.com - Lasers, Seismology, Astronomy, Skepticism
Seismic FAQ: http://www.skywise711.com/SeismicFAQ/SeismicFAQ.html
Quake "predictions": http://www.skywise711.com/quakes/EQDB/index.html
Sed quis custodiet ipsos Custodes?

AES wrote:
> So, how does a frisbee fly, anyway?
Its all done with invisable strings!
Rocky

"Casey Wilson" <N2310D @ gmail.com> wrote:

>
>"AES" > wrote in message
...
>
><< some text deleted>>
>
>> So, how does a frisbee fly, anyway? Another of his favorites is just a
>> 10" diameter weighted outer rim filled in with a slightly saggy "cloth
>> drumhead", which visibly bulges upward 1" or so at the center into a
>> fair imitation of an airfoil when you throw it. I've always figured the
>> heavy rim kept the thing spinning and thus semi-rigid, and the forward
>> motion of the airfoil shape gave the lift.

<more snippage>
>I
>agree with the metal mass providing fly wheel effect

There you have it. It's the fly wheel effect. Everyone knows that a
rapidly spinning massive disk is referred to as a fly wheel.
Obviously, our predecessors didn't give them that name just on a shim.
Obviously someone must have observed that they fly. Which is probably
why they make cars so heavy, so that their rather large fly wheels
won't lift them off of the ground.

Glad we got that one figured out.
--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.

alexy > wrote:

>"Casey Wilson" <N2310D @ gmail.com> wrote:
>
>>
>>"AES" > wrote in message
...
>>
>><< some text deleted>>
>>
>>> So, how does a frisbee fly, anyway? Another of his favorites is just a
>>> 10" diameter weighted outer rim filled in with a slightly saggy "cloth
>>> drumhead", which visibly bulges upward 1" or so at the center into a
>>> fair imitation of an airfoil when you throw it. I've always figured the
>>> heavy rim kept the thing spinning and thus semi-rigid, and the forward
>>> motion of the airfoil shape gave the lift.
>
><more snippage>
>>I
>>agree with the metal mass providing fly wheel effect
>
>There you have it. It's the fly wheel effect. Everyone knows that a
>rapidly spinning massive disk is referred to as a fly wheel.
>Obviously, our predecessors didn't give them that name just on a shim.
^^^^
If I'm gonna be a smarta$$, I should at least type more carefully! <g>

>Obviously someone must have observed that they fly. Which is probably
>why they make cars so heavy, so that their rather large fly wheels
>won't lift them off of the ground.
>
>Glad we got that one figured out.

--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.

> Matt Whiting > wrote in news:Fj%ng.29$Pa.4943
> > Then how do you explain how well a simple flat disk such as a CD will
> > fly? It certainly has no airfoil shape.

Skywise wrote:
> They don't. At least none of the CD's that I've ever thrown went
> very far. They all roll immediately and change direction.

I agree, CD's fly about as well as a crumpled up piece of paper. You
can throw them across the room, but they're not really flying due to
lift. Spinning the CD just keeps it somewhat stable, but I don't think
it generates any lift. I think throwing a CD vertically will go about
the same distance as throwing a CD horizontally.

"Skywise" > wrote in message
...
>> Then how do you explain how well a simple flat disk such as a CD will
>> fly? It certainly has no airfoil shape.
>
> They don't. At least none of the CD's that I've ever thrown went
> very far. They all roll immediately and change direction.

They fly as well as a frisbee (kleenex, q-tip, big deal) that has similar
size and mass distribution.

You can improve things at that scale somewhat by adding more mass around the
edge to stabilize it, but as anyone who's tried to toss a small 5" or so
frisbee knows, they really don't fly that well at that size, even when they
are designed as a frisbee rather than a CD.

IMHO, there are two key elements to frisbee aerodynamics: the mass and its
distribution (providing stability); and straight-up Newtonian deflection for
lift.

It's possible that there's a smidgen of airfoil effect due to some oddity of
airflow around the disc (air damming up at the front or something like
that), and of course there are a number of specialty discs (used in golf,
ultimate, etc.) that have specific aerodynamics built in that affect the
course of the disc. But otherwise, I would be surprised to find a frisbee
is a heck of a lot different, lift-wise, from your hand stuck out the window
of a car.

Pete

"cjcampbell" > wrote in message
oups.com...
> That, and a positive angle of attack. The spin keeps it gyroscopically
> stable. As the forward motion decreases the Frisbee begins to settle,
> increasing the angle of attack until becomes a kind of parachute.

True, but the increase in angle of attack is strictly a result of the change
in relative wind. The frisbee remains in basically the same attitude
throughout. It has no means of trimming for constant lift or anything like
that.

> But
> not always. Throwing the Frisbee up will give it a positive angle of
> attack as it climbs.

The vertical path is primarily a result of one throwing the frisbee in that
direction. The path would curve down ballistically except for the basic 1G
of lift that the relatively modest angle of attack, basically identical to
the AOA in straight and level flight, provides.

> Once the forward motion stops the angle of attack
> can become negative,

Negative. As in, not true. The frisbee still has positive angle of attack,
and descends back along roughly the same path it took upward. It's a bit
lazy-eight-ish and, as you know, you don't need negative lift to do those.

> generating downward lift and causing the Frisbee
> to accelerate downward and back toward you like a boomerang. It comes
> down faster than it would simply fall and it accelerates the whole way.

No, it doesn't come down faster that it would simply fall. It does
accelerate, just as any falling body accelerates, and just as the rising
body of the frisbee decelerated on its way up.

If the frisbee had positive lift going up and negative lift coming down, it
would never return to the person who threw it, or even come close. It would
have the same horizontal speed in each direction (reversed when plotted
against time), but significantly different vertical speeds (ie, not simply
reversed), resulting in significantly different flight paths.

Pete

Skywise wrote:
> Matt Whiting > wrote in news:Fj%ng.29$Pa.4943
> @news1.epix.net:
>
> <Snipola>
>
>>Then how do you explain how well a simple flat disk such as a CD will
>>fly? It certainly has no airfoil shape.
>
>
> They don't. At least none of the CD's that I've ever thrown went
> very far. They all roll immediately and change direction.
>
> I used to work at a CD plant, so I had a few to throw around.

You need better technique. I can get 50' out of a CD. A larger and
heavier thin disk will go a lot farther even.

Matt

Bucky wrote:

>>Matt Whiting > wrote in news:Fj%ng.29$Pa.4943
>>
>>>Then how do you explain how well a simple flat disk such as a CD will
>>>fly? It certainly has no airfoil shape.
>
>
> Skywise wrote:
>
>>They don't. At least none of the CD's that I've ever thrown went
>>very far. They all roll immediately and change direction.
>
>
> I agree, CD's fly about as well as a crumpled up piece of paper. You
> can throw them across the room, but they're not really flying due to
> lift. Spinning the CD just keeps it somewhat stable, but I don't think
> it generates any lift. I think throwing a CD vertically will go about
> the same distance as throwing a CD horizontally.

If you give it a positive AOA at release and it is spinning fast at all,
it will fly just fine for a ways. It is too light to go far, but that
isn't due to lack of lift.

Matt

"Peter Duniho" > wrote in message ...
> "cjcampbell" > wrote in message
> oups.com...
>> That, and a positive angle of attack. The spin keeps it gyroscopically
>> stable. As the forward motion decreases the Frisbee begins to settle,
>> increasing the angle of attack until becomes a kind of parachute.
>
> True, but the increase in angle of attack is strictly a result of the change in relative wind. The frisbee remains
> in basically the same attitude throughout. It has no means of trimming for constant lift or anything like that.
>
>> But
>> not always. Throwing the Frisbee up will give it a positive angle of
>> attack as it climbs.
>
> The vertical path is primarily a result of one throwing the frisbee in that direction. The path would curve down
> ballistically except for the basic 1G of lift that the relatively modest angle of attack, basically identical to
> the AOA in straight and level flight, provides.
>
>> Once the forward motion stops the angle of attack
>> can become negative,
>
> Negative. As in, not true. The frisbee still has positive angle of attack, and descends back along roughly the
> same path it took upward. It's a bit lazy-eight-ish and, as you know, you don't need negative lift to do those.
>
>> generating downward lift and causing the Frisbee
>> to accelerate downward and back toward you like a boomerang. It comes
>> down faster than it would simply fall and it accelerates the whole way.
>
> No, it doesn't come down faster that it would simply fall. It does accelerate, just as any falling body
> accelerates, and just as the rising body of the frisbee decelerated on its way up.
>
> If the frisbee had positive lift going up and negative lift coming down, it would never return to the person who
> threw it, or even come close. It would have the same horizontal speed in each direction (reversed when plotted
> against time), but significantly different vertical speeds (ie, not simply reversed), resulting in significantly
> different flight paths.
>
> Pete

So, tying this into a couple of recent threads... can a frisbee stall?
What would happen if it had dimples on it?
How about vortex generators? : ' )

Joe Schneider
N8437R



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On 2006-06-27, Peter Duniho > wrote:
> It's possible that there's a smidgen of airfoil effect due to some oddity of
> airflow around the disc (air damming up at the front or something like
> that)

A flat plate (which essentially is what the spinning CD will be) will
work as an airfoil if it has any angle of attack. John Denker's site has
some explanations.

--
Yes, the Reply-To email address is valid.
Oolite-Linux: an Elite tribute: http://oolite-linux.berlios.de

"Dylan Smith" > wrote in message
...
> On 2006-06-27, Peter Duniho > wrote:
>> It's possible that there's a smidgen of airfoil effect due to some oddity
>> of
>> airflow around the disc (air damming up at the front or something like
>> that)
>
> A flat plate (which essentially is what the spinning CD will be) will
> work as an airfoil if it has any angle of attack. John Denker's site has
> some explanations.

I think better analogies would be that it works like a sled on snow or a
rock skipping across water.

But wait a minute. A good frisbee thrower can make a frisbee rise
straight up (like a golf ball does). The frisbee may take one path for
awhile but then starts heading up, just like a properly hit golf ball
(although not mine golf balls :)). The golf ball is well understood to
rise as a result of its backward spin and low pressure on top (B).
Anyone who claims that a golf ball just follows its original path has
certainly never seen one properly hit.

-Robert

"Robert M. Gary" > wrote in message
ups.com...
> But wait a minute. A good frisbee thrower can make a frisbee rise
> straight up (like a golf ball does). The frisbee may take one path for
> awhile but then starts heading up, just like a properly hit golf ball

Yes. As I said in a different post, there are subtle aerodynamic effects
that can be used to affect the exact flight path of the frisbee. Release
attitude (pitch and roll), initial flight path, rotation speed, even impact
(intentional or otherwise :) ) with some object or surface mid-flight, these
all have small-but-interesting-and-useful effects on the exact course the
frisbee follows.

But those are very minor, the frisbee at all times is following basic rules
of inertia and lift (without the radical changes in configuration that CJ's
post suggests), and the original question was simply how does the frisbee
*fly*. That is, why is it possible to throw a frisbee and have it maintain
any stable path, and remain aloft longer than a thrown rock would.

Pete

"Peter Duniho" > wrote

> Yes. As I said in a different post, there are subtle aerodynamic effects
> that can be used to affect the exact flight path of the frisbee. Release
> attitude (pitch and roll), initial flight path, rotation speed, even
> impact (intentional or otherwise :) ) with some object or surface
> mid-flight, these all have small-but-interesting-and-useful effects on the
> exact course the frisbee follows.

A large factor is also the gyroscopic affects (effects?) resulting from the
change in plane of rotation, like the spinning bicycle wheel being held by
the person on the turntable.

That is why (for a right handed person, throwing with the standard clockwise
rotation) the release position for a straight throw, is with the side
opposite from the hand to be held lower than the side the hand is holding.
--
Jim in NC

Robert M. Gary wrote:
> But wait a minute. A good frisbee thrower can make a frisbee rise
> straight up (like a golf ball does). The frisbee may take one path for
> awhile but then starts heading up, just like a properly hit golf ball
> (although not mine golf balls :)). The golf ball is well understood to
> rise as a result of its backward spin and low pressure on top (B).
> Anyone who claims that a golf ball just follows its original path has
> certainly never seen one properly hit.

I haven't seen an analysis of a golf ball, but I saw an analysis a while
ago on a baseball. I think it may have been in Popular Mechanics, but
I'm not sure of that. The claim was that a baseball could be thrown so
as to rise (I forgot which type of pitch it is called) on its way to the
plate. The article pretty clearly debunked this myth. The spin
imparted to the ball can make it sink a little less slowly than a strict
ballistic trajectory, but the RPM required to actually make the ball
rise was something simply unattainable by a human.

I suspect the same is true of a golf ball (I'm a golfer, but not a
terribly good one). I've watched a number of balls hit by amatuers and
pros and I've never seen one rise above the launch trajectory. The
backspin will certainly make the trajectory much flatter than a
ballistic trajectory, but I don't think the ball will rise above a
tangent line to the path leaving the club face.


Matt

Matt Whiting > wrote in news:wN7og.35$Pa.5633
@news1.epix.net:

> Skywise wrote:
>> Matt Whiting > wrote in news:Fj%ng.29$Pa.4943
>> @news1.epix.net:
>>
>> <Snipola>
>>
>>>Then how do you explain how well a simple flat disk such as a CD will
>>>fly? It certainly has no airfoil shape.
>>
>>
>> They don't. At least none of the CD's that I've ever thrown went
>> very far. They all roll immediately and change direction.
>>
>> I used to work at a CD plant, so I had a few to throw around.
>
> You need better technique. I can get 50' out of a CD. A larger and
> heavier thin disk will go a lot farther even.

Well, the clean room was only so big.....

My take on it is that a CD simply has insufficient mass to
maintain gyroscopic stability. If you spin it fast enough,
yes, but by hand it's not easy. If it were metal I'd expect
it to fly just fine.

BTW, the CD's came out of the pressing machine with a small
plug in the center hole that had what amounted to a small
axle through it. This was punched out automatically by the
machinery. But, I had a few sample discs with it still in
place and you could actually make it spin like a top if
you could get it spinning fast enough. I usually used a
blast of compressed air, since it was handy. I mean FAST
fast. Twirling it by hand was not fast enough.

Brian
--
http://www.skywise711.com - Lasers, Seismology, Astronomy, Skepticism
Seismic FAQ: http://www.skywise711.com/SeismicFAQ/SeismicFAQ.html
Quake "predictions": http://www.skywise711.com/quakes/EQDB/index.html
Sed quis custodiet ipsos Custodes?

Skywise wrote:
> Matt Whiting > wrote in news:wN7og.35$Pa.5633
> @news1.epix.net:
>
>
>>Skywise wrote:
>>
>>>Matt Whiting > wrote in news:Fj%ng.29$Pa.4943
:
>>>
>>><Snipola>
>>>
>>>>Then how do you explain how well a simple flat disk such as a CD will
>>>>fly? It certainly has no airfoil shape.
>>>
>>>
>>>They don't. At least none of the CD's that I've ever thrown went
>>>very far. They all roll immediately and change direction.
>>>
>>>I used to work at a CD plant, so I had a few to throw around.
>>
>>You need better technique. I can get 50' out of a CD. A larger and
>>heavier thin disk will go a lot farther even.
>
>
> Well, the clean room was only so big.....

Yes, and it wouldn't be clean long if you were breaking CDs.


> My take on it is that a CD simply has insufficient mass to
> maintain gyroscopic stability. If you spin it fast enough,
> yes, but by hand it's not easy. If it were metal I'd expect
> it to fly just fine.

Yes, I also suspect that low mass is the limiting factor.

Matt

Matt Whiting wrote:
> Robert M. Gary wrote:
> I suspect the same is true of a golf ball (I'm a golfer, but not a
> terribly good one). I've watched a number of balls hit by amatuers and
> pros and I've never seen one rise above the launch trajectory. The
> backspin will certainly make the trajectory much flatter than a
> ballistic trajectory, but I don't think the ball will rise above a
> tangent line to the path leaving the club face.

Golf balls clearly have lift and Cl is one of the criteria used when
evaluating ball standards. Here is a pdf describing some of the
formuals used and how the coefficient of lift for different balls
effects flight.
http://www.usga.org/equipment/technica_report_for_publication.pdf

"It has been shown (Bearman, Harvey, 1976) that the two aerodynamic
coefficients, CD
and CL, are related to the dimensionless Reynolds number (Re) and spin
ratio (W)."

Spin is one component that determins the lift produced by the ball.

Here is an article from Cislunar Aerospace, Inc
http://wings.avkids.com/Book/Sports/advanced/golf-01.html

"How a Golf Ball produces Lift

Lift is another aerodynamic force which affects the flight of a golf
ball. This idea might sound a little odd, but given the proper spin a
golf ball can produce lift. At first, golfers thought all spin was
detrimental (not good). However, in 1877, British scientist P.G. Tait
learned that a ball, driven with a "backspin" (the top of the ball
turning back toward the golfer) actually produces lift.

The dimples also increase lift. Remember, dimples help keep the flow
attached to the sphere. The dimples also cause the flow to be "focused"
into the flow of the wake. In this figure, the smoke shows the flow
pattern around a spinning golf ball. The flow is moving from left to
right and the ball is spinning in a counter-clockwise direction. The
wake is being forced downwards. This downward movement of the wake
means that a lifting force is being applied to the golf ball.
"

-Robert

Looks like someone figured it out. A frisbee produces lift by traveling
through the air just like an airplane wing. The spinning of the frisbee
does nothing to increase the lift but it does produce the stability to
keep it properly oriented to produce lift.

http://www.physlink.com/Education/AskExperts/ae16.cfm

"A frisbee has the same shape, in side view, as an airplane wing: the
curved uppper surface causes the air to move faster accross the top
frisbee than it does across the 'flat' bottom, when the frisbee is
thrown. The 'lift' is then produced by the pressure difference between
the bottom and top sides of the frisbee - the lower pressure is on top
and the higher on the bottom - therefore the net force on the frisbee
will be up - producing the needed lift.

The turning of the frisbee mostly produces 'stability', that is the
spinning keeps the frisbee level in flight due to the 'gyroscopic'
effect, i.e. any spinning disc likes to stay spinning at the same
angle.

You can see for yourself that the spinning has nothing to do with the
actual 'flying' of the frisbee by noting that you can spin a frisbee in
place, on a stick or whatever, and it will not 'lift up'. You also can
see that the frisbee is still spinning at nearly 'full speed' when it
finally hits the ground, so you have another piece of evidence that
shows that the spinning doesn't lift the frisbee."

Robert M. Gary wrote:
> Matt Whiting wrote:
>
>>Robert M. Gary wrote:
>>I suspect the same is true of a golf ball (I'm a golfer, but not a
>>terribly good one). I've watched a number of balls hit by amatuers and
>>pros and I've never seen one rise above the launch trajectory. The
>>backspin will certainly make the trajectory much flatter than a
>>ballistic trajectory, but I don't think the ball will rise above a
>>tangent line to the path leaving the club face.
>
>
> Golf balls clearly have lift and Cl is one of the criteria used when
> evaluating ball standards. Here is a pdf describing some of the
> formuals used and how the coefficient of lift for different balls
> effects flight.
> http://www.usga.org/equipment/technica_report_for_publication.pdf

I never disputed that golf balls have lift. I simply said I don't think
they will rise above the launch line as was suggested.

The lift will cause them to descend more slowly that they would due to
ballistics alone, but that is far different than saying they will rise
upwards above the launch path.


Matt

It's more of a cheer, isn't it?

Fly wheel, fly wheel, go on, now, fly wheel!

"alexy" > wrote in message ...
> alexy > wrote:
>
>>"Casey Wilson" <N2310D @ gmail.com> wrote:
>>
>>>
>>>"AES" > wrote in message
...
>>>
>>><< some text deleted>>
>>>
>>>> So, how does a frisbee fly, anyway? Another of his favorites is just a
>>>> 10" diameter weighted outer rim filled in with a slightly saggy "cloth
>>>> drumhead", which visibly bulges upward 1" or so at the center into a
>>>> fair imitation of an airfoil when you throw it. I've always figured the
>>>> heavy rim kept the thing spinning and thus semi-rigid, and the forward
>>>> motion of the airfoil shape gave the lift.
>>
>><more snippage>
>>>I
>>>agree with the metal mass providing fly wheel effect
>>
>>There you have it. It's the fly wheel effect. Everyone knows that a
>>rapidly spinning massive disk is referred to as a fly wheel.
>>Obviously, our predecessors didn't give them that name just on a shim.
> ^^^^
> If I'm gonna be a smarta$$, I should at least type more carefully! <g>
>
>>Obviously someone must have observed that they fly. Which is probably
>>why they make cars so heavy, so that their rather large fly wheels
>>won't lift them off of the ground.
>>
>>Glad we got that one figured out.
>
> --
> Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.

"AES" > wrote in message ...
> Just got our dog a new frisbee (he goes thru 'em pretty fast if we're
> careless and leave them within reach after a session).
>
....
> So, how does a frisbee fly, anyway? Another of his favorites is just a
> 10" diameter weighted outer rim filled in with a slightly saggy "cloth
> drumhead", which visibly bulges upward 1" or so at the center into a
> fair imitation of an airfoil when you throw it. I've always figured the
> heavy rim kept the thing spinning and thus semi-rigid, and the forward
> motion of the airfoil shape gave the lift.

It is magic! Just like flying an airplane...

These folks are trying to explain away the magic here: http://mae.ucdavis.edu/~biosport/frisbee/frisbee.html

Really, it's just magic...

Matt Whiting wrote:
:
> I never disputed that golf balls have lift. I simply said I don't think
> they will rise above the launch line as was suggested.
>
> The lift will cause them to descend more slowly that they would due to
> ballistics alone, but that is far different than saying they will rise
> upwards above the launch path.

That is not what I've observed. When watching professional golfers hit
balls they appear to travel a traditional trajectory (often call the
"cannon" route) for the first couple hundred feet and then take a
noticable up path when they should start to sink. That up path seems
quite dramatic to me. Its often called the "second wind". That's just
my observation.

-Robert

In article . com>,
"Robert M. Gary" > wrote:

>
> The turning of the frisbee mostly produces 'stability', that is the
> spinning keeps the frisbee level in flight due to the 'gyroscopic'
> effect, i.e. any spinning disc likes to stay spinning at the same
> angle.
>
> You can see for yourself that the spinning has nothing to do with the
> actual 'flying' of the frisbee by noting that you can spin a frisbee in
> place, on a stick or whatever, and it will not 'lift up'. You also can
> see that the frisbee is still spinning at nearly 'full speed' when it
> finally hits the ground, so you have another piece of evidence that
> shows that the spinning doesn't lift the frisbee."

And, the "soft frisbees" that are sold in pet stores, and that fly quite
well, consist of a thick and quite heavy but soft tubular ring around
the outer perimeter (it's the size of your thumb or larger, and almost
feels as if it had sand in it), and then just a thin piece of plastic-y
cloth like a saggy drumhead across it.

Because of the weight of the outer ring, you can put a good spin on it
when you launch it, at which point the "drumhead" takes up an upward
dome shape, and it maintains that shape and spin throughout its entire
flight.

As another data point, a sudden gust of wind coming head-on at it can
make it suddenly "jump" vertically upward by a sizable amount -- and a
gust from behind can make it suddenly drop, even "crash-land".

So, the physics of this seems to hold up . . .

Robert M. Gary wrote:
> Matt Whiting wrote:
> :
>
>>I never disputed that golf balls have lift. I simply said I don't think
>>they will rise above the launch line as was suggested.
>>
>>The lift will cause them to descend more slowly that they would due to
>>ballistics alone, but that is far different than saying they will rise
>>upwards above the launch path.
>
>
> That is not what I've observed. When watching professional golfers hit
> balls they appear to travel a traditional trajectory (often call the
> "cannon" route) for the first couple hundred feet and then take a
> noticable up path when they should start to sink. That up path seems
> quite dramatic to me. Its often called the "second wind". That's just
> my observation.

That is the same thing people claimed about baseballs, but it turned out
to be a combination of an optical illusion (the mound being higher than
the plate) and people's mind expecting the ball to drop more quickly
than it did and then perceiving this as the ball rising, when it fact it
was simply dropping at a slower rate.

I was watching golf this past weekend and they had several side aerial
shots of the drives. It was pretty easy to see the trajectory of the
ball from the lift or whatever they were filming from as the height was
about the same level as the apex of the drive. The ball was clearly
dropping away from the path of launch when viewed from the side at an
elevated position.

If you get a chance to see these sorts of shots on TV in the future,
look closely and I think you'll see the same thing.


Matt

Matt Whiting > wrote in news:4chog.41$Pa.6285
@news1.epix.net:

> Skywise wrote:
<Snipola>

>> Well, the clean room was only so big.....
>
> Yes, and it wouldn't be clean long if you were breaking CDs.

True, that!


>> My take on it is that a CD simply has insufficient mass to
>> maintain gyroscopic stability. If you spin it fast enough,
>> yes, but by hand it's not easy. If it were metal I'd expect
>> it to fly just fine.
>
> Yes, I also suspect that low mass is the limiting factor.

Hmmm...I was just thinking...I bet the 12 inch glass masters
1/4 inch think would have gone pretty far too. :)

Brian
--
http://www.skywise711.com - Lasers, Seismology, Astronomy, Skepticism
Seismic FAQ: http://www.skywise711.com/SeismicFAQ/SeismicFAQ.html
Quake "predictions": http://www.skywise711.com/quakes/EQDB/index.html
Sed quis custodiet ipsos Custodes?

Matt Whiting wrote:
> That is the same thing people claimed about baseballs, but it turned out
> to be a combination of an optical illusion (the mound being higher than
> the plate) and people's mind expecting the ball to drop more quickly
> than it did and then perceiving this as the ball rising, when it fact it
> was simply dropping at a slower rate.

It may not be humanly attainable to make a baseball or golfball "rise",
but it's theoretically possible, right? I think wiffle balls can rise.

Bucky wrote:

> Matt Whiting wrote:
>
>>That is the same thing people claimed about baseballs, but it turned out
>>to be a combination of an optical illusion (the mound being higher than
>>the plate) and people's mind expecting the ball to drop more quickly
>>than it did and then perceiving this as the ball rising, when it fact it
>>was simply dropping at a slower rate.
>
>
> It may not be humanly attainable to make a baseball or golfball "rise",
> but it's theoretically possible, right? I think wiffle balls can rise.

I suspect it is theoretically possible if you can put enough energy into it.


Matt

Peter Duniho wrote:
> "cjcampbell" > wrote in message
> oups.com...
>> That, and a positive angle of attack. The spin keeps it
>> gyroscopically stable. As the forward motion decreases the Frisbee
>> begins to settle, increasing the angle of attack until becomes a
>> kind of parachute.
>
> True, but the increase in angle of attack is strictly a result of the
> change in relative wind. The frisbee remains in basically the same
> attitude throughout. It has no means of trimming for constant lift
> or anything like that.
>
>> But
>> not always. Throwing the Frisbee up will give it a positive angle of
>> attack as it climbs.
>
> The vertical path is primarily a result of one throwing the frisbee
> in that direction.
> The path would curve down ballistically except
> for the basic 1G of lift that the relatively modest angle of attack,
> basically identical to the AOA in straight and level flight, provides.

I don't quite fully understand what you are stating. Probably my English is
not good enough. Do you think the lift (created by AOA and possibly
bernulli-shaped foil) does create a significant amount of lift or not? You
say that the (vertical) path is primarily a result of throwing, hence
determined by ballistic effects. Yet you state 1G of lift. If the lift is in
the order of magnitude of 1G, then it's certainly significant. Most
airplanes create lift in that range.. That holds also with my experience,
you don't need to give a frisbee much initial rate of climb (or any at all)
to make it go a long way without loosing much altitude. Although I have
never measured this :-) I even believe you can make it climb after releasing
it with a horizontal trajectory.

I think I have an explanation, why it doesn't work so well when throwing
CDs: As has been stated, CDs will quickly turn sideways when released in an
horizontal attitude. But a frisbee will do just the same, only slower! If we
look at the frisbee (or CD) as an airfoil creating lift (whether newtonian
or benoullian is not really important), the center of the aerodynamic force
will alwas be forward of the middle line of the plane (as with all aircraft
wings). With the cg in the middle of the disk, the aerodynamic force
supporting it, will at the same time try to pitch it up! The gyroscopic
force from the rotation translates this torque round the horizontal axis
into one round the longitudinal axis, thus a rolling torque. In fact, when
throwing a frisbee, at the point of release the disk should be slightly
rolling in the opposite direction (and/or in a rolled attitude), to keep it
roughly horizontal as long as possible.

Only due to the much lower inertia this doesn't work as well with CDs, as
the roll is so much faster!

>> Once the forward motion stops the angle of attack
>> can become negative,
>
> Negative. As in, not true. The frisbee still has positive angle of
> attack, and descends back along roughly the same path it took upward.
> It's a bit lazy-eight-ish and, as you know, you don't need negative
> lift to do those.

As to the mechanics of making a frisbee return to the thrower, I don't
understand the explanation given by CJ, especially the assumption of
negative lift. However, it can not be explained purely by ballistics, unless
it's thrown vertical. There needs to be some aerodynamic force towards the
thrower beyond drag, drag stops the moment the forward motion stops.

If, at the point of zero horizontal movement, the disk maintains it's
attitude towards the horizon (that is, slightly pitched up in the direction
of the original movement) it is now also pitched down in the direction
towards the thrower. While moving towards terra firma, it will gain speed
towards him, just like an aircraft will gain speed at the expense of
altitude when pitched down.

regards,
Friedrich

"Friedrich Ostertag" > wrote in message
...
> I don't quite fully understand what you are stating. Probably my English
> is not good enough.

Probably. Nothing in my post states that the primary determinant for the
path the frisbee takes is ballistics, and in fact I specifically point out
that aerodynamic lift is what prevents a ballistic flight path.

> Spin is one component that determins the lift produced by the ball.


Spin is one component that is totally ignored when determining the lift
produced by the ball. Calling it lift is based not only on the false
premise that the ball is not spinning but on the intentional ignorance
of the the fact that it is.

> wrote

> Spin is one component that is totally ignored when determining the lift
> produced by the ball. Calling it lift is based not only on the false
> premise that the ball is not spinning but on the intentional ignorance
> of the the fact that it is.

???????????????????????????

What turnip truck did you just fall off of, and in what reality?
--
Jim in NC