So, how does a frisbee fly?

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.

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 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
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Sed quis custodiet ipsos Custodes?

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.

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

"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

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

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

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?