So, how does a frisbee fly?

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.

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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.

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"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