Boomerangs in space...

[dlavery]

I recently ran across this article about Takao Doi's on-orbit boomerang toss, and the interesting results. My college roommates and I used to have long arguments about why boomerangs fly and the effects that actually cause them to return to the thrower. We argued endlessly about whether the dominant factors were from the aerodynamic effects, the rotating off-center center-of-mass, the relentless pull of gravity on the J-shaped trajectory, etc, etc, etc. Every argument was invariably followed by a very-late-Friday-night experiment in the apartment parking lot, several off-target throws, missed catches as we stood too close to the neighbors cars, broken car windows, car alarms going off, running away as the security patrol came around, etc, etc, etc.

Anyway, it does seem that this experiment indicates that the returning flight path of a boomerang is caused by dynamic CG-effects alone. If the boomerang does not require gravity to fly properly (since the zero-gravity effects do not impact the flight of the boomerang) then the lift effects of the rotating blades must also be excluded. Any thoughts?

-dave



.

[Molten]

That is awesome. I never gave it much thought myself, but that does sound cool. I am looking forward to the video being posted.

[i_am_samus]

I was not aware that the blades created the lift effect of the boomerang, but rather it depended on the throw.

And if gravity isn't a factor, then you should theoretically be able to throw it horizontally and expect it to come back.

[Schnabel]

Now wait a minute, we learned in physics that it isn't truly 0 Gravity. We learned that the space craft, with all of it's contents, is just as a constant acceleration downward. Would gravity still have an effect on this then. Also what about gravity from the Moon, Sun, and other stars?

[vivek16]

Originally Posted by Schnabel

Now wait a minute, we learned in physics that it isn't truly 0 Gravity. We learned that the space craft, with all of it's contents, is just as a constant acceleration downward. Would gravity still have an effect on this then. Also what about gravity from the Moon, Sun, and other stars?

Yes, gravity still has an effect on it but in relation to the spaceship and thrower, the boomerang is nearly weightless. (I think)

I don't think the gravity from the Moon, Sun, and other stars is as significant as the 9.8m/s^2 on the earths surface.

-Vivek

[DonRotolo]

I am having some serious brain fuses popping... The boomerang's return is from aerodynamics, it flies in a banked attitude that causes it to turn, with a proper throw it returns to near the release point. The shape of the 'wing' is what allows it to maintain altitude while the off-wing COG makes it bank and 'climb' through its turn.

In orbit there is no aer to effect aerodynamics.

Could Doi be messing with our heads? Part of me thinks so, but these astronaut guys don't seem the type to play a prank on the unsuspecting public. Thus the fuses.

I suppose the video might convince me. Maybe they'll let me go up and see it for myself?

Don

[Jeff Rodriguez]

Originally Posted by Don Rotolo

I am having some serious brain fuses popping... The boomerang's return is from aerodynamics, it flies in a banked attitude that causes it to turn, with a proper throw it returns to near the release point. The shape of the 'wing' is what allows it to maintain altitude while the off-wing COG makes it bank and 'climb' through its turn.

In orbit there is no aer to effect aerodynamics.

Could Doi be messing with our heads? Part of me thinks so, but these astronaut guys don't seem the type to play a prank on the unsuspecting public. Thus the fuses.

I suppose the video might convince me. Maybe they'll let me go up and see it for myself?

Don

Sure there' air. He threw it while inside the craft, not outside. Aerodynamics still apply.

[SteveJanesch]

Gotta get my hair splitter out...wait...oh, here it is.

There's a whole lot here that we don't know - that article is basically a sound bite. Having not seen the experiment ourselves, we don't know what Doi meant by "flew the same way it does on Earth". Did it just curve a bit, or really come back to where it was thrown? Was it a really-scaled-down experiment? If I recall correctly, last time I threw a boomerang it traveled in about a 25 foot radius and up to 15 or 20 feet in altitude. I'm pretty sure the inside of the ISS isn't that big.

I'm a little confused now about the contribution of gravity to the boomerang's flight. Was the experiment performed repeatedly and with the same results in different orientations? I recall that the boomerang's trajectories (bank, climb, radius) are sensitive to their orientation at release as well as forward speed and spin, and that the boomerang banks differently as it follows its path. Doesn't the sensitivity to orientation have to be the influence of gravity, if forward speed and spin are constant? If gravity is out of the equation, wouldn't the boomerang follow a perfectly circular path (which wouldn't be "the same way it does on Earth")?

Can't wait for the video.

- Steve

[Molten]

From my experience, boomerangs don't come back for me. So for me throwing it and it going straight would be "the same way it does on Earth". Just a thought.

[ChrisH]

Originally Posted by dlavery

Anyway, it does seem that this experiment indicates that the returning flight path of a boomerang is caused by dynamic CG-effects alone. If the boomerang does not require gravity to fly properly (since the zero-gravity effects do not impact the flight of the boomerang) then the lift effects of the rotating blades must also be excluded. Any thoughts?

Actually I don't think it is true the lift must be excluded. Gravity may not have all that much to do with the flight path here on Earth. The only thing gravity does is insure a landing, somewhere.

I can't recall ever playing with a boomerang, but I have thrown plenty of rocks. Once you throw a rock, it only changes course when acted on by an outside force. A rock with the proper shape might be able to curve a little bit due to aerodynamic forces, but not to the same level as a baseball which is much less dense and therefore requires less force to change course visibly. But a rock on Earth will always tend to arc its path down no matter what angle you throw at because gravity is acting on it.

Take the same rock up in the Shuttle and throw it. It will travel on the same vector until it hits the wall. This assumes minimal aerodynamic effects. The one thing it won't do that it will do on earth is arc downwards. If you were to repeat the experiment outside the Shuttle, the rock would continue forever or until it got pulled in by gravity whether it be Earth's or some other body's.

So some force must be acting on the boomerang to cause it to return to the thrower, and the only place for that force to come from that we know is the air in the Shuttle. There are alternative explanations (ie telekenesis) but I don't think any of them have been demonstrated to exist.

So the way I would explain it is this:

On Earth the thrower throws a little high to account for the downward acceleration due to gravity, but the force due to gravity is much smaller than the force required to cause the boomerang to return. I'm not sure what a boomerang weighs, but if somebody can tell me it shouldn't be too hard to calculate some reasonable approximations to verify this.

In the atmosphere of the shuttle, there is no need to "add a little up" but due to the inexperience of the thrower and the casual setup (no mechanical throwing arm) it is difficult to tell whether lack of the minor effect of gravity affects anything.

Finally, were the experiment to be repeated outside the station and shuttle I predict that the boomerang won't, because there will be no aer to provide the aerodynamic force to cause it to return. But for this one you'd better have that mechanical throwing arm, because as I understand it, it would be very hard to throw one in an EVA suit due to low mobility.

If somebody will send it up, I volunteer to build a throwing arm and run the tests, on location, personally.

[Leav]

I think that the effect that makes the boomerang turn is the difference of air speed across it's wings cause by the rotation.

(see attachment)

The center of mass is moving forward at speed V
the left side has an effective speed relative to the wind V1
the right side has an effective speed relative to the wind of V2

the speed hold the relation: V1<V<V2

thus the right side would have more lift, causing the boomerang to rotate around it's axis (the axis which is pointing in the direction of V).

This only creates a corkscrew effect. (similar to pushing the joystick left in an airplane)

To explain the banked turn I believe you must consider the Boomerang as a flying wing, which is always creating lift perpendicular to the surface it's rotation describes.

Since the wing is curved, the center of this force is off the center of gravity, creating another rotation motion - this time similar to that created in an airplane when the stick is pulled back.


I believe these two phenomenon, not only explain the Boomerang's behavior here on earth but also serve to explain why the same effect would occur in space.

-Leav

[raymaniac]

The way boomerangs work is simple: magic.

Sheesh, I'd expect the intelligent people of CD to know that.

[Lil' Lavery]

http://www.youtube.com/watch?v=q2ozs...g_zero_gravity

[Molten]

Awesome video. Now this just gives me more to wonder. Am I the only one watching it to notice that it is a different kind of boomerang then we were discussing before? Is this going to have any effect on the science?