Quote:
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.