Whale in an Airplane

RalphInCA

RalphInCA

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physics/aerodynamics question:

If a whale is in a tank of water and the tank of water is in the cabin of a airplane, does the CG of the airplane change when the whale swims from the front to the back of the tank?
 
I would think it depends. The whale probably has a different density than the water he displaces. If so, then the answer is yes. If his density is the same as the water, then no.

BTW, that must be one really big airplane!
 
Fallsrider said:
I would think it depends. The whale probably has a different density than the water he displaces. If so, then the answer is yes. If his density is the same as the water, then no.

BTW, that must be one really big airplane!
Click to expand...
Yeah. I was just about to edit my post to say much the same thing.
 
I'm no biologist, but I'd guess whales are pretty close to neutral buoyancy. So no. Unless the distribution of their mass is really really asymmetrical within the body for some reason.

Edit: discussion of the "birds in a truck" problem comes next?
 
The whale's buoyancy will be determined by how much air he's holding, but I suspect he will be close to neutrally buoyant. He will therefore displace water that weighs what he does, so when he moves from one end of the tank to the other an equivalent weight of water will shift to the area he vacated.

So no, the CG will not change appreciably, certainly not by the weight of the whale.
 
RalphInCA said:
physics/aerodynamics question:

If a whale is in a tank of water and the tank of water is in the cabin of a airplane, does the CG of the airplane change when the whale swims from the front to the back of the tank?
Click to expand...
no
 
Disclaimer - I actually do not know the answer to this problem. I heard the problem presented on a podcast without the answer given.

Here's the way I think about it:

The weight of the whale becomes part of the total weight of the water. The mass of the whale does displace water but since water is a fluid the displaced water is evenly distributed at all times.

So no matter where the whale swims the CG would be the same. The forces placed on the airframe is the same.
 
As long as the whale is floating the CG does not change. If you feed it enough lead that it sinks to the bottom, or if you hang it from a sling, then the CG moves.
 
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There be whales here!
 
The real issue is the airspace above the water that is needed for the whale to breathe. That allows for the water to slosh around and shift CG.
 
How does the whale breathe in a sealed tank of water?
 
I think the premise that sloshing aside, the CG remains constant when the whale swims back and forth is valid as long as the whale is at or above neutral buoyancy. If the whale is below neutral buoyancy, e.g. resting on the bottom or imparting a downward force to stay afloat, then the CG would change.
 
What kind of whale was it? A Pilot whale would know better than to swim back and forth possibly upsetting the CG. A Blue whale would probably just float there depressed and not cause issues. A Killer whale wouldn’t care.
 
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