dragchute has it right I'm afraid chaps! You see, most people believe that air weighs nothing and that anything suspended in it weighs nothing also. The fact is that whatever is in the airplane, whether it be air, water or solid - including feathers has a weight and it matters not whether the matter is lighter or heavier than air, it all weighs the same no matter what position it occupies within the space. In the scenario where the wood floats on the vat of water, does the vat weigh more or less when the wood becomes waterlogged and sinks to the bottom of the vat?