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In this month’s Pilot Magazine quiz, question 5 has us imagining that a Beluga A300-600 is transporting 3000 kilos of unrestrained live geese. During the flight they all take-off. The magazine suggests that this will have no impact on the weight of the aircraft. Shurly Shome Mishtake.
Let us imaging that each of these geese were sitting on a set of sensors attached to a digital weight read-out. As this mass disturbance took place the scales would drop from 3000 kilos to 0 kilos. Now I agree that if they were all in ground effect there would still be some weight on the aircraft but I maintain the weight of the aircraft would drop and it would shoot up in the air. </font>
The aircraft will have a marginally lower weight but the mass will not change if the geese all decided to fly at the same time. I should point out that the changes in weight we a re taking about here are
VERY small.
The reason for the weight decrease is that the geese will move slightly further away from the Center of Mass (COM) of earth.
As you know the gravity formulae is gravity=G*M1*M2/R^2, as the geese move slightly further away from the COM of earth the gravity acceleration will
SLIGHTLY decrease (as a function of 1/R^2).
As you know the weight of an object is give by weight=gravity*mass, as the gravity reduces slightly the weight reduces slightly. The best example of this is in astronauts who are large distances away from earths COM, their mass remains unchanged, but their weight has reduced significantly as a function of 1/R^2.
This is fairly basic physics, what they are saying is analogous to saying that a hovercraft overcomes gravity to float above the ground, we know this is not that case. Using the hovercraft analogy, does a person sitting on a hovercraft weigh less when the hovercraft is floating above the ground ? Does a persons mass change ?
The answers to these two questions are yes,
SLIGHTLY as I have said above as you a moving away from earths COM by the smallest amount, no you don’t lose any mass.
The mass of the aircraft remains unchanged if you view the aircraft and its contents as a control volume, then the aircraft can been seen as point mass based upon its COM.
Sorry to disappoint you, but if this was the case Boeing and Airbus would have air seats to levitate everyone above the floor to reduce the takeoff weight.
Cheers
