My thanks to previous correspondents.

What intrigues me is the progression between a completely closed box and and an open cage. No doubt a sealed box includes the normal weight of the cararies, flying or not. When, flying the mass cannot "disappear": If small holes are drilled round/through the top (and only top) of the box then eventually under equilibrium the pressure just under the top can only be atmospheric at that height. So the excess over atmospheric pressure just above the base must be just enough to account for the weight (the air being "forced down by the bird's wings"). Conversely. with holes at the bottom, the pressure just under the top will be less than atmospheric and the total pressure difference on the top surfaces will "support" the canaries.

With holes top and bottom, there will be over and under pressures balanced to "support" the mass of the canaries while at the same time causing equal volumes of air to flow in through the top holes and out through the bottom holes (no matter what their relative and absolute sizes) keeping the whole system balanced and stable.

Do you agree ?

We are told that, counter-intuitively, aeroplanes are held up by a lower pressure on the top of the wings than on the bottom (venturi) : - not because the under surface drives the air down. If the canaries were gliders, how would the excess pressure on the base be generated ?The question seems to be - with an aerofoil moving through air with streamline flow where is the weight "taken" , eventually.

Further from the author of 8 tons....  I am grateful for the two answers so far submitted. What I really puzzle over is what happens if a "closed" container has holes (how far apart ?) round the bottom so the air pressure cannot be greater than atmospheric. 

Presumably eight tons of canaries sitting on perches in a lorry weigh eight tons. If the canaries are all flying in a wire cage there will be no effective weight. If they are all flying in a closed container - eight tons ? A "closed" container with holes in it so any air pressure is released ?

I have recently heard that a boomerang will return to the thrower, even in space. I was under the assumption that a boomerang works because of it's unique aerodynamic properties, these would be useless in the vacuum of space so I don't think the boomerang can return to the thrower, am I right?

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Note to the editor: Please, feel free to edit this question to your liking.

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(a) Let's imagine a boat. The engine pushes the boat in the direction the bow is heading. When rudder is applied, it pushes the aft to the side, changing direction the bow is heading to. Now,  the engine pushes the boat in the new direction. The turn has been made.

(b) Now let's imagine a plane. The plane engine pushes our plane in the direction the nose is heading. When rudder is applied it pushes the tail to the side, thereby changing direction the nose is heading to. Now  the engine pushes the plane in the new direction. The turn has been made.

But no... the turn is, in fact,  done differently.

(c)  The pilot applies the ailerons, banking the plane, thereby splitting the aerodynamic forces from the wings, that has been vertical so far, into vertical and horizontal components; the horizontal one pushes the plane to the side; now the plane is still heading in same OLD direction, but is moving in NEW direction, moving in fact sideways. But  the engine still pushes the plane in the OLD direction. To correct that, the pilot applies the rudder, to change heading of the plane to the direction of its true movement. Now , the engine pushes the plane in the new direction. The turn has been made.

(d) So, here comes the corker. As the rudder in (c) is used for precisely the same  (objective?), as in (b), that is to change the heading of a plane into new direction, why not skip ailerons altogether? Why does a sideways movement need to be introduced first? What purpose does it serve?

Over last twenty years, I have asked this question several pilots, including commercial ones, including airliner pilots. On the (a), (b) and (c)  they had said it is 100% correct. But on (d) best I got back is “It is more efficient that way”. While inquiring further “What does it exactly mean 'more efficient' ? “, they usually assume face, that says “you are obviously too stupid to comprehend... ” and leave it at that.... . Looked to me very much, that they did not know themselves..... .

So, anyone wants to have a go?

Jerzy Sierzputowski, Melbourne, Australia.

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Note to the editor: Please, feel free to edit this question to your liking.

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