>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 ?<

With reservations. It is not clear from your wording, but with holes top and bottom, it is logically possible for there to be some reduction of weight as experienced by the chassis of the truck.

Also, beware -- "keeping the whole system balanced and stable" is not necessarily a simple matter. In real life such systems are prone to developing oscillations, often disastrously so. The net effect is that the books may balance, but only over a sufficient period to cover some cycles of oscillation.

>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. <

As a schoolchild I also learned that about 80+% of the lift was Bernoulli effect from above, but I have since encountered some emphatic reactions to the contrary from aerodynamicists. High performance planes especially are likely to rely more on angle of attack and flat wings, than reduced pressure on a curved upper surface. This is why many of them fly about as well upside down as erect. At a good speed even the curved-surface wings work upside down at the right angle of attack. (If not, the "lift" would lift the plane right down through the ground, no?)

>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.<

No matter what the explanation for the lift mechanism might be, it always amounts to the necessary upward force being derived from direction (or deflection) of a suitable mass of air downwards at a speed sufficient to counter the downward force of the mass and momentum of the plane. This generally is the sum of the reduced pressure above, and the increased pressure below. That irreducible requirement remains in force whether we are discussing a frisbee, a helicopter, a canary, a bumblebee, or an A380.

Was that what you had in mind, or have I misunderstood the intent of the question?

Jon

From the original author of the question.

It has been pointed out to me that the "Myth busters" on tele looked into this. They found no change in weight when a helicopter  or a flock of birds  was either resting or flying. See Google for myth busters and birds. I have not found an experiment on drilling bigger and bigger holes in the sealed container.