The following are submitted questions from inquiring minds and our answers. Check them out before sending in your question(s) via our Contact page.
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Why does the lower pressure/vacuum break down on the upper surface of the wing?
A) The lift on a wing is caused by air being drawn almost straight down by a lower pressure. This lower pressure draws in a layer of air over the wing. The pressure is lowest near the front of the wing and increases toward the trailing edge of the wing. The air is always at a lower pressure, but it is flowing into a higher pressure. It is kind of flowing uphill. If the angle of attack is too great, it runs out of energy before it gets to the trailing edge, and so it separates. If the air that is doing the lifting hadn’t drawn in that, the wing would not have stalled so soon.
For details regarding how the lower pressure, aka vacuum, breaks down, refer to Lift Details Stall section
If we're matching forces, why does a 1 ton airplane need to move many tons of air to develop lift?
A) It’s like shooting a bullet into a block of wood to move it. A small bullet has to go very fast. A large bullet can go much slower. The larger the bullet the slower the bullet has to go and thus the less energy has to be expended. The wing is efficient because is accelerates a lot of air at a slow speed.
You state all wings have exist on the same lift line. But I've seen graphs that show a wing's flap position changes the slope of the lift line. Why the discrepancy?
A) All real wings have different lift lines. They are similar when the lift is corrected for such parameters as area and aspect ratio. When you lower the flaps, you are reconfiguring the wing. You are certainly changing the aspect ratio and the angle of attack.
I thought an aircraft propeller moved air like a boat propeller does by pushing on the air?
A) You are not the first to have this confusion. Some once thought that a rocket would not work in space because there was no air to push against. Clearly, they work well there. The propellers accelerate the air or water to create a thrust forward. Energy is put into the fluid. It is like when you throws a large rock. It goes one way and you go the other.