Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: DoctorBeaver on 11/09/2007 08:07:47
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We get a few military jets around here at low altitude. I saw 1 yesterday while I was working in the garden. It came across our local hill, banking so sharply to its right that its wings were vertical.
Apart from waving my rake at it menacingly and hurling curses in its general direction for startling me & disturbing my rural peace & quiet, I got to wondering how it was still in the air. Planes get their lift from their wings, so if the wings are vertical, how can they stay up in the sky?
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Engine thrust - surely with a jet engine - must be an important parameter, too. Druing air shows, you see planes flying upside down, if lift came from the wings alone this should create negative lift. But I don't remember seeing a glider fly upside down, maybe they can perform rolls, but I can't recall ever seeing even that.
Planes - just like motorcycles (or even bicycles)- bank or tilt when turning so that this angle matches the reultant from gravitational force on one hand and centrifugal force on the other.
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I thought flying upside-down involved using the wing flaps to create lift on the underside of the wing.
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Although aircraft wings are shaped to give the best lift when they are the correct way up they will still give lift when inverted if the angle of attack is modified albeit somewhat less efficiently
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Although aircraft wings are shaped to give the best lift when they are the correct way up they will still give lift when inverted if the angle of attack is modified albeit somewhat less efficiently
Even when they're vertical?
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Military aircraft can turn at anything up to 9G hence the wing can be near vertical and still be providing lift,see contribution from Eric 1 and of course some lift is provided by the body of the aircraft at high speed.
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You are missing the point - a plane generally banks in a turn. Generally, if you put a plane into a bank, it will automatically initiate a turn, and so you have G forces that are not merely pulling the aircraft down, but also pulling the aircraft sideways. So long as the lifting forces for the wings are directly opposed to the composite G forces, the plane will fly. If the plane is trimmed so that the composite forces are not opposed to the lift forces, then you will lose efficiency in flight (a great way to cause a plane to rapidly fall through the air is to throw the ailerons in one direction, so trying to force the aircraft into a bank, while throwing the rudder in the opposite direction (on powered planes, unlike gliders, the rudder is rarely used to initiate a turn, but it can influence the turn).
Yes, in military jets, where the thrust of the engine is sufficient for ballistic flight (i.e. the engine thrust exceeds the weight of the aircraft), you don't even need wings for lift - and you can just stand the plane on its tailpipe, and fly straight up; but you are scarcely likley to achieve this in a Cessna 152, where the propeller thrust is only just enough to keep the plane flying with the wings attached.
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Thanks, everyone. I get it now.
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a plane generally banks in a turn.
It's the only way to turn a plane, effectively.
If you just turn the 'rudder' to left or right, there is so little force to change direction that the plane will just face left or right but carry on (crabwise) in the same original direction.
Banking will produce loads of force.
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a plane generally banks in a turn.
It's the only way to turn a plane, effectively.
If you just turn the 'rudder' to left or right, there is so little force to change direction that the plane will just face left or right but carry on (crabwise) in the same original direction.
Banking will produce loads of force.
I knew that. My question was about how the plane could bank so much that the wings were vertical yet still remain in the air.