Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: chris on 19/06/2008 21:54:10
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If the structure of a wing is such that it creates lift when it's in its normal attitude, how does a plane remain airbourn when flying upside down?
Chris
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With the right angle of attack and high enough speed you can make almost any shape fly. If, when upside down, the leading edge of the wing is above the trailing edge you can create lift. It won't be very efficient and you won't go as fast but you will still be flying.
Aerofoil sections of faster aircraft are very mild so it is probably easier than with slow, old fashioned designs.
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Just to back up what sophie has said, here's a photo of Geofrrey Tyson, the Saunders Roe test pilot flying the SR-A1 inverted at one of the early SBAC shows at Farnborough in the early 1950's.
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.spatial.plus.com%2FSR-SR-A1-Another_Eyebrow_Raiser%21.jpg&hash=0d5ca245de1dc22f80847da8f325dee1)
Look at the angle of the wings - it wasn't pulling out of an inverted dive at the time but flying level. The angle of the fuselage is irrelevent - it's the angle of attack of the wings that give lift.
Edited to use a smaller image.
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Just to elaborate a bit: you can get symmetric and asymmetric aerofoils. The difference between them is that an asymmentric aerofoil is thicker on one side of the centerline than the other. This difference in thickness is called 'camber' - if an aerofoil is thicker above the centerline it has positive camber and if it is thicker below the centerline it has negative camber.
A wing with positive camber will generate lift at zero degrees angle of attack (the angle of the aerofoil centerline relative to the direction of travel) but an aerofoil with zero camber will not. However, an aerofoil with zero camber will generate lift with a positive angle of attack i.e. with the wing angled upwards (see pic above).
In general, if you want an aerobatic aircraft that can be controlled over a wide range of attitudes you use a symmetric aerofoil, which works just as well upside down as it does right way up - you just have to get the angles right - but if you're not planning on doing anything like that you'll be better off with an asymmetric aerofoil.
Modern aircraft use both leading and trailing edge flaps - sections that can be tilted up or down - to effectively change the camber of the aerofoil according to what's required i.e. takeoff, landing, cruise or aerobatic manuevouring.