Originally posted by Angus
I have touched the dihedral (somewhere in some thread) as a possible factor.
Why?
It's bound to reduce lift. A dihedral of 90 degs would for instance produce no upwards lift at all.
It's basically a stability enhancer, however it must effect lift, and therefore drag, be it little or not.
At the wingtips one has upwash, right outside of it. This will probably give the tip a bit of a push upwards.
(what turned out to be strong enough to bend the Hurricane's wings upwards when dived to the limit)
So I'm wondering where this would come into the equation.
For some reason, a typical dihedral is somewhere between 4% and 6%.
Any comments?
As I recall from ground school, dihedral enhances directional stability. If a sideways air load strikes the top of one wing, it must strike the bottom of the other. This rolls the plane into the sideways load, maintaining direction. Another commonly used explanation is that when the plane rolls, the lift of the high wing decreases as the lift of the low wing increases--at least until the low wing becomes horizontal, at which time the high wing lift decreases faster than the low wing's lift. The high wing will always have a steeper angle to the horizon, you see.
The wingtip vortices are ALL drag--any lift they (arguably) provide is overshadowed by the huge drag penalty--remember that moving air is work (in the sense of basic physics) and work requires energy. Many modern planes have wingtip end plates to decrease the amount of spanwise spillage--the actual cause of vortices. Theoretically,this reduces drag and also decreases the strength of the vortex that has been blamed for so many "clear air turbulence" accidents when light planes follow heavy planes too closely.
According to mr. trigonometry, by the way, dihedral should have a very small effect on lift. Doing the math, a 4 degree dihedral would decrease lift by 7% in straight, level flight.
shubie
