I knew that, always enjoy a good point of argument...

On that note, enjoy Cajun:

Hi Chuck,

At 12:16 AM 1/29/2003 -0500, you ([email protected]) wrote:
>Question:
>
>Sharp leading edges.
>
>Do they result in pitch instability and/or "hunting" If so, is it due to
>slower flying speeds, weight/power ratio? If not , can you explain why?

Sharp leading edges are an interesting topic. And it has to do with boundary layers and boundary layer separation. Right next to any moving surface is a very thin layer of air called the boundary layer where the velocity changes very rapidly from the surface to the free stream. The flow in the boundary layer has very little energy .. so it is easily moved and modified by changes in pressure. Near a sharp leading edge, the pressure changes very rapidly with distance. So near a sharp leading edge (at very moderate angles of attack) the boundary layer will separate from the surface. When this happens, the effective shape of the surface changes (since the outer flow follows the edge of the boundary layer .. not the physical surface). If it changes to a nice smooth contour, the pressure gradient goes away and the boundary layer re-attaches .. only to be re-separated .. it's a very
unsteady phenomenon. It's actually the same physical process that produces a wing stall on any airfoil at higher angles of attack. But it is localized on a sharp leading edge. This would produce pitch instabilities, since the pressure profile across the entire wing is affected by separations near the leading edge.

A very special Thanks to Tom for this information..

Tom Benson
Engine Systems Technology Branch
NASA Glenn Research Center, MS 5-11 "Turn up the signal ..
Cleveland, OH, 44135 Wipe out the noise"