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Old 01-23-2009, 12:07 PM
Join Date: Oct 2004
Location: Arroyo Grande, CA
Posts: 719
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Default RE: Sterling Spitfire

Hi Chris,

Sorry to take so long in replying to your question on incidence, but I changed internet service providers and it took longer than expected to get back on line.

Regarding my inconsistencies in incidence angles, I'm afraid I played fast and loose with with how the angles are measured. The "chord line" of an airfoil is typically a line drawn from the center of the leading edge radius to the point of the trailing edge. If the airfoil is symmetrical, such as on a stabilizer, then the "chord line" and the angle of zero lift are the same. But for non-symmetrical airfoils, the angle of zero lift doesn't coincide with the chord line. To be consistent, I should have used all chord lines or all zero lift angles, but not mixed the two.

In my January 5 post, I said, "the stab should be about 1° negative relative to the wing". What I was trying to express there is the angular difference between the zero lift line of the wing and the zero lift line of the stab. When we use the chord lines in a discussion it is very common to find the stab positive relative to the wing if the wing airfoil isn't symmetrical.

Did I clear it up or just make it worse?