Aeronautical engineer question?

[Kitfox Pilot]

I am far from the title but my question is, what percent of the weight of a kitfox sti is carried on the bottom of the main wing and what percent is carried from the lift on top of the wing?
I have looked at several wing profiles in the NACA files but I am still not smart enough to figure anything out.
http://airfoiltools.com/search/index...&m%5Bsort%5D=1

[jiott]

I'm no AE either Harlan, but it's an interesting question that I also have wondered about. I think it has been established that a large portion (how large?) of the lift is due to the downward deflection of the airstream which Newton's Second Law says an equal upward force is produced, which is why a flat sheet of plywood will fly. The Bernoulli reduction of pressure on the top side of course adds to it, but my suspicion is that this force is smaller, at least at the speeds we normally fly. I'm sure this mix of lift forces changes substantially as AOA changes, such as cruise vs. landing/takeoff. In the old days wings were usually much thicker; I think because people were more tuned into the Bernoulli Principle rather than downward deflection reaction forces, because it takes wind tunnels and fluid dynamic modeling to study this. Maybe someone who really knows will chime in with some numbers?

[Kitfox Pilot]

I'm no AE either Harlan, but it's an interesting question that I also have wondered about. I think it has been established that a large portion (how large?) of the lift is due to the downward deflection of the airstream which Newton's Second Law says an equal upward force is produced, which is why a flat sheet of plywood will fly. The Bernoulli reduction of pressure on the top side of course adds to it, but my suspicion is that this force is smaller, at least at the speeds we normally fly. I'm sure this mix of lift forces changes substantially as AOA changes, such as cruise vs. landing/takeoff. In the old days wings were usually much thicker; I think because people were more tuned into the Bernoulli Principle rather than downward deflection reaction forces, because it takes wind tunnels and fluid dynamic modeling to study this. Maybe someone who really knows will chime in with some numbers?

Thanks Jim. I have always thought there was a good bit of lift from the top of the wing in the thinner high-speed air if you will. But after watching some videos of the top of fabric planes in flight I've notice some with loose fabric sometimes just kind of waves or ripples in the wind at times instead of Constance ballooning like it was stretched tight lifting. This has led me to believe that most of the plane is carried on the underside of the wing. Nothing scientific about my quote just observations.
I'm sure someone will know. Harlan

[109JB]

The pressure distribution varies with angle of attack, so can't really give one number percentage. Have a look at this example of pressure distribution and you will get an idea.

[Kitfox Pilot]

You are absolutely right John. I am interested in cruise flight. I failed to mention that. Thanks.