Airfoils for scale build...

[irish_lord99]

So I'm thinking of possibly building this Deperdussion 1913 some time in the future, but I'm not sure what to do for an airfoil. I know that a lot of people say that the original airfoil profile may not be suitable for a smaller scale model, but that leaves me wondering what to use?

Any thoughts? I want it to look as scale as possible, but still fly well.

Thanks

[Brandano]

I believe that on the older thin winged high cambered designs the scale wing will work just fine. The thicker, more modern profiles only began to be used much later, when engineers started to realize that the profile wouldn't perform as well on the full sized plane as it did on their wind tunnel scale model.

[podavis]

At very low speeds the under-cambered airfoils are superior to the standard 'fat' airfoils. The good low speed performance of GWS planes like the J-3 and Pico Moth demonstrate this. At the lowest speeds flat air foils are the best.

[irish_lord99]

Thanks guys, that helps out a lot. I love this forum, anytime I have a question there's answers here. :D

[KenSt]

I used a NACA 6409 on my 34" span Bleroit XI. It works fine, looks very scale, and has enough thickness not to NEED external bracing.

[ghoti]

At very low speeds the under-cambered airfoils are superior to the standard 'fat' airfoils. The good low speed performance of GWS planes like the J-3 and Pico Moth demonstrate this. At the lowest speeds flat air foils are the best.

Is this true? Best at what? How come we don't see them fly once in a while? Bill

[MarkusN]

Is this true? Best at what? How come we don't see them fly once in a while? Bill
Ever seen a dragonfly fly?
But then, insects flap their wings for both propulsion and lift, so they need more or less symmetrical characteristics.

But at very low Re there really is no big difference between a flat and a cambered plate.


As for the original question: The bird profiles of the old stringbags usually work quite well. You will need bracing, though.

[podavis]

MarkusN, maybe you read the same article by Jeff Raskin that I did? Intuitively I stick with the flat plate at very low Re because a flat plate is a cambered plate with an infinite radius. There has to be a limit to how much camber is effective and it has to be a function of Re. Can you refer me to a recently published resource with info about lo Reynolds numbers, I am interested.