Good Undercambered Airfoil?

[vonJaerschky]

Anybody know a good, undercambered airfoil that would be suitable for a slow flying, lightly loaded WW1 high aspect ratio wing? I have Profili 2 Pro, but there are so many airfoils that I don't know where to start.
Thanks for any advice.

[groundfx]

How big? The best choice depends on the Reynold's number you're operating at.

Here's some possible starting points, I'd be looking at:

If you're talking very low Reynolds numbers a simple 4% curved plat is known to work well. A so-called 4-40 (4% camber with peak at 40% away from leading edge) works better. See http://jef.raskincenter.org/published/airfoil.html

If you're talking a little larger, maybe look at something like a (Michael Achterberg) MA409.

If it was a bigger model, I don't see a benefit of using an undercambered airfoil. I'd be tempted to fake it and just use a good-old flat bottom airfoil. Is there a reason why you want an undercambered airfoil?

[vintage1]

Undercambered wings stall slower (and a bit more viciously) than other types..

If its WWI scale, copy the original and use the rigging to achieve torsional rigidity. Also wash the wings out a bit.

[vonJaerschky]

Wingspan will be around 78", with a chord of 7.25". The main reason I wanted to go undercambered is the scale appearance. I'm flying Aerodrome R/C's 57" Albatros C.III, and it has a scale undercambered airfoil and flies beautifully. Lots of lift, and a real treat on landing and takeoffs. And with the scale undercambered airfoil, it looks perfect.

Thanks for that link; interesting reading.

There will be lots of rigging to maintain torsional rigidity, and I would probably use carbon tube spars, too.

[vintage1]

Shoot a pigeon, and examine the wing section. Thats probably how they did it WWI.

Previous to that, the examined the entrails, and were far less successful.

[yoyoML]

Shoot a pigeon, and examine the wing section. Thats probably how they did it WWI.



I wonder what they shot to design the Albatross...

[vonJaerschky]

Shoot a pigeon, and examine the wing section. Thats probably how they did it WWI.

Previous to that, the examined the entrails, and were far less successful.

I wish you had told me that two days ago, when my kids found an injured pigeon in the back yard. They were silly enough to take it to the local SPCA. "Pidgy" could have been sacrificed for science. What a shame. :D

[vonJaerschky]

I wonder what they shot to design the Albatross...

...or a Fokker...

[Sparky Paul]

When Albatross went to the V... they copied (the fools) the wing strut arrangement of the Nieuport 17. And golly, their wings began to fall off too!

[BMatthews]

A friend of mine built a SPAD XIII over the winter using the scale airfoil and it flies superbly. I would not have suspected that it would be all that great but these old airfoils seem to work very nicely.

[Ollie]

It is bad luck to shoot an albatross bird.

[vonJaerschky]

A friend of mine built a SPAD XIII over the winter using the scale airfoil and it flies superbly. I would not have suspected that it would be all that great but these old airfoils seem to work very nicely.

That wouldn't be Greg Heath by any chance, would it? I saw his small SPAD at Chilliwack this year, and it was absolutely gorgeous. A very nice flyer, too.

[Work in Progress]

In an attempt to actually answer the question, may I commend NACA 6409 for narrow-chord, slow-flying wings? If you need more thickness then try NACA 6412.

WW1 biplane wings are often very thin sections, and reproducing them exactly on an RC model may required you to use functional rigging. 6409, and 9%, is about as thin as I dare go on a cantilever wing. It was used on A2 towline gliders so with a good spar set-up can be made to provide decent bending stiffness and strength.

[KenSt]

Good recommendation Work.

I have a Bleroit XI that uses the 6409. It is only 33" span with a 7-3/8 chord but it looks very scale. it flys just fine. At 4.7 oz./sq. ft. wing loading it is a real floater. It only weighs 7-1/2 ozs. so an hour before dusk (no wind) is prime flying time. The wings have multiple spars like a guillows kit top and bottom. I would imagine it is quite turbulated. Shrink covering gives it many facets. No rigging was needed.

[vonJaerschky]

Thanks for the reccomendations, guys. I may just go ahead and use the same airfoil that is on my C.III. Like I said, it flies so nicely. I think I can make the wing assembly fairly stiff, as it is a 3-Bay, high aspect ratio bipe. OK, secret's out, it's a Gotha G.IV. I hope for that to be my winter build project.

[BMatthews]

That wouldn't be Greg Heath by any chance, would it? I saw his small SPAD at Chilliwack this year, and it was absolutely gorgeous. A very nice flyer, too.

That's the one. But his last name is Davis.