Design > Stunt design
Transitional Airfoils
Ken Culbertson:
My first ship to rebuild after the fire that claimed my fleet is going to be the PA ship that I had just finished. It had a rather unique airfoil, designed by Ton Niehbur that I would like to understand better before I duplicate it. It was the typical thick blunt fully curved shape common in most of today's top designs at the root but it gradually tapered to a flat back starting just behind the high point at the tips. The taper started at about mid span.
Any thoughts - Ken
Tim Wescott:
I think you need to document the airfoil for us. Usually I do this with scrap cardboard, trimmed by whatever method is convenient until it lays nicely along the whole length of the airfoil. Then I trace it out on paper with a pencil. Get one at the root, one at the tip, and one in the middle.
And yes -- time consuming PITA. But sometimes you just need to do the tedious stuff.
Ken Culbertson:
--- Quote from: Tim Wescott on February 08, 2020, 08:49:25 AM ---I think you need to document the airfoil for us. Usually I do this with scrap cardboard, trimmed by whatever method is convenient until it lays nicely along the whole length of the airfoil. Then I trace it out on paper with a pencil. Get one at the root, one at the tip, and one in the middle.
And yes -- time consuming PITA. But sometimes you just need to do the tedious stuff.
--- End quote ---
Tim:
This is the best I could do without any of my drafting stuff. It is pretty much freehand. Actual is a bit more blunt, a bit thicker and the "mid" is a bit thinner at the back. The point is the transition from rounded to flat.
Ken
Tim Wescott:
Thanks Ken. I know that Brett Buck, who's about my age but spent his whole life flying instead of taking a 30-year break in the middle for college and kids, doesn't like the ice-cream-cone airfoil -- I can't remember exactly what he doesn't like, but I think it's that its jumpy around neutral.
Having it only flat at the tips may make that better overall, but if the tips have a "jumpy" airfoil and the rest of the wing doesn't, it would make the plane jumpy in roll, which can't be a good thing.
Ken Culbertson:
--- Quote from: Tim Wescott on February 09, 2020, 01:00:04 PM ---Thanks Ken. I know that Brett Buck, who's about my age but spent his whole life flying instead of taking a 30-year break in the middle for college and kids, doesn't like the ice-cream-cone airfoil -- I can't remember exactly what he doesn't like, but I think it's that its jumpy around neutral.
Having it only flat at the tips may make that better overall, but if the tips have a "jumpy" airfoil and the rest of the wing doesn't, it would make the plane jumpy in roll, which can't be a good thing.
--- End quote ---
I am not promoting this airfoil, I am trying to understand it and why it flew so well. I didn't have enough flights on it when it burned to tell if it had any minor issues. It did want to float up in level flight a bit which I traced to flaps not neutral. That was corrected but never tested. I agree that jumpy at the tips is a bad thing. Maybe it has to do with stall characteristics. It is not a true "Ice-cream-cone" since the flat starts well aft of the high point. It also could have been a bit of block sanding too late in the evening. I am also not convinced that the exceptional cornering and smoothness in rounds that the plane had was due entirely to the airfoil.
Ken
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