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Biplane aerodynamics

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Mcmark

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Back with some different questions.
If both wings are the same airfoil, shape and AOI and I want the top wing to stall first, upright and inverted, how can I accomplish this?
Will stall strips do it ? Or do I need to vary the airfoil to do it?
Thanks
Mark
 

TFF

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As you know Pitts made the bottom airfoil thicker for the symmetrical. I believe the first attempt at S1S wings had equal airfoils and inverted stall scared Pitts enough to ground the plane until he could rethink the bottom wing. Non symmetrical when inverted with stall strips may work but only testing will tell; i bet the break will not be same airspeed or reaction. One way may be mushy and one sharp.
 

Aerowerx

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... I want the top wing to stall first, upright and inverted, how can I accomplish this?
Will stall strips do it ?
By no means am I an expert, but I remember reading about one recent (late 20th century) biplane design. It had the lower wing forward and the top wing to the rear. The bottom had a couple of degrees incidence and the top was at 0.0 degrees. The air flow off the lower wing affects the upper wing such that the lower wing stalls first. As I recall, the plane does not actually stall, as we usually think of it, but sort of just mushes along.

My point is that you may not have to do anything other than choose the proper stagger and incidence.
 

djschwartz

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As you know Pitts made the bottom airfoil thicker for the symmetrical. I believe the first attempt at S1S wings had equal airfoils and inverted stall scared Pitts enough to ground the plane until he could rethink the bottom wing. Non symmetrical when inverted with stall strips may work but only testing will tell; i bet the break will not be same airspeed or reaction. One way may be mushy and one sharp.
I'm afraid you have this backwards. The bottom wing is thinner. It's a NACA 0012. The top wing is a 15% thick 64 series airfoil. The earlier S1C used an M6 for both wings
 

BJC

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The upper Pitts S-1S wing airfoil is a NACA 63a-015, and the lower wing is a NACA 0012.

The upper airfoil has a slightly smaller leading edge radius, and it stalls at a lower angle of attack.


BJC
 

TFF

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I re read the Pitts patent and he was really smart in wording it. He never mentioned any airfoils,but states the differences in Cl of both airfoils in relation to each other. Pretty much covered every airfoil in one swipe.
 
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