gschuld
Well-Known Member
I have read several suggestions regarding the use of carefully selected airfoil shapes instead of aerodynamic twist to improve the stall, low speed performance of double tapered wing planforms. By carefully selected, I mean by using a more "stall resistant" airfoil at the tips compared to the root. Such as using the same family of airfoils, but using a say 12% thickness to chord ratio for the root area and tapering to a 15% ratio out at the tips. Or a similar thickness ratio but different profile shapes with inherently different stall characteristics to ensure as much as possible the root areas stall first.
My understanding is that the main reason to have a wing with twist or washout is to improve the low speed stability and stall characteristics while retaining the same or similar airfoil profiles for construction simplicity sake. The downside is in the increased drag as a result of the airfoils not being inline when at higher speeds. For low, medium speed craft, a 1 1/2 to 2 1/2 degreed washout seems to be accepted practice as the easiest way to give a double tapered winged plane reasonable stall performance.
Orion, among others, have suggested that for fairly high performance craft (200mph or higher perhaps), using no washout but employing a carefully executed airfoil selection could achieve the same low speed performance and still allow better higher speed performance based on the idea that the zero washout would create less drag.
I'd love to hear more on the subject, and an idea as to what planes have used this technique successfully. And if the zero washout idea makes sense, why does it not seem to be more popular(or is it?)? I assume the extra build complication would be a big factor for most, but that doesn't bother me much. For the record, I plan on going with laminar airfoils with composite (wood, foam, glass) wings. A bigger concern is whether it can be done with a reasonable degree of assurance that the low speed performance will be comparable to a more conventional approach. There's definitely something reassuring about going with a tried and true method like washout, but I just have to ask
onder:ara:! Curiosity has gotten the best of me again!
George
My understanding is that the main reason to have a wing with twist or washout is to improve the low speed stability and stall characteristics while retaining the same or similar airfoil profiles for construction simplicity sake. The downside is in the increased drag as a result of the airfoils not being inline when at higher speeds. For low, medium speed craft, a 1 1/2 to 2 1/2 degreed washout seems to be accepted practice as the easiest way to give a double tapered winged plane reasonable stall performance.
Orion, among others, have suggested that for fairly high performance craft (200mph or higher perhaps), using no washout but employing a carefully executed airfoil selection could achieve the same low speed performance and still allow better higher speed performance based on the idea that the zero washout would create less drag.
I'd love to hear more on the subject, and an idea as to what planes have used this technique successfully. And if the zero washout idea makes sense, why does it not seem to be more popular(or is it?)? I assume the extra build complication would be a big factor for most, but that doesn't bother me much. For the record, I plan on going with laminar airfoils with composite (wood, foam, glass) wings. A bigger concern is whether it can be done with a reasonable degree of assurance that the low speed performance will be comparable to a more conventional approach. There's definitely something reassuring about going with a tried and true method like washout, but I just have to ask
onder:ara:! Curiosity has gotten the best of me again!George
