GESchwarz
Well-Known Member
Harry Riblett and I had a long phone conversation a few months back regarding the selection of my airfoil. Based on the following he thought I shold go with the GA37A318.
Criteria:
1. Max thickness at 37% chord gives greatest potential for laminar flow at cruise to top speed (~220 mph).
2. 3% camber good for soft stall. (The 37% characteristic hurts low speed performance, so the 3% camber is to make up for that.)
3. 18% thickness for added strength to the wing fold hinge and for fuel capacity. I'll also be making a baggage compartment just outboard of the fuel tank in each wing. This extra thickness shouldn't result in too significant of a drag penalty. Will also result in less spar weight for the longish span of 29'. (I wanted the same wing area as the RV-8A but more than it's 23' of span. So my chord is reduced from 58" of the RV, to 52" to get the same wing area. 18% also contributes toward soft stall.
The reason why I'm posting this thread is that I'm worried about the 3% camber.
1. Is it going to be generating unwanted lift at cruise speed?
2. Is it going to be generating excessive pitching moment?
As it is, I will have rather large Fowler flaps. Is my obsession with low speed performance going to hurt my top end speed?
Should I go with less camber? I was thinking that I can get the best of both worlds by reflexing the flaps and even ailerons at high speed to reduce the camber. That's easy enought to do with the flaps, but a bit more trouble with the ailerons. And if I don't reflex the ailerons too, I'll get a big crazy vortex between the flap and the aileron.
If I go to 2% or 1% camber how much will by stall characteristics suffer? How bad will by pitching moment be with a 3% versus a 1 or 2%?
Criteria:
1. Max thickness at 37% chord gives greatest potential for laminar flow at cruise to top speed (~220 mph).
2. 3% camber good for soft stall. (The 37% characteristic hurts low speed performance, so the 3% camber is to make up for that.)
3. 18% thickness for added strength to the wing fold hinge and for fuel capacity. I'll also be making a baggage compartment just outboard of the fuel tank in each wing. This extra thickness shouldn't result in too significant of a drag penalty. Will also result in less spar weight for the longish span of 29'. (I wanted the same wing area as the RV-8A but more than it's 23' of span. So my chord is reduced from 58" of the RV, to 52" to get the same wing area. 18% also contributes toward soft stall.
The reason why I'm posting this thread is that I'm worried about the 3% camber.
1. Is it going to be generating unwanted lift at cruise speed?
2. Is it going to be generating excessive pitching moment?
As it is, I will have rather large Fowler flaps. Is my obsession with low speed performance going to hurt my top end speed?
Should I go with less camber? I was thinking that I can get the best of both worlds by reflexing the flaps and even ailerons at high speed to reduce the camber. That's easy enought to do with the flaps, but a bit more trouble with the ailerons. And if I don't reflex the ailerons too, I'll get a big crazy vortex between the flap and the aileron.
If I go to 2% or 1% camber how much will by stall characteristics suffer? How bad will by pitching moment be with a 3% versus a 1 or 2%?
