H- stab airfoil

[WHY]

Question for those in the know, If you are going to make a horizontal stab with an airfoil, which would be better one that is symetrical or one that is A-symetrical. The A-symetrical would give some lift but that might be a good thing and then it might not??????

This of course would be on a tractor design with a good moment arm.

Tony

[magilla]

No reason to really have a lifting component - either positive or negative - you are just adding drag.

If, however, your thrust in relation to CG is not aligned, having a positive or negative lift could offset whatever thrust offset you have - ala the Magni.

Most helicopters have a negative lift airfoil to compensate for the forward tilt of the fuselage with forward cyclic at high airspeeds (even the UH-1 Huey with underslung rotor system had a negative lift horizontal stabilizer).

As far symmetrical or asymmetrical - the stabilators and horizontal stabilizers I have seen are all asymmetrical. I believe you would want an asymmetrical airfoil, especially with it being a non-moving component.

[chuter]

I made mine symetrical; not because I know what I'm doing, I just figured an airfoil is better (more efficient?, responds to changes in angle of attack quicker?) than a flat plate, and the angle of attack will change in updraft/downdrafts.

[Doug Riley]

Camber (=asymmetricality) does pretty much the same thing for an airfoil as incidence. For example, a wing with camber will, depending on how MUCH camber, have nearly identical characteristics as a symmetrical wing having between two and four degrees of incidence.

The "nearly identical" part has to do with lift-to drag ratio. A wing cambered so that it's the equivalent of an UNcambered wing with four degrees of incidence has slightly less drag for the same amount of lift.

The difference isn't going to matter on a gyro tail. Uncambered is simpler to build in many materials. I used a NACA 0012 on the Gyrobee/Watson tail kits, including my own Gyrobee. Three degrees of negative incidence on his symmetrical tail was more than enough.

A NAC 2412 (the same airfoil, but with modest camber) would behave about the same as the 0012 with two degrees of incidence. A NACA 4412 (same airfoil, but with more camber) would equate to four degrees of incidence on the 0012.

[Alan_Cheatham]

I agree with Doug, on a light tractor gyro with long tail arm I would go with the NACA 0012 airfoil, although if you wanted to get technical about it the tail could be designed to provide some engine torque compensation like the big boys of the past.

[magilla]

Thanks for that photo! Just what I needed for my tractor - with an 84" prop, I'm going to need a camber difference between the left and right.

My prop turns CCW, so I believe I will need the same set up. I have an OH-58 negative cambered H-Stab, and I was planning on attaching trim tabs to it on the left and right to achieve the same effect.

Anyway, thanks for the pic!