I'm scratch building a 1/7 scale Fokker D7. From my research, Fokker incidence angles are, 0 degrees for the top wing, +1 degrees for the bottom wing, +3.5 to 4 degrees pos. for the stab. I am wondering if thats going to work, and need to know what other D7 are using.
Thanks in advance
Vlad

Hej Vladimir,

I am designing a 1:6 Hannover CLIII. After reading a lot of different opinions on incidences on RCU I decided to go for the following setup which I have been told should work OK.

Wing profile: Eppler 193
Tail incidence: 0
Upper wing incidence: +2
Lower wing incidence: +1
Engine: -3

Good luck with your project!

Jens

Hey guys, what's the best way to measure all of these incidences? Incidence meter? Which brand?

Hi Vlad,

Re your incidence angles. IMHO a positive (Leading Edge Up) stabilizer incidence angle on a model DVII is not what you want. That's because cambered airfoils have a nose down pitching moment in addition to their Lift and Drag. For the airplane to be in equilibrium the nose down pitching moment of the airfoil must be balanced by a nose up moment generated by a down force at the horizontal tail acting on the long lever arm to the CG.

I would think the stabilizer incidence should be 0 deg, parallel to the fuselage Centerline. In the air in level flight the wing, because of the strong lift generated by the DVII's thick cambered airfoil, will probably trim out at -1 to -3 degrees. This effectively puts the stabilizer at a negative angle of attack, generating the down force needed.

Hope this is of some help. Your DVII sounds like a great project. Good luck with it.

Tom

Hello Vlad,
I hate to contradict, but I have different data about incidence angles, or lateral dihedral as it used to be known. I can't explain the science behind it, but from actual experience, your model should have positive incidence in both upper and lower wings, and the tailplane as well. With a scale-type airfoil, you might try these angles for starters: Upper and lower wings set at +3 deg, tail(stab) set at +1 deg, engine set at 0 deg. If you fly the model fast, you may want to shim the stab to 1.5 deg, or possibly more, to prevent the model from balooning. I`ve messed around with these angles quite a lot, on different ww1 designs. I tried 0 deg once, and needed 4 deg engine downthrust to keep the nose down. Other input on this subject would be great, I'm learning that simply using the full size a/c angles don't always work the best.

John

Hello John,

I don't see much of a contradiction in what you wrote. I think your experience matches pretty well with the theory. Here's why.

Regardless of where you set the incidence angle, in level flight the wings generate only as much Lift as is needed to balance the weight of the airplane and the airfoils (and the airplane) will trim to the angle of attack to generate that amount of lift. If you set the incidence at +3 deg. vs +1 or 0 deg. the airfoils of the wings will still trim out at the same angle of attack in flight. So the Centerline of the fuselage will trim out a little more nose down with +3 deg. incidence than with +1 deg.

The horizontal tail likewise need only generate enough down force to balance the pitching moment (I'm simplifying by neglecting Lift and Drag forces acting away from the CG). If you increase the incidence angle of the wing the CL of the fuselage is more nose down and the horiz. tail can produce too much down force. In that case you would want to raise the LE of the horiz. tail just as you stated.

So I think we're in violent agreement! And I would certainly defer to your hands-on experience is setting the incidence angles.

Best regards,

Tom

Good explanation Tom, thanks! I once read that Fokker, and possibly others, intentionally set all of the surfaces positive. This meant that the fuselage flew tail high, and gave the pilot a little better forward visibility.
The main reason I prefer this setup is that when you come back on throttle, the a/c is already in a glide attitude. Oh yes, when I mentioned 0 deg engine thrust, I meant longetudinal(sp?). Side thrust can often help these models.

John