JHuisman

I've just put the first few flights on my new Pitts Special, scratchbuilt from MAN plans (60" span, OS91 FX, 10lbs).

First couple of flights . . . Thank God it flies!!!

Next couple of flights I started to get a little more adventurous with it and noticed a few odd tendencies that I believe are related to incidence.

This biplane will not knife-edge. When rudder is applied, it immediately rolls out to level, and pitches down, acting like a high wing aircraft.

Second, when on a vertical line, at full throttle, as the airspeed bleeds off, there is a sharp pitch down before the aircraft stops.

I believe that these are related to relative wing incidence (currently both wings and stab are set to 0 deg)

If anyone can help out, I'd sure appreciate some input.

Thanks
Jason Huisman

tmproff

My Feedback: (5)

I know that on my Skybolt bipe, they stress a -1 degree incidence on the leading cabane.

JHuisman

I've thought about resetting the top wing to -1, but was concerned about a possible need to shift the balance point due to a change in lift.
Where does the skybolt recommend balance? Mine is at the leading edge of the bottom wing.

Jason

tmproff

My Feedback: (5)

The skybolt blueprints show the CG on the leading edge of the bottom wing as well.

Rodney

I think you are correct, decrease the angle of attack on the upper wing. I have built and flown at least 10 different bipes and found that all but two needed minor changes in wing incidence to fly as I liked them too. Most required an decrease in upper wing incidence. most of mine fly best with about -1.5 degrees in top wing and 0 in lower wing. Thrust angle can also be critical. most of mine like about 5 degrees down thrust and three degrees right thrust. This covers all sizes from .40 sized Moth to 19 pound 1/4 scalers and seven different Lou Andrews Aeromasters.

CAPtain232

My Feedback: (40)

Look at the April 2002 issue of MODEL AIRPLANE NEWS. On pages 100-102 it has an article on this subject, a very good one in fact.

Jeff