Angle of incidence on top wing

Andy Borgogna
I know this has be talked about before, but I don't remember the outcome. I am about to locate the top wing on my biplane and want to know at what incidence the top wing should be set to. I seem to remember that +1 degree was suggested, but a paper I got on the internet (for RC biplane) the designer said -1 degree. For sake of discussion what is wrong with 0 degrees of incidence.

Anybody care to voice an opinion?
Andy

LAST EDITED ON Oct-13-06 AT 10:48 AM (CST)
 
I am not sure we should care too much. Do not take what is said about RC or full size planes to matter as much here.

They used to set full size planes up so the wing without the ailerons, usually the top one, would have more incidence and thus would hopefully stall first.

I have built a number of CL biplanes and I did not get the wings on there the straightest, but they still worked. I might well go with zero if I was designing my own. Making them have different incidence will add drag, if nothing else.

Floyd Cummins

For RC the top wing is usually set at -1 or -2 degrees with respect to the botom wing. The thinking for this is that when landing the wing with the highest angle of attack will stall out first (which will be the bottom wing) making the lifting force (the top wing) way above the CG. This will provide more axial stability (pendulum effect) which will counter any tip stall problems. Also negative incidence in the top wing seems to give more pitch stability in inverted flight. However, I don"t know of any use for this application in C/L flight.

Phil

Phil Coopy AMA609

"Better to remain silent and be thought a fool, than to speak and remove all doubt."

I don't really know the real answer, but it would seem to me that you would want the top wing to stall first. My reasoning for this is the CG in a biplane is typically behind the top wing and forward of the bottom wing. If all you have is the top wing lifting, the center of lift is now in front of the CG, perhaps leading to a major pitch UP of the plane. This seems to be bad to me if you are already in a stall configuration--especially an accelerated stall. COuld be way exciting!!
If the top stalled first, the the natural inclination of the plane would be to pitch down, which is what I would want to happen (I think!!)

Andy - I set up my Staggerwing with all surfaces at zero incidence. Flies perfectly.

Andy Borgogna
Thank you all for your input, I will set the two wings to 0 degrees of incidence and go with that.
Andy

It was I that recommended the 1-2 degrees NEGATIVE incidence for the top wing. The reason for this was the scratchbuilt Bipe that I built to test this. Trailing edge was adjustable with clevises at the cabane struts, and the center post had a notch that the center rib trailing edge pinched with a 4-40 bolt. Make it adjustable. See for yourself. It MAKES a difference.

The typical Bipe tends to balloon; negative incidence in the top wing neutralizes this. I suppose a little positive incidence on the stab might accomplish the same thing. You shouldn't get carried away; 1 or 2 degrees is all it takes.