Biplane Decalage
 

I have an old Aeromaster biplane that has been in storage for too many years that I am rebuilding. I don't have the plans as to where to reset the wing decalage.

My intentions are to set the both the horizontal stabilizer and the bottom wing at zero angle of incidence. My question is should the upper wing be set at zero as well or a degree or so of positive incidence?

RE: Biplane Decalage
 

It will probably fly best if the upper wing is about -1.5 degrees with respect to the lower wing, i.e. negative incidence. I have built 7 of those and all flew best with less incidence in the upper wing than in the lower wing.

RE: Biplane Decalage
 

Steve, I just finished building a GP Super Aeromaster. Everything but the top wing was at zero and the top wing is -1 degrees. Hope this helps.

Don

RE: Biplane Decalage
 

Full-scale wind tunnel tests conducted in the early 1930s ago indicated that giving the upper wing slightly more incidence reduced induced drag very slightly. However, I find that bipes are better at aerobatic line holding with about one degree less incidence in the upper wing than the lower.

By the way, the old story that giving the upper wing more incidence (positive decalage) on a bipe with positive stagger makes the nose tend to drop before stall occurs was proven false during the same test series. Although the loss of lift of the upper wing would tend to lower the nose, the large increase in drag of a stalled upper wing tends to cause the nose to rise. The drag-produced pitch-up effect was found to exceed the pitch-down effect of loss of lift, causing the nose to tend to rise, instead of to fall, as the wing ventured into stall territory. Positive decalage tended to make this unhappy tendency worse.

RE: Biplane Decalage
 

The set up on the 1/3 scale Jungmeister Im building is stab 0,bottom wing 0,top wing -1o .......and most of the reading I have done on the subject uses the same set up.
Im going to re check the incidence set up on my GP Christen Eagle as I suspect the top wing has no minus set up and might even be positive,which may cause the tendancy this design has to spring back into the air on any less than perfect landing.
The RC Guys 1/3 Pitts I am assembling also uses 0/0/-1 and the sample I flew lands like a dream and has no bad flight habits.

RE: Biplane Decalage
 

Thanks for the info gents! Hopefully I'll have the old bird back in the air soon I appeciate the help.