Bi-planes: should the AOA of wings be parallel or should one differ?

[Scott Richlen]

i am putting together my SiG SPAD and it sticks in my mind that there was a discussion on here (but I can't find it) that said the AOA of the upper wing should be a couple degrees higher than the lower wing.  Is that correct?  How many degrees?  Or am I mis-remembering the whole thing?

Thanks,
Scott

[Steve Dwyer]

Scott,

Interesting question, I think you're going to get as many responses/opinions as there are biplane builders here. And then some will sprinkle in the need to factor in wing sweep. There are a good many writings on the topic in the RC Forum. My Pat King Ringmaster Biplane has zero incidence in either wing and it flies straight and level, however... I also had much interest in the Luciano Compostalla (Sp?) Falco bi plane several years back which I may build it yet. The drawing shows zero incidence in either wing but it was a well powered CL stunter that also performed well in European contests. Depending on how you plan to fly the SPAD 7, wing incidence may not play much into how it fly's. I do know an RC guy here that recently completed two large 20s and 30s era biplanes, I'll ask him his opinion and get back to you.

Steve

[Dave_Trible]

If you intend to stunt the airplane and want it to fly the same upright and inverted, inside and outside,  there can be no incidence in either wing.  Full scale or RC info isn't helpful here.   I have seen the SIG Fokker D7- basically the same airplane fly a recognizable full pattern.  I built from plans the Spad a few years ago and to me it was a dismal failure.  It flew OK at slow speeds but once up to stunt speed it hunted-really oscillated wildly up and down while trying to fly it level.  I never attempted to really solve it.  I can only guess there may have been some negative incidence in the upper wing.  If I were to build another I would try to make the incidence adjustable in some way-at least the upper wing.

Dave

[Miotch]

Based on my most recent build, keep the wings parallel.  I've seen real planes with each wing having different degrees of incidence, but when I tried it on a model, it just made it unstable.   I think you are also safest using 0 degrees angle of incidence, but it would probably depend on the plane.  If you have an engine that isn't mounted sideways, you can always shim the engine a bit to change the thrust line a bit if necessary.

[Steve Thompson]

On a full-scale biplane, the forward wing (upper) has a higher angle of attack so it will stall first.

Control line models with symmetrical ribs have different needs.

Search for "38 Special" on the forum.  I believe the consensus was make them 0-0 (parallel to trust line) or the top wing 1 degree positive.

[Steve Dwyer]

Scott,

Below is the response I received from my RC buddy.

Steve


In general, the idea is to ensure one wing stalls before the other to improve stall characteristics.  I don't believe this is an issue for CL planes.  This is one of those topics if brought up in a forum the discussion raves on and on. 

Looking at the SPAD plan there is no call out for incidence so I would build per the plan dimensions and leave it at that.  I did print out an 8 1/2 x 11 copy of the plan and measured it.   It appears that the wings are 0-0 incidence which is what I would have thought it would be. 

Hope that helps.

BTW I just follow the plans and I've had good success.

[Scott Richlen]

Thanks everyone.  I'll go with 0 incidence on both wings.

[Joseph Lijoi]

Thanks everyone.  I'll go with 0 incidence on both wings.

Peter Miller Dancing Girl plan has the upper wing at negative 1 degree incidence. He got that from the DeBolt biplane. Make it adjustable. If the upper wing flies off it will be a very scale like catastrophic failure.   

[Gerald Arana]

FWIW, I have an RC Sig Smith Mini biplane and it has about a degree or two of Neg . (LE down) in the top wing and it flies great! But then its RC.

Cheers; Jerry

[john e. holliday]

I have had both kits that were built box stock.  Never gave any though other than to make both wings line up with the angle of zero incidence on every thing.  The Fokker and Spad were crowd pleasures.   

[John Park]

Yes, the DeBolt Super Bipe (the aerobatic development of the original Bipe) had 2 degrees negative incidence on the top wing - but that was 75 years ago!

[pat king]

I set up all my multi-wing airplanes to have all wings parallel. For full scale or R/C the top wing normally has a slight amount of more angle of attack than the bottom wing. That is so the top wing stalls first. If you can stall a C/L airplane it is severely underpowered. If the wings are parallel you will not be building in any nasty habits.

Pat

[Ken Culbertson]

Interesting.  The popular answer would be that they be the same.  But what would be the result of having them different but symmetrical.  + on one - on the other.  Probably just drag.

Ken

[Dan McEntee]

  I haven't been able to find the thread I think I'm remembering, but here is one that has some info worth reading. This one goes back to when Stuka Stunt was still active, so I may have read it there. Anyhow, see what you can find here. It has some good responses and there are some other links in a post from John Miller: https://stunthanger.com/smf/engineering-board/incident-set-up-on-a-bipeplane/msg226839/#msg226839

   Type at you later,
      Dan McEntee

[Robert Zambelli]

This topic brought back some really fond memories.
I've always been a fan of biplanes but I never built one.
While designing subsystems for Augusta Helicopter in Coscina de Costa, Italy, I met up with some incredibly skillful modellers from the Aeromodellisti di Monza.
Among them, a true gentleman, Luciano Compostella. One of his favorite designs was his Falco (Falcon, Hawk) biplane. Powered by an OS Surpass 48, it flew an absolutely beautiful pattern and garnered him quite a few awards.
Speaking about the design, he mentioned that there was no incidence between the two wings and none between the fuselage and wing(s).
As I recall, he built two Falco bipes but I'm not aware of any differences between the two.
He also gave me plans for the Tango, Lampo and Falco.  In the diagram posted by Steve Dwyer, that's me (bob) in the lower right corner.
This freindship between Luciano and me inspired me to design and build my Staggerwing Beech 17, which turned out be be an outstanding design.

Yes, I plan to build a Falco but since I don't have a Surpass 48, I'll us an ENYA 46.
Luciano and I became close friends and I was truly saddened by his death.
If anyone is interested in the Tango or Lampo, I will send full-size plans - just cover my expenses.

Bob Z.