I copied this from Kangke's manual for their Waco. Is the reference to positive and negative incidence typical of all biplanes or is it specific for this plane?

Chuck

It is simply confusing .
What they intend to say is that as speed increases - the wing(s) will generate more lift- pretty std stuff
So at faster speeds - to keep from needing to reset tail plane angles - reduce positive wing angles .
In my book -for models such as this - the wings all should be fully symmetrical- and set at zero -zero
For THIS type plane, the airfoil used is of very little -if any importance as long as it is thin, strong , stiff and accurate.
So make sure your model checks out -use a stick marked to check assembled measurements and make left/right sides the same - use solid control links and acurate servos.
Then trim for your favorite flying speed by shifting CG and tail plane incidence .

I love bipes so many of my planes have been just that--BIPES--. On all of them ( 7 Airomasters, two Phaeton 90's, one Phaeton 40, two large Lazy Aces, one smaller Lazy Ace) flew best by having the upper wing set at about -1.5 degrees relative to the lower wing. Just a minor change of 1 degree or so can turn a doggy flyer into a real pleasure to fly. If you can, when and if you go to a bipe, make sure that you can change the incidence of the upper wing easily and then just try out some minor changes. I think you will be surprised by the big change in flight characteristics you get with minor change of incidence. I also found that proper engine thrust line had quite an effect. Most of my bipes all liked about 3 to 5 degrees downthrust and about 2 or 3 degrees right thrust. However, some bipes do like 0/0/0 on surfaces so first, go by the recomended settings but don't be afraid to experiment with minor changes.

Seems to me back in the cob webs of my brain that you want the lower wing to stall before the upper wing and thus you set the lower wing incidence so that the lower wing has more positive incidence relative to the horizontal stabilizer. This will give a softer stall because the upper wing is still trying to fly.
The upper wing should have relative incidence of 0 degrees relative to the horizontal stabilizer.
Could not read the instruction sheet copy you sent but believe what they are saying is the same as I have said.

3dbob

When the wings are staggered, the forward wing will stall first. In this case, the top wing is set negative to the bottom wing to make them stall evenly (more aggressive). Having the forward wing stall first makes for more gentle stalls, since loss of lift ahead of the CG will naturally cause the nose to drop when it stalls, while the bottom wing still flies.

Right...On negative stagger biplanes like the Beech Staggerwing, Beercat, Stitts Skybaby, etc., the lower wing is set to stall first.

When two wings operate in close proximity such as a biplane, especially with the lower wing a little behind the upper wing, the downwash from the upper wing effectively reduces the angle of attack of the lower (rear) wing slightly. Thus when both wings are set at the same incidence, the upper wing will be carrying a little more than its share of the load, and will stall first. By setting the upper wing at a slightly lower incidence, the load is distributed a little more evenly and both wings will tend to stall at the same time.

This interaction between wings was explored extensively in the era when most airplanes were biplanes and the wind tunnel tests generally confirm it in numerous NACA reports.

Thanks for that explaination. I like the logic of the top wing with greater incidence so it will stall first, etc, however, on my models, they always seem to fly better with the top wing -1 to 1 1/2 degrees to the bottom. I could never figure out why.

Theory -and then -practical application:
On a model -best set em equally -if they are same size.
Why?
The model will fly BEST- when the total drag of the two wings is minimized. both exactly the same
At what AOA do you think your model will be in level cruise?
If it is light -I will bet it is under one degree ( that is about 1/4" in one foot)
Of what good will it be to create a drag brake by setting an angle DIFFERENCE, greater than the AOA needed to fly?
Much research on bipes was done on slow , heavy, full scale stuff .
Totally different ball game than our models -unless you like really heavy models .
When w e did fully aerobatic bipe models (TOC 89-91)-we found best setup was always 0-0-0.
then have enough power to maintain speed .
If speed is constant -- trim remains the same
If speed changes dramatically with any change in pitch -due to low power well-- that's another story.

My Kyosho PT-17 Stearman has -2 in upper win, 0 in bottom wing and 0 in stabilisator. These wings are lifting profile (semisymetric profile).

If the plane are stalling, then upper wing will take over and keep lift while the bottom wing are in stall. Near same as monoplan with wash-out.

Jens Eirik

well now that it's clear as mud, i'll go 0 0 0 and move from there.
tinker

do it - if the plane is reasonable weight and you have decent power -it will be just fine -get the CG such that it is not too sensitive for your own taste and away you go -
If the theories don't make sense -it is usually because they are really not so.
FWIW the shape of the airfoil on your model bipe means very little. it can be a 12% fully symmetrical or a 12% Clark Y or a 2412 series etc. and if the wings are straight and true and equal - I defy you to tell which is best .
Why? wing area and loading are the same in these three examples and if you set AOA equally -they will all fly about the same -even inverted .
On a full sized bipe - yes there is a difference --the airfoils and angles were all developed to get best performance at a specific task - be it weight /speed or very broad speed range etc..

Aerodynamic theory says that total drag should be minimized by having both wings develop the same lift, for an equal-wing biplane. Since the lower wing flies in downwash produced by the upper wing, this would seem to dictate using more incidence on the lower wing, in order to offset the effect of downwash. However, in the early 1930s, when bipes were still the dominant airplane species and a lot of talented people were fine-tuning their aerodynamics, extensive full-scale wind tunnel testing revealed that total drag was actually very slightly lower with the upper wing set at about 1-1/2 degrees higher incidence than the lower wing. The reason for this is still, I think, unclear, but the effect on drag was so low that is was hard to measure.

The concept that having the upper wing stall first will produce a gentler stall was found to be untrue, at least in wind tunnel testing. The reason for this appears to be that when the upper wing stalls, the loss of lift is relatively small in compared to the great increase in drag, and although the loss of lift up forward should cause pitch-down, the sudden increase in drag acting well above the CG tends to cause a pitch-up moment that exceeds the pitch-down moment of
the stalled upper wing. The overall effect on pitch was not great.

Biplane lower wings were found to remain unstalled, due to the effect of downwash of the upper wing producing a sort of slot effect, up to more than 30 degrees positive angle of attack. This definitely does produce a gentler stall - the lower wing hangs in there, and its ailerons remain in business, well after the upper wing is in deep stall.

I too, find that my bipes perform better with the upper wing set at slightly lower incidence than the lower wing - maybe one degree or so at most. Aerobatic line holding seems to be improved.

I went out today and tried my Tiger Moth with negative incidence on the upper wing. There was a substantial change, and now it will stall and spin, which I like to do. I could not get it to do this before. So this seems to lend credence to the theory that with the negative incidence, both wings stall at the same time.

In fact, I thought that it flew better all around.

Just for information, the Grumman American AgCat crop duster, built for the sole purpose of dusting, will stall the upper wing first. I flew this plane. You can feel the upper wing beginning to stall and correct for it.

Good information Snitch, you have found out exactly what I was trying to say above; most often 0-0-0 is not the best setup. You need to do a little expermentation to get the most fun out of your bipe. All will be slightly different but most often you will find that having the upper wing at a more negative incidence than the lower will improve performance.

Is there a more aerobatically capable .60 sized bipe than the GOLDBERG ULTIMATE? Will your LAZY ACE, TIGER MOTH, PT 17, etc. knife edge loop, loncevak, flat spin and then land like a trainer? Check the specs on the "CG "bird. Incidence? We don't need no steenkin' incidence[>:]! All we need is light wing loading, lots of power, symetrical airfoils and a CG as far back as you can stand it. If I could play with any thing, it would be to have a way to remotely shift the planes' CG for different parts of the flight routine

If playing around with your particular birds' angles brings y'all more fun and enjoyment, that's all that really matters though. I do believe that no 2 different models [especially bipes], are created equal and no single set of "rules" could ever be made absolute to fit all cases.