Greetings RCers,

I've asked this question of a couple of different people and each had a different answer. What is the proper way to set up the incidence on a biplane (I'm building the Midwest Stearman )?

My hunch is that I want the upper wing to have about 1 degree of positive incidence and the lower wing and tail feathers to be set at zero degrees. With this setup the upper wing will stall first (theoretically) and the nose will drop without losing stability.

Am I all wet? uhh... maybe I should ask if that is correct hehehe.

Thanks,

Cuban8

Hello,
The way I've always set up a biplane is to give the LOWER wing abou 2 degrees if positive incidence, so that it stalls first, thereby making the stall nose first. Just works for me. later, jnkessler

Most of the biplanes that I have built over the years have from Zero to Neg.1 degree Top wing and Positive +1 to +2 on the lower wing. The difficulty to your question is what type of flying are you going to do because Stab incidence plays a major role in determining the type of flight you are trying to achieve. Most stabs are set at a positive number -- this will allow the aircraft to fly at a slower speed but if the stab is negitive then the aircraft will fly faster and you will have to rethink your incedence for the wings but, aside from all that it is good practice to have the lower wing stall first so you will be able to have smooth control throughout the flight envelope.
Hope all the babbling helped.
Dr.Tim

My experience has shown that on most bipes, the upper wing should have about 1.5 degrees less angle of attack than the lower wing. Different planes can require more than this. I find that fine tuning the incidence of bipe can turn a dog into a ***** cat. Thrust lines are also more critical on a bipe than on a monoplane, at least from my experience. I find I usually need about 3 degrees right thrust and about 5 degrees downthrust to get one to fly well. It pays to experiment a little as small changes can give vast improvement. Rod

Hi Cuban8,
I am thinking about building a Stearman PT17 and have only found the Midwest kit. Can you tell me why you choose midwest? How is it going together. How would you rate the kit. Can you keep me informed of your progress and the results of flying Anything you can tell me.
Thanks,
Alan
[email protected]

Biplane incidence can vay depending on your application.

First, you will probably need a little positive incidence in the stab. This is due to the wing wash from the top wing.

Next, think of the wing with the most positive incidence as stalling first. Say, for example, the top wing has positive incidence and the lower wing is at zero. With this case, the top wing stalls first. To visualize what happens, imagine you have removed the top wing. It is stalled. Now we have a plane with the lower wing only. This new "plane" has the wing set pretty far back and has a long nose, so it is more than likely nose heavy. This means it will recover from the stall fairly quickly. Nose heavy planes also aren't snappy.

Now look at a plane with the lower wing at a more positive incidence. The lower wing now stalls first. Imagine a plane with the lower wing removed. The top wing is forward so we have a tail heavy plane that tends to be fairly snappy.

These scenarios are for normal stagger and a reverse stagger would have the opposite effect.

A lot of this in mitigated because most RC biplanes use only a small amount of stagger as opposed to full scale planes where a full span stagger was common.

So you can see you set your bipe up depending on how you want it to fly. Do you want a snappy acro, fun fly type bipe or a more sedate one. I tend to like the more snappy ones, but for a scale Stearman, you might want a more sedate flying plame.

Thanks to you all for your input and suggestions. Ed, that's the best explanation I've heard yet and your reply makes very good sense. It's not being built for aerobatics but I'll certainly use the info I gained here on the aerobatic bipe I'll build next

The Stearman does have quite a bit of stagger, about 30% of the cord. Thanks for the tip about the stab incidence too. I hadn't even considered it.

The wings and tail feathers are framed and covered and the fuselage is ready to receive the radio gear and engine.

Thanks again to everybody for the ideas and help

Cuban8

I would get Harry Higley's book called Bipes. It is a very informative source of information on biplanes and how to correctly set them up. What engine will you be using?

That's a good idea, oceandiv. I didn't realize there was a Harry Higley book on bipes. I have a couple of his books on engines already. I'll be using a Zenoah G-23. My first gasoline powered RC plane. Any tips or advice on it would be appreciated too

Cuban8

Well ive built 2 now 1 being the GeeBee Dreamer and it calls for top wing negitive 1 deg,bottom 0 and stab 0 also ..U want the bottom wing to stall first then u will still be stable..Thats my 2cents worth..
Thomas(ka0hyz)

Extensive wind tunnel testing done in the 1920s and early 1930 showed that using virtually the same incidence on both wings of a bipe would maximize lift/drag. Theory indicated that slightly negative incidence for the upper wing, relative to that of the lower wing should be most efficient, but tests did not support this. Somewhere around one degree more positive incidence for the upper wing seemed best, but the improvement was hard to measure. I often use about one degree less incidence in the upper wings of my bipes - seems to help aerobatic line holding. I went into this in a bipe tech series I did for M.A.N a few years ago.

Cuban Eight: is it done and have flown by this time? Results with the G23? Here is mine with a OS .90 4-stroke. Has your factory soft aluminum gear bent out of whack yet?

My Sig Hog Bipe calls for zero, zero, and zero, i.e. top, bottom, and stab.

Full-scale bipes, carrying people have reason to be designed to be auto-stabilizing.
Models don't!
That's what the pilot provides.
0-0-0 is common on models... -1,0,0 is also common.
Scale models, OTOH, should adhere to the full-scale settings, for realism of flight...
Stearman setup is +4 upper, +3 lower, +3 stabliizer. Very obvious on the 3-views and full-scale..
Jn-4, +2 both wings, 0 stabilizer..
SE-5a, +5, +6, 0 stab.. (it's British, of course.)
I believe the Pitts uses -1, 0 and 0..

I don't claim to be an expert , but IMHO it seems pretty silly to expect a plane to recover from a stall with half the lift [ one wing stalled ] It seems to me setting two wings at different angles of incidence just increaces drag .
The little Pitts I had had demonstrated no unexpected characteristics with both wings set the same . Sure ,
it would snap with too much elevator input at too high a speed , just a matter of flying it properly . Interestingly , after a few dead sticks where I was afraid of using too much elevator and it came down like the space shuttle I discovered that I could input nearly full up [ while dead stick ] to get some semblance to a decent glide .
I doubt those of you who think different angles are the way to go will change their minds . Dave Patrick uses the same angle for both wings .
Have fun
Maj. Crash

I have scratch designed and built 3 different Bipes plus 2 kits. My experience shows -1.0 top wing incidence, lower wing zero, horizontal stab zero. Goldberg ultimate was 0,0,0 and flew great. Down thrust was tried, but produced very bad flying characteristics. Side thrust (right) 2 to 4 degrees very helpful and essential for aerobatics.

Modelers tend to worry, I think, unduly about incidence angles. My original design bipes all use essentially 0-0-0 incidence. I try to design out the need for thrust offsets, chiefly by using subfins and subrudders. Equal rudder and fin area above and below the thrust line will remove the need for any right thrust. If incidence angles were all increased equally, for example, to +6 upper, +6 lower, and +6 on the horizontal stab, and 6 degrees of upthrust added, the airplane would fly just about the same, except that the fuselage would be inclined downward 6 degrees in flight, giving the pilot better visibility over the nose. This is the main reason for using positive wing incidence. It has little or nothing to do with aerodynamics.

A few years ago, I designed and marketed a couple of sport scale triplane kits, the Fokker DR-I and the Sopwith. Both had flat bottom wings, 3 degrees of right thrust, 3 degrees of downthrust and the incidence was set as follows:

Bottom wing 0 degrees to the horizontal
Middle wing -3/4 degrees to the horizontal
Top wing -1 1/2 degrees to the horizontal

Both flew great and had no bad habits.

My 2 cents worth...

Jake

PS,
Here is a photo of the last tripe that I built from one of my kits...

Of the dozen or so different bipes I've built, I've found that 0,0,0 suits me best with a couple of degrees of right thrust and a couple degrees of down. Most of these have had symmetrical airfoils. With a flat bottom airfoil more down thrust is needed.

Most of my bipes simply mush when stalled, so I never really saw any reason to try to make one wing stall first. If there are ailerons on only one wing it would definitely be advantageous to have the other wing stall first.

These were all scratch builds mind you; if I built from a kit I'd start with the manufacturers recommendations.

Here are some of my bipes. 1 is from a kit, 2 are from plans and the rest are my designs. Sizes range from 20" span to 61" span. .049 to .90 All 0,0,0.

I loooooove bipes!

Bipe Flyer,

Do I see a military version of a Staggerwing there? SWEETT!!!

I'll post some pics of my latest bipe after I finish covering. It's a Sportster Bipe-40, an old kit from GP.

8-)

It's done in the colour scheme of a Staggerwing that was used by the US embassy in London. I can't recall the year.

Have been trying to fly my Midwest Stearman for some two years now and have had many instances of stalling and fortunately have survived most crashes with minimal damage. Mostly bent gear and a pushed-in firewall. This is a very disappointing model to me as I have some 25 years of RC flying and have tried most all model configurations. With 30oz. of lead in the nose, my Stearman comes in around 15 lbs., wet. The other day I computed the wing loading using a 15% reduction in measured wing area for biplane inefficiency and walla, mine comes in at a wing loading of 33oz/ sq. feet. The Stearman is not suppose to fly with wing loading like a WW2 fighter. But, that apparently is the sad state of affairs with this plywood disaster! Yep, have had some good flights but doesn't make up for all the stalling problems. I guess I am too comfortable with my Phaeton 90 bipe which really flies! Oh well, back to the canards. The one attached really flies well! [sm=drowning.gif]

Hi Flicka: Most bipes, in my book, do not have anywhere near enough vertical tail area, resulting in nasty handling anywhere near stall. The airflow over the tail feathers of bipes is messed up a lot more than that of monoplanes by an extra wing and its cabane struts, and the lower reynolds numbers of models worsens this nasty effect. The best cure for this is to enlarge the vertical tail area. I like to give the fin and rudder at least 15% of the total wing area, for non-scale designs with normal layouts. The Ultimate is a good example of a bipe with enough vertical tail.

The simplest way to try out a bigger vertical tail is simply to tape a cardboard extension to the trailing edge of your rudder. It does not need to be at all robust, since you do not need to fly very fast to determine whether it works. If your rudder authority was already strong enough, simply reduce rudder travel in proportion to the increased area. I would be inclined to roughly double the total vertical tail of the Stearman to get really friendly handling. Trying different size cardboard extensions is very easy, and can be done during a single flying session.

A little washout in the wings also helps, and beware of washin, - even a tiny bit poisons handling, and four ailerons are vastly better than two - much less adverse yaw and less tendency to bite you with snap rolls at inopportune times.

Bipes do not carry weight as well as monoplanes, but this can be overcome with more power. If you are carrying all that noseweight anyway, maybe a bigger engine would be worth trying.

The Stearman now has the original OS .90 4-stroke. Once it is airborne it goes too fast and I cruise at less than full throttle. Maybe I should put in my OS 1.20 4-stroke or better,yet, my OS 1.08 2-stroke? Had the Dave Platt Jungmeister bipe that really flew well with the OS 1.08. It was no where near the wing loading of the Stearman.

Maybe the secret is to fly the leaded Stearman at full throttle from takeoff through cruise and then dive for the runway when landing, hoping not to stall and hoping not to run out of runway?
The 1.08 would give me some extra zip while taking off and turning and also, probably need to go out farther on the approach, keeping the speed up to avoid stalling while making the final turn. I still think the designer could have done better with this kit! Worse flying design in my stable.
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