How much and what size?

Need some info from all you folks that understand aerodynamics as I am somewhat lacking in this area. Trying to design a competitive Biplane and could use some figures. In general terms the distance between the upper and lower wings and how thick should the airfoils be. My understanding is the space between the wings should be at least the wing chord or more. My guess is the airfoils should be about 15-16 percent due to the extra drag of the additional wing. Any help would be kindly appreciated. Bob Whitely

Hi Bob,
I have designed and built three bi-plane stunters over the years, and they are a hoot to fly. I never thought that they were competitive, but I do think it is possible to do so. The best one had the wing the same distance apart as the wing cord but with only a 14% thick airfoil. I always wanted to build a new set of wings that were thicker for it, but lost the model before I had a chance to do so. My Ultimate Fun Fly does pretty well converted to C/L and flies a respectable pattern with enough power. The Ultimate has an 18% thick airfoil with the wings the same distance as the wing cord. The interesting thing about the Ultimate is how it corners with out wobbling or going nuts. The swept back wings really contribute to the stability in the corner. I also found that the use of flaps dampened and smoothed the corners as well. Four wing flaps were too much and wound up using only the flaps on the lower wing and even at that, were set at a 2 to 1 elevator ratio.

So what I would suggest is to design a model with both wings swept with an airfoil thickness of 15% (maybe16%), at around 600 square inches depending on what you want to power it with. Flaps on the lower wing only and space the wings the same distance apart as the average cord of the wings. The area of the stab and elevator on my models were on the small side at 18% of the wing area. This seemed more than adequate with plenty of authority.

Good Luck

Ok Mikey,
So with our "modern" tendencies, we should end up with a %23-%24 tail (maybe even more) extend the tail at least another inch and a half, pump up the airfoil, increase the aspect ratio, reduce the flaps to 2/3rd span or less, and install at least a .65! But remember, you MUST use 3 1/2 to 3 3/4 lb wood through out with most of the main parts vacuum bagged from CF.
TFIC
Bill <><

Bob and Mike,
A swept wing Staggerwing will just not look right.
Chris...

Speaking of aspect ratio, isn't it the nature of the beast to have a pretty high aspect ratio? If it's additive both wings on my Dancing Girl figures out to something like 11 to 1 or doesn't it work like that? Individually they are 5.2 to 1...

From what Mikey says... Take the wings from a 38 special, add a little sweep, flaps on the bottom wing and put them in a built up fuselage like the Dancing Girl. Could make for a pretty neat bipe.

>From what Mikey says... Take the wings from a 38 special,
>add a little sweep, flaps on the bottom wing and put them in
>a built up fuselage like the Dancing Girl. Could make for a
>pretty neat bipe.

Bob,
Doing mods to a kit is a great way to try a few ideas. Yes! It would make a nice looking model but I would like to start with a clean sheet of paper. Maybe something like Sean Tuckers airplane would be really cool.

Bill,
No! I would not do that at all LOL. But even 20% may be too much for a Bi-Plane.

Whitely,

I think it needs to be noted that not only did we not notice you were no longer active on Stuka Stunt, we got along pretty well without you.

There was a slap directed your way via some NW-based curmudgeon a week or so ago, something to do with one of Larry's Fox 35s and Pete Peterson, but if you failed to catch it, we're all good to go.

A bi-plane? You are kidding, right?

If not, you have set a high standard for years, so if a future project is to some in 2s, how about two wings, two engines, two fuselages, two fins, two rudders, two bellcranks, two much...

>
The Ultimate has
>an 18% thick airfoil with the wings the same distance as the
>wing cord. The interesting thing about the Ultimate is how
>it corners with out wobbling or going nuts. The swept back
>wings really contribute to the stability in the corner. I
>also found that the use of flaps dampened and smoothed the
>corners as well. Four wing flaps were too much and wound up
>using only the flaps on the lower wing and even at that,
>were set at a 2 to 1 elevator ratio.
>
Hello Mike you caught my attention with the Ultimate bipe.This is the Sig fun fly bipe?What did you do with the bell crank and lead outs.Did you just place the lead outs between the wings at a height to get a lateral CG?Was the bellcrank mounted on top of the lower wing and the side of the fuse.Was the Cg similar to the R/C location.Finally 46 power? Thanks for any help.Do you have any pictures.I love bipes.Dennis

Dennis,
Sorry but I didn't see your post until now. The U/B needs the power from a ST .51 or a really good .46 or some kind. The bell crank was mounted between the wings on the fuselage side with the leadouts passing through the left interplane strut. The position of the bellcrank was mounted on the engine thrust-line and seemed to be about right. I used the Sig 4" with the pushrod on the inside hole of the bellcrank and later I drilled a new hole in the bellcrank to slow the controls down even slower. The C.G. was moved all over the place but if I remember right it was at or slightly ahead of the forward C.G. limit listed in the book.

I don't have the model here at this time or I would post a few pictures for you.

Later,

> Need some info from all you folks that understand
>aerodynamics as I am somewhat lacking in this area. Trying
>to design a competitive Biplane and could use some figures.
>In general terms the distance between the upper and lower
>wings and how thick should the airfoils be. My
>understanding is the space between the wings should be at
>least the wing chord or more. My guess is the airfoils
>should be about 15-16 percent due to the extra drag of the
>additional wing. Any help would be kindly appreciated.

What engine are you thinking about?

Thanks for all the help so far. As for Dirts' input thus far I am still waiting for some thoughtful and reasoned comments. As for the slap of a few weeks ago, I logically deemed it beneath my station to even warrant my time much less a reply. Moving right along, the craft in question will be an S.E.5 and of relatively scale outlines and built to a competitive edge. Engine will be a P.A. .60 or .65. Wing span about 48-49 inches, maybe 650-670 squares, about 60ozs. I do believe this can be done if all the right numbers are used and the weight kept within reason. Did I mention that it will have a piped engine? And just for Dirt, there is a good chance that the machine guns may be operational. The power is available now, just a matter of putting it all together in the right package. Sooooooo...... Bob Whitely

Yep, sounds like the 38 Special wings wern't quite what you have in mind

>Moving right along, the craft in question
>will be an S.E.5 and of relatively scale outlines and built
>to a competitive edge. Engine will be a P.A. .60 or .65.
>Wing span about 48-49 inches, maybe 650-670 squares, about
>60ozs. I do believe this can be done if all the right
>numbers are used and the weight kept within reason.

That's a pretty high aspect ratio - I get almost 7:1 (335 sq in per wing, 48" span, 7" chord). I might be tempted to make it even bigger by going to maybe a 8.5" chord. It will still be a pretty compact airplane, and should fit in the back seat of a '57 without much problem.

I think you're right in the ballpark on the airfoil. I might even be tempted to go even thinner, if you could keep the LE from getting too pointy.

Brett, Appreciate the thoughts. Some quick questions. Will the .61 or .65 have enough power? It will use a pipe. Can the total drag be overcome? Would you put flaps on all four wings or just top or bottom? Where should the high point be? I'm guessing 30-35 percent. Should the wings have any incidence to each other or just use 0-0 throughout? I understand about the LE and will work it as much as possible. Can maybe shorten the AR some but would like to stay with the basic concept of the S.E. 5 look. Thanks, Bob

LAST EDITED ON Feb-07-04 AT 09:57 AM (CDT)
 
Hi Bob,

This sounds like a great project! I can't see how a PA 61 or 65 couldn't be enough power.

Did you get my email?

Thanks
Bill <><

Hi Bob-

The Stearman that Bart put up over 500pts at Clovis a few years ago had about 16% foil, 0-0 incidence and flew just great. You going up against the Red Baron??? Give some consideration to the SPAD. It has no stagger between the wings and the wire trailing edges would look so cool! Don't forget to use a round bellcrank for neat exit holes.

Hutch

>Brett, Appreciate the thoughts. Some quick questions.
>Will the .61 or .65 have enough power? It will use a pipe.
>Can the total drag be overcome? Would you put flaps on all
>four wings or just top or bottom? Where should the high
>point be? I'm guessing 30-35 percent. Should the wings
>have any incidence to each other or just use 0-0 throughout?
> I understand about the LE and will work it as much as
>possible. Can maybe shorten the AR some but would like to
>stay with the basic concept of the S.E. 5 look.

Well. 800 is a lot of area - but it's really just two Flite Streak Wings. I honestly don't know if it's too much. I'm also not sure you need flaps. I think it will be hard enough to trim out the roll without introducting the complications of lateral CP shift, and I would think it could be pretty light.

I am pretty sure I would start with 0-0. As for the high point, keeping the LE radius up probably means it will be pretty far forward.

This is quite a project. If I was doing it, I might make a test model first, to see if the gross characteristics are right. Like start with two Skyray wings and a box fuse, and monokote. Then if it works, ballast it up until you get a feel for how heavy it can be. This is so far off the edge of cut-and-try experience that I would not feel confident about getting everything right on the first try.

I don't know if this is the right thread but I just had to chime in. Talking with Bob (Alphadog) the other day about this subject, he mentioned the possibility of a Hyperbipe, experimental biplane as a stunter. The fuselage has flat sides and is airfoiled in shape so it is a lifting body and can weathervane around the pattern. As such there are three lifting surfaces to contend with thus a possible heavier weight overall is possible with comparable wing (and fuselage) loadings. Sounds very interesting to me as a scaled down version for say 40-46 powered models.

What are your thoughts on lifting body concepts for a stunter and the hyperbipe in particular for 40-46 power?

Bob Smiley
A Lancair 360 builder/pilot trying to be a modeler

>I don't know if this is the right thread but I just had to
>chime in. Talking with Bob (Alphadog) the other day about
>this subject, he mentioned the possibility of a Hyperbipe,
>experimental biplane as a stunter. The fuselage has flat
>sides and is airfoiled in shape so it is a lifting body and
>can weathervane around the pattern. As such there are three
>lifting surfaces to contend with thus a possible heavier
>weight overall is possible with comparable wing (and
>fuselage) loadings. Sounds very interesting to me as a
>scaled down version for say 40-46 powered models.
>
>What are your thoughts on lifting body concepts for a
>stunter and the hyperbipe in particular for 40-46 power?

Mr Whitely and I talked about this about, wow, 10 years ago. I don't know about the lifting body part, but the Hyperbipe would make a great subject - no cabane struts, easy to build and align. The only issue I see, and the one that has kept me from trying it, is the stab. The prototype is a very low aspect ratio with a tiny elevator. I don't know how I would make it the right size without making it look really funny. Much easier to disguise on a more conventional tail.

I have some plans, but they aren't a lot more than chicken-scratching.

I'll toss in my two cents if you don't mind....try starting with the Guillows SE5a plans. They are for a 24" model so if you double them you have a 48incher and all the scale outlines done for you. I have been working on this myself for a while now, just not as large as yours. I am going 0/0 for bottom wing/stab/motor, but -1 degree on the top wing. Everything I have read or heard has said this will smooth the flight out quite a bit. If you would like a copy of the plans let me know and I'll email them to you. Hope I have helped and not increased the confusion!

>I'll toss in my two cents if you don't mind....try starting
>with the Guillows SE5a plans. They are for a 24" model so
>if you double them you have a 48incher and all the scale
>outlines done for you. I have been working on this myself
>for a while now, just not as large as yours. I am going 0/0
>for bottom wing/stab/motor, but -1 degree on the top wing.
>Everything I have read or heard has said this will smooth
>the flight out quite a bit. If you would like a copy of the
>plans let me know and I'll email them to you. Hope I have
>helped and not increased the confusion!

I don't know about it for sure, but I think that this is so that the lower wing stalls first, turning your bipe into a Parasol monoplane. 1 degree probably doesn't matter, but I don't think this is necessarily what you want for a stunt plane. That's why I suggested a test model to see, first. There's a lot of unknowns in this deal. Be a shame to spend all that time and find that you guessed wrong.

The Hyper Bipe would make a good subject. The low aspect tail would not be a problem if increased in area slightly. Just look at Gid Atkins Laser, one of the best cornering models I ever seen (and I have seen a bunch). Just for fun look at the February issue of Model Aviation on page 166. Chip Hyde flew a model called Double Vision at the Nationals. This is what I had in my minds eye only with the fuselage slimmed down a bit and a different rudder shape. I know it is not a "scale" but still really cool. If you look really close you can see the pipe on the bottom of the model.

Later,

WRT the comments about Aspect Ratio: I think biplanes have a much lower effective AR than the geometric AR. With that in mind, how do you think this would figure into the thoughts in the "lower AR in the junk" thread? ...just wondering... Biplanes have an appeal to me too.

>The Hyper Bipe would make a good subject. The low aspect
>tail would not be a problem if increased in area slightly.
>Just look at Gid Atkins Laser, one of the best cornering
>models I ever seen (and I have seen a bunch).

Yes, it worked so good you have a whole generation of models copying it - mine included! But 4.25:1 and 1:1 are pretty far apart, and making it higher really screws up the shape. We're not talking "whale fluke" aspect ratio - more like sun perch.

I'm not saying it couldn't be done - just that this is the holdup for me.

Hi Guys; I haven't had much experience with C/L bipes outside of a Flying Fool I built about 40 yrs. ago. Very fun plane at the time. I have lots of exp. with R/C bipes having built about 6 or 7. Somebody mentioned that swept wings on a bipe really make them groove, and this seems to be true in the ones I have had. In R/C wing sweep gives a diehedal effect without the actual thing. I am just finishing up a Bucker Junmiester for R/C that is 1/4 scale, and with both wings swept, and a fairley long fuse, ( and suuper good looks) I think It would make a really cool C/L bipe. It does have a good sized fuse, but I think it could be built light. I believe the full scale job had about 2 deg. neg. in the top wing, but then it also had a flat bottom wing. I keep looking at the plans and at my Fox 59 and wondering about scaling down for a stunter. Bipes are a lot of work but are very rewarding when they fly well.

What about upscaling Don Hutchisons Stearman about 5% I think this would be about 700 Sq and using a Saito .72? I have had the ribs for this drawn on wood for about 5 years and the plans enlarged 5%. It sure seemed the Stermans that Don had flew very well? I will finish another Biceps 740Sq for Classic this year I hope with a .60 2 stroke for power. This has flaps on the top and bottom wing. I think
it flew pretty well considering the wing ribs were very thick for a bipe. However I really would like a Big Stearman with a Saito .72 and a 14" prop! Any comments re the Sterman design as compared to the Se-5? Walter Hicks

I would think for scale fidelity the SE 5a would be better because of the longer nose moment and an enclosed engine. As far as I know there where no cowled motors on any of the military Stearmans. I may be wrong on that, as I am not an expert on them by any means. And besides....the SE 5a is just so darned cool!!