Author Topic: Biplane Design (Read 2269 times)

Dallas Healey · « **on:** October 29, 2007, 06:26:28 AM »

I love my high aspect ratio self designed 46 sized stunter and it is a beautiful flyer that does everything well until it comes to wind. The high aspect ratio wing has never come close to stalling and it will turn as tight as you want it to but it is all over the place as soon as the wind is more than a gentle breeze. I have been thinking about how to use a high aspect ratio wing design but keeping the span small to reduce the effect of wind buffet. One way is to use a lot of taper in the design (such as the Firecrackers). Another way maybe to go to a biplane design to achieve sufficient area while reducing the span and still retain a high aspect ratio. Even better would be to also use a central motor/fuel tank pod with twin booms to allow the elevators to operate right on the thrust centreline and still remain out of the aerodynamic "shadow" of the flaps. Even better yet again would be to have the biplane wings the same distance apart as the diameter of the prop to allow the use of very short undercarriage legs (maybe even wheels that only project half their diameter from the bottom of the wing) to achieve the same flight performance during inside and outside turns. It certainly would not be a pretty model but would combine high drag (for reduced speed), high lift, good control surface authority and almost identical flying characteristics when turning in either direction. Has anybody ever put a 60 in a biplane F2B stunt design that was successful? If not, why didn't it work? The only real advantage of a monoplane over a biplane is the reduced drag which allows greater speed. This is not an advantage in F2B so why aren't there competitive biplane designs around? With the advances in compositites it must be possible to make a strong and light biplane design now. How have other biplane designs handled wind? Anybody got any thoughts on this or do I have to build one first and find out for myself what a crap idea this is and finally understand why nobody else is doing it?

PatRobinson · « **Reply #1 on:** October 29, 2007, 07:32:56 AM »

Hi Dallas,
Go to search : for a 2 page thread titled Stunt-Biplane started by Bill Bowmer and you will see a picture of a high aspect wing biplane designed by noted designer Steve Buso and this one was built by John Duncan. Unfortunately, there was no details about this plane other than the picture so I would suggest you contact Steve Buso about the viability of your similar design concept. I don't have Steve's contact information at hand but I am sure someone probably has it. I will also see if I can find it as well.
Hope this helps.
Pat Robinson

PatRobinson · « **Reply #2 on:** October 29, 2007, 08:05:28 AM »

Hi Dallas,
Sorry, I couldn't find an e-mail address for Steve Buso, he is listed in PAMPA with street address and US phone number but no e-mail. Randy Smith of Aero Products sells Steve Buso plans so he might have an e-mail address for Steve. However, It would probably be best to contact Randy through private message and not on an open forum. I am not sure if Randy sells plans for this Buso bi-plane or if he can get access to them for you but it won't hurt to ask. Maybe someone else can help out with information on this plane or with e-mail info for Steve.
Best of luck,
Pat Robinson

Mark Scarborough · « **Reply #3 on:** October 29, 2007, 08:16:24 AM »

Dallas,
very similar ideas to what I have been thinking, I have a design worked up along these lines, its in line to be built soon. we should talk

Randy Powell · « **Reply #4 on:** October 29, 2007, 09:09:19 AM »

Dallas,

I've talked about this before, but I've built a lot of High Aspect Ratio planes. A lot. There are a lot of design problems to get around, but the one that I could never quite overcome was the sensitivity to turbulence. All planes are troubled by turbulence, but the high AR jobs are worse. In some cases much worse. The last one I designed a couple of years ago did the best. Even in high winds, as long as the air was clean, it preformed very well. The problem came down wind of obstructions. Man that plane could be a tough nut in turbulent conditions.

The only thing I can think of at this point to moderate the problem is to go to a high aspect elliptical planform. Much like Dennis Adamisin's Futurist.

Here's the last one I built. It's still sitting in the rafers after the fuselage fractured in high winds. It will get repaired some day.

phil c · « **Reply #5 on:** October 29, 2007, 07:37:14 PM »

If you want a higher aspect wing to work you need to reduce the tip chord. The last plane like this I built had a 15 in. root chord, 6.25 in. tip chord, and 64 in. span, AR of 6. It handles turbulence remarkably well.

Dallas Healey · « **Reply #6 on:** October 30, 2007, 04:26:30 AM »

I still haven't read an argument as to why a top F2B stunter can't be a biplane. I found the other biplane thread and it seemed more a case of they don't win contests because the top flyers aren't using them. The only negative comment I saw was that staggerwing designs turn differently inside and outside which is only logical. Isn't there an aerodynamic theory wizard out there that can explain why biplanes aren't capable of top F2B performance? To get back to my original problem, does a biplane handle wind/turbulence better than a monoplane design due to the reduced wingspan?

PatRobinson · « **Reply #7 on:** October 30, 2007, 11:10:21 AM »

Hi Dallas,
Over the years ,a lot of people have dabbled in some fairly respectable bi-planes like Claus Makis has created or Tom Dixons good flying ".38 Special" However, if you are looking for definitive answers and guidelines on what
"to-do" or "not-to-do" to create a "top-level" stunt-bipe then I don't think there are any to be had.

At the heart of the matter, as far as I know, no one has brought their passion, commitment, desire and ingenuity plus hard work to the process of creating an ultimate stunt bipe, in the same way a guy like Al Rabe did to the process of creating a "scale looking" plane that could compete at top levels.

Dallas , until some serious and commited empirical testing is actually done by someone that yeilds useful "real world answers" then arguments for, or against a top-level stunt-bipe design are at best just guesses.

Do research on existing designs, bounce your ideas off people on the forums, formulate your own designs and then test again and again till you succeed. That is the only path I can see to follow.

I want to wish you the best of luck with your quest for a top-level stunt-bipe.

Pat Robinson

rustler · « **Reply #8 on:** October 30, 2007, 02:45:15 PM »

I think the wisdom on bipes is that the two wings generate less lift than a mono wing of the same area. I would think you can overcome this by increasing the area of the bipe. Of course this would lead to more drag, - not a bad thing in a stunter.

Mark Scarborough · « **Reply #9 on:** October 30, 2007, 04:41:47 PM »

two wings gnerate the exact same amount of lift as one wing of equal size. What creates the loss of efficiency is the proximity of the wings with each other. Now that is not all a bad thing. we have the capability to generate way more lift than we need, assuming the correct airfoil and reasonable building practices, not to mention the flaps capability to generate lift. I personallly think that drag isnot really a bad thing in design of a stunter. So in essence what we need to look at is to first use a slight bit more wing area than we anticipate in order to get the wing loading in the right range. next, take advantage of the fact that the wings brace each other and build them lighter! Then insure that you allow enough space between the wings, as in a minimum of 1 to 1-1/4 chord between them. This is a standard that was used when Bipes were in vogue as far as I can tell. Problem is, when you have a chord of say 11 inchs as a normal stunter would have, thats a really tall distance to seperate the wings. SSo, as I have envisioned, High aspect ratio could be a key. this would allow a narrower chord and hence the wings could be closer together. I have one drawn up, but I am waitning to build it until I fly just a touch better, righ tnow I am not sure if I could tell whether it was working or not

If anyone is SERIOUSL:Y interested in pursuing this direction email me and we can talk about it.

Don Hutchinson AMA5402 · « **Reply #10 on:** October 30, 2007, 05:39:33 PM »

I have messed with biplanes for a while now. I don't find any difference in the turns with the positive stagger of the Stearman, I think it is a matter of trim to make them equal. I do find they are a bit unstable in the roll axis in a wind as the distance from the bellcrank to the leadout guide (the "N" strut in my case) is a lot less than a normal model. Makes it a bit "rocky"! A good flyer has put up 500+ scores with one of these in good air.
Don

minnesotamodeler · « **Reply #11 on:** October 30, 2007, 06:33:41 PM »

Here's one I drew up for a buddy a few years ago...he got it partly built, lost interest and gave it to me. I nearly finished it before I lost interest in it myself. So here it sits...95% done.

I don't know why one couldn't be made to fly as well as a mono, but as for handling wind better, I dunno...you're dealing with considerably more side area, with the extra wing and struts.

I designed some 1/2A solid-wing triplanes that actually flew quite well. But, 3 built-up wings for one airplane? Gives a new meaning to "labor-intensive".

--Ray

rustler · « **Reply #12 on:** October 31, 2007, 03:33:07 PM »

Quote from: Mark Scarborough on October 30, 2007, 04:41:47 PM

two wings gnerate the exact same amount of lift as one wing of equal size. What creates the loss of efficiency is the proximity of the wings with each other.

Mark - An interesting point and one which I hadn't considered. It is the interference between wings which degrades the lift available, but I wonder even if there were no interference could two wings generate exactly the same lift as one wing of equal area? I'd need someone who knows aerodynamics to confirm, but might not things like scale effect and Reynolds No's. mean this is not true? I suspect the one wing would generate more than twice the lift of the two smaller wings. Of course biplanes do inherently have more drag than a monoplane of equal area.

Mark Scarborough · « **Reply #13 on:** October 31, 2007, 07:33:41 PM »

Ok you cauight me, to be totally accurate, you would have the losses inherint with two sets of wingtip vortices so there would in fact be greater loss as a result of that, and also the inherant drag associated with the vortices. again, things that are minimized by high aspect ratio wings. Good catch

Paul Smith · « **Reply #14 on:** November 01, 2007, 06:57:53 AM »

I am the owner of a Sig S.P.A.D. that stunts, but not all that well.

My theory:

In the mythical five-foot turn, the top wing is at maximum angle of attack, while the bottom wing (on the outside of the turn) in at substantially lower AOA. This is partially compensated by the fact the bottom wing is travelling a little faster, but not enough to have both wings operating at optimum lift in the turn.

One fix might be to have a degree of so of positive incidence in the top and negative in the bottom. That would slow it down level, but it's not a race.

This is one more huge difference between CL and RC/real aviation where the loops are gigantic.

Bob Zambelli · « **Reply #15 on:** November 01, 2007, 10:13:07 AM »

Dallas wrote: "The only negative comment I saw was that staggerwing designs turn differently inside and outside which is only logical. Isn't there an aerodynamic theory wizard out there that can explain why biplanes aren't capable of top F2B performance? To get back to my original problem, does a biplane handle wind/turbulence better than a monoplane design due to the reduced wingspan?"

Hi, Dallas - that's what I expected but it proved to be untrue. My Staggerwing has no apparent difference in turning ability even though the stagger is more than most.
It has no flaps nor does it need them.
The turning symmetry is in fact related to the gear - it is close to perfect when I retract the gear but a bit off with the gear extended - I've proven this by experiment. When retracted, the gear has a very favourble effect on the flying characteristics.
The turns are sharp with very little force needed (I use a Hot-Rock, 68 foot .018 lines)

The wing loading is low as the bird has over 800 square inches and weighs just over 60 ounces.

Now for the bad news - it is definitely not happy in the wind. Although line tension is maintained, it does get bounced around a lot.

Bob Z.

Randy Powell · « **Reply #16 on:** November 01, 2007, 02:54:02 PM »

I imagine tubulence would be a thrill.

Bob Zambelli · « **Reply #17 on:** November 01, 2007, 02:58:43 PM »

I imagine tubulence would be a thrill.

OH, YEAH!!!!!

A regular riot!!

Bob Z.

Randy Powell · « **Reply #18 on:** November 02, 2007, 11:45:10 AM »

Bob,

It's one of the reasons I haven't tried another high aspect plane. The sites we fly in here are virtually all tree encircled. When the wind blows, it's turbulent. Every time. I got tired of seeing both the top and bottom planform on every maneuver.

Dallas Healey · « **Reply #19 on:** November 02, 2007, 07:09:04 PM »

Ok that definitively answers the big question of whether the biplane concept, combined with high aspect ratio wings, will handle wind/turbulance better than a high aspect ratio monoplane design. I had hoped that I might have been onto something there and would have broken away from the tedious procession of rakish monoplane designs all based around similar numbers. In the end I suppose that is simply because they work the best under most conditions. Have we now reached the pinnacle of F2B design? Is there no other direction to head in F2B aerodynamics? It looks like the future is simply electric versions of the current designs and more extensive (read expensive) use of composite materials. Maybe that is being a bit pessimistic, at least it will mean that it really does always come down to the skill of the pilot in the end and that is what F2B should really be about.

Paul Smith · « **Reply #20 on:** November 03, 2007, 07:09:10 AM »

Modeling is about the skeels of the designer, builder, and pilot.

Dallas Healey · « **Reply #21 on:** November 05, 2007, 01:07:57 PM »

I had considered including the designer and builder but with the event of ARFs it seemed to be less of a factor now. While to current crop of ARFs generally require some internal surgery and then have to be properly trimmed, the building side of the sport looks to be on the wane. The next generation of ARFs should hopefully be very competitive by being lighter and having decent control systems fitted. This would only leave trimming. It's not inconceivable that once a very good and affordable ARF hits the market that you could end up with many flyers in a particular comp actually flying the same model at advanced and expert level (like is already happening at beginner level). You may not like it but it is probably heading that way in the long term. Again this would only leave pilot skill (and some luck with weather conditions) as the final determining factor.

Bob Zambelli · « **Reply #22 on:** November 06, 2007, 08:18:25 AM »

Now you fellows really have me thinking about aspect ratios.

For what it's worth, the Staggerwing has a 52.5 span, 8.75 chord, yielding an aspect ratio of 6:1.

Is this considered high?

The photo shows the wing from a high angle.

Bob Z.

phil c · « **Reply #23 on:** November 08, 2007, 08:11:43 AM »

bob, anything over about 5.5 AR is pretty high for a monoplane, unless you do some layout tricks to minimize unwanted rolling from turbulence. The tip needs to be down around 45-50% of the root.

The Staggerwing looks great and flew great when I saw it. I especially like the retracts. Gotta do some in my next plane.

Dallas Healey · « **Reply #24 on:** November 09, 2007, 03:57:22 PM »

Now we are back to the original question of how to have a high AR wing for the great lift that it gives for a given area without also copping the problems of poor handling in turbulence. The whole idea of the biplane was to keep the wingspan low compared to the total wing area. Could the performance of the biplane in turbulence be improved by minimising the side area of the fuselage? It is possible to come up with almost a double combat wing (with a single set of tail booms) and still be able to fit undercarriage. Combat wings aren't affected by wind much, partly because of their high speed and partly because they have little side area. Again we are talking about an unattractive design but could it work?