I can't believe it, I'm almost finished with the 2 Bits Bipe plans. It's a design I've had on the burner since about 2004, but, I had to make some changes as I learned more about biplane design.

I wound up with a pair of relatively high aspect ratio wings, spaced about 1.3 chords apart, Though the individual wings are High A.R. the combined chords make it fall into the more normal A.R. we see in stunt ships. I'm depending on the individual high A.R.'s will give me the efficiencies these planforms are known for, and the combined lower A.R. will help to avoid the tendency to become unsettled in turbulence.

I also decided to make it into an extreme take apart to make it easier to travel to contests.

Attached is a pair of jpeg's of the plan sheets. Tomorrow, I'll finish up the pattern sheet. Can't wait to get started building this one.

John-

You've really outdone yourself on this one! That is just a great effort, AND it is the only CL bipe design I've ever seen that gets to the heart of advantages biplanes may have. You've apparently done your homework, something I doubt has been done before in CL. The high A/R wings are also necessary to get the numbers to work well. Your gap is impressive, and we all should remember that biplanes with that gap can be very efficient!

Bipes are sometimes shunned due to complexity, asymmetry, and parasite drag (struts, braces, wires,...), effects reduced with modern materials and probably not a problem in CL stunt anyway. Before your plane, most in CL seemed to ignore the fact that biplanes are otherwise more efficient than equivalent-area monoplanes. Since each wing needs only to supply half the required lift, their individual induced drags at large gaps are each only 1/4 of the total drag of the monoplane. With realistic gaps, the interference drag does not eat up the remaining advantage. Illan Kroo's Stanford group (and I in the lost posts in the SH crash), has computed that something like your bipe should still have an effieciency of 1.36 or better, meaning that your bipe should have a L/D ratio of 1.36 times that of an equivalent elliptical wing - barring lost efficiency due to lower Reynolds numbers.

Your plane is the first CL stunter I've seen that seems to employ these potential biplane advantages, and I'm really looking forward to hearing about your prototype's performance. I haven't read anything about the R/C pattern bipes, but they must work. My only concern is that your design performance may vary a bit more with size, due to Reynolds Number effects.

Anyway, Way to go!

SK

 Looks great John, this will be interesting for sure. Looks like you've got everything covered.

 This is trivial I know, but the only thing I'd change (being my usual nit-picking self) is the outline of the wheel pants. I'd make them with a straight-ish raked L/E to better tie in with the profile of the fin/rudder. Just a little detail that stands out to me on the drawing, and would help tie things together.

What are the numbers on this one?  Span, area, engine size ?

What are the numbers on this one?  Span, area, engine size ?

Hi Allen, the span is 51.5 inches, area is 688 sq. inches, and the power is .60 and up. I'm showing a Stalker .61RE, but that would be the smallest I would consider.

Just curious, what's the wing chord from the L/E to the hinge line at the center of the wing?

6.395" leading edge to flap hinge. 8" leading edge to flap trailing edge. 

John,

The only issue I can see is it will need to be light. I'd do everything I could think of to insure that it comes in under 70oz. Be a trick, but I have faith.

Very cool design, my friend.

Thanks again guys for the helpful suggestions and encouragement.

I must tell you that I may n ot have gotten over the major hurdles without Norm Whittles helpful suggestions. The mans an incredible designer in my not so humble opinion. Norm will tell you "It's Old Math son, old math."

I agree that weight will be my biggest challenge. Especially as I'm flying at 4600 ft ASL to start with. 70 oz's  here will be a brick.

As it stands, I estimate the airframe, everything, but the covering, and finish, in the low to mid 50 oz range. It remains to be seen if I can stick to that projection.

Making it a one piece airplane might shave off about 3 to 4 oz's, but I really want to make it a take apart. I used much the same techniques on a Sheeks Stagger Wing and it came out OK.

Well, with the laser cut files, I'll find it easy to perhaps build 1 of each style.   

looks good John
dont know if you remember seeing it but my dad and i colaborated on a bipe a couple of years ago. it flew fairly well but crashed after only about five flights due to what appeared to be a launching accident,(the rudder and fin got hit while being released and came loose after a few minutes of flying).
anyway I redrew the design with a few mods but havent yet built another one. i think i showed some promise but had a few problems that we were going to fix.
one was to make the flaps larger, which you have allready done, another was to reduce the weight ours was 69 ounces dry and definitelly flew like it was a little heavy allthough yours has a definitelly higher aspect ratio  i would try  to keep the weight way less than what ours weighed (we had a PA65 on pipe so power wasn't the problem).
the last thing we addressed was to use a thicker more blunt airfoil on the next one, yours is about what i put on the second version. i was worried about drag in verticals but it was a non issue and the thicker airfoil might have helped the hard corner issue
other than slowing down in hard corners quite a bit it wasnt too bad a flier.
one issue that wasn't really addressed on the second redraw was the dificulty we had reaching the needle valve and glow driver with all those wings in the way while the engine was running. (just something to be aware of, it was a little precarious reaching around the carbon three blader when it was running)
one thing i noted on your plans that we came up with on ours was the bellcrank to flap pushrod angle. we elected to run the pushrod from the bellcrank directly to the elevators and then another back forward to the flap horn. it allows a much better angle at the horn and less chance for unintended diferential.we figured the extra carbon fiber pushrod length was worth it.
 one last thing, the C/G on your plans looks way far forward of what i would have come up with ? just a thought.
anyway good luck with the bipe! ours looked great in the air unfortunaley it didn't last very long.
Dave jr.

the last thing we addressed was to use a thicker more blunt airfoil on the next one, yours is about what i put on the second version. i was worried about drag in verticals but it was a non issue and the thicker airfoil might have helped the hard corner issue
other than slowing down in hard corners quite a bit it wasnt too bad a flier.
one issue that wasn't really addressed on the second redraw was the dificulty we had reaching the needle valve and glow driver with all those wings in the way while the engine was running. (just something to be aware of, it was a little precarious reaching around the carbon three blader when it was running)
one thing i noted on your plans that we came up with on ours was the bellcrank to flap pushrod angle. we elected to run the pushrod from the bellcrank directly to the elevators and then another back forward to the flap horn. it allows a much better angle at the horn and less chance for unintended diferential.we figured the extra carbon fiber pushrod length was worth it.
 one last thing, the C/G on your plans looks way far forward of what i would have come up with ? just a thought.
anyway good luck with the bipe! ours looked great in the air unfortunaley it didn't last very long.
Dave jr.

Hi Dave, did the one that slowed down in hard corners have the thin or the thicker wings?

It's always a bit dicey to get your fingers that close to the prop. I'm hoping that the nose is long enough to allow easy access to the needle.

I considered doing the same thing you did. I set up the controls that way on my Staggerwing bipe, and it worked well, but probably did add some extra weight. I spoke about my plans to Norm Whittle, whose opinion I respect, and the result of that conversations was to try and keep the controls simple.

I checked the angle at the horn, and found that it was essentially the same as on a normal mono-wing design, 9 degrees. Since it works fine on a mono-wing, I figure it'll also work fine in this case. It also made it simpler to remove the wings.

Interesting comment about the CG. I computed it based on the combined wing plan view, when observed from directly above.I found the MAC of the combined wings, then set the Cg at the 24% point on that MAC line. That's what I've shown. I have a belief that it's located pretty close to where it needs to be, though recent readings seem to indicate that it should be no further aft than 23% of MAC. Thank goodness that it's all adjustable.

I've sent the laser cut files out for quotes, hope to be soon starting constructiom. 

John,
What ever happened to the Kraut Twin?

It was showing great promise until I had a control system failure. The flap rod came undone from the horn. It pained me immensly watching it go in. I have the pieces, and it is repairable, but it'll be one of my projects for this building season.

Up until that point, I had gotten the engines sorted out. It was tracking very nice, upright and inverted. I had the turn rates pretty close, and was at the point where the next flight was going to be the first full pattern. Post mortem showed that I had possibly forgotten to tighten down the lock nut. I know I didn't secure it with loc tite. "Aint gonna happen" agin.

Edit: In view of my next post, I've changed this edit. I should know that aspect ratio is only indirectly related to induced drag, since it is span loading that determines the actual amount. So I've rethought what follows here and submitted another post below.

I agree,

...and if the aspect ratio allows the plane to have the same lift and span as an elliptical monoplane wing, then with sufficient gap, the induced drag should be significantly lower than an elliptical monoplane wing's.  Of course, John's aspect ratio is not extreme enough to give that monoplane wing an aspect ratio of 5+, but I doubt that he will be penalized much or perhaps at all with additional induced drag.

For aspect ratios that would do so (like 10?) there would be some real gains with a bipe. Taking into account interference drag and assuming a gap/span (yes, span) ratio of 0.2, such a bipe theoretically will have 36% higher efficiency (ratio of induced drags) than that elliptical monoplane. I got this from Stanford's Illan Kroo (who analyzed wakes) and used the old Walter Diehl/Munk method to get the same result. With infinite gap, that theoretical efficiency goes to 200%. I've posted this in the past, but closing in the tips to form a box plane gives theoretical gains of around 45%.

John's gap/span is about 1/6 = 16.7%, and aspect ratios seem to be around 7, but I still think that his model's induced drag will compare well with a comparable monoplane stunter. I doubt that I'll have time to check on it, but I'm seure that John has come pretty close to the best aspect-ratio/structure compromise. The Reynolds Numbers are the only real worries that I can see. Really, it should work well. I think it's a pretty fine effort!
SK

 Huh?

Where the heck would the aerodynamic centre of a biplane be?

If its between the wings then I just can't see it turning as sharply as a model that has the AC actually on the wing.

And would not the stagger give an inbuilt pitch effect that has a bias that going to be a real biatch to trim out?

Just thinking out aloud here!

Chris, I'm more visual than mathematical. I'll leave it to Serge and others to answer your question in detail.

What I will do is answer based on my visual abilities.

Your attached drawing looks pretty darned close to what I came up with, with the exception that the two wings are different in chord, and therefore area. That alone may cause some biasing. If they are also different in span, as well, there may be even more biasing.

I truly do not believe the sharpness of the turn will be that different from a mono wing. with the way I set mine up.

Let me walk you through the way I visualize the wings in flight.

While the wings have positive stagger, they are of the same span and area. The individual wings have a high A.R., about 7.2-1, but with the stagger, they should act together during the turns as if they are a mono wing at about 5-1 A.R., with one major possible difference.

The top wing should be flying in cleaner air during level flight than the lower wing, possibly carrying a significant percentage of the total weight. The lower wing may have some interference from airflow from the forward fuselage, and circular flow from off the prop. Possibly 25%, or slightly more of the lower wing, may be partially blanked by this flow. In level flight, the plane should be stable both upright, and inverted, with possibly a slight percentage better stability when inverted.

I see this because inverted, the top wing, (now the lower), is flying in cleaner air, and there should be slightly less percentage of fuselage/prop blanking by the now top,(lower), wing. This relationship, may alter the force arrangements, making the flying plane seem slightly nose heavy, depending on the planes attitude. I believe that careful design, can help to minimise these effects in level flight.

Now, during the turn, and we're talking about the corners here. It appears to me that during a hard inside turn, the lower wing may see slightly less blanking. The upper wing should be now carrying more of the weight, and making the arrangement appear to be slightly more tail heavy during the turn. More elevator authority may help the turn considerably, but as soon as the design is brought back to level flight, the apparent CG should now appear to move, back to the original force configuration.

Does the same thing happen during the outside turn?

Visualization leads me to believe it does.

So, in my estimation, there are positive expectations that can result from a proper Biplane platform. The problem appears to be figuring out the way to get the LD under control without getting the induced drag too high. I believe that it's possible, and I hope my design is a step in the right direction.

Having said all the above, I realise that since I'm more visual in my application, the proper application of the mathematics may show me that, either I'm correct, totally wrong, or somewhere in between. I trust that people like Serge, and others, will help guide us with either verifying, or pointing out, the errors, or correct assumptions, those of us who are more visual make.

Once the plane is built and flown of course, a lot of questions should be answered.

theory is all well and good, its even fun to hash out ideas and try them.
John and I talked biplanes at the regionals what, three years ago? LOVED the conversation, I to am a biplane fan, and beleive that one can be built that will perform a very suitable pattern. Will it ultimatly be better than an Impact, Patternmaster, any of the other current designs, maybe , maybe not,, it remains to be seen . As John says,, a lot of questions will be at least INITIALLY answered, and further answered as flights build up.
The bottom line is, its a model, no one is risking life and limb to verify the outcome, and John is having fun doing it. I am QUITE certain this model is at least as capable when trimmed as John is of flying it,, it will be cool, and fun to watch this one progress..
Get on it John,, Hey, did the  pilot in the twin survive, maybe he would like a ride in this one too?

John-

I think that biplanes - especially - are extremely complicated, so that math at my level is more likely to indicate what is practical, and if the input is "good", some relative effects and proportions. I didn't do any real engineering. Mine is, I hope, a reasonable estimate. For instance, I cannot tell from what I read how much twist or other aerodynamic variation is assumed in the simple biplane performance cited and how that relates to CL models with symmetrical sections that become cambered with pitch (flaps). These results I cited were said to be "optimized"  <<snip>>

   More generally, we really have no idea what parameters we need to optimize in order to make the airplane fly better - because we haven't ever determined in any engineering sense, what "better" really is. When things like changing the tipweight by 2 grams makes more difference than changing the aspect ratio from 5 to 6, I think it's going to be pretty tough to work it out in enough detail to make more than educated engineering guesses as to what we want. That's why "cut and try", guided by some fundamental principles used to do the analysis of the results, is about as far as we have ever gotten. Or probably ever will.

   What doesn't seem to work so well is "cut and try" guided by fencepost wisdom and a vivid imagination, which is sadly about where most people are, and almost everybody was before the  mid-late 70's. Most of the stunt folklore about design and analysis has been and continues to be utter and complete nonsense. By dint of perseverance there were a lot of good results, and some insights, but it was definitely the hard way. That's why it's still important to try to get to the fundamentals and argue out the reasoning, even if it don't lead you straight to the final answer.

     Brett

Another cool project, John.  My main caution would be the flap interconnect pushrod.  Aft weight on a control surface can cause flutter, and aft weight on a flap could reduce maneuvering stability, the reduction of which may be what Ted calls "excess lift".  Although it would be some bother to do, I'd put the flap control horn arms to which the pushrods attach forward of the hinge line.

You could take advantage of the biplane configuration and use wire bracing.  Then you wouldn't need the zigzag ribs or surface spars. 

You could take advantage of the biplane configuration and use wire bracing.  Then you wouldn't need the zigzag ribs or surface spars. 

    I like it, - you could tweak it by changing the tension on the wires. And Orville Wright is no longer around to sue you for patent infringement, either.

    Brett

Remember that there are other than geometrical effects that make an otherwise symmetrical model really asymmetrical. For instance, prop wash, torque, and for pitch especially, the ever-present gyroscopic precession, which pitches the plane up in ccw flight, unless the prop rotation is reversed. Balancing upper structure vs. landing gear for drag and c.g. purposes is not exact either. SO...you have to trim and design around these things. I'd suppose that stagger is just another part of the overall sum of things for which one must trim and adjust anyway. Still, I agree that no stagger would be best.

SK

     Do you have contra-rotating props?

     Brett

Touché! Oh and you might want to add gravity to that list as it is very asymmetrical.

   It's not just a matter of verbal jousting. The almost universal need for down elevator, downthrust, or positive stab incidence to acheive proper tracking is, I think, the result of a nose-up torque arising from precession.

    Brett

Interestingly a friend who flies electric uses a clockwise prop and reports that the opposite trim is needed.

I have launched his model (Firecracker) and witnessed that it pulls very strongly out of the circle at the moment that its released.

Thanks.

Greeting Claus, thanks for your comments, and reviewing your experiences with Biplanes in competition.

I have to agree with you that they are fun, and may garner some "Wow" points, but your experiences with comps. that included some very good pilots, seems to show that designs like your Duetto, can be serious enough to consider,

Now, to your question about my thoughts about performance upright and inverted. First My thoughts come from visualizing what is happening rather than pure mathematics. So a warning, I may be all messed up.

The statement in it's entirety is included. I believe we should look at it this way to explain my thinking.

"The top wing should be flying in cleaner air during level flight than the lower wing, possibly carrying a significant percentage of the total weight. The lower wing may have some interference from airflow from the forward fuselage, and circular flow from off the prop. Possibly 25%, or slightly more of the lower wing, may be partially blanked by this flow. In level flight, the plane should be stable both upright, and inverted, with possibly a slight percentage better stability when inverted.

I see this because inverted, the top wing, (now the lower), is flying in cleaner air, and there should be slightly less percentage of fuselage/prop blanking by the now top,(lower), wing. This relationship, may alter the force arrangements, making the flying plane seem slightly nose heavy, depending on the planes attitude. I believe that careful design, can help to minimise these effects in level flight."

 

Upright, I see the top wing flying in clean air, but the lower wing has disturbed air from the prop, and front of the plane disturbing a section of the lower wings area. I believe that this makes the top wing more efficient than the lower wing. The plane, with more efficiency from the top wing, may be more stable in level upright from the "parasol effect" with the top wing.

Inverted, I still see what was the lower wing being affected by pretty much the same forces. Some vectors may change, but essentially the lower wing seems to be interfered with. The top wing, now on the bottom, may have some interference, but it will still should be in relativly clear air. It appears to me that a higher percentage of the available lift will be coming from the wing less interfered with. Normally, it appears that the CL will apparently move forward, based on the percentages of actual lift provided by the two wings. This should affect the stability in flight. I feel that the plane will be slightly more stable inverted, but I could be wrong, and it would become slightly less stable.

It's one of the parameters I hope to explore once the plane is built and flown.

Again, thanks for your interest and comments Claus

John,
You showed this drawing in November. so can we assume that it will be in the air in a few weeks? We are looking forward to hearing and seeing more.

And build pictures, please?

Then the last corner of the triangle and the hourglass just were not corners.
If I had to do it again I think I would noticeably increase airfoil thickness, slightly increase gap, and maybe increase flap width

I take all this to mean that you ran out of lift at the critical points in the schedule and so are looking for ways to regain it.

Just wondering if an increase airfoil thickness on just the lower wing might do the trick here.

Chris, your idea of increasing thickness on one wing only sounds funny. Maybe some experts should take a look at this experiment. For this old lazy guy here this is not a suitable solution : I fabricate ALL ribs for both wings in one stack !!
Regards,  Claus

If as John says "the top wing (is) more efficient than the lower wing" and therefore producing more lift then it makes sense to modify the lower wing to try and regain its lost efficiency, no?

I believe that Al Rabe used asymmetric airfoils due to his scale looking models needing more lift in one flight orientation than the other and it could be the same here.

I am no expert on this but just an avid observer though!

Mather=w,
generally incidence on biplanes exists to control the center of pressure as the angle of attack changes, IE the top wing stalls first, and the CP moves back making it "nose heavy" which then self trims the angle of attack somewhat to keep it from stalling. Not something we want on a stunt plane IMHO

A really good bipe is like the last frontier - I LIKE what John is doing and he has a great chance of success.

I agree on the use of extreem power for this design. I'm considering a Rustler-Belko .76 for it. I've been deeply imerseed in a bunch of "for pay" projects that have kept me away from starting construction. I did get quotes for the Laser Cutting. I don't mind building it during the summer.

Hi Derek

I tried to avoid making it extreemly draggy, but with the cabain struts, and the wig tip struts, there is additional drag due to being a Bipe.

I strong PA .51 on a pipe may indeed be enough, and using PA's may be a good because they can be easily upsized should the pilot feel it's needed. I'm considering the engines I am, because I'm still enamored with a good 4-2-4 stunt run. I know I should at least try running a pipe, but with the advent of reliable electric power, I may wind up going over to e-power before I go to using a pipe.

Here's what I did on the Stab and elevators, along with my thinking about the whys and wherefores.

The stab and elevator is almost 19% of the combined area of the two wings. Since the stab and elevator are removable, I wanted to test the idea that since both wings act as one, they may not require the larger area of 24-26% to be effective in this planform. If I'm wrong, I will be able to change them out rather easily.

I've a few projects still under way, but, I hope to order the laser cut parts within the next few weeks. I'll be happy to let you know how the parts look before you start one for yourself. I imagine that should you decide to build one, it'll be after you've finished your main stunter for the next season.

John- Looking at the drawings once again I see that there are flaps on both wings. My experience with the last Stearman might be of some use to you when it comes time to fly. I only have flaps on the lower wing but when first testing, I could not get it to turn. The flaps were almost overpowering the elevators for pitch control. I then lengthened the flap horn and now it turns fine. Just measured the horn the other day and it is 2 inches long, twice the length of the elevator horn. If your test model doesn't turn just like any other model, having this much adjustment available may help the situation. Looking forward to hearing some flight reports.
Don

I imagine that should you decide to build one, it'll be after you've finished your main stunter for the next season.

Yes, the new one is almost done, its in final silver now and waiting for trim. I really like the look of your bipe and I have always wanted one so it is definitely on my to do list.

Greetings Roger. I'm building a new, larger, set of wings that will give me a better wing loading as well as more flap area. I wound up near the edge wing loading wise, and though it flew well in the rounds, the last corner in the squares needed some help. I expect to finish building the new wings after I get back from VSC. After that, I plan on building another and use some weight saving methods I've been thinking about.

I believe it will be a decent stunter, once the wing loading is at the proper level.

As I said, the plane flew decently except for the last corner of the squares. It has a very decent glide after the power shuts down, unlike several other Biplanes I've seen.

Hi TY, Yes, I'm sure it'll fly the square corner better at lower altitude. But, If I get it flying the square corner better up here at 4600ASL, it should be a cinch at lower altitudes. I've extended the wings, and made the flaps larger. Norm Whittle has been helpful with his suggestions.

Ken, thank you for your kind words. Unabashedly, I find I agree, it does have nice lines. It is drawn in CAD, and I have the laser cut files for it as well, I've released a few to other builders, but with the larger wings and flaps. Send me a PM if you want more information.

Hi Charles, Thank you for the compliment. As you are probably aware, encouragement of our friends, and peers, helps to keep us motivated.

Alas, due to less than desirable experiences in the past, I rarely, if ever, release my cad, or vector, files into the wild, but I can supply you with hard copies, or  PDF files that you can have printed locally.

I have offered, and sold a few, short kits. I prefer the short kit, as the customer usually has his own products that are preferred. Also. sheet stock of balsa, and plywood can be ordered from the various suppliers and delivered for only the one shipping cost.

Contact me via PM or E-mail and we'll talk.

John Miller
www.cadclassics.net

While on the subject of biplanes:

Nobody will mistake me for an engineer, but I was also wondering if the flaps sometimes create more drag than lift.

Excellent comments guys. Let me address my thoughts on them.

Roger, I'm a big fan of using less flap rotation that elevator. Typically, I set my planes up initially with about 25 degrees of flaps and about 33 degrees of elevator. I only go to 1/1 when the plane is heavy, and needs the extra lift during a hard corner.

PertiMe is correct that Flaps can cause more drag than lift. Seldom, even with very portly planes, does one see more than 15-20 degrees of flap rotation. High flap rotation, IMO, comes from trying to fly with too narrow a flap chord for the lift needed in the maneuver.

What I am now working on, based on suggestions by Norm Whittle, who studies these things, is increasing the total area of the wings. This also includes the area of the flaps. I have extended the wing tips and increased the chord of the flaps. This will give me about 50-70 sq. inches of additional wing area. ( I don't have the charts handy, or I could give you exact numbers.)
The wider chord will allow more lift to be created with out having to deflect the control surface as much as with the narrower flaps.  It should lessen the drag that's created at extreme throws. It should also increase the net total lift produced in the maneuver at the same time.

Chris, Using the cabane struts as tip plates has merit, but they may not work as well in that function, due to being asymmetrical in application, being mounted between the upper and lower wings, with nothing on the other side of each wing. I have mounted them about as far out as seems wise. At the point where they are located, they are supported by the wing structure, and form an important part of maintaining the structure, and stregnth of the wings. If I moved them further out, I still would not be able to go much further out than they are, without messing up the elliptical properties of the wing itself.

It's the high AR, and the elliptical properties of the wings that should make more differences in lift generation, IMO, than much else I could do with tip plates. Don't get me wrong a rectangular wing with tip plates can work pretty good, but, An elliptical platform really doesn't need tip plates, again, IMO.

Still, good suggestions that show innovation, and thought.

I have extended the wing tips and increased the chord of the flaps. This will give me about 50-70 sq. inches of additional wing area. ( I don't have the charts handy, or I could give you exact numbers.)
The wider chord will allow more lift to be created with out having to deflect the control surface as much as with the narrower flaps.  It should lessen the drag that's created at extreme throws. It should also increase the net total lift produced in the maneuver at the same time.

Hinge moment increases with the square of flap chord.  That could result in the pickle that Don mentioned above.

Chris, Using the cabane struts as tip plates has merit, but they may not work as well in that function, due to being asymmetrical in application, being mounted between the upper and lower wings, with nothing on the other side of each wing. I have mounted them about as far out as seems wise. At the point where they are located, they are supported by the wing structure, and form an important part of maintaining the structure, and stregnth of the wings. If I moved them further out, I still would not be able to go much further out than they are, without messing up the elliptical properties of the wing itself.

It's the high AR, and the elliptical properties of the wings that should make more differences in lift generation, IMO, than much else I could do with tip plates. Don't get me wrong a rectangular wing with tip plates can work pretty good, but, An elliptical platform really doesn't need tip plates, again, IMO.

For the real lowdown on that stuff, see http://www.smartcockpit.com/data/pdfs/flightops/aerodynamics/Wingtip_Devices.pdf

I also read through it, as I'm interested in finding the best possible solution to taming the corner. Especially the last corner where the added effects of gravity come into play.  

What I got from it is that there are a number of solutions, but nearly all are the result of compromises. I can see where the vertical cabanes between the wings can have some positive, as well as negative effects. How to deal with them, seems to be up for interpretation. Is that about right Howard?

Ted's comments have got me thinking. It would be rather simple to cut the flaps and experiment with reduced area. I'm not certain that there's a good set of numbers for flap ratios, throws, and such for a Biplane. I've seen some non-flapped Biplanes fly some rather decent corners, when loaded at a reasonable level. At least, if nothing else, it may contribute to the knowledge base for Biplanes flying in our cl stunt regimens.

I'm attaching jpegs of the new wings for comparison. You'll be able to see what I've been up to.

 

Good point Tim. It does look really kewl out there on the end of the lines.

Doesn't Al Rabe refer to modern stunters with large tail volumes as 'horizontal biplanes' anyway?

So if all this is about 'vertical biplanes' then perhaps factoring the tail would in fact produce a triplane!