Wings and wings airfoil for the full size stunt plane

[Matt Piatkowski]

Happy Holidays from snowy Toronto.
https://stunthanger.com/smf/open-forum/wings-and-more-wings-all-kinds-of-wings/ started the discussion about wings.

I have read it with interest, but I have not found the answers I am looking for now.

Specifically, I would like to hear your opinions about two wings parameters:

1. Airfoil - ice cone, classic, semi-laminar (Max Bee II), from Yatsenko's RTF models, etc.
2. Shape - swept but straight leading edges with straight trailing edge, semi-elliptical, and elliptical with diminishing thickness towards the tips. Please see the attachment.

I would like to limit the scope of discussion to the full-size stunt competition model, having the RTF weight 63-65 oz., wings span 59-61 in.,  the wing's with flaps area 650-700 in^2, and powered with the glow engine or an electric motor.

What airfoil will be the best for such a model?
What wing's shape will be the best?

Regards,
M

[Perry Rose]

It's what you can live with. I have planes with most of your airfoils and they all fly very well. The same with the wing planform. The planes flown by the BIG boys are designed to showcase their talents and may not fit anyone else to the same degree.

[Brett Buck]

Happy Holidays from snowy Toronto.
https://stunthanger.com/smf/open-forum/wings-and-more-wings-all-kinds-of-wings/ started the discussion about wings.

I have read it with interest, but I have not found the answers I am looking for now.

Specifically, I would like to hear your opinions about two wings parameters:

1. Airfoil - ice cone, classic, semi-laminar (Max Bee II), from Yatsenko's RTF models, etc.
2. Shape - swept but straight leading edges with straight trailing edge, semi-elliptical, and elliptical with diminishing thickness towards the tips. Please see the attachment.

I would like to limit the scope of discussion to the full-size stunt competition model, having the RTF weight 63-65 oz., wings span 59-61 in.,  the wing's with flaps area 650-700 in^2, and powered with the glow engine or an electric motor.

What airfoil will be the best for such a model?
What wing's shape will be the best?

     That's like asking "which woman is the most beautiful" - there is no correct or definitive answer. Just like everything else in stunt, there is no real engineering behind it aside from some vague notion of which parameters seem to matter, arrived at by cut-and-try over 70 years, with some ex post facto analysis of what a particular feature might have been doing, particularly in the case of failed attempts.

  And, as an aside - of course they are going to be in that size range, that's what has been competitive for 30-40 years, and about as big as you can practically fly on 70' lines. 

  Having said that, airfoil-wise, anything that is too pointy is unacceptable, and I would very strongly urge you to not use "ice cream cone" airfoils, just because they seem to be nearly universally associated with difficult-to-fly airplanes, and very high control forces. What you refer to as "Max Bee" "laminar flow" should properly be referred to as Rabe-style, since he pioneered that in the late 60's early 70's. Of course, it doesn't actually create laminar flow, what it does do is give extra curvature in the aft section of the airfoil, fairing it in better with the deflected flap - note, the inverse of the "ice cream cone" airfoil, which makes it as discontinuous as you can without it being a pollywog.

   The most successful airplanes have in the modern era have had airfoils been blunt with the high point relatively far forward. How thick to make it is debatable - some very thick airfoils like the Patternmaster have been shown to be very questionable, with some much thinner sections providing much better performance (like the Diva).

     The thickness has more to do with the drag than the lift, it made sense in the 4-2 break era to add a lot of parasitic drag, and some of the first airplanes designed for piped use continued that idea (Trivial Pursuit/"Star Gazer" {which are one and the same} and the Infinity) but I am pretty well convinced (30 years later +- a month...) that it was over-the-top even for an ST60 and certainly not necessary for piped systems or electric, where you have pinpoint control over the power delivery.

     Note that the Impact was not nearly as exaggerated, neither is the Werwage Thunderbolt/"Thundergazer" (which as far as the airfoil goes, also identical), and both are very close to the grandaddy of the "thick" forward-high-point airfoils, the Imitation. I would point out that that Billy seems to have worked up from thinner to that standard and a lot of other people have worked down from the comically thick airfoils like the Infinity back to that - and Paul had the right idea all along.

 As a general rule, anything that it qualitatively similar to the Impact, Imitation, "Thundergazer", or the Yatsenko airplanes are about right. Anything that looks about like these and is 18-20% thick, is probably indistinguisable. If you want to copy something, copy the Imitation. If you just want an airplane known to fly well, go get a Impact, Trivial Pursuit, or Thundergazer kit, build it and that will be sufficient as far as design goes.

 I would point out for sake of full clarity and to give credit where credit is due  - the hard-cornering, no-windup flying style current favored by the FAI judges is essentially identical to what Paul Walker was doing in 1988. Ted, David, and I watched about 4-5 maneuvers of that at our regional contest in 1988 and immediately went off and bought piped engines and designed new airplanes (Trivial Pursuit and Infinity) because we took one look and knew that if we didn't do that, too, we would never win another stunt contest. It just took the FAI 25 years to catch up.

  But as always, the usual caution - you might make a series of correct, right-down-the-middle, decisions - and still learn nothing about the design or even have it fly poorly. That's because while you can make bad design decisions that will screw you up, making good decisions does not guarantee success. Construction quality, trim, power, control setup can easily swamp the small differences between different reasonable designs. It is very easy to design an airplane, build it, fly it for a while, and then jump to the conclustion that the design was good or bad depending on how that one airplane flew - when in fact, one small detail somewhere that you have never identified undid all your good design work. Only by very careful experimentation over years and multiple airplanes, can you hope to determine whether a particular design feature is good or bad. And even then you are guessing, and any change you make us subject to the same guessing.

    Brett

[Chuck_Smith]

I like what Brett said with one exception, the induced drag isn't a function of section thickness, it's a function of aspect ratio (and to a smaller extent the taper). Form drag would increase with thickness.

Interesting in the original post you refer to different plan forms. The elliptical shape is great for drag reduction in corners but in practice a tapered wing will work just about as well and is a lot easier to build, especially if you like foam wings.

Thickness will not add appreciable lift due to the thickness - the lift slope of any symmetrical airfoil is the same - but it does affect the curvature and pressure recovery aft of the the high point and allows a teeency bit higher AoA and makes the stall less dramatic,. i.e., the  L/D curve becomes more rounded at the stall point.

So thickness *in general* adds to better handling. My opinion (which is only that) is that a thicker wing is better because it allows for a smoother curve on the LE and it's easier to build.  Lack of power isn't exactly an issue in modern CLPA planes.

A better question might be: Where to place the high point on the airfoil for stunt?  Since our CLPA planes fly at Reynolds Numbers that have no bearing in the world of full-scale airplanes there's not a lot of hard data one can work with⁽¹⁾. At our airspeeds and chords viscous forces may be much more important than on a full-sized aircraft. It may turn out to be the case that moving the high point aft, with an elliptical radius leading edge may be just what we need to do "tune" the rotation of the air to the shear forces. Visualize the air moving over the leading edge whist the friction causes the shearing action.

The only part of a full-sized aircraft or racecar I've encountered that shares much with a CLPA place is actually the horizontal tail on a sailplane. About the same size and needs to operate at the same airspeed.  In that case, we worried more about the effects of bugs on the LE than anything else. That had the most dramatic effect on the drag. There might be a lesson there for us.  Keep that LE smooooooth.

In peace,

Chuck


(1) There is a newer branch of aero work that may be applicable.  Since the density of Mars' atmosphere is so low there are some looking at low Reynolds flight. Just as in the good old days we would pressurize a wind tunnel to increase the density to achieve a higher Reynolds number, some vacuum tunnel work is being done to simulate the lower ones that would be encountered on Mars. The new Mars rover has a helicopter on it to test the results.

[Brett Buck]

I like what Brett said with one exception, the induced drag isn't a function of section thickness, it's a function of aspect ratio (and to a smaller extent the taper). Form drag would increase with thickness.

    I edited that upon reading, I meant parasitic drag. It never helps to have more induced drag. The goal was to reduce the ratio of induced drag to parasitic drag, so the overall drag changed less in the corners. Of course to do that, you have to have heroic amounts of power. That's why you *don't* want to do that with a Fox or other vintage engines, and why Aldrich didn't - because he didn't have the power, he needed something with low drag to permit it to carry momentum through the maneuvers and through the wind, rather than brute-forcing it.

   That's also what Big Jim appeared to be doing - taking the extra step of having relatively high aspect ratio to reduce the induced drag while increasing the parasitic. Otherwise, take a Nobler airfoil, scale up the Y ordinates and you get the Patternmaster.

   Similar reasoning was behind the Trivial Pursuit and Infinity - because we explictly discussed exactly this during the conversation that Keith Trostle, Ted, and I had at Shareen's Thanksgiving party in 1989 that led to the Trivial Pursuit and infinity, with me opting to go with a lower aspect ratio for hoped-for better performance during turbulence.

    Brett

p.s. I won't speak for Ted, but it is my opinion that we overdid it with the parasitic drag - because we didn't fully appreciate the level of control over the power we would eventually have. The next generation was - the Thundergazer, where David took the fixed part of a Werwage Thunderbolt wing, and put Imitation-style flaps and wingtips. Basically another full-fuse Imitation. This was  to address the overdone wing thicknesses we had before, once we had a full appreciation of the abilities of the engine to control the speed.

[Matt Colan]

p.s. I won't speak for Ted, but it is my opinion that we overdid it with the parasitic drag - because we didn't fully appreciate the level of control over the power we would eventually have. The next generation was - the Thundergazer, where David took the fixed part of a Werwage Thunderbolt wing, and put Imitation-style flaps and wingtips. Basically another full-fuse Imitation. This was  to address the overdone wing thicknesses we had before, once we had a full appreciation of the abilities of the engine to control the speed.

How does much does penetration in the wind change when you go from a thick TP/Infinity airfoil down to a Thundergazer wing, all things being equal, and having a giant PA 75 in the nose? My TP/Thundergazer comparisons go back almost 10 years now with two different engine setups, and when I still very much a novice when it came to trim and engine setup so it’s hard for me to compare based on my own experience

[Brett Buck]

How does much does penetration in the wind change when you go from a thick TP/Infinity airfoil down to a Thundergazer wing, all things being equal, and having a giant PA 75 in the nose? My TP/Thundergazer comparisons go back almost 10 years now with two different engine setups, and when I still very much a novice when it came to trim and engine setup so it’s hard for me to compare based on my own experience

    Most of the time, in most places, you can't tell the difference. And the PA75 provides nothing like the medium-period speed stability that something like first-generation 46VF/12-3.25 or PA51, it runs a lot more pitch. But I flew the first Thundergazer during the first flying session, and it felt pretty normal to me most of the flight. As a general rule, properly-trimmed airplanes generally feel very much alike regardless of the design/power, etc. (which is another way of saying the same thing I was talking about earlier). But it was a bit windy, nothing terrible, 10-15 maybe. I go into the overhead 8, no problem, all feels normal, start turning back into the wind - and I almost lost sight of it. I expected it to fly like the others and slow down, so in comparison it was like someone hit "turbo boost" and it just kept going the same speed.

   I would note that this is one of the legitimate knocks on the Trivial Pursuit or even more so, Infinity, even back to the Imitation compared to some of the thin-wing airplanes people flew at the time - they always make it, but you have to be willing to wait for it. It's a compromise in situations like that to eliminate/better control the wind-up in the lower maneuvers.

      We first noticed it clearly at the 2004 WC, where it was windy most of the time. One of the guys from South Africa, Loren, was flying a Citation V or something similar, with a 46VF, just like it was 1992 all over again. He crashed it lightly, so I helped him put it back together (with "help" from Windy, less said about that, the better...) and then he went out to fly it. Ted and I are watching since we had vested interest, so, same thing, he's going slow overall  but making it through the upwind/headwind portions everywhere, and particularly the overhead 8. I turned to Ted and asked "why is it that we don't fly those sorts of airplanes anymore?". Similar when we see the *original* Citation V fly, even with 4 ounces of lead and the bottom having been cut out of it once, still goes slowly but penetrates better. Of course, that was 16 years ago, you can see how much use Ted and I have made of this great revelation. David had a Thungazer about a year and a half later.

     Brett

[Brent Williams]

For those who are curious, here are the root and tip airfoils, minus the sheeting, from Bill Werwage's Thunderbolt and later, David Fitzgerald's Thunder Gazer. 
Airfoils were taken directly from scanned Werwage P-47 plans. 
.077" balsa sheeting is shown on the drawing.

[Ken Culbertson]

For those who are curious, here are the root and tip airfoils, minus the sheeting, from Bill Werwage's Thunderbolt and later, David Fitzgerald's Thunder Gazer. 
Airfoils were taken directly from scanned Werwage P-47 plans. 
.077" balsa sheeting is shown on the drawing.

This is without question the most popular airfoil in our flying group.  On my last ship (my Avatar) I went back in time to when Al Rabe was very influential with out designs.  A few years ago we had a thread on "laminar flow" airfoils.  I was always impressed how well Al's Mustang, and to some extent the Bearcat cornered with such small wings.  On my last ship from that era I moved the highpoint back to nearly 40% but, against his advice, I did not thicken and add curvature to the TE.  That was my best flying plane in that era (Late 70's).  I duplicated that airfoil on my 1st PA ship when I returned.  It also flew and cornered well but it did not like to stay in the same place on rounds.  I had to fly it much more than I liked.  When I built Engame it had 1/16" per side more thickness 1" from the TE and recurved the aft part.  It was an experimental wing Tom Neibuhr had built for a new Top Hat he never finished.  That gave me a smooth taper on the top surface at about 20 degrees flap deflection.  That made a huge difference in the tracking through the rounds.  At the same time Mike Scott built a MaxBee which has slightly more aft curvature and he reported the same change in control during rounds.

So I am of the opinion that a blend of the Thunderbolt and Rabe airfoils may be the compromise I have been looking for.  Brett's first post here says it all though.  Almost any of the "modern" wings will outperform most, if not all, of our abilities and it is a matter of power, trim and familiarity.

Ken

[Keith Renecle]

    Most of the time, in most places, you can't tell the difference. And the PA75 provides nothing like the medium-period speed stability that something like first-generation 46VF/12-3.25 or PA51, it runs a lot more pitch. But I flew the first Thundergazer during the first flying session, and it felt pretty normal to me most of the flight. As a general rule, properly-trimmed airplanes generally feel very much alike regardless of the design/power, etc. (which is another way of saying the same thing I was talking about earlier). But it was a bit windy, nothing terrible, 10-15 maybe. I go into the overhead 8, no problem, all feels normal, start turning back into the wind - and I almost lost sight of it. I expected it to fly like the others and slow down, so in comparison it was like someone hit "turbo boost" and it just kept going the same speed.

   I would note that this is one of the legitimate knocks on the Trivial Pursuit or even more so, Infinity, even back to the Imitation compared to some of the thin-wing airplanes people flew at the time - they always make it, but you have to be willing to wait for it. It's a compromise in situations like that to eliminate/better control the wind-up in the lower maneuvers.

      We first noticed it clearly at the 2004 WC, where it was windy most of the time. One of the guys from South Africa, Loren, was flying a Citation V or something similar, with a 46VF, just like it was 1992 all over again. He crashed it lightly, so I helped him put it back together (with "help" from Windy, less said about that, the better...) and then he went out to fly it. Ted and I are watching since we had vested interest, so, same thing, he's going slow overall  but making it through the upwind/headwind portions everywhere, and particularly the overhead 8. I turned to Ted and asked "why is it that we don't fly those sorts of airplanes anymore?". Similar when we see the *original* Citation V fly, even with 4 ounces of lead and the bottom having been cut out of it once, still goes slowly but penetrates better. Of course, that was 16 years ago, you can see how much use Ted and I have made of this great revelation. David had a Thungazer about a year and a half later.

     Brett

Hi Brett, the South African was indeed Loren Nell and the model was very close to the original Trivial Pursuit plan from PAMPA. After your repairs, Loren went on to place 25th which was his highest ever placing in world champs. Our team was really grateful for the help after his rather low wingover pull-out which retracted the outer landing gear leg trough the wing. Loren now lives in New Zealand and we still speak of the camaraderie at the 2004 world champs. He made 19th flying a Max Bee in 2014 in Poland, and was looking good for the top 15 in 2018 in Australia, but hit the deck badly just before his first round while we were practicing in dead calm air after hitting wake turbulence. This time, even your expert help would not have brought that one back to life!

Keith R

[Brett Buck]

Hi Brett, the South African was indeed Loren Nell and the model was very close to the original Trivial Pursuit plan from PAMPA. After your repairs, Loren went on to place 25th which was his highest ever placing in world champs.

    Yes, I am embarrassed that I couldn't remember his last name - I remember every silly thing I run across, to my detriment, shame on me for not recalling.

    He was a very nice young man and we (Me and Windy) were happy to help out a competitor so far from home. 

      Brett

[Keith Renecle]

It is those kind of gestures that create lasting impressions and also encouragement. I can remember Dave Fitz taking Loren off to buy him a coke, telling him with a smile that he's not gonna be of much use to help after his crash. Loren is still going strong in stunt. When I read Ted's article on the Trivial Pursuit it just looked like a good design to build and was not too complicated either. I flew quite a few locally that were not built well at all, but they all came out of sharp corners straight. I believe that it is one of the most forgiving models to build, and the OS .46VF on a pipe certainly worked well. Everything (wing, flap and tail area's etc.) is just so well balanced. The airfoil is good and the wing in total is very well thought out. Ted is not just a great pilot, but also a world class stunt designer. Here are a few pics of Loren and the TP.

Keith R

[proparc]

     That's like asking "which woman is the most beautiful" - there is no correct or definitive answer.
    Brett

I agree with just about everything Brett said except "the most beautiful woman" part. Halle Berry is what's up!!

Seriously, Walker and Fancher's aerodynamics pretty much represents the end game for us in F2B but, NEITHER section is as pretty or aerodynamic as Halle Berry.

I do feel that Big Jims aerodynamics had merit except for me, their being just too much of it. That is, the wings was just to big. I happen to own a Patternmaster, and my assessment was, close but smaller span. It seems to tax the ST 60's a it too much.

Casales and Big Jim were trying to move past the Nobler aerodynamics into big motor territory and, I think they did a good job of it,(a lot of victories were racked up with those sections) but like all things, further progress was in the offing. Fancher and Walker would push the science further.

[Matt Piatkowski]

Please see the attached.

I would suggest starting another, separate thread, exclusively about women.

Holiday Greetings,
M

[TDM]

I did not see any remarks referring to the type of powerplant that will be used.
While all the above answers are valid they all assume IC type powerplant.
I fly electric and I use a a wing that has an elliptical lift distribution with super success. It is 16 percent thickness at the root and 14 at the tip. This is a low drag setup that works great with electric powerplants.

[Brett Buck]

I agree with just about everything Brett said except "the most beautiful woman" part. Halle Berry is what's up!!

    Definitely on my short list! Some of my examples are a lot more obscure...

I do feel that Big Jims aerodynamics had merit except for me, their being just too much of it. That is, the wings was just to big. I happen to own a Patternmaster, and my assessment was, close but smaller span. It seems to tax the ST 60's a it too much.

Casales and Big Jim were trying to move past the Nobler aerodynamics into big motor territory and, I think they did a good job of it,(a lot of victories were racked up with those sections) but like all things, further progress was in the offing. Fancher and Walker would push the science further.

      You could see the reasoning, and Jim at least was experimenting with it long before a lot of the other developments. If you start out trying to figure out what you should to do deal with a ST60 or similar, and you have no other basis, that's what you might end up with. He didn't have the advantage of all the subsequent information - someone has to be first. And he wound up with a very sound design - the Patternmaster. If it is not the best ST60 design, it is certainly a competent design if built and trimmed correctly. I have seen a few of then that flew wonderfully well. That's a lot more than you can say for some of the "modified Patternmasters" by others who *knew far less*. And he used one of the few alternate approaches that existed at the time - an extension of what Al Rabe was doing. He solved Al's long-term problem of not enough power by using the biggest engine in common use at the time and took it much further and without Al's self-imposed limitations.

   But, that was nearly *50 years ago*. That other people have since learned many other things that suggest that was not the optimum approach is not a ding on what Big Jim did.

    The problem has never been with Big Jim himself - I met him only once, and know something about what he did from extensive study. This issue I and many other have had is that certain groups of individuals accuse *absolutely everyone* afterwards of copying it, basing their airplanes on it, etc., and also wildly exaaggerating the results it managed. The reality is (and I know this will spin up the usual suspects with the poison-pen letters), it never did very well, no one ever paid much attention to it, and it was not particularly influential. That, apparently, was the most dastardly of all insults, and we all paid the price for that one.

    As far as the airfoil goes, I took the Green Box Nobler airfoil, scaled it up in the Y direction until it was the same thickness, and the Patternmaster was within a pencil width. I note for the record that I didn't do this until something like *2003*, since I had never more than glanced at the plans and certainly did not have them to compare to.

    But I think you can also see how it came to be, and particularly, why the giant flaps grew - because the leading edge is too pointy. Get rid of that, and you don't need to do the rest of it. And, sure enough, the best-flying examples I have seen have had that rounded off, the Patternmaster derivative Strega that Kent Tysor flew could not have been constructed off the Patternmaster plans, and both Baron's and Mike Rogers' were rounded off about as much as you could to it within the nominal construction.

     But the ARF Strega, which appears to use the Patternmaster airfoil straight off the plans I had, could not be flown without stalling in perfectly normal sea-level summer air. Part of that is that both Ted and I were attempting to fly it to 2010-style standards (see Ted's comments in the "pattern smoothness" thread...) which were unheard of in the days the Patternmaster came to be- with me ultimately *stalling it entering the 4th loop of the clover*, that is,  *entering a round loop*!   I have flown many, many airplanes with far thinner airfoils and far smaller flaps at similar or higher wing loading, and never stalled them once. The Diva airfoil, for example, is well less than *half* as thick, and I have flown airplane with vastly higher wing loading, with no particular problems. If you are asking about stunt airfoils, that appears to be directly on point. Yes, if you round it off, as it says/said on the Brodak website, that more-or-less fixes it.

   My only point is that there are plenty of them that *don't* need a fix.

    BTW, it is the size it is for a fairly obvious reason, and much bigger than, say, an Imitation. They didn't call him Big Jim for no reason. And Ted Fancher, a sterling human being, is not a big guy. One of the knocks everyone had about the "far-forward CG with a giant tail to force it around corners" was that it also required you to manufacture enough line tension. Both of which had the effect of taking an immense amount of effort to fly, and tons of pull.

     I am sure you can make decent airplanes using a patternmaster or derivative airfoil. And it is certainly a matter of opinion what airfoil to use, as the first words in my first response notes. But my opinion is that there are much better starting points with vastly better history.

    Brett

[proparc]

I went back and looked at my post, and realized that I had done a tremendous disservice to the great Igor Burger, (too busy doing service to Halle Berry). Unbeknownst to many, Igor for many years, had a website where he posted his work on aerodynamics and control systems, (which we associate him with).

But, some very strong and original work was being done by Igor, regarding not only wing sections and planforms, but very insightful work on tail sections for a given Alpha etc.  What is especially noteworthy, is his work relating the wing AND tail together at various Alphas. 

Igor “would come to worldwide prominence with “eyebrow raising” 7th at the Worlds with his OS MAX 46 powered Max.  And later, the multiple World championship wins with his plane in the hands of Richard Kornmeier. Igor of course, would go on to hit pay dirt with his own multiple European and World Championship wins.

[Matt Piatkowski]

Hi, proparc,
Igor's contribution to the C/L stunt/F2B flying, understanding, and research is indeed quite remarkable.
Regards,
M

[Matt Piatkowski]

Hi TDM,
16 - 14% wing is too thin for the competitive stunt, IC or/and electric.

Wings with elliptical lift distribution produce less induced drag in the steady-state flight.
The pattern is not a steady-state flight, though.

The stunt models with elliptical and semi-elliptical wings and tails are the product of fashion rather than necessity.
Sometimes they look very cool.
See the attachment, please.

Regards,
M

[PJ Rowland]

Wing airfoils will and have already started to adapt to this decade.

Electric powerplants with speed control and Boundary layer control has provided new directions to go.

In my view, the thicker the airfoil DOESNT equal more lift. More flap deflection wont give you a harder corner.

What we are looking for is stablility of the lifting profile across the wing during a manouver, we want to have control of the speed of the airframe and penetration into directional wind angles.

I mean if you seriously experiments with airfoils, you will find that even a section from 1951 will give you a great base.
Albeit those eras also ran the CG further back.. due to lighter fox style engines..

Problem was back then they didnt have the power of speed control we have today.

Lift has never really been the problem...


Brett constantly is telling the same correct story and why people dont listen is beyond my comprehension.

Reread his post as you might learn collectively about airframe design and essentially how much of the grunt work was thought out through that stunt think tank group.

What they figured out was what worked and continues to work today and the wing section currently employed by many top fliers is VERY VERY VERY similar.

Forget about trying to find the next stunt revolution; build a plane, use the section that will provide lift in the corner,  an engine to power it and go PRACTICE..

If you want to win just practice.. thats the secret !!

Look at Brett, same design, same engine, same thinking as 25 years ago and he is STILL better than 98.5% of the planet..

Its not "rocket science" its way easier...
" not an official quote.. "

[Ted Fancher]

It is those kind of gestures that create lasting impressions and also encouragement. I can remember Dave Fitz taking Loren off to buy him a coke, telling him with a smile that he's not gonna be of much use to help after his crash. Loren is still going strong in stunt. When I read Ted's article on the Trivial Pursuit it just looked like a good design to build and was not too complicated either. I flew quite a few locally that were not built well at all, but they all came out of sharp corners straight. I believe that it is one of the most forgiving models to build, and the OS .46VF on a pipe certainly worked well. Everything (wing, flap and tail area's etc.) is just so well balanced. The airfoil is good and the wing in total is very well thought out. Ted is not just a great pilot, but also a world class stunt designer. Here are a few pics of Loren and the TP.

Keith R

Keith,

Thanks very much for the kind words.  Glad to hear the "stuff" worked out well for you and your friends. 

FWIW, the .46VF still stands up pretty well although it appears pretty obvious that the ECO Friendly and wimpy sounding alternative is well upon us.  Still doesn't sound or smell like "stunt" to me nonetheless.  I've got jeans from my "teens" that still smell like stunt!

Ted

p.s. Well...maybe that last remark was more a bit more of a memory trip than actually a statement of fact.

[Keith Renecle]

Hi Ted,

You're most welcome! I also have never forgotten you giving me an hour or so at the "Beer & Pizza" evening at the 2001 VSC, where you shared many valuable lessons in stunt design that I still remember clearly. Those expert shortcuts would have taken me years to figure out on my own, so that was another special event in my stunt life. In fact, the whole VSC was a special adventure for me!

Looking back now after many years, your design philosophy just makes so much sense. Seeing that this thread from Matt P is discussing wings and airfoils, there is plenty to learn from your wing layouts and airfoils, plus of course your stab/elevator area's in relation to the flaps. The success of your models in serious competition as well is outstanding. I personally don't believe that the actual airfoil shape is that important to be 100% accurate to a certain airfoil's data, as long as it is reasonably close to that shape. I seem to remember Brett saying that you can use the outline of your favorite shoe to get close to a good curve. What is important however, is to get everything working together in a good balance. It is like the "Goldilocks" formula. I believe that the Trivial Pursuit is the Nobler of modern stunt!

Because I get a lot of personal satisfaction out of trying to design my own models, and I am a born tinkerer, I've tried all kinds of different configurations of wing, airfoil, and even aspect ratio's. Most of my attempts failed, but a few were successful, and the more successful designs were the one's closest to the Trivial Pursuit configuration. So to my friend Matt, I would suggest having a good look at the overall layout of the Trivial Pursuit.

Keith R

[TDM]

Hi TDM,
16 - 14% wing is too thin for the competitive stunt, IC or/and electric.

Wings with elliptical lift distribution produce less induced drag in the steady-state flight.
The pattern is not a steady-state flight, though.

The stunt models with elliptical and semi-elliptical wings and tails are the product of fashion rather than necessity.
Sometimes they look very cool.
See the attachment, please.

Regards,
M

You might not have noticed my work. Or it is the, you are not the World champion thing therefore your stuff doesn't count.

[Brett Buck]

    For my money, I think the problems (i.e. design problems) with electric are significantly different that we were trying to solve, because you do have to consider the efficiency of the system, and the speed stability in the corners, even with a governor-only system, is *drastically better* than any IC system, for a given efficiency. We improved the IC system (from the 4-2 break/ST46/60 days) by using the effectively unlimited shaft power to swing exceptionally inefficient propellors. That way you get the desired speed stability from a small enough diameter prop to make it work, and who cares if it is extremely inefficient - you can always make the tank bigger. That how you wind up like David swinging a 13" prop on a piped 75 - that's a break-in prop, you could probably safely run a 15-inch 3-blade on such a monster. But that would kill the cornering.

    The large parasitic drag plan was just an element in the same system, an extremely inefficient way to enhance speed control.

    But for electric, "making the tank bigger" carries a much more severe cost, because the specific power of the battery is so low compared to glow fuel. So you are caught in a corner of trying to increase the efficiency of the system overall, without screwing up the cornering. You can't afford to run larger diameter, more efficient, props, because it kills the cornering. You can't add a bunch of parasitic drag and count on more power to fight it, because the battery gets too big. What you *can* do is make a less-draggy airplane, and run more pitch, so that you both require less power, and you get more prop efficiency. That would be a catastrophe on a 4-2 break motor, that's more-or-less what a Fox 35/Nobler did, without the hard cornering - basically, try that, and while you might be ideally placed to win the NATs, it would be the 1955 NATs, not 2021.

     The thing that makes it different is that an feedback system, or even just a governor system, controls the RPM and thus the acceleration *vastly vastly better* than any IC system. The overall power is still very low by tuned-pipe IC standards, but it can really throw the coals to it for brief periods, apparently far better than the very best tuned-pipe IC systems. A Fox couldn't do that, that's why you couldn't corner (to modern standards) with it.

     So you are able to run acceptably efficient props in a low-drag system, maybe not much more power overall than an ST46, and still be able to corner to modern standards. That is going to require a low-drag airfoil, within reason, as thin as you can get away with, and higher aspect ratio within the bounds of cornering and structural considerations.

       I think Dorin might be on to the same idea, and I wouldn't dismiss the idea of 14-16% airfoils too lightly.  There are plenty of them already in that range or thinner, the Diva being a hallmark example, which has proven to handle *much higher wing loadings* with more-than-adequate lift, far, far more than, say, a Patternmaster, and vastly more than the Nobler, without requiring outsized flaps.

     I don't have Diva plans in front of me, but I would bet that it is more like 12% at the tips. Jim's airplane, while it had other problems flew at something like 18 ounces/ square foot with no indications of running out of lift - at least with electric power. Tell me how well a 93 ounce Patternmaster/ST60 is going to fly, or for that matter, a 73 ounce Nobler/Fox 35.

    Bottom line is that electric design should be/needs to be different. If you tried to run my airplane on electric with the standard 12.5-3.75 3-blade, you would have to carry two or three batteries instead of one It's not a good electric design, it was designed with overkill for nearly infinite available power but limited corner speed control. And even then the airfoil is probably excessive.

   Electric is a different deal, so current transitional designs are only the first step.  My electric design *does not* use the Infinity airfoil, it's a slightly-thinned out Imitation airfoil and a much higher aspect ratio planform. Dorin's airplane is mostly unproven, but it looks a lot more like I think we are going to end up with than what we are currently doing.

    And, PJ, more like 99.99....

      Brett

   

   

[TDM]

Watch the outside square that starts at a little over 30 degrees elevation. Time stamp 2min 5sec you can pause the video when the model is in best view and verify the elevation. There is not much climb after that and I do the outside square with hard corners and well defined straight lines effortlessly. Actually all maneuvers are under 35degrees as I found out after the fact. I am working on correcting it.

[Dane Martin]

You might not have noticed my work. Or it is the, you are not the World champion thing therefore your stuff doesn't count.

I feel it's more of the latter. I've made recommendations on things I know quite well to receive the same type of response. True, I'm just your average competitor in stunt. But when the question is about something of which I'm very familiar; ie not actually about stunt flying airplanes, I feel my experience is helpful to others. But I'm mistaken.

[Tim Just]

Nice flying TDM!

[bob whitney]

where dose McFarlands Shark and Stiletto fit in this lineup design wise

[Brett Buck]

I feel it's more of the latter. I've made recommendations on things I know quite well to receive the same type of response. True, I'm just your average competitor in stunt. But when the question is about something of which I'm very familiar; ie not actually about stunt flying airplanes, I feel my experience is helpful to others. But I'm mistaken.

    Stunt is filled with very "interesting" people, many of them with massive egos (except for me, of course...) and many times, touchy as hell over nearly nothing. Once you get over that, then, you don't have to take it personally.

    Here in this thread, and in design evaluation in general, people tend to jump to wild conclusions very prematurely. You build an airplane with your chosen killer feature or pet theory, and if it flies well, almost everyone assumes that the pet theory or killer feature is *why* it flew better  - when in fact, it may be coincidental or due to something you are completely unaware of. So, next time, it might have the same killer feature and fly like crap, also for something coincidental or something you are unaware of. That's because the way the engine runs, the way the airplane is built in fine detail, and how it is trimmed has far, far more influence on the way it flies than the different between the "not killer" and "killer" versions.

   You see this in other areas, too, where new pipe users figure everything wrong with their engine run is due to the pipe, ignoring the other 500 things that might be wrong with it, or, even more so, Rabe Rudders, where absolutely every trim issue is somehow going to be fixed by adjusting the rudder. Both things are theoretically sound, can be made to work correctly, but are frequently obsessed upon.

    Design is even harder because proper trim and power can make almost anything work well enough to win most contests. Thats why (as PJ notes above) you see people running very similar airplanes over decades, because that's what it takes to figure it out.

    Brett

[Brent Williams]

Speaking of Phil.  Here are a set of Phil Granderson's airfoil templates, as as shown by Jim Aron in his Systrema V.2e plans. 

With the 1/16" sheeting these would read 2-5/16" x 10.375 " at the root which equates to 22.28% thickness minus flaps.  At the tip, adjusting for sheeting, I measure 1-3/4" x 7.875", for 22.22% thickness.  With typical flaps, these would both be around 18% total thickness.

[Brett Buck]

Speaking of Phil.  Here are a set of Phil Granderson's airfoil templates, as as shown by Jim Aron in his Systrema V.2e plans. 

With the 1/16" sheeting these would read 2-5/16" x 10.375 " at the root which equates to 22.28% thickness minus flaps.  At the tip, adjusting for sheeting, I measure 1-3/4" x 7.875", for 22.22% thickness.  With typical flaps, these would both be around 18% total thickness.

   It's always stated with flaps, unless you are Al.

    But look at the shape- far forward high point, blunt, and plenty of curvature in the surface toward the TE. Scale the patternmaster to the same chord, and compare and contrast, particularly up to the high point!

    Brett

[PJ Rowland]

Where I feel comfortable is a personal choice.

There are certainly things that work and there are clearly things that DONT work. Ive spent the best part of 40 years flying these toy planes, and Ive gotten to learn a few things.

I was lucky in that I grew up flying Noblers, Impacts and reading iconic articles such as Ted Citation Series and deaign philosophy. Back in THOSE days you had to request photo copies if you didnt have access to stunt news.

There is only ONE real way to figure out what works and what doesnt and thats by testing things for yourself.

Test, write down, evaluate, build multiple versions testing ideas, then ( as brett points out ) evaluate on multiple airframes to confirm ( or dismiss ) the theory.

And even if you ARE right, there are always countless people whom misunderstood the correct reasons certain planes "grooooove "


Brett is also spot on, with respect to the electric design changes, the days of thicker airfoils for drag are long LONG gone. If your not seriously thinking 100% about the airframe your not in the game.

[Dane Martin]

I believe both Brett and PJ have touched on what I was replying to TDM. I think we can all say TDM's composite plane flys very well. Having read the reports from other flyers who've put it through its paces, I'd go out on a limb and say it's very very competitive. He has put in the practice to be good enough to experiment. And yet he's met with this response, stated so matter of factly.

"16 - 14% wing is too thin for the competitive stunt, IC or/and electric."

I myself would not try to offer design advice. I know almost nothing about it. But when I read that, I had a little chuckle.

[phil c]

Where I feel comfortable is a personal choice.
.......

There is only ONE real way to figure out what works and what doesnt and thats by testing things for yourself.

Test, write down, evaluate, build multiple versions testing ideas, then ( as brett points out ) evaluate on multiple airframes to confirm ( or dismiss ) the theory.

........

One thing I notice here is a kind limited design philosophy.  Following an iterative, one change at a time process can produce endless "not-quite-right" designs.  If you are interested in trying new and different variables or changes look into "designed experiments".  This is a process, used extensively in WW-II to optimize things such as the clearances in an airplane engine needed for optimum performance and manufacturing details- optimum oil ring clearance, opt. cylinder clearance, head shape, bearing clearances, etc.  Once many of these variables are optimized they can be used to optimize different designs with a good starting place say for a larger version.
From the discussion there seems to be some agreement- leading edge shape, high point position, trailing edge/to flap shape, flap shape, overall thickness ratio, ratio without flaps, flap shapes(at least 3 variables), balance point, motor prop inertia, tail moment, stab area, elevator percentage.
What most people would have a problem with is that experiment would involve building 16 different assemblies, or perhaps some combination of an adjustable fuselage that can take different wings, tail moment, and stabs with fully adaptable controls.

Another problem, which is harder, is how to evaluate the effects on each assembly.  Control "feel", "tracking", "pointability" and more.

Most flyers probably wouldn't want to undertake that.  So a way to proceed is build 3-4 iconic designs and maybe a couple of test beds to first compare an engine versus an electric motor and get them working. ( if the flying site requires less noise that more or less dictates electric though).  Pick the combo you like!

Meanwhile, a few cheers for a "way in the background" technique that helped win WW-II.

[Brett Buck]

One thing I notice here is a kind limited design philosophy.  Following an iterative, one change at a time process can produce endless "not-quite-right" designs.  If you are interested in trying new and different variables or changes look into "designed experiments".  This is a process, used extensively in WW-II to optimize things such as the clearances in an airplane engine needed for optimum performance and manufacturing details- optimum oil ring clearance, opt. cylinder clearance, head shape, bearing clearances, etc.  Once many of these variables are optimized they can be used to optimize different designs with a good starting place say for a larger version.

   All that is true, of course, but I am not sure why you think that doesn't go on already. We have had decade-long series of these sorts of experiments, for the entire time I have been doing this. For example, I mentioned it in another thread, but there is a very long email thread about a topic of relevance between Paul, Chris, David, PJ, Jim, Howard, Frank W., Derek, and I, which dozens of such experiments. David wrote up one of these series of experiments will 4-5 different tail airfoils and at least 5 various types of rigging in Stunt News, but that is hardly the only one. We have flown with "slippers" over the wings to try different airfoils, Paul has long made all the control services removable, and interchanged parts, I ripped that off and have 3 sets of flaps for one of the airplanes. I might be doing that again pretty soon, as a matter of fact...

   It works so well that people came to the conclusion the contests were rigged.

     That's how almost everything on the airplanes is the way it is - it is how evolution happens.  My point above is that the "decades long" part is very frequently short-circuited and people jump to conclusions far too quickly. We do something at every flying session, it is very rare indeed that we are going out to just fly, *they are all experiments*. Same with practice flying - trimming is just adjusting the design, and you change the design for the next airplane based on what you found with the current one.

     It's also what I mean about telling people exactly what we are doing, I think I have more-or-less summarized everything we have found over the last 35-ish years of this sort of collaboration - and everybody argues with me!  Just look at the "engine setup" forum, oy gevalt.

     That's how you protect the best ideas, tell everyone exactly what to do an why, so they go off and do the opposite.

    Brett

[Teodorico Terry]

Brett,

I read through your comments about electrics vs. IC and I was wondering if a slower turning, larger diameter prop of higher pitch would allow for decent cornering.  With electric, you can normally use a lighter prop (the 20" CF prop in my pattern plane weighs 2 oz, the comparable APC electric was nearly 4 oz...) which would reduce the gyroscopic effect.  Lowering the RPM would also allow further reduction.  I think that electrics are being run at high RPM and low pitch mostly due to limitations on the controllers (RPM needed to govern properly) as well as by the design of the motors (fairly narrow can out runners which limits the available torque for a given current).  Any thoughts?

Thanks,

Teo

[Brett Buck]

Brett,

I read through your comments about electrics vs. IC and I was wondering if a slower turning, larger diameter prop of higher pitch would allow for decent cornering.  With electric, you can normally use a lighter prop (the 20" CF prop in my pattern plane weighs 2 oz, the comparable APC electric was nearly 4 oz...) which would reduce the gyroscopic effect.  Lowering the RPM would also allow further reduction.  I think that electrics are being run at high RPM and low pitch mostly due to limitations on the controllers (RPM needed to govern properly) as well as by the design of the motors (fairly narrow can out runners which limits the available torque for a given current).  Any thoughts?

   Diameter seems to be the killer, and while making the moment of inertia and or angular momentum of the prop smaller does seem to help, getting diameter off seems to be more important, for whatever reason. Not having to handle the axial torque pulses of an IC engine helps - it's vastly higher than you would expect - makes it possible to make the props much lighter, and people are doing that. Igor's and several other types are hollow.

   The kicker is that you don't need large diameter, the thrust reaction in the corners seems to be so much better that you don't need it, and the slower poles of the system, like climbs and speed recovery during the maneuvers is handled by the feedback system.

   It still seems that the less efficient props, low pitch at high rpm, still works better, the limit being the power available from the battery, which seems to boil down to weight.

     I have only my observations of others efforts, of course, so I could easily be wrong, I am still thinking it through for myself.

    Brett

[PJ Rowland]

No Brett, you are still correct.

Time and time again Diameter is the corner killer.

As far as high pitch 6 to 8"

vs Low pitch;

4.5 to 5 ) I will stick by my own observations, lower pitch will give you a nicer cleaner corner.

Its still about efficiency, Ive run up to 9" of pitch on a 61 and qas still able to get the powerband such that it chugged around. How much air your biting into and how much diameter the airframe sees are the keys.

There is also a limit to the Diam argument,  a 8" dia just doesnt have any pulling or stopping power, nice turn but there is no force pulling the plane.

I think props are about as far as we can go personally in our understanding of what work vs what doesnt..

Brett if anything the electric is more efficient with respect to how much forward momentum the prop sees.

The IC ( well your piped setup is pretty good so its hard to be specific as to where you may see improvements )
I found electric response to be a little more linear and controllable in a variety of condiitons.

[frank williams]

"Diameter seems to be the killer, and while making the moment of inertia and or angular momentum of the prop smaller does seem to help, getting diameter off seems to be more important, for whatever reason."

I think the angular momentum effects are accentuated by the basic propeller thrust, power , and torque effects ..... which are highly a function of the diameter.    Like power required, is proportional to the diameter to the fifth power.

[Brett Buck]

Brett if anything the electric is more efficient with respect to how much forward momentum the prop sees.

   It absolutely is, and has to be, because the specific energy and energy density is so low.

    Brett

[Teodorico Terry]

Not knowing any better, when I got back into C/L I carried over something of the things I had learned from R/C as it relates to electrics.  I have been flying electric R/C since 2004 or so and at the time, given the fact that NiMH s were still common, there was a lot of emphasis on efficiency.  As a result for normal sport flying slow turning, larger diameter props of higher pitch were preferred.  The props I use normally have a P/D (pitch/diameter) ratio of greater than 0.5.  Normal props would be 12x6, 12x8, 13x8, 13x10, 14x10, 14x12 all the way to 20x13.

The model I currently fly is modified SIG Fazer which weighs 56 oz (heavy) and uses a Hacker A30-10XL (900KV) for power.  The battery pack is a 4S 2800 mah TP and the ESC is a Castle Phoenix running in governor mode.  I did lengthen the model quite a bit, the distance between the flap and elevator hinge lines is 19" but the nose is short at 8" from the leading edge to the spinner back plate.  The stab/elevator are also much larger than original.  This is what I have learned:

1)  For a given lap time, the power requirements are fairly similar with a variation of about 15%:  smaller diameter props needed a little more power, larger diameter props being more efficient.  After reading that reverse rotation props might work better I made the switch which limited my choices to either a 12x8 or 13x8 prop for the time being.  Line tension improved.

2)  For a given prop I would set the RPM needed to give me the pitch speed I was looking and then fly the model.  Generally, I would have to increase power on the following flights because the calculation did not account for drag.  The initial flights would be only 3 min in length after which I check on the mah consumed, adjust the power if needed and/or increase the flight time.  I would fly the sequence on each flight; the number of maneuvers were limited by what could be accomplished in the given time.  Once the flights got to be long enough to include the vertical 8 and hourglass things got interesting:  I had to keep increasing the RPM (power) when using the 12" prop more so than when using the 13" prop.  In the end, for the same number of mah consumed, the flights using the 12" prop had to be about 45 sec shorter than those using the 13" prop.  The 13" prop appears to be more efficient.

To my inexperienced self I did not see a significant difference in how the model handled between the 2 props.  Even with the 13" prop the model will turn a sharp corner when asked to.  I am not flying in front of judges so I am not sure that the corners have the 5' radius or not but based on my past experience they do look tight.  For the square loops, the corners are tight enough that I am able to fly a straight segment in between the corners within 45-50 deg limit.

Any thoughts?

Teo


P.D.  Regarding the equations you have to keep in mind the magnitude of the change:  Going from 12" to 13" in diameter represents a 8% increase where as going in RMP from 6000 to 8000 or more is nearly a 33% increase (in my case, 10 pitch to 8 pitch).  Even with the powers involved, depending on pitch, the equations can be dominated by RPM.

[TDM]

"Diameter seems to be the killer, and while making the moment of inertia and or angular momentum of the prop smaller does seem to help, getting diameter off seems to be more important, for whatever reason."

I think the angular momentum effects are accentuated by the basic propeller thrust, power , and torque effects ..... which are highly a function of the diameter.    Like power required, is proportional to the diameter to the fifth power.

Frank typically if you run small diameter low pitch high rpm you are running 3 blade props and if you run large diameter high pitch you usually use 2 blade props. Are those formulas based on single blade? For sure the moment of inertia is directly proportional to the number of blades you swing assuming they are identical.
FYI I run a 12X6 2 blade at low rpm (because the plane is relatively clean aero). I have no idea how low does it run but for sure less than what is run on average SV with the same prop. I am guessing somewhere around 9000rpm.

[Brent Williams]

Norm Whittle did some early development with thinner wing sections around 11 years ago.  Too bad he doesn't fly CL anymore, as Norm was pretty competitive with it among top level guys up until he quit.  His Sultan-E had a thin, 14'ish% wing and the airplane was pretty clean from an aero-drag standpoint.  He and others that flew it said it turned very cleanly even up here in the thin Utah air.

Wing Span 61.5", Wing Area 695 sq. in.
1.89" at the root.  14.4 % (with flaps)
5.3 Aspect Ratio, Weight 59oz

And let's not ignore Phil Granderson's skinny Diva which used 15% root and 9% tip.  ~690sq.  54oz, piped Magnum 36.

[proparc]

Norm Whittle did some early development with thinner wing sections around 11 years ago.  Too bad he doesn't fly CL anymore, as Norm was pretty competitive with it among top level guys up until he quit.  His Sultan-E had a thin 18% wing and the airplane was pretty clean from an aero-drag standpoint.  He and others that flew it said it turned very cleanly even up here in the thin Utah air.

Wing Span 61.5", Wing Area 695 sq. in.
18% thick  1.89" at the root.
5.3 Aspect Ratio, Weight 59oz

I've seen Norm and his Sultan fly.

[Brett Buck]

BTW, I certainly hope that no one imagines that there are any *conclusions* here - this is a series of on-going experiments, back to about 1948, and continuing for the forseeable future. We are seeing snapshots of the current state from various people's perspectives, I make no claims that mine are any righter than anyone else's, aside from presenting the reasoning behind it.

   As always, contest results always trump any theories.

     Brett

[Brent Williams]

So where do all of these important wing design data points converge, if at all? ( I just read a lot.  I ask this with no hidden agenda.)

Looking at all of the wing designs discussed in this thread, it seems like the main important design similarity is that the leading edge is appropriately blunt.  Aside from that, there are examples of many good choices with Nats and World win records.  You have the PTG style airfoils with the high point very far forward and then in direct contrast you have Igor Burger's airfoil with the high point very far aft.  Whittle's Sultan and Dorin's Revolutions are on the skinny side and the Geo-Bolt/Thundergazer has become the perennial popular choice of late in the goldilocks thickness zone for competitive, modern electric planes.   

Where do Igor's graphs and data fall into this discussion related to his aft high point design?

And then there are the related discussions of lift augmentation accessory devices.  The flaps are also providing a continuously variable camber.  There are the trip strips, zig-zag tape and/or vortex generators on most or all of the top guys airplanes it seems.   

A lot to consider. 

[PJ Rowland]

I dont think there ever will be a convergance of design specs.
I certainly dont think there is one universal solution.

What Judges like to see, how easily the electric scene allows virtually anyone to get a perfect motor run with fairly little output.

If anything we are governed by ;

Line length, and an approx minimum weight requirements of engine, hardware and tip weight; yeilds certain wing requirements that are satisfied by achieving more than enough lift to get the plane to lift and turn.

If anything the use of boundary control has shown the direction Top fliers want to progress is toward consistency.

Consistency will bestmost things.

I can sight COUNTLESS examples.. the more consistent you can make your setup the easier practice becomes.

[Brett Buck]

So where do all of these important wing design data points converge, if at all? ( I just read a lot.  I ask this with no hidden agenda.)

Looking at all of the wing designs discussed in this thread, it seems like the main important design similarity is that the leading edge is appropriately blunt.  Aside from that, there are examples of many good choices with Nats and World win records.  You have the PTG style airfoils with the high point very far forward and then in direct contrast you have Igor Burger's airfoil with the high point very far aft.  Whittle's Sultan and Dorin's Revolutions are on the skinny side and the Geo-Bolt/Thundergazer has become the perennial popular choice of late in the goldilocks thickness zone for competitive, modern electric planes.   

Where do Igor's graphs and data fall into this discussion related to his aft high point design?

And then there are the related discussions of lift augmentation accessory devices.  The flaps are also providing a continuously variable camber.  There are the trip strips, zig-zag tape and/or vortex generators on most or all of the top guys airplanes it seems.   

A lot to consider.

   Note that none of these are particularly "skinny", they look that way only compared to the sort of extremely thick airfoils like the Trivial Pursuit/"Star Gazer" and the Infinity. Even Al's were not nearly as thick as ours - which started as a misunderstanding since Al invented his own standard for thickness, that ignored the flap.  18-20%, I would consider "normal" range. I would also note that the SV-11, Gemini/Genesis, Saturn, etc, are all in the are of 18ish percent and have been the entire time.

   Noblers and a lot of Billy's airplanes are more on the skinny side until very recently.

    And to be entirely clear - the "laminar-flow" (really "lots of aft curvature") airfoil in stunt dates back to about 1970 and Al Rabe's car hood experiments. Igor may or may not have known about that and may or may not have come up with the same idea independently - presumably for the same reason, that is, fairing into the flaps when deflected. Igor has done much more generalized engineering work, that can be used in other cases, rather than Al's "point design" approach. If you don't exactly replicate Al's wing, you have no idea how it will work, and nearly no information on how to figure out what will happen. Igor has provided actual engineering data about that sort of airfoil, which is applicable beyond a specific implementation.

  That what I mean - Al's stuff was copied in various forms for 30+ years, myself included to some extent, mostly by people not understanding it and making mistakes in the process (which I decline to specify, not being immune to bullets...). This line of development then sort of dead-ended. 

    After all that time, Igor looks at it or comes to a similar conclusion, but also provides an *explanation of what is going on*, bingo, now you can use the 30-year-old information without necessarily making the same mistakes, and the dead-end suddenly opens up again.

    As far as tripper strips, VGs, turbulators, etc, go, that's still on-going with lots and lots of experiments in progress and very interesting results - but no real idea why any of it works. You don't necessarily need to understand it to make use of it, and there are plenty of theories, but nothing much like an engineering analysis or information about what to do. Right now it seems to be almost entirely cut-and-try, which is fine as far as it goes, but right now doesn't seem to yield any real conclusions.

    Brett

[Chuck_Smith]

I'll add onto what Brett said that turbulators react differently in different conditions too. So yes, on that one perfect morning with a light, steady breeze they may help, but later in the day they might make things worse.

In general, the purpose of the turbulators are twofold:

1) They can reduce drag hence L/D - which in CLPA isn't a concern

2) When placed far enough back on the section they increase flap effectiveness - but that's at high speeds.  We'd have to have a CLPA place flying 200-300 mph to be dynamically similar the full-size application. Since our chords are so short and our airspeeds so slow it might take a small mountain to trip the flow. It's really hard to go to turbulent flow in a few inches at 40 mph!

It may have already been noted, but IIRC Rabe's airfoil was simply designed to have a smooth curve on the top with the flap deflected. I have a Rabe Bearcat and it's a great flying plane. The wing is surprisingly "slippery" for having such an odd section. It is a "different" corner than something more modern, but in a nice old-school way. It's more of a "fly the corner"  approach than the  "change the direction vector" corner of a modern design.

Chuck

[Brett Buck]

I'll add onto what Brett said that turbulators react differently in different conditions too. So yes, on that one perfect morning with a light, steady breeze they may help, but later in the day they might make things worse.

In general, the purpose of the turbulators are twofold:

1) They can reduce drag hence L/D - which in CLPA isn't a concern

2) When placed far enough back on the section they increase flap effectiveness - but that's at high speeds.  We'd have to have a CLPA place flying 200-300 mph to be dynamically similar the full-size application. Since our chords are so short and our airspeeds so slow it might take a small mountain to trip the flow. It's really hard to go to turbulent flow in a few inches at 40 mph!

    That's certainly a theory. However, we have very frequently applied turbulators with remarkable effect, like "gonna crash" to "make the flyoff" different. Same with VGs.

    Brett