Model Weight

[Steve Dwyer]

I'm curious when (time frame) builders became interested in the weight of their models and the effect on performance. CG locations showed up on early 50's plans which is not a huge surprise but I don't recall any discussions early on about the weight or quality of the balsa supplied in kits, or the overall final model weight. I do recall one senior builder at the field in the early 60s saying his Bearcat, a fully sheeted control line model being the worse flying model he ever built. No further comment or discussion ensued.

Steve

[fred cesquim]

I'm curious when (time frame) builders became interested in the weight of their models and the effect on performance. CG locations showed up on early 50's plans which is not a huge surprise but I don't recall any discussions early on about the weight or quality of the balsa supplied in kits, or the overall final model weight. I do recall one senior builder at the field in the early 60s saying his Bearcat, a fully sheeted control line model being the worse flying model he ever built. No further comment or discussion ensued.

Steve

i never cared about weight until i startet do compete on F2B, then the weight started to make difference. even worse if you fly e-power. my goal is to have the best finish with minimum weight. I had a fully sheeted Hellcat and turned out to be as light as my other monokoted / painted ships. Now i switched to fully sheeted models when practical.

[Paul Smith]

In designing a golf driver, an I-beam, a Corvette, or a model airplane wing, material as far as possible from the neutral axis has the more strength value than  material inboard.  Hence, the center spar as seen on the Voodoo and Ringmaster adds the most weight for the least strength value.  You can mitigate the mass of the sheeting by dispensing with the spars.

[Dave_Trible]

The first I recall any real discussion about weight was in the late 60's some would mention replacing some kit wood pieces-usually fuselage sides.   Then in the mid to late 70's it seemed to be more important ( in CL) as guys were trying to push the Fox .35 too far in size and weight.   The use of the ST .46 helped with this but again- we started bigger airplanes with better finishes so the scales swung the other way again.    Then the ST. .60.........we have come to understand light weight really makes the difference between 'ok' performance and outstanding performance-regardless of power.  Being confined in flying space and size with all the power needed,   the only meaningful gain left is lighter construction to a point.  The airplanes still need to be strong enough to stay together for a while at least.   We see catastrophic failures once in a while.   These show the places we walk pretty close to the line in minimizing structural weight.

Dave

[Steve Dwyer]

I was out of modeling for a while and into life by the late 60s. Why CL model weight was not a common topic in the early years (50s and early 60s) certainly makes one wonder. But then if you look at the thin airfoils of the era you might ask how important weight and performance really was. However, I do wonder how many CL builders came from the 40s stick and tissue days when weight of the gliders, powered and unpowered had to be paramount. 

Steve

[Brett Buck]

I was out of modeling for a while and into life by the late 60s. Why CL model weight was not a common topic in the early years (50s and early 60s) certainly makes one wonder. But then if you look at the thin airfoils of the era you might ask how important weight and performance really was. However, I do wonder how many CL builders came from the 40s stick and tissue days when weight of the gliders, powered and unpowered had to be paramount. 

    Weight was a critical matter from WAY back, but before appearance points no one much talked about it because making reasonable weights was not that hard using the finishes of the day (a few coats of color dope brushed on, or colored tissue with clear dope. They were all multiple-discipline modelers, they built lots of different categories including FF.

   After appearance points, then, given the power of the day, it became a trade-off between finish quality and weight. If you read "Stunting can be smooth" AKA the Nobler article, you can see that GMA himself designed the Nobler on the assumption that the finish would add considerable weight, and he still only had a Fox 35. Also, very early on, people could see that the ultimate limit on cornering was the wing loading and Cl. Certainly Palmer knew about it, Wild Bill went out of his way to explain it to people in the early 50's. So it has more-or-less always been an issue in the serious competitors- whether or not the sport fliers/casual competitors considered or not.

   It also became obvious that *power* drove a lot of what you could practically do. That became blindingly clear when they started using 45/46s in maybe late 50's.

    The real revolution was, of course, in 1988, when all the old wing loading rules were made definitively obsolete by piped engines running 4" of pitch. The old rule used to be "12 oz/sq ft MAX!!" for 4-2 break engines, and that was about right and about what you could practically do with a decent finish. There were anomalies below that (the most notable I am aware of being Larry Robertson's "Golden Bantam" at 720 square inches and 42 ounces with an ST). Since then, almost every NATs winner has exceeded this "limit", sometimes by A LOT.

      Brett

p.s. I would also note that currently, the airframe weight is generally going down, or way down, because electric is very heavy and has nearly no vibration, so you both need to make it lighter, and can make it lighter because it won't fall apart from the shaking.

   

[Steve Dwyer]

Because of my age I never seemed to be privy to "technical" discussions if any amongst the older builders. Our senior builder built some beautiful models including the Veco Mustang, a similar size Spitfire and the DMECO Debolt Continental. All were outstandingly beautiful glass like ships from my perspective. All were powered with the Fox 35 and the standard of course was using a lot of Pactra Sanding Sealer, the white syrup like Milk of Magnesia stuff even on the silk over the wings. I rarely saw any of these beauties (or clunkers) fly, but I do recall when the old timer loaded the trunk for the field it seemed he always had his favorite a Galaxy profile with a Veco 35.

More recently one of our modelers brought a Checkalaroma, an early era 50s model he'd recently scratch built to the field. With a fox 35 in it I wasn't sure if I was holding anything when picking it up. He is notorious for exceptionally light builds and minimal finish. He did the pattern with it, and the following year said a wing came off in flight. Last I heard he was doing some "redesigning".

Obviously, the early years had their growing pains.

[EricV]

I'm curious when (time frame) builders became interested in the weight of their models and the effect on performance. CG locations showed up on early 50's plans which is not a huge surprise but I don't recall any discussions early on about the weight or quality of the balsa supplied in kits, or the overall final model weight. I do recall one senior builder at the field in the early 60s saying his Bearcat, a fully sheeted control line model being the worse flying model he ever built. No further comment or discussion ensued.

Steve

Weight probably became more of a "thing" when the Old Time pattern became the current AMA pattern, and people with a 40+ ounce Ringmaster or other plane with similar weight to lift ratio started to pancake in at the bottom of the V8 or HG when the density alt went up or the wind blew over 10, etc. (gigantic elevators notwithstanding, that's another discussion, heh)

EricV

[Ken Culbertson]

.....With a fox 35 in it I wasn't sure if I was holding anything when picking it up.

I once asked Gieseke (Mr Light himself) how you knew your plane was too heavy.  He answered "if you can feel it in your hand  carrying it back to the car it is too heavy"  Things have changed.  We certainly know more about the effects of weight than we did 45 years ago when I got that advice.  As Brett pointed out the biggest change is power.  It is now virtually unlimited for our needs.  I used to live by the 11 ozft2 "rule".  Now I think it is more like 14.  Maybe it is just me but I think that a properly powered reasonably heavy plane is a better choice that a light one.  If the wing is capable of producing enough lift to make a "tight" corner and your controls have enough leverage to produce that lift in the places we need it most then the improved line tension and stability IMHO outweigh the benefits being light and of the thousand or so stunt fliers out there I am sure about 3 agree with me!

Ken

[EricV]

I once asked Gieseke (Mr Light himself) how you knew your plane was too heavy.  He answered "if you can feel it in your hand  carrying it back to the car it is too heavy"  Things have changed.  We certainly know more about the effects of weight than we did 45 years ago when I got that advice.  As Brett pointed out the biggest change is power.  It is now virtually unlimited for our needs.  I used to live by the 11 ozft2 "rule".  Now I think it is more like 14.  Maybe it is just me but I think that a properly powered reasonably heavy plane is a better choice that a light one.  If the wing is capable of producing enough lift to make a "tight" corner and your controls have enough leverage to produce that lift in the places we need it most then the improved line tension and stability IMHO outweigh the benefits being light and of the thousand or so stunt fliers out there I am sure about 3 agree with me!

Ken

I "think" what you are tap dancing around is what I call the "performance envelope" when talking stunt with my flying bud's.

For a given design, with a given power plant, we usually have a pretty good idea what is an "optimal" weight range for the most varied environments we are likely to need to fly in, at least in our personal opinion.

I've built a design and variations of it over and over enough to know, what is too heavy, and what is too light, and they are hardly EVER too light, because that would mean sacrificing finish, or structure with eminent or pending catastrophic failures if you like to get several years of constant flights from an airframe, and we tend to self-correct for that tendency with time and build to what we feel is an acceptable weight, and only occasionally push that envelope by trying new things.

I don't want to start a debate, so I'm intentionally being vague here about square inches and airfoils blah blah blah... for the design I normally fly, 62 to 64 ounces seems ideal, and you can miss the power setting by a wide margin and still be confident in putting up a flight, 65 to 67 is very acceptable but not quite as magical or inspiring like you can do no wrong with the former, 68-70 is also very doable, especially in dense air, but you definitely loose ultimate ability and some confidence as conditions change, power delivery always has to be "on" and perfect, and 70 and up narrows the useful working range of the airframe, and acceptable flying weather greatly, these would not qualify to be my contest ships... (I don't want to hear about how many 70+ oz planes won the Nat's, or how great your 80 oz plane flew/flies, those were not this design, and even if it was, we all know how much the weather, altitude, density alt, and many other factors play into it) I'm strictly talking about planes I ENJOY flying more, and that feel like world beaters at the end of the lines and what we individually shoot for weight wise.

Another factor is power plant availability and longevity. Most pipe engines can easily spin double the RPM we run them at, especially those that started life as high performance R/C engines, (I would imagine electric have an optimal range where they last longer as well) but they were only designed to do that at short bursts, we run them the same RPM for 7 minutes which is another kind of stress, maybe worse in some ways... I tended to want to conserve on my engines I had left, and if given a choice for practice and sport flying, to keep the piped engines a few hundred RPM lower than what is probably "ideal" for the "ultimate" power delivery if I used a flatter pitch. It makes a huge difference in engine life span. It's a personal choice, we all make them and live with the results. If I began flying regular again and wanted to enter contests, and had an unlimited supply of engines, sure, I'd go for the 11K run, lock that puppy in and chew em up and spit them out with glee. In the reality, while I was still flying competitively, I chose to build light enough to run my engines in a more modest RPM range that would give a seemingly unlimited lifespan if well cared for. So back to weight, yeah, it matters for a lot of different reasons to different people.

That's my .02, from a washed-up has-been, heh.
Eric

[Dave_Trible]

I once asked Gieseke (Mr Light himself) how you knew your plane was too heavy.  He answered "if you can feel it in your hand  carrying it back to the car it is too heavy"  Things have changed.  We certainly know more about the effects of weight than we did 45 years ago when I got that advice.  As Brett pointed out the biggest change is power.  It is now virtually unlimited for our needs.  I used to live by the 11 ozft2 "rule".  Now I think it is more like 14.  Maybe it is just me but I think that a properly powered reasonably heavy plane is a better choice that a light one.  If the wing is capable of producing enough lift to make a "tight" corner and your controls have enough leverage to produce that lift in the places we need it most then the improved line tension and stability IMHO outweigh the benefits being light and of the thousand or so stunt fliers out there I am sure about 3 agree with me!

Ken

I think it's pluses and minuses.   Weight can help penetrate the wind going into it but exacerbate acceleration and wind up downwind.  Having a full stable of heavy airplanes (but not all of them!)  I can say that you can rotate the airplane around a turn but it will then sink or slide further down some meaning to have to get used to making your bottoms turns a smidge sooner to allow for the sink.  They may also slow or lack acceleration once the turn is made.  Rotating more mass has to make the turns a little larger than you could do otherwise with less weight AND bleed off some momentum.   I have found in most all cases I have to fly the heavy airplane faster to stay locked in a groove and stay out on the lines overhead.
You can sure get used to all that and fly very good patterns with a heavier airplane with practice-but at least for me the heavy ones wear me out a lot faster at the field.   A 75 ounce airplane will have me pooped after 5 flights.   A 68-70 airplane and I'm good for 10-12 flights in a session.   A 45 ounce classic and I am usually not worse for wear at all.

Dave

[EricV]

I can say that you can rotate the airplane around a turn but it will then sink or slide further down some meaning to have to get used to making your bottoms turns a smidge sooner to allow for the sink.  They may also slow or lack acceleration once the turn is made.  Rotating more mass has to make the turns a little larger than you could do otherwise with less weight AND bleed off some momentum.   I have found in most all cases I have to fly the heavy airplane faster to stay locked in a groove and stay out on the lines overhead.

My buds and I used to call that "skidding" through the corners, where you changed orientation but not direction, at least not immediately, heh. An effect of inertia overcoming lift and control surfaces I suppose.

You can sure get used to all that and fly very good patterns with a heavier airplane with practice-but at least for me the heavy ones wear me out a lot faster at the field.   A 75 ounce airplane will have me pooped after 5 flights.   A 68-70 airplane and I'm good for 10-12 flights in a session.   A 45 ounce classic and I am usually not worse for wear at all.

Dave

You said a mouthful there... The heavy ones will wear you out in a hurry, or some with a big honking 3B prop on a .75 even in a light plane can be like an extended pull test. This was brought home to me when I built the little 40 sized pipe plane that came out around 47 Oz... I hadn't been into the pipe scene during the 40's popularity, and started with a .61... so it was a revelation to me... even at faster lap speeds, the light little .40 plane with 11 3/4 2B is a lot less fatiguing than the .75 plane, even though their wing areas aren't all that different (something like 640 vs/687?) with the .75 I'm feeling it after a half dozen flights, whereas the little 40 plane I can just about go all day long still feeling pretty fresh and on top of it.

EricV

[Brian Hampton]

Many years ago I designed a model with the full intent of aiming for a very light wing loading but also very high lift. Final weight was 59 ounces and wing area was 820 sq inches so wing loading was 10.4 ounce/sq foot. Engine was a G51 (Italian CL version) running at a full 4 stroke the entire flight. From the very first flight, especially the first square turn, I was amazed at how easily it snapped through turns. Sure, it needed some final trimming, mainly adding some tip weight and sorting out flap/elevator ratios, but after that all was good .

[Dave_Trible]

Eric what's this washed up has been stuff?  I'm sure you are in the younger half of the stunt crowd here.   No sandbaggin'!   You just gotta show up man....Muncie hasn't moved-still in the same place.

Dave

[Brett Buck]

Because of my age I never seemed to be privy to "technical" discussions if any amongst the older builders. Our senior builder built some beautiful models including the Veco Mustang, a similar size Spitfire and the DMECO Debolt Continental. All were outstandingly beautiful glass like ships from my perspective. All were powered with the Fox 35 and the standard of course was using a lot of Pactra Sanding Sealer, the white syrup like Milk of Magnesia stuff even on the silk over the wings. I rarely saw any of these beauties (or clunkers) fly, but I do recall when the old timer loaded the trunk for the field it seemed he always had his favorite a Galaxy profile with a Veco 35.

    It's not that difficult to build a good-looking "lead sled". The guys who can build a good-looking airplane that also flies well and lasts long enough to get trimmed is A LOT harder.  That's one of the great things about the event, everything counts.

More recently one of our modelers brought a Checkalaroma, an early era 50s model he'd recently scratch built to the field. With a fox 35 in it I wasn't sure if I was holding anything when picking it up. He is notorious for exceptionally light builds and minimal finish. He did the pattern with it, and the following year said a wing came off in flight. Last I heard he was doing some "redesigning".

Obviously, the early years had their growing pains.

   Of course! When Davey Slagle was winning, doing a loop was a pretty big deal and he wowed everyone with the new invention - reliable inverted flight!  A Checkala Roma light enough and with enough power  to do an recognizable modern stunt pattern would be a great challenge to keep together for long, it absolutely was not a good candidate for something like repeated square corners.

    People greatly underestimate the loads on stunt planes. It's hard to even get current airplanes to stay together, we are repeatedly hitting 15G corners and your wing - with a structure that weighs maybe 12 ounces without a finish - might have to take 50-60 lbs of load - at least thousands of times but usually much more.

     Of course, people were just as smart then as they are now - they just didn't have 80'ish years of experience. You can't have what we have without someone builiding a Checkala Roma first, and a lot of other things, too.

     Brett

[jerry v]

More recently one of our modelers brought a Checkalaroma, an early era 50s model he'd recently scratch built to the field. With a fox 35 in it I wasn't sure if I was holding anything when picking it up. He is notorious for exceptionally light builds and minimal finish. He did the pattern with it, and the following year said a wing came off in flight. Last I heard he was doing some "redesigning".

Obviously, the early years had their growing pains.

John Ward scratch built Checkala Roma as authentic as possible. He even tested the engine Cyclon 60. (Vibration was horrible) The weakest area of the model is two balsa spars. John powered the model with OS MAX - S 35. Finish - poly span and clear / orange dope. Dry weight is 33 oz. John’s Checkala Roma was handling full pattern well. And flew much better than Ringmaster.

Jerry

[Brett Buck]

John Ward scratch built Checkala Roma as authentic as possible. He even tested the engine Cyclon 60. (Vibration was horrible) The weakest area of the model is two balsa spars. John powered the model with OS MAX - S 35. Finish - poly span and clear / orange dope. Dry weight is 33 oz. John’s Checkala Roma was handling full pattern well. And flew much better than Ringmaster.

Jerry

   The spar setup is pretty classic for the era - with the results described earlier! These airplanes were just not designed for hard cornering. Compare this construction (or a Ringmaster, which the same thing except even less good) to a Nobler - which is built like a tank by comparison.

     Brett

     

[Dave Hull]

And then there was a hybrid transition phase that included designs like Ducharme's Lieutenant: Biggish center spar stick; leading edge planking with the aft edge of the planking supported by small spar sticks; rib cap strips; sheeted trailing edge.

Another one that is interesting (I can't recall the name off the top of my head) was by Larry Scarinzi. In that one, the center spar stick was effectively swept aft because it was built from overlapped sticks (front to back). That raises the question of torsional stiffness and was the spar tailored to help avoid twist or just out of convenience of laminating things, or just to be different, etc.? As I recall, the article extolled the extreme speed of the plane and the impressive "flex" of the wing....

Different times, for sure.....

[Steve Dwyer]

   The spar setup is pretty classic for the era - with the results described earlier! These airplanes were just not designed for hard cornering. Compare this construction (or a Ringmaster, which the same thing except even less good) to a Nobler - which is built like a tank by comparison.

     Brett

It's interesting to consider the similarities and thinking of model wing design compared to early construction design of buildings. It wasn't until early to mid-twenty century that homes on the east coast at least began using I beam construction. Earlier construction for the most part consisted of a large wood beam supported by many closely spaced vertical posts. Post spacing was later increased as steel I beams were introduced, spacing of course was limited to the web dimension, the ceiling height and the loading specifications of the beam itself. This was carried until the laminated beam LVL entered the picture changing span loading even further.

We know the model designers of the early 50s liked the forward and rear spar configuration similar to the Ringmaster and Checkala Roma designs. Somewhere there had to be a tradeoff, was it the 42" span? What did they learn from wings folding in flight? Somewhere around the mid to late 50s it appears they changed the spars to the vertical configuration while moving to the monocoque shell leading and trailing edges also further improving wing loading. Perhaps these mid 50s designers with shops in their basement happened to look up to see the I beam supporting the floors overhead. Or perhaps at a post war air show while looking into the wheel well of a B-17 they saw the massive I beam spar and had an idea...who knows?

So, I have to ask, if early 50s wing loading limitations limited hard corners when did the pattern changes come about? What was the corresponding pattern of the late 40s to early 50s. Was there a published pattern during the early years, were the late 50s design changes the turning point and when did the more precision pattern come about? A timeline would be interesting.

Steve

[Steve Dwyer]

And we mustn't forget to question, was the later stronger thicker wing with the vertically stacked spars necessitated due to more space required for a sandwiched bell crank the earlier early 50s thinner wings horizontal spars couldn't provide?

Again, does anyone know the timeline when the pattern changed as the wing structure became more capable? Was there an earlier (weaker wing) printed pattern during the early 50s? When did the later precision pattern evolve?

Steve

[Paul Walker]

And we mustn't forget to question, was the later stronger thicker wing with the vertically stacked spars necessitated due to more space required for a sandwiched bell crank the earlier early 50s thinner wings horizontal spars couldn't provide?

Again, does anyone know the timeline when the pattern changed as the wing structure became more capable? Was there an earlier (weaker wing) printed pattern during the early 50s? When did the later precision pattern evolve?

Steve

A vertically oriented spar is less efficient than a horizontal oriented spar. The same spar area oriented horizontally is stronger and deflects less in bending.
But vertically oriented is easier!

[Brett Buck]

And we mustn't forget to question, was the later stronger thicker wing with the vertically stacked spars necessitated due to more space required for a sandwiched bell crank the earlier early 50s thinner wings horizontal spars couldn't provide?

   I am not sure what you mean with a "sandwiched bellcrank" here. I am 100% sure that they very quickly figured out via trial and error,  or people with actual engineering knowledge informed them that having the spars separated vertically opposed the tendency to fold due to maneuvering. That's not exactly breakthrough model design development, it is one of the most basic of structural engineering principles. That it also neatly cleared the bellcrank was just a bonus.

   Consequentially thicker wings were a function of aerodynamic thinking rather than structural thinking, although it helped. Not until you had far more powerful engines (in the mid 80s) did you have to seriously consider making your wing thicker to handle the loads. The New Jersey guys were the first to encounter self-destructing models with the ST60- more loads because of the better cornering but failing because of improper construction methods, specifically, putting on the silkspan AFTER the model was assembled instead of doing it tip-to-tip before installation. Even the Nobler plans showed the correct method for that.

Even now, it's far from clear that it is necessary or beneficial and some of us (particularly Ted and I) went "over the top" with the idea. The aerodynamic thinking has various reasoning, in my case intentionally trying to generate more parasitic drag  than any lift advantage. Lift capability is hardly scaling 1:1 with the thickness of the airfoil, doubling the thickness  might get you 5-10% more AoA before it stalls in the best case.

    Compare how well a typical Patternmaster or clone corners compared to a Diva or Skinny Diva. I have seen people corner Divas harder than any Patternmaster ever managed and they both stay together - but the Skinny Diva wing is about 1/3 as thick.

Again, does anyone know the timeline when the pattern changed as the wing structure became more capable? Was there an earlier (weaker wing) printed pattern during the early 50s? When did the later precision pattern evolve?

     They tried to make a real pattern in 1952 and the current pattern was in the 1957 rule book. Before 52, in Davey Slagle times, you just did random stunts like "glider pickup" and Davey's breakthrough "inverted flight".   

    The aforementioned "built like a tank" Nobler wing (double-covered with 1/16 balsa in the center section, and covered tip to tip with GM silkspan) was in "Stunting Can Be Smooth" in I think 1952, or at least the models were certainly around in the early 50's. If you are in Texas, flying with engines like a Fox 35 (a powerhouse at the time), and routinely practicing  dozens of flights a day in Texas winds, you are going to want as strong a wing as you can get, I am sure that was a "discovery" young GMA made (in conjunction with HIS stunt hero and Lockheed Aircraft Company employee Bob Palmer). After 3 loops dead downwind, it's going 100 mph.

     Everything was plenty fine structurally until the ST60 came along in early-mid 80s (which weeded out the bad techniques as above) but then much more so, tuned pipe engines with Paul Walker showing us what you could accomplish with that kind of speed stability. After that, wing failures became much more common an people have had to be much more careful about it. Electric is the same sort of thing. No one in the good old days could have dreamed that the sort of cornering we are routinely managing now was possible.

     I also note that we did it the old-school way for 28*¹ years and have been doing it the modern way for  37*² years. I am always surprised how many people have yet to realize that anything changed.

     Brett

 *¹1957 to 1985
*²October 1988 to 2025

[Steve Dwyer]

A vertically oriented spar is less efficient than a horizontal oriented spar. The same spar area oriented horizontally is stronger and deflects less in bending.
But vertically oriented is easier!


Paul,
I'm not sure what you mean by "less efficient", a vertically stacked spar configuration (one spar spaced above a lower) and covered with a film or balsa offers a stronger wing more resistive deflection than two spars positioned horizontally. Essentially, we are approaching the configuration of a bar joist.   Is a thinner airfoil with the spars positioned horizontally more efficient aerodynamically if this is what you mean? I'd prefer to leave this up to the aero guys here.

Bret,
I'm saying a "sandwiched bellcrank" means a bellcrank positioned within the space afforded between the upper and lower spars in the later thicker airfoil. The configuration or "sandwiched location" came about as a result of the thicker wing and essentially realized as a better engineering concept as you say.

Thanks for the response.

Steve

[Brett Buck]

A vertically oriented spar is less efficient than a horizontal oriented spar. The same spar area oriented horizontally is stronger and deflects less in bending.
But vertically oriented is easier!


Paul,
I'm not sure what you mean by "less efficient", a vertically stacked spar configuration (one spar spaced above a lower) and covered with a film or balsa offers a stronger wing more resistive deflection than two spars positioned horizontally. Essentially, we are approaching the configuration of a bar joist.   Is a thinner airfoil with the spars positioned horizontally more efficient aerodynamically if this is what you mean? I'd prefer to leave this up to the aero guys here.

    I think you and Paul are talking about two different things. You are talking about fore/aft spars right in the middle of the airfoils (like the Checkalaroma example above) VS top and bottom (at the high point on the top and bottom). He it talking about the way the top/bottom spars are oriented -either "vertically" or "flat", Suppose your spars are 1/8x1/4, do you put the 1/4" up and down or front to back? Answer= front to back. You still want the spars at the high point of the wing.

    Note also that sheeting is like taking the "front to back" idea to the limit, it's like a very thin and very flat spar. You want your structure/mass as far from the center as possible, the outer surface is as far as you can get it.

     Brett

[Steve Dwyer]

Brett, and everyone, 

It would have been fun to watch more of the early "old clunkers" being flown (attempted) to fly the new pattern. I guess it was an era of broken spars and a vertical learning curve.

Thanks for sharing