What About Those Not-So-Golden Oldies?

A couple of weeks ago I got the following email message:

Hi there, I recently bought a “Capitol Models Stinson Gullwing 54” Balsa model. I’m planning on building it and making a R/C flyer.It came with a giant blue print but no smaller detail instructions? Also some pieces are missing? I was wondering if you can help me find them?
Thanks, Steve

I thought about that for a while and then sent Steve this response:

That sounds as if it might be quite an interesting (but BIG) project. Can you spread out all the stuff that came in the box, along with the plans and the box itself, and send me a picture or two so I can see what you have to work with?

I was looking forward to helping Steve turn a classic “dusty old kit” into a neat electric RC scale airplane. It was not going to work out that way. I’m going to share this less-than-happy ending to the story online because I know there are LOTS of similar questions out there waiting to be asked. When he responded with more info and some new questions along with several photos, that turned out to confirm my suspicions about what was going on. If you have been reading my stuff over the past few years, you already know that I am always interested in built-up balsa (stick-and-tissue) kits from the 1930’s, ’40’s, and ‘50’s as well as lots of new kits based on those old designs. (Check out the Dumas Piper J-4  kit conversion I’m working on in the blog series right next door.) Most of these were designed as rubber-powered free flight models. Many of them make good subjects for conversion to electric powered RC…BUT…not all of them are cut out for excellence. It is, unfortunately, all too easy to find kits of that genre that are probably not worth the time and effort you might be willing to put into turning them into practical flying models using today’s technology. Also unfortunately, the Stinson kit Steve came across fits into that category. I’ll try to explain what’s going on, what you might choose to do about it if you have one like it, and some of things to lookout for when checking out vintage airplane kits for possible new projects of your own.

Photo 1

There are several characteristics of some of the vintage balsa kits out there that we all need to be on the lookout for. Some of them contain inferior wood…perhaps poor quality balsa, either too soft and “punky” or too heavy and hard, stiff , and ready to crack and split to be worth working on. There are lots of “wartime materials shortage” kits around where balsa wood of any quality was replaced by poplar, pine, or even cardboard. Some of these kits, aside from being of interest to collectors, are so poor that even an expert modeler would have difficulty getting them built, let alone into the air. Just about as bad were what I’ll call “minimalist” kits whose entire structures consisted of an obsessively light framework, mostly of 1/16” sq. and maybe 1/8” sq. balsa that was barely capable of holding itself  together under the stress of even the most lightly doped tissue, let alone in flight. You could make one of those featherweight jobs fly with a bare minimum of rubber, the delicate touch of a surgeon, and the gentlest of calm evening air, but you had to work at it. I’ve seen it done, but not often. Even to meet today’s indoor rubber scale standards most of the old kits I’m describing here would demand expert modification. Right alongside this issue you were just as likely to find non-existent structural  engineering, where wing panels might be attached to a fuselage simply by gluing the faces of the wing root ribs flat against 1/16” balsa sheet base plates on the fuselage with no structural carry-through…not even a spar. The landing gear in one of these kits might be two struts (triangular pieces of sheet balsa) glued to the lower fuselage longerons. There might be NO landing gear strut/axle to bend from a piece of fine steel wire…you might be expected to stick a bent pin through each wheel and into the bottom of the balsa strut legs to support the airplane. That’s not all. As often as not the kits of those days NO instruction book…no instructions at all beyond a few “hints” on the plan itself.  You get the picture. An experienced builder either knew enough to spot kits like these on the store shelf and leave them there, or to modify the design and replace material on his own initiative if he happened to want to build a particular airplane enough to invest all that extra effort. In fact, most of us who learned to build model airplanes in the old days figured out how to do all that without thinking much about it. If you weren’t an expert, you either learned the hard way or you got left out of doing model airplanes.

Unfortunately my friend Steve happened upon one of these less-than-great kits. This is not his fault, and probably not the fault of whoever sold him the kit, either. This is one of those “you have to know about  that…” situations. Looking at the box label in the image Steve sent me might not be enough to tip you off. At first glance you’d think this Capitol Stinson Gull Wing SR-9 kit might be a good subject for RC conversion. It’s just the right size for practical outdoor RC flying at a 54” wingspan, it’s a “Guaranteed Giant Flyer” according to the promo, and the kit even features an “Aluminum Cowling”! According to the box label illustration, it’s a pretty fair scale replication of the SR-9, too. This particular model kit exhibits several of the shortcomings I’ve discussed…it’s one of those “minimalist” jobs, with just enough balsa designed into the wing and tail outlines and the fuselage framework to hold itself together under its own weight. There ISN’T any internal structure to speak of. This kit also provides a good example of non-existent structural engineering… AND what you got along with that was an almost complete lack of building instructions.  Let’s look at those issues in detail using the photos Steve sent me. They’re kind of fuzzy, but they’re also good enough to get then message across.

The first hint that things aren’t going to work out that way comes with the little portion of the plan that Steve included with the box front in that photo. Look at the vertical tail/rudder image on the section of the plan you can see…the leading edge looks like 1/8” sq. balsa. The curved tip and trailing edge outline parts appear to be cut from 1/8” sheet balsa, and are way too narrow. Not many model builders could actually cut out those parts, even from really good quality balsa, without having them split apart, and even if the loads imposed by even the most gentle tissue shrinking didn’t warp them into potato chip curls, the slightest bump during normal handling could  break them. The fuselage cross section belies a repetition of the same problem…those 1/8” sq. stringers on a model that big wouldn’t tolerate much handling.

 

Photo 2

Let’s look at photo 2. The big problem that’s exposed here is the wing-to-fuselage mounting structure…there pretty well isn’t any. You are expected to keep the wing attached to the rest of the airplane by gluing the adjacent faces of the wing root rib to that airfoil-shaped section of the “side of the fuselage”. There is NO leading edge, trailing edge, or spar  carry-through structure that I can see. I can remember seeing a ten-or-fifteen MPH wind blow the wings RIGHT OFF models like this while some other kid was just trying to hold on to the thing.

 

Photo 3

In photo 3 it just gets worse. Steve asked me about “the landing gear…and how to connect the cowl to the rest of the fuselage”.  Check out the plan. Can you find the structure that provides a mounting base for the cowl? What about mounting plates/pads/fuselage cross braces to manage the loads those 1/8” sheet balsa landing gear struts are going to encounter? There ISN’T any. I have difficulty understanding the mindset of whoever it was that drew those plans. Were you just “supposed to know” that the landing gear would never stay attached to the fuselage unless you designed and built your own modifications, or what? It doesn’t appear that there were any “construction detail notes” on the plan to address that issue. I’ve seen plenty of kits/plans where there weren’t any. This is where I get to address Steve’s specific question regarding how he can find a copy of the original instruction sheet or book that was missing from his kit. He can’t. There never was one.

There’s even more poor engineering exposed in this image. Look directly above the middle of the triangular landing gear strut, at the top of the bottom fuselage longeron where three fuselage upright and diagonal strips come together. See that “other” wide component that’s drawn in at about a thirty degree angle to the right (toward the tail)? That represents the main wing strut. What does the plan show you about the way the lower end of the strut is supposed to be attached to the fuselage? NOTHING. If you followed the directions implied by the plan you would butt-glue the strut against the fuselage…and it would fall off the first time you picked it up. Same deal at the top end of the strut, too.

 

Photo 4

Photo 4 shows a pair of very thin, almost “profile” wheel pants assembled and ready  for shaping and sanding. What’s wrong with these is that they won’t look anything like the big, round bulged-out wheel pants on the airplane in the picture on the box. Could you fix this by cutting and laminating extra parts to “fill out” the correct shape? Yes…IF you knew enough to do it without being told anywhere on the plan.

 

Photo 5

Photo 5 gives you a look at some printwood and stripwood from the kit. Steve didn’t tell me whether that’s all there was in the box, or not. In keeping with that minimalist character of this design, there probably wasn’t very much more. Without some expert knowledge/model building background it would be very difficult  to work out what might or might not be missing…and what to do about it. Take a closer look at the printed wing rib patterns and you’ll see several built-in shortcomings of this kit in terms of its suitability for conversion to electric RC (or even for actual building as designed). The airfoil (wing cross section) is markedly thinner that it should be if correctly scaled for the full scale airplane. It should be nearly twice as thick (top to bottom) for better flight characteristics, structural strength, and scale appearance. Look at the spar…there’s not much to it, and a total re-design into a workable load-bearing structure would be necessary to make it flight-worthy as an RC conversion. Same thing with the leading edge. You can see from the marked cut-out that it’s tiny… just 1/8” sq. balsa set on edge. Aside from offering practically no “crush protection” in the event it hits something, the 1/8” of surface is WAY too narrow for proper attachment and support of tissue or silkspan covering (or modern plastic either, for that matter). What you’d get if you  tried to cover that wing would be a thin, too-sharp leading edge with puckers and wrinkles where every one of the ribs joined the leading edge. Something like ¼” x ½” light balsa sanded to shape would have been a much better choice. Could that be fixed by drawing in the changes and building to the new pattern? Sure, but that would mean redesigning all the ribs while you were at it, then cutting out all new ones and throwing away all the old ones.

 

We could go on and dissect this poor old kit some more, but you get the idea.

 

So…what’s the answer for Steve (and all you other guys out there who have encountered the same issues), who has a LOT of questions about this model? I don’t have one. What I can offer is a whole series of new questions in return. Do you have enough model airplane building experience to design and build an entirely new landing gear, a very different wing structure and center section carry-through, a new firewall/motor mount that includes cowl attachment features, more substantial tail surfaces with working control surfaces that won’t collapse when you pick up the model, and so on? Could all that be done? Sure it could. Could I do it? Yes…if I REALLY wanted to “save” this particular old kit and fly it as an electric RC job. Would I recommend doing that to you? No.

 

My honest, straight-from-the-shoulder advice to Steve (and the rest of you) is to PASS on “converting” this model  or any of the many others like it that you might come across in checking out all the interesting old kits that are waiting out there for us to rescue. Build it as-is for the experience and hang it up for decoration, but forget flying it. There are several contemporary lines of traditional built-up stick-and-tissue kits with up to date engineering, high quality materials, and well written instructions. Some of them are intended for rubber powered free flight and others are already “converted” for electric RC. The kits advertised by Dumas and by Dare Design (now part of Brodak) are all well worth checking out. I have built and flown several of them myself. In my experience the very best are designed by Pat Tritle. Pat knows what he’s talking about when it comes to very light electric powered RC scale model airplanes that FLY. Building and flying a couple of those (without having to re-invent or fix anything) will give you the experience you need to make good choices regarding the old-time stick-and-tissue kits you’re going to come across in the future.

 

Go for it!