Roddie's Cox-powered triplane

Many of you know about this model, built back in the early 90's.. I've posted some pics.. and wrote a little about it's construction. It was powered by a Cox .049 reed-valve engine with the horseshoe back-plate and a small Perfect wedge-tank. I believe I used a 6" x 3" two-blade "Zinger" wood-prop. running either Cox Super-Fuel.. or Sig Champion 25.



To "summarize".. it's of my own design (I drew-up plans) and uses "built-up" (framed) flat-wing construction.. with "similar" construction applied to the profile-fuse.. covered in Top-Flite's "Mono-Kote" of that current vintage.



All three wings are 80 sq. in. constant 4" chord/20" span. The center-wing has a functional full-span flap of approx. 17 sq. in. area. The top/bottom wings were built with flaps too.. but only at the tips.. 1" x 4" and linked with .025" music-wire. They were never connected to work.. which was dumb.. because I'm sure that they "buffeted" in flight causing drag. All hinging was done with Sig CA hinges.. so these flaps were fairly rigid.



On maiden; the model was a HANDFUL.. and I was committed to trying to fly it.. until it ran out of fuel. It was a frantic 3 minutes of handle-input to control it. Worse than any wind I've flown in. It was tail-heavy.  I didn't have many options.. and it was questionable where the C of G would be, when building it. I decided to try mounting a "heat-sink" (Cox Sand-Blaster part) clamped to the glow-head for nose-weight. It worked.. and I could now achieve level flight with minimal control-input. I flew the model a few more times.. but retired it, because it just wasn't right. I was losing power from an over-cooled engine... and had excess weight to make it balance.

Fast-forward 25 years.... I decided to cut the flaps off the top/bottom wings. Being Sig "Easy-hinges".. this was easy to do with a razor-blade.



This was done this past Winter.. and set aside. The discarded pieces were saved.. and I ran-across the two .025" music-wire flap-links a few nights ago.. and decided to weigh them up.. along with the flaps I'd cut off.



Almost 1/2 oz. of weight there.. X-amount of inches rearward of the C of G.

Should I try to fly it again without the heat-sink attached?... The aforementioned heat-sink weighs .5 oz. but the nose-moment (to the engine's cylinder) is only 4" forward of the center-wing's L/E. The three wing's L/E's are offset 1/2" back from top to bottom. It's basically a "crap-shoot"..

It wasn't a terribly heavy model to start with.. because of its' construction. Weight now (less engine) is under 6 oz.



This model is on my "to fly" list.. along with several others. The wing-construction is what I really wanted to share with you. "Flat-wings" don't lend themselves well to stunt.. but there are plenty of little designs that utilize them. Building them as a "frame-work".. does save weight.. as well as building your fuse's tail-section "framed-up".. as opposed to a solid plank of wood. Covering is needed.. but why not give it a try? The two models that I've built this way have stayed dead-straight for almost 30 years.



Here's a backlit framework-shot of the mono-plane, through it's Mono-Kote covering. It's simply 1/8" balsa pieces.. CA-glued together in minutes.



You can incorporate a 1/2" wide piece of 1/8" Spruce as a spar.. if you want.. and still be lighter than a solid 1/8" balsa full-sheet wing.