SIMPLE TR ? WE'LL SEE
I'm planning a trip to Portugul, for a contest, and wanted an international event type airplane to compete with. Since diesels are the norm in Europe and I needed something quick building, why not Sinple TR. We'll see how simple I can make it without the use of high-tech building approachs, namely vacuum bagging.
I've started by modifying Goran Olsson's TR, available from his web site, and redrawng it into a profile plan. The wing is started by using 3/16" 6 lb wood and arranging it in a jigsaw puzzle effect as viewed in the first photo, with the grain running in an anglular direction. The bottom part is 3/32" 5 lb wood with the grain running in a direction parallel to the leading edge. When gluing the edges together, promote no stress to mate them, so make sure the joints are perfect, this helps to keep from warping. Put on a coat of nitrate dope on the laminating surfaces and sand off the fuzz then, top and bottom are glued together with two layers of.03 oz carbon veil between, the dope prevents the epoxy from wicking into the grain, wet the veil on a plactic surface and use the playing card techique to squeegee out the resin so, it looks almost dry then, put between the top and bottom, roll out and press between two pieces of glass, with pressure. This process forms a ply, type lamination with excellent torsion stabiliy, add three stripes of 3/32" basswood on the outboard wing and one on the inboard leading edge, weight is 109 gm, at this point.
Now comes the fun part, sanding the airfoil. I prefer to leave the center section alone and sand around it for a more accurate mating surface as shown. I used a razor plane to start, once roughed out, I switched to a 8" t-bar block with 80 grit paper on it and a smaller block with 100 grit. Great care has to be taken when sanding, let the sandpaper do the cutting, not shear force. Heat and pressure are the enemys here, to prevent warping.
I added some 1/32" ply and inlayed them on the top and bottom of wing to act as a spar and mount for the bellcrank. Also added a small piece of 1/8" ply, 3/8" x 1 3/16", tapped several 2-56 holes for adjustable leadouts and added 7 gm of tip weight. The wing weights 85 gm at this point.
Start the fus by using 1/4" 4 lb balsa, cut out the outline, and slots for 1/4" square red oak motor and gear mounts, epoxy in place. On the outboard side, laminate 1/16" ply on the front and 1/16" balsa on the back of the airplane, when dry, cut out slot for wing, as shown to the right. I cut out the plank to try to save alittle weight, it only amounted to 1.5 gm. Now for the inboard side, laminate 1/32" ply toward the front and 1/32" balsa to fill in from the back of that ply to the rear, and 3/8" 4 lb balsa over all to build up to 5/8" total fus thickness. Inlay a 1/16" ply rudder on the out board side and start sanding. I inbedded a piece of 3/32" aluminum tude for the fuel shutoff trip wire which will be attached to the pushrod.
I brushed on two coats of nitrate dope to the wing and fus and applied .6oz glass cloth with thinner and then one more coat of nitrate. If you haven't tried this method before, give a shot instead of bagging. After the thinner, you can use epoxy and scrape it off but, I think this is just as strong and lighter. I gained 9 gm on the wing and 2 gm for the fus and it's plenty strong plus, it's pretty much sealed. Lay some additional glass to the front wing fus join.
Photos to the right show the assemblied plane at a weight of 159 gm, individual weights are 97.5 for the wing with horn and hings installed and 61.5 for the fus with gear.
Next photo of the side shows the rudder and skid, looks kind of like a fishing lure, in fact I've been looking at some of those and may try a paint sceme to emulate one.
Next is some of the hardware, fuel shutoff/overflow switch and, the controls weight 8.3 gm combined. Bellcrank is carbon fiber with bottons for direct line attachment, down on the pushrod is an adjuster for the fuel cutoff cable.
Below is the painted model, rules require canopy, either painted or clear with pilot, I choose to paint it in with a clown as my pilot, just couldn't put on a fishing lure paint job with the required pilot rules, it just wouldn't look right, weight pictured is 172.5 gm. Assembled weight with APC prop is 387 gm.
It hasn't come out to bad for my first attempt however, there are some procedures I will change on the next one. Weight reduction can be had by, using 4 lb wood instead of the 5 & 6lb for the wing (I wasn't going to waste my good stuff) and, use one layer of carbon veil or none with a thin, laminating resin, that can pull off 1/2 oz. I liked the attachment of the glass coth with nitrate dope but, after attaching with thinner, scape on expoxy because I think it would give a more rigid structure, or bag the thing. The hardware really adds up quickly, the tank at 9 gm can lose about 4, maybe I'll do a carbon one. The fuel shutoff, I like, one thing about the airplne structure is that it's hard the grab, the bar configuration is so I can grab it with my thumb to hold while flipping also, the venturi is right there for choking.
If you have some problems with the engine cooling down since, it's exposed, use some O-rings over the fins to retain heat, add as many as neccessary.