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Gasoline Conversion Using a O.S. .20 Four-Stroke Engine
Written by Sam in Arizona
I have just returned from the test flight of my latest Easy Built kit a 50" wingspan R.A.F. SE-5. This is my second kit from your company. My first was a Jodel D-9, 50" wingspan originally designed for electric flight. I powered it with an O.S. .20 four-stroke engine, cut ailerons into wing and used standard servos. It flew well, but was grossly overpowered. A low-speed, low-altitude accident ended it’s career early. Only later did I learn an incorrect wing incidence setting was to blame for its vicious stall characteristics, not the kit design. Recently, I happened upon an advertisement in one of the model magazines advertising a 50" wingspan, jumbo free flight SE-5. Out of curiosity, I ordered one, knowing full well that this aircraft was close in size to a Sopwith Camel F-1 I had built about 10 years ago. The Camel was powered by a .91 four-stroke, covered with silk and dope, and flew quite realistically.
After receiving my Easy Built kit SE-5, I sat down at my computer and fed in some numbers. The weight, wing area, power, and construction looked like it should fly with the same O.S. .20 four-stroke engine that overpowered the Jodel D-9.
I started off with a light-ply box that tied the engine, landing gear, wing, and Cabane struts together. Then I built the plane around the box, exactly as the plans show. Of course, I had to add some spars to the wings that also serve as anchors for the ailerons. The leading edges of the wings are 3/16" hardwood dowels, and the main spars are spruce. Cabane struts are streamlined aluminum tubing, and the wing struts and landing gear are also spruce, the same size as shown on the plans. This proved to be quite strong and for safety, I added aramid-kevlar cables for bracing, these are also adjustable for rigging.
The plane was rigged with all surfaces and the engine at 0° to the datum line of the fuselage. I later rigged the upper wing at 2 °+ to improve the stall characteristics. After my first test flight, I have found it necessary to add 4° downthrust to the engine.
The plane was covered with the silkspan tissue that came with the kit, it appears to be a very high quality covering. Three coats of clear nitrate dope and two coats of colored butyrate dope gave the structure surprising structural and torsional strength. I am presently hand-painting the various roundels, numbers, and insignia. The instrument panel was used as a model to fabricate one on my computer using photographs of the instruments, gages, and controls. Then they were printed on glossy paper and fuel-proofed. The control system was made up of aramid-kevlar cables routed over pulleys and fairheads duplicating that of the original aircraft. The aircraft flies quite smoothly and realistically with the O.S. .20 four-stroke turning an APC 11x4 propeller with no tendency to tip-stall or any other nasty traits associated with biplanes.
The only thing that put me off at first was the lack of die-cutting. But, I've seen some really good kits that were all but ruined with bad die-crushing. I have three models partly built because the die-cut parts were unusable. Cutting printwood is not difficult if one takes his time. Laser cutting would be ideal, but costly. I think maybe printwood was actually an advantage in a kit-bash since many parts were modified before they were cut out saving wood in the process.
I will always have something good to say about Easy Built Models and I will heartily recommend them to anyone wanting a challenging, well designed model kit.
Thanks again for a very good kit design. I will keep in touch.