DH 88 Comet (oz12034)

About this Plan

DH 88 Comet. Radio control scale model twin, for 2 x .20 engines. Scale is 1/8.

Quote: "Radio control scale model based on four-color Bjorn Karlstrom centerspread drawing in January 1969 issue of American Aircraft Modeler. Designed by Skip Williams, redrawn and inked by Frank Elminger. Uses two .20 sized engines, four channel radio control system. Scale 1.5 in to the foot."

Direct submission to Outerzone.

Update 27/03/2020: Added scan of the Bjorn Karlstrom colour drawing, thanks to RFJ.

Update 01/03/2021: Added article, thanks to rocketpilot.

Quote: "FOR RADIO CONTROL World-famous DH-88, winner in 1934 of the England-to-Australia race, makes sleek, fine-flying protect with two 19's. By Skip Williams.

WHEN I was flying. I was one of those who said: A scale model doesn't fly well enough to be worth building. In R/C, this is still true. In some cases the real problem is that no one really knows if it will fly or not until one has been built and tried. I always want something different and original, so I have a problem. The big decision must be: what plane will I build? From experience in flying competition scale and pattern. I have listed the requirements for a good contest scale plane.

The plane must be simple and sturdy in construction. It must fly well, and it must be able to take advantage of the maximum scale operations which are available for that particular craft. Needing something to start with, what could be better than the January color centerspread from AAM?

I had in mind a small twin-engine plane for some time and, before I saw the Comet, I had considered the World War II Messerschmitt 110. After seeing the sleek lines of the de Havilland and the possibilities of cowling in the engines, along with good-sized tail surfaces for stability, there was no doubt this ship met my requirements.

Now that a selection had been made on what to build, what about size? The proper scale has to be figured to give the right size plane for power: that is, square inches of area vs expected weight. I always feel sorry for the poor guy who puts in so much work and time on a beautiful plane that doesn't have enough lift to get off the ground. He has eliminated himself from competition at the start. With this lesson as a guide, let's do some figuring.

I believe a 1.5 in scale is right because the dimensions seem to be right for two 20-size engines, with enough area to carry the weight required for toughness in rough landings; so for scale competition we must keep the craft as close to true scale as possible. However, the AMA rules do allow you to cheat a little to enable the plane to fly. So this is what we must do. The rudder is large enough, just as it is, but the stabilizer is a little short, so we add about 20% to its span and it still looks scale.

The dihedral is good as it is, but the airfoil is too thin - especially at the tips. You pattern boys know what a bad thing a tip stall can be on a slow landing. In order to improve this condition, which one can anticipate even before building, we can thicken the wing, more so at the tip. I found this change valuable. Even so, you have to land the ship fast with the tail up to prevent tip stalling. I am sure this is the way the original also was landed. The only other change is to make room for a fuel tank and engine in each nacelle and still have room for the landing gear. I added about an inch to the nose of each nacelle, but some of your engineers may find a solution that permits accurate scale.

Construction is similar to many other models, except that we are building the equivalent of three fuselages, counting the engine nacelles. In small pattern planes I have been using 3/32 to 1/8 heet balsa sides, laminated with 1/32 plywood for strength, from the engine to behinfd the trailing edge. I have crashed planes very hard, and not had a crack at this section..."

Supplementary file notes

Article.
Karlstrom drawing.

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