Semiscale Kadets

By Lawrence E Klingberg Jr.

As seen in the May 2000 issue of Model Aviation.

After I built a couple of Sig Kadet Seniors, I noticed that the basic design was very close to many of the cabin-type airplanes that were prevalent during the Golden Years of aviation. I am a scratch­builder at heart, and it is very difficult for me to open up a Kadet kit and not get inspired as to the possibilities of what it could look like with a few simple changes.

The square fuselage of the Curtiss Robin makes it an excellent choice for conversion to a semiscale model.

There is nothing quite like taking a new semiscale airplane to the field, and after everyone has “examined” it, simply telling them, “Well, it’s made from a Sig Kadet kit.” Usually most of the gang can’t believe you are telling them the truth.

I’ll outline how to modify or change these Kadets into semiscale aircraft. It is quite easy, and is limited only to a builder’s imagination. The finished aircraft usually come out to about 1/5 to 1/6 scale—large enough to be able to be seen by “old eyes” and handle very well from a flight standpoint.

If you are a modeler of average skills and would like to pursue this adventure, the first thing to do is buy a Kadet kit and decide which full-scale airplane that you would like to model. Look through old magazines, or better yet, if possible, go to the library and check on all the neat airplanes in Joseph Juptner’s series of civil aircraft. The books are full of airplanes just begging to be brought to life through your efforts at the workbench.

The best choices for a first attempt would probably be a Curtiss Robin or a Bellanca Monoplane, since they both are quite simple. Other possibilities are the de Havilland Beaver, Fieseler Storch, or Monocoupe, just to list a few.

Bellanca W-82 Miss Columbia weighs 9 pounds and uses an O.S. 90 four-stroke. Solartex covering, MonoKote graphics, Sig butyrate spray dope.

After you have selected an airplane that appeals to you, be sure and ask yourself if it is close enough to the basic fuselage outline without too much rebuilding. Then locate some three-views or pictures so that you can see what the finished airplane is supposed to look like. (I like to choose airplanes that have very striking graphics on them; this is what takes an airplane out of the “Cub” category.)

It has been my experience that most of the modified Kadets will be in the eight- to 12-pound range, and all have flown very well after conversion to semiscale. The engines that I normally use for these conversions are 70 four-strokes for the landplanes and 90 four-strokes for a model that may have a pair of floats installed on it.

It generally takes roughly six months to build one of these semiscale models, but after all, we are not just building a “trainer” but a nice-looking airplane.

With a set of three-views and the Kadet fuselage plans on the bench, your next job is to put some thin tracing paper over the plan and change the fuselage outline to that of the three-views. Keep in mind that you are still using the same fuselage box shown on the plan. Usually this means building a new “front end” on the fuselage and making the fuselage fatter by adding three or four stringers on the sides and possibly the top and bottom, depending on the airplane being modeled.

By tracing side views and overlaying them, it is easy to see what has to be changed to make a semiscale model of the Columbia.

Be sure to leave the wing and stabilizer in their respective locations so as not to change the center of gravity (CG) and thus the flying performance of the airplane.

The shape of the wingtips will also need to be altered so that the airplane will have the same configuration as the three­view. This can usually be accomplished by laminating 1/16 x 1/2 balsa strips around a cardboard template then gluing and sanding them to a smooth contour, blending into the leading and trailing edges of the wing.

While on the subject of wings, you should cut in some ailerons during construction. They should be from 18 to 22 inches long and approximately 3-1/2 inches wide. A single servo·in the center of the wing can be used, with long pushrods to the bellcranks, or a servo can be placed in each wing panel, with the wires leading to the center section, and then connected to a Y harness to the radio.

Sometimes it’s a good idea to make a wing center section and attach it to the fuselage. This method allows the two wing panels to be removed for transit, and also gains about 13 to 14 inches in span, if you need more wing area. If this plan is adopted, it is necessary to make some wing struts, but most (full-scale) airplanes have them already.

If a longer-than-usual wing is needed, a wing kit can be ordered from Sig, so additional materials such as ribs, spars, leading edge, etc. can be purchased quite economically.

The stabilizer and rudder are probably the easiest job of all during this changeover; all that is needed is to draw the new outlines and make a stabilizer and rudder using good building practices. Keep in mind not to change the location of the stabilizer in relation to the fuselage. The wing and stabilizer should be zero­zero Z (no angular difference) in relation to each other.

I generally install wires or struts from the rudder to stabilizer; they can be made from 1/4-inch streamlined K&S aluminum stock with flattened ends, attached with 2-56 screws and nuts. The stabilizer and rudder should also be installed with 4-40 screws or some other means so they can be covered individually and also be removable in the event of a crash/repair.

The rudder and stabilizer will also need different control linkages made up, and these can be done any way the builder may see fit. A tail wheel will usually be needed, and this can be attached to the rudder bottom so that the airplane handles well during taxi.

The portion of the airplane from the leading edge of the wing forward to the tip of the propeller will generally be the most daunting job; this is where you will have to make templates, firewall, and engine mountings. The windshield is also sometimes a problem, but it must all come together and look like the three-view from the side and top views.

Some airplanes have exposed radial engines, and some have fully enclosed watercooled engines, so this is where one has to decide how to carry this out and make everything look right. Generally, a radial engine with one cylinder being the model engine looks great, if skillfully done. Dummy cylinders that look like the model engine are not difficult to build, and add much to the airplane's appearance.

The enclosed engines on some airplanes require mounting the engine with the cylinder coming out the side or operated in an inverted fashion. In other words, try to hide the model engine and muffler as much as possible, for appearances sake.

Don’t forget to make air outlets or louvers, so your engine won’t “cook” in the confines of the cowling. If a round cowling is needed to enclose a radial engine, the bottom portion of a one-gallon fuel jug makes a cheap cowling and is just about the perfect diameter.

I recommend covering these airplanes with Solartex, with MonoKote graphics and trim. Sig butyrate spray dope and Rust­Oleum are excellent for painting the Solartex.

When locating the fuel tank, radios, batteries, etc., try to place everything as far forward as possible, since most airplanes are tail-heavy. Be sure to check the CG before flying.

Bellanca with quick-change floats added. Floats are 40 inches long—no problem for this 80-inch-wingspan model.

The photos presented with this article are representative of what can be done to modify a kit, and are shown as typical examples of some of my “conversions.” I think it would be quite interesting if clubs would have contests based upon creating semiscale airplanes built from the Kadet kits or others.

The author assumes no responsibility for results or performance of any modified kit, and has submitted the information purely for the enjoyment of creating a semiscale airplane from a trainer kit. This article was written with the intent to inspire builders who would like to come to the field with something besides another Cub to place on the flightline.

With a little extra work and imagination, many existing kits can be modified into semiscale airplanes that are sure to be conversation pieces. It has been my experience that, if carefully done, all will fly in a scalelike manner, and the end result will be very rewarding.

I hope that all those who try some of the ideas set forth in this article have as much fun as I have had in making basic changes in an existing kit, with the end result being the creation of an out-of-the­ordinary airplane.