Waco YKS-6 (oz12656)

About this Plan

Waco YKS-6. Radio control scale biplane model.

Quote: "1936 Classic Waco YKS-6, by John Burns.

Who can resist the charm and appeal of the cabin Wacos of the 1930's? Our author couldn't, and ultimately came up with this 1/8-scale replica that has proven to he a fine flier. Original model is powered by an O.S. Wankel, but conventional engines of .25 to ,40 cu in displacement could also be used, a shame to have a cylinder sticking out of that cowl, though!

Another biplane that is built like an overgrown Peanut Scale model and powered with a Wankel rotary engine? Of course! I'd been bugging Mr. Northrop for some time to publish another article, when I finally realized I had to get his attention. I don't want to give away any trade secrets, but those three color photos of my Waco YKS-6 biplane model were like flashing the green light at the drag strip. Hence, this article. To quote a famous expression: If it has two wings, it's got to be good.

Every modeler has his favorite planes, warbird, classic, current - so when I saw this beautiful red-and-white VKS-7 at Oshkosh in 1970 and again at a couple of EAA conventions, I had to build a model Waco. Naturally, several photos were taken of the VKS-7 and of other cabin Wacos.

The Waco cabin airplane article in Historical Aviation Album Volume II was memorized, and drawings of the YKS-6 were obtained and used as the basis for the model drawings. My pile of magazines was ransacked to find the January 1956 MAN and June 1970 AAM articles on Waco models. Wylam's drawing of the C-6 Waco was obtained, and several EAA Sport Aviation magazines were cut apart to extract pictures of Waco cabin airplanes.

If you have been listening carefully, you just noted several sources for data and documentation so necessary for a scale model, not just for contest use but to draw and build it in the first place.

When this model was designed, the object was to have a model that could be handled fully assembled, so 1/8 scale was chosen. That puts it in the approximate wing area range of the Falcon 56, Skylark, and similar models that perform well on .30 to .40 size engines. Imagine my joy when I found my Wankel engine fit perfectly inside the scale fiberglass cowl! A round-engined airplane needs a round engine, right?

Another good reason, besides its power, for using the Wankel is that biplanes tend to be tail heavy, and the extra weight of the rotary over a conventional .30 or .40 engine is just right to balance this model. Also, no cylinder head sticks through the cowl.

This model has one-piece wings fastened with dowels and two screws for the top and one screw for the bottom wing. However, there are twelve little screws that hold the wing interplane struts, so the model is left assembled most of the time. It is definitely not a field assembly project. Besides, has your screwdriver ever slipped and gone through your beautifully doped silk covering? #@$%*!!

Because the plane is a smooth and stable flier, a quarter-scale version would be great. Additional design to make the four wing panels removable is needed, and socket head screws for the strut fastenings would simplify that problem. All you need is to get the plans, double the drawing sizes, and have a vehicle that can handle the 75-3/4 inch overall fuselage/tail length. No, there is no Wankel engine that size. I'd recommend an engine rated at three horse-power, swinging a 22x14 prop.

CONSTRUCTION: This model is built like an overgrown Peanut Scale model with a structure like the full-scale steel tube construction. The major fuselage material is 3/16 square spruce, which is strong, tough and not that much heavier than balsa. Even a quarter-scale version could be built with1/4 square spruce with 1/8 x 1/4 stringers. It would be light but strong and durable.

The only sheet material is in the front, to help support the firewall and a few gadgets. The forward bottom is a thick balsa block which is easier to shape and more durable than sheeting.

Appropriate use is made of plywood for the firewall, a unique engine mount for the Wankel, bulkheads for the wing dowels and fastening screws, the landing gear base, the dihedral braces, and all the places where the wing struts are attached.

The main landing gear wire is formed like on many control line models, with a large 'U' loop J-bolted to the ply base. The rear struts float in the fuselage at the rear end. The large balsa fairings on the main struts are epoxied, wrapped, etc to the wire. Mine still split after a while.

The tailwheel was made steerable with two small springs from a horn on the bottom of the rudder, but experience dictated replacing one spring with 1/16-inch wire for better steering.

Wings and tail are conventional balsa, spruce and plywood construction with the components in their approximate scale positions. The four ailerons were not done in the corregated skin method used on the full-size planes. There were 34 corregations in 67 inches, about two inches per corregation.

The interplane struts were made from streamlined aluminum tubing, epoxied together. The ends were carefully flattened, bent to the correct angle and drilled for the No. 2 screws that attach them to the wings. A simple jig was used to hold the wings in correct alignment while the struts were being fitted, This is a fussy, but most necessary procedure to assure true alignment. A quarter-scale version would need stronger strut construction since they would be fully functional with the four removable wing panels.

The fuel tank extends from the fire-wall to back of the instrument panel. It is easy to look down through the windshield to check the fuel in the tank. A streamlined Robart fitting on the upper right side aft of the cowling connects the tank fuel line through the fitting to the carburetor. Thus, the tank can be filled without disconnecting the fuel line at the carb.

The radio switch and charging jack are mounted on a ply panel on the left side above the lower wing leading edge. The jack must be on the outside skin to charge the airborne pack..."

Direct submission to Outerzone.

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