Peanut Scale : Walt Mooney : B.A.T. Baboon [This article was published in the June 1975 issue of Model Builder magazine.]

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Peanut B.A.T. Baboon

Did someone write a recent article about using weird names for airplanes? They were almost 60 years too late! The B.A.T. Baboon indeed! Another wild Peanut and some special hints by … WALT MOONEY


B.A.T. Baboon Walt Mooney
It would seem that someone designed this airplane for modelers first, and the built it full size. Lots of area, wide landing gear, simplicity. Photos by Fudo Takagi.

There are a lot of different reasons that one can have for selecting a particular airplane to be made into a Peanut Scale model. Because Peanut Scale models are limited in span, it is desirable that that the design have relatively low aspect ratio wings, in order to obtain the largest possible wing area. This airplane meets the low aspect ratio criteria, and has two wings. The design should have a fairly long tail moment, which this design also has. For good R.O.G. takeoffs, it should have a stable landing gear arrangement. This aircraft probably has the widest track landing gear of any WWI airplane (Or of any other era, for that matter! wcn). Some dihedral is also desirable.

Of course, the real reason a design is selected to model may be different from all of the above. In 1918, the British Aerial Transport Company constructed their Type F.K. 24, (“F. K.” for Frederick Koolhoven) and gave it the name of “Baboon.” What better reason to build a model than the fact that its name is unforgettable? Therefore, here is a Peanut Scale model of the “B.A.T. Baboon.”

The basic design was meant to be a very simple-to-build, easy-to-rig, and simple-to-maintain, trainer. This tends to make for a simple model. The model is simple with the exception of the dummy seven cylinder engine. With the availability of Williams Brothers plastic cylinders, even the engine is not difficult to make.

B.A.T. Baboon Walt Mooney
Long tail moment adds to stability, promotes smooth flight. To get the proper coloring, Walt dyed his own tissue. Explained in text.

The fuselage is constructed by first making two side frames directly over the plans. The side frames to be constructed are shown hatched, for clarity. The very first bay of the sides is filled with sheet balsa. When the cement is dry, remove the sides from the plans and carefully separate them. (If desired the frames can be built separately, but I find they are more apt to be exactly alike when I build them at the same time.) Now cement the two side frames together at the extreme aft end. Set this assembly above the top view of the fuselage so the correct angle of the sides at the tail post is obtained, and let it dry thoroughly. Then add the horizontal cross braces at each station, moving toward the nose. Note that the longerons will have to be cracked at the first station forward, in order to give the sharp corner.  Everywhere else, the longerons will bend enough to take care of their change in direction.

When the basic box structure is complete, the top formers, “A” through “F” can be added. Cut the 1/8 sheet bulkhead, “A,” and cement it into the nose of the box so it is just flush with the front end. Use soft, flexible 1/32nd sheet balsa to cover the upper deck of the fuselage, and carefully cut out the cockpit openings. Add 1/16th by 3/16th cross braces across the bottom of the box at positions in line with “B” and “B.” These are cemented to the normal 1/16th square crossbraces and to the uprights and will provide some structure between the roots of the lower wings.

The horizontal and vertical tail are simple structures, built directly over the plans, using 1 /16th square sticks and corner gussets cut out of 1/16th sheet balsa. Remove from the plans and carefully sand the outlines to a half rounded section. Don’t omit any of the gussets, they are essential for keeping covering wrinkles from occurring.

B.A.T. Baboon Walt Mooney
How to get 48 legal square inches of wing area in a Peanut … build a Baboon!

The wings are conventional structures, using notched ribs, leading and trailing edges, and two top surface spars. The tip pieces are 1/8th square balsa. Again, note and install the gussets. Cut four root ribs from 3/16th sheet (or cut out twelve from 1 /16th and laminate them three at a time to give the correct thickness). Cut out twenty-one of the regular ribs from 1 /16th sheet.

Pin the leading and trailing edges to the plan. Cement the ribs in place. Cement in the tip structure and the gussets. Add the two spars, by cementing them into the appropriate notches. After the cement is dry in the rib notches, cut the spars to exactly fit at the tips and cement them in place. The spars should be flush with the top of the tips.

The lower wings end just at the inside of the root ribs. The top wing has a centerline rib. This is cut off even with the back of the aft spar and a triangular cross-section piece of balsa is used to fill in between the root ribs. The dihedral break for all wings is located at the outside of the thick root ribs. Carefully cut the outer panels free of the roots and reassemble the wings with 5/16th inch dihedral under each tip. Taper the ribs to give a good fit.

When the cement is dry, sand the leading and trailing edges to the rounded and tapered cross-sections shown. Wing tips are also rounded.

Use lightweight tissue for covering all the components. To get an approximation of the right color for the upper surfaces I used “Brown” and “Olive Green” RIT dye, dissolved in rubbing alcohol, to dye a sheet of plain white tissue.

To dye tissue, you first have to make a frame to hold the sheet that is to be dyed. Cement one together out of 1/4th by 1 or similar balsa, like a picture frame, and cement your sheet of tissue to it. Pull it as tight and smooth as possible. Then spray the dye onto the tissue as evenly as you can. If you have no spray gun, it may be possible to dye the sheet using a cotton wad wet with dye, but much care will have to be exercised.

After the parts are covered, use a light fog of water to tighten the tissue. A single coat of clear dope (thinned about half and half with thinner), was applied all over, and then a second coat was applied to the fuselage. If you can get decals for the insignia, use them. If they aren’t easily available, now is the time to paint on the roundels.

B.A.T. Baboon Walt Mooney
The extremely wide landing gear tread shows up well when seen from this angle. Williams Bros. cylinders used to make the engine.

Assembly of the major components can proceed after the struts are made up. The struts on the B.A.T. Baboon are of round cross-section, not streamlined, and can be made from lengths of 1 /16th diameter dowel. Drill a small diameter hole through each end of the struts. This hole is used after assembly of the wings to facilitate the installation of the rigging. Cement the tail parts in place on the fuselage. Now cement the lower wings to the fuselage sides. Make sure they are accurately in the right place, and block up the tips to give the correct dihedral. Cement the four cabane struts in place on the top of the fuselage. A small hole will have to be cut into the top decking to accommodate each strut. Note that the rigging holes should be arranged to li ne up in a spanwise direction. Now careful y cement the top wing in place on the cabane struts. Look at the model from directly above and make sure the top and bottom wings are aligned.

When the cement holding the struts in place is dry, install the rigging, using 2 pound test monofilament fishing leader to represent the wires. Drafting tape is handy to hold the loose ends as the rigging is threaded through the holes. When al l the rigging is in place, check the wing alignment and get it correct. Then put a small drop of cement at each of the strut holes to hold the rigging permanently. When dry, trim off all the overhanging ends.

Cut the tail skid and the two main Ian ding gear legs out of 1/32 ply. Bend the main gear axle from 1/32nd diameter music wire. Cover the inverted “V” portion of the wire with 1/16th diameter spaghetti tubing to give the axle the right diameter. Cement the wire in place in the bottom of the fuselage. Add a filler to the bottom of the first bay of the fuselage to reinforce it. Cement the tail skid in place. Slip a wheel over each end of the axle wire and cement the gear legs in place on the bottom of the lower wings. A washer and a drop of cement can help retain the end of the axle in the leg.

Now make up the dummy engine. The crankcase is a piece of block balsa with the grain parallel to the airplane center line. Use the front view to get the seven sides accurately carved. Cut the square hole to fit the thrust bearing. Install the cylinders by making a hole to fit the thrust bearing. Install the cylinders by making a hole to fit the base of each cylinder exactly in the center of the seven faces. Add a circular balsa cylinder head to each one and use cut-off straight pins to simulate the valve lifter rods. Much more detail can be added to this engine if you have access to a copy of the 1919 Janes, which has a picture of the engine, as well as the three-view of the B.A.T. Baboon.

The fuel tank is wrapped up out of three pieces of bond paper. The ends can be carved from block balsa, and the center can be wrapped out of bond paper. Paint it silver and cement it in place on the wing.

Before flying your model, make sure it balances somewhere near the C.G. shown on the plans. Look at the wings and make sure that you have about an eighth of an inch of washout at each tip. This can be instituted by holding the wings in the correct position and holding the airplane over a source of heat which will shrink the loose wires and hold the wing permanently twisted with the correct washout. Too much heat will break the wires, so hold a bare hand between the heat source and the model. When it hurts, remove everything from the heat source.

This is a rather large, draggy model for a Peanut Scale, and it requires a bit more rubber to fly than you might expect. The original was powered just about right for outdoor flying with a single loop of 3/16th Pirelli, about 12 inches long. Have fun.

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