Scratchbuilt 1/32 Scale
Wipaire Fire Boss

by Dr Frank Mitchell

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We sometimes get into models in strange ways.

For example, I was idly looking over the magazines at my friendly Barnes and Noble when I spotted this airplane on the cover of Canadian Aviation. 10 seconds later I had decided to build one in 32nd scale.

Thanks to some very kind people at the float manufacturer and the Canadian representative, I was able to obtain drawings and information on the floats, and, along with some more data gathered on the Internet, there was enough to begin.

Before I go into construction, however, I guess I ought to describe the aircraft.

The Airplane:

The Wipaire Fire Boss is a quick response fire-suppression aircraft with an 820-gallon maximum hopper capacity. The airframe is an Air Tractor AT-802 agricultural aircraft. It is powered by a P&W PT6A turbine engine and has a span of 58 feet and length of 35 ¾ feet, making for a 1/32nd scale span of about 22 inches.

Not a small airplane.

The floats and fire-fighting equipment are added by Wipaire, Inc., in St. Paul, MN. Since it is an amphibian, the aircraft can operate as a land-based tanker or, using scoops built into the bottom of the floats, it can pick up water by skimming the surface of nearby lakes and rivers, which would seem to be an interesting technique to learn.

I have attached a number of “in-construction” photos, so feel free to watch the bouncing ball.

The first step of construction was to carve molds for the floats, wings, tail, canopy, and engine/nose. These were vacuum-formed using my old tried-and-true techniques (see photo at right).

The molded floats were cut out and formers installed, leaving suitable openings for the wheel wells and trying to maintain sharp edges where possible. I also tried to make sure to add a former or some other support for the float struts and landing gear mounts.

Click the thumbnails below to view larger images:

The main part of the fuselage (from the engine back) was built up using 60 thou sheet styrene, with attention given to making it as square and straight as possible. A wood block was added to the top rear and sanded to shape.

The fitting the floats to the fuselage was fiddly because of trying to make sure that everything was square and reasonably sturdy. The rear struts are large faired shapes which also contain the water uptake pipes, so each of them were made using a brass wire skeleton with a wooden fairing around the struts. The visible portion of the uptake pipes were made from plastic tubing. All-in-all, lots of trial and error in this area since I couldn’t come up with a jig that wouldn’t get in the way, while trying to keep everything unglued for painting and finishing. Nobody said it would be easy.

The landing gear was made from brass and aluminum tubing (main) and brass sheet/tubing (nose), along with a bit of soldering. The wheels were resin copies of a couple of wheels from the scrap box using a RTV molds.

The two molded halves of the nose were glued onto the balsa molds (for strength and to make mounting it and the prop easier). The nose was cleaned up and keyed to the main fuselage with two pieces of aluminum tubing. Several scoops and vents were molded over balsa forms and keyed to the cowling with brass wire. A spinner was turned from acrylic rod, while the prop blades were made by cutting the basic shape from sheet styrene and then adding half-round strip to the lower section. This was all covered with epoxy and sanded to the proper shape. They were then keyed to the spinner using brass wire.

Click the thumbnails below to view larger images:

The exhaust stacks were made from styrene tubing bent using tube benders and a bit of heat.

The wings were made by gluing (epoxy) the molded wing skins to the balsa molds. The fuselage was prepared for the wings by drilling holes through the structure and supergluing brass tubes that would receive smaller tubes mounted in the wings. The reason I went to that trouble was that the wings are rather long, and I needed all the strength I could get.

The tail was made in the same way as the wings, but supporting struts for the stabilizer were made from brass wire and the small stabilizer and under-fuselage fins were cut from styrene sheet.

All the control surfaces were cut out and re-mounted with brass pins.

The actuators for the ailerons/flaps consist of arms cut from brass sheet, which were then soldered to a piece of brass rod (a photo helps to make sense of that). This was then cut between each arm. They were mounted in the wing by supergluing the pointed ends into small slots cut in the appropriate places on the bottom of the wings. Brass wire was run through the small pieces of tubing into the control surfaces.

When taped together, the model and revealed itself to be a confirmed tail-sitter. That was fixed by drilling a couple of ¼” holes into the balsa core of the engine, and dropping into each of them several lead fishing weights. A drop of superglue was dropped down the hole to keep everything in place.

The top of the main tank was clear 1/32nd plexiglass molded over a balsa form which was trimmed to fit the fuselage and the nose. There is a large vent in the top of the tank to allow over-fill to escape when scooping water. That was made from styrene; a matching hole was cut into the tank top. To get the look I was after, a bit of yellow paint was mixed with brown and thinned probably 80%. A light coat of this was sprayed inside the cover. The point was to make the tank top semi-translucent. The tank interior was sprayed flat black.

The canopy was trimmed and sanded to fit the rear fuselage and the water tank, and the interior was detailed in all the usual ways.

At this point, all the parts were primed and sanded (several times) using automotive lacquer primer. When I was satisfied with the surface, the pieces were scribed as necessary. Mercifully, there wasn’t all that much on this airplane.

Now came the painting process. This is a fairly large model, and it is essentially all gloss yellow, not the easiest color to work with.

The first coat of paint was Testor’s semi-gloss white. Although it covers reasonably well, I really didn’t try to make it flawless. The yellow was also by Testor but was the little square jars of enamel that have been around for a hundred years. I still think it has the finest pigment and is the best there is for gloss (and a lot of flat) paints. In this case, I mixed two bottles of gloss yellow with one bottle of flat yellow along with some lacquer thinner (I wanted a slightly flat surface because of the masking that had to be done). I shot three coats of yellow at one sitting, then two more the next day, adding maybe a half bottle more of the gloss to even-out the thin areas. By using several coats, there was a minimum of lost detail. The bottom line is that white and yellow, particularly gloss, can try one’s patience, and the only solution is several thin coats, giving each ample time to dry.

The next step was the blue and black trim, and for this, I needed several yards of drafting tape. One of those three-hours-to-mask-and-thirty-seconds-to-spray situations.

When that was done, I shot a coat of Future to achieve the high gloss I wanted. From all the pictures I have, these aircraft appear to be kept in pristine condition, so there was no weathering applied.

The decals were mostly from the Master, Mike Grant. He nailed them, as usual. There were a few other small ones that came from the scrap box. Another light coat of Future was shot over the decals as a seal and to make them match the rest of the model.

There was now nothing left to do but assemble the beast. This was one of those models that was very satisfying to finish up. Everything still fit, and I left only a few glue fingerprints on the paint. An accomplishment for me.

When all is said and done, this is a fascinating aircraft and an interesting, if somewhat protracted, project.

Next, I think I might next try a new invention I just heard about; it is called a kit, and all those parts are supplied for you.

Amazing...

Click the thumbnails below to view larger images:

Model, Images and Text Copyright © 2004 by Dr Frank Mitchell
Page Created 17 February, 2004
Last Updated 17 March, 2004

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