1/32 scale scratchbuilt
Federal Aircraft Factory (FAF)
N-20 Aiguillon

by Frank Mitchell

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Did you ever build one of those models that fought you every inch of the way? Well, this is one of them. Lots of re-making of things that I screwed up, or glue going into the wrong place, or having to paint the bloody thing twice, etc. Trust me, you are never too old or too experienced to have these things occur, nor is it any less frustrating. However, the fact that this model was actually built at all is a tribute to the great people that inhabit the modeling sites of the internet.

For example, one day, while avoiding doing something constructive, I threw out a question asking if anyone had information on obscure Swiss aircraft. I almost immediately heard from Mike Kirk, a Brit who has lived in Switzerland for many years. He first disabused me of the idea that the airplane is obscure—it isn’t, in Switzerland. From then on, he was a fountain of photographs and help, and I could not have done it without his help. The good news, in fact, about this project is that Mike kept sending lots of good pictures and information. The bad news was that he kept sending me lots of good pictures, which meant that some things had to be redone or modified as the later information became available. There were a few cases (which I will not point out) where the information was too late to be added without tearing the model apart, but for the most part they were included. I had no idea so much information about the N-20 was out there.

Background

For those of you who are, like I was, rather ignorant of this airplane, the N-20 Aiguillon (Sting) was ordered in May 1948, and contained several very new features. Its four British-derived Mamba turbofan engines were buried in the wing, and the cold air from the fans were ducted through additional combustion chambers on each side of the engine. This reheat device, which doubled the normal thrust of the engines, was to be used mainly for take-off and combat. For short take-off and landing, the secondary airflow could be deflected through large slots on the upper and lower wing surfaces. When the lower slots only were open, the deflected air acted as an aerodynamic flap; with both systems in operation, the deflected air acted as a thrust reverser. As a substantial proportion of the air flowed through about half the wingspan, the aerodynamic drag of the relatively thick wing was very low. To extend endurance, two of the four engines could be shut down in flight.

Performance estimates included a maximum speed of 680 m.p.h. at 3,280 ft.; time from 3,280 ft. to 32,800 ft., 2 minutes; take-off run 760 ft. and landing run 777 ft.

The N-20 was designed to have a detachable weapons-bay that could be changed in 10 minutes. Alternative loads were 1,764 lb. of bombs, six 20-mm. cannon, four 30-mm. cannon, thirty-two missiles, cameras or additional fuel. Two 20-mm. Cannon were permanently mounted in the nose. Anticipating the F-111, the pilot was provided with a watertight escape capsule, ejected by an 8,810-lb.thrust rocket.

Due to problems with its engines, development of the N-20 was cancelled in 1952. It was not flown, although it did have a number of high-speed taxi tests and, according to one source, actually did lift off for a short distance.

The model is an excellent example of the old adage that the simpler something looks, the more complex it can be. Although the lines are lovely, the intakes, along with those curvy engine fairings, the exhaust/bypass outlets, the cockpit, and the landing gear all combine to make a difficult-to-capture-and-look-decent shape. As usual, the pictures will show most of the construction, and probably better than words.

It seemed impractical and a lot of excess work to build the wing as it is on the airplane, so the drawings were manipulated to make a straight piece. It did mean constant checking to assure that everything would be straight when the wings were finally cut apart, but it made life much easier while getting there.

Once the basic wing was cut and sanded to shape it was formed using my usual technique for big pieces, i.e., clamping the styrene in door hinges and heating and smashing. The main wheel wells were cut into the outer wings and the wells themselves made up from styrene sheet. The skins were then attached to the wings with epoxy. Now the real fun began.

The first thing tackled were the intakes. After some thought, it seemed that the easiest way to get identical, smooth intake surfaces inside and out was to mold them from resin. In order to do that however, one needs a mold. So, on a dull Saturday afternoon, I sat down with a chunk of basswood and drilled, carved, and sanded away. 3 hours later, I had the master seen in the pictures. A mold was made from RTV, and four intakes were made. The appropriate openings were cut into the wing leading edges, but before they could be mounted, I needed to find some engine faces. They are close to the intake lips and very visible. After some prowling through the backlog, I found some perfect ones in the exhausts of a 48th S-3 Viking. I used one of those to make an RTV mold and did four of them (This model was much like a ship in its need for replication; that bloody wing needed either 4, 8, or 16 of everything). Notches were cut into the wings so that the engine faces would be equally spaced behind the intakes, but before they were glued into place, the exhaust and fan outlet areas were built.

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An section was cut from the wings the size of the exhaust areas. The rest is probably easier seen in the pictures than described in words, but basically the whole structure was built-up from sheet styrene. Just couldn’t figure out any other way to make sure everything was open and visible they way it should be. Once complete, the two sections were epoxied into the wings, as were the engines and engine faces.

A simple mold was cut from balsa for the main engine fairings and eight of them were heat-and-smashed, cut out, and glued into place on the top and bottom of the wing. Now the entire wing was filled and sanded ad nauseum until everything looked straight and smooth. The control surfaces were cut from the wing, nav lights were put into place, and the wing was ready for the dramatic moment of being cut apart and reassembled at its proper sweep back angle. It was, and everything even lined up properly. Amazing. Riding on that high, I (thankfully) put the wing aside so that the fuselage could be attacked.

The fuselage was vacuum-formed over my usual balsa molds. The nose wheel well was the first opening cut, and the well itself made up from sheet styrene which was painted and detailed.

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The cockpit opening was cut out and lined with styrene sheet. The consoles were made from balsa and also covered with thin sheet. The instrument panel was made in my usual way; a sandwich of styrene backed with clear vinyl and having the instruments white-glued to match the holes in the outer styrene. The control column was made up from various bits and pieces of aluminum tubing and brass wire, and all the usual cockpit detailing was added.

As an example of the earlier statement about this being a complex project, the canopy, of all things, turned out to be a bit of a hassle. For reasons that I assume had something to do with the escape capsule, the N-20’s canopy is attached to a fairing that slides with it as it opens. The fairing is rather thin and, to make life more interesting, the canopy to which it attaches is entirely framed in clear plexiglass. I could have just closed the thing and gone on with my life, but cheaters never win, so after a bit of head scratching, my approach was to carve a basswood mold for the windscreen/canopy and heat and smash several vinyl copies. Then, on the mold itself, a line was drawn which outlined the inside of the inner framework. One of the canopies was cut down to that line, while another was cut to the overall canopy outline. These were then (carefully) glued together with superglue, and the edges sanded and polished. Next, the fairing was cut from sheet styrene and glued to a spacer that was shaped to the bottom of the canopy. This assembly was glued to the canopy itself, and epoxy was used to form the final shape. Involved, but I couldn’t think of any other way to do it.

The windscreen also had its problems, again caused by the ejection pod. There is a clear plexiglass panel at the rear of the screen, covering the area of the arch. From a modeling standpoint, that means that the windscreen is a sealed chamber, and that the fit has to be decent or it won’t look right (or good). This was tackled by taping the windscreen to the fuselage and carefully measuring the distance between the bottom edges. That was then duplicated off the model using tape to make the windscreen have the same shape it would have on the finished model. The arch was then traced onto cardboard and then onto clear vinyl, measuring and shaping all the way. When the fit seemed to be reasonable, it was glued using very small amounts of superglue while trying very hard not to get my fingers as well. The completed windscreen was not actually glued on until the last second before painting began.

Once that was finished, the fuselage was put on the building board and the outline of the wing cross-section was drawn on its sides. That area was removed, and the wing was fitted in place. It was not glued yet; lots to be done before that took place.

Next up was the landing gear, since they are all three trailing link designs, and were made from brass and aluminum tubing with a bit of soldering and supergluing. There was also some basswood used for the nose gear leg shape; it surrounded a piece of tubing that supplied the strength. Other bits and pieces included some square aluminum tubing, and some colored plexiglass (the bottom of the nosegear that was also the pivot for the trailing arm). The wheels were cast in resin using for masters a main wheel from an ancient Monogram TBM (main wheels) and something from the discarded parts stash (nose gear). The gear doors were built up from sheet plastic.

A mold was made for the small wheel fairings that are on the top and bottom of the wing, and eight copies heated and smashed. These were cut out and glued in place, although the bottom ones were applied in several pieces as they were attached to the geardoors as well as the wing. The relevant gear doors also had to be modified to reflect the fairing shape.

Next came the weapons pod. Don’t let anyone tell you that you can’t mold undercuts using a vacuum-forming setup. You can; it just takes a little thought. The mold was carved and sanded from balsa and smoothed using my favorite primer, Kilz. The mold was then vacuum-formed in the same way as the other pieces of the model, just using care and patience to make sure that the plastic is as warm as it will get, short of melting. Then turn on the shop-vacuum, and quickly place the warm plastic over the mold. I also use a pair of soft gloves to make sure the plastic has followed the shape. The result can be seen in the photos. Note that this really doesn’t work very well with sharp-edged shapes, but in this case, the curves of the pod did very well; a bit thin, but useable.

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With all the main components built, it was time for a little priming and sanding followed by scribing of panel lines, hatches, etc. When that was finished (if it ever is), the wings were glued into place, followed by the weapons pod, followed by the fin, with lots of sanding, priming, and scribing taking place between each step.

Natural Metal Finish

The airplane was in natural metal when it was tested, and that I what I decided to do. I did cheat in one respect; I left off the nose test probe. Looks much cooler that way.

I used Alclad, masking off various panels using frisket. The control surfaces, and other small parts were painted with varying shades of Alclad and Testor’s Flat Aluminum. As I said earlier, I completely screwed up paint job #1 and, after letting the thing sit for a couple of weeks, I sanded off all the old paint and started over.

Markings

The decals are few; the Swiss tail marking came from a Hunter decal sheet, and the sweep spear was a combination of paint (forward), and decal sheet (aft). The name was done by the simple expedient of blowing it up to 8.5 x 11, and tracing it with the blackest marker I could find.

When reduced to a little over an inch long, all the jiggly lines disappeared and it was copied on to clear decal sheet. I looked hard at all the pictures I had, but could not find any of the tiny-written so common today. Either it was too small, or I missed it.

So anyway, it is (finally) finished, and it does make an intriguing addition to the collection. For anyone coming to the Atlanta Nationals, it will be on display; just don’t look too close.


 

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Model, Images and Text Copyright © 2005 by Frank Mitchell
Page Created 01 June, 2005
Last Updated 01 June, 2005

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