Twelf (oz16858)

About this Plan

Twelf. Free flight sport bipalne model. Wingspan 38-1/2 in, for OK Cub .049 engine.

Quote: "A 38-1/2 in wingspan free flight biplane for small engines. Twelf, by Eric Marsden.

We all have, or have had, Frank Zaic Yearbooks and similar works, over which we have tended to sit and daydream of maybe's and one day's. Frank Ehling's Elf Biplane (oz4724) has always been one such of mine, among others of similar vintage. So when a couple of years ago Bob Schlosberg sent me shots of his latest, an Elf powered with a Cox Pee Wee, converted to CO2, and looking as Bob's models always do, a sure-fire Concours job, I was hooked once again.

Between Bob Schlosberg and myself, however, there is a great gulf fixed - he is an undoubted artist as to building and decorating - I am by comparison a plumber, an aeromodeller for the working day. If it's not needed, I don't fit it. Cover well enough for a good flying life - waste little time on decoration.

So it was decided that the model would be Elf in spirit, but simplicated - tongue and box fittings for the lower wings are OUT, and replaced by one-piece through wing installed in the usual wing seat, with ugly but very practical rubber bands. Similarly for the undercart -sooner or later U/c's which are built in solidly are apt to meet with the immovable object and bequeath disaster upon their adjacent piece of fuselage, so I went for a good strong set of legs strapped simply into place with more rubber bands. And if packing for transport matters, this is also handy.

From the three-views available, the method of engine mounting was not obvious, but for small engines I prefer the bulkhead mount wherever possible, as being easier to obtain downthrust and right thrust settings - although the standard hardwood beam mounts do make finishing off the fuselage around the nose much easier, in that slabs of balsa are easily applied and shaped, whereas on small models the separate engine mount may leave little room for such building. To date mine still flies with a naked nose - and may never be graced with a cowl - hence the dotted line at the nose on the drawing. Make your own in your own way - which is probably what you would do anyway.

These thoughts established the idea of the Twelf - my version of the Elf. Prepare to be bored! Why Twelf, I have been asked. Well, this would be one after the Elf, and 'elf is eleven in the language of one of our European neighbours - which makes the choice of Twelf quite inevitable. Well, it does to me.

Building notes: As to building the model, the fuselage and wings are simple, straightforward structures, as is the undercarriage. The tailplane seat, and the lower wing seat are made by laminating strips of balsa to the necessary curve, for added strength, but could be cut from sheet if so wished, as could the wing tips. When laminating wing tips, by the way, it is useful to make them from strips tapering in depth from the depth of the leading edge to the thickness of the trailing edge spar - in fact, slightly full, to permit shaping down to a clean, fair joint, and a little full in thickness, to allow for sanding flat and clean on the underside before fitting and shaping to section.

The wing halves are joined by butting the root ribs together with white glue and then wrapping with cloth or bandage, again using plenty of white glue well soaked into the fabric. Where possible, it is better to use fabric 'on the bias' for this purpose, as this effectively doubles the strength of the material across the joint line, but it does require a little more care to get a neat lay.

The tailplane requires the outer frame to be assembled and glued and then, when properly set, raised on to packing blocks to permit the ribs to be set into place. The tips of the mainspar pieces need to be bent or cracked slightly, to allow them to meet the outer tip fairly. The sheeting should be applied to the top side before removing the tailplane and turning over to fit the lower spar and skinning..."

Twelf from Aviation Modeller International, November 1998.

Direct submission to Outerzone.

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