DH Tiger Moth (oz4494)

About this Plan

DH Tiger Moth. Rubber scale model biplane. 44in wingspan, scale is 1/8.

Quote: "A 1/8th Scale De Havilland Tiger Moth, by Rupert Moore.

The accompanying colour and flying photographs by our chief photographer Mr DBM Wright, splendidly illustrate the scale appearance of this unique model. Its authenticity both in flight and appearance are a pleasure to observe. So difficult is it to differentiate between the model and its full sized counterpart that we would mention here our cover painting. This is in fact a view of the origrnai machine over the Wirral Peninsular, Cheshire and, together with the photographs, will we hope tempt readers into building one of the finest scale models the Aeromodeller has yet published.

The model here described is a second and greatly improved version of the original appearing in Plans Service in October 1943, and incorporates the ' Moore Diaphragm,' a self-adjusting tailplane, a 'knockoffable' false nose and airscrew, and other unusual features. In order to deal fully with certain features l shall have to skim over the more usual portions.

The Structure. The centre-section struts are the key unit of this biplane, and, therefore, the top longerons are cut to allow them to continue unbroken to the bottom of the fuselage. The joints are reinforced with ply biscuits. The two sides, complete with centre-section struts, are built on a board and then assembled with temporary spacers in the top. Aft of the pilot's cockpit the stringers are braced with 3/32 sq balsa after being fixed.

The Wings. Dihedral and sweep-back differs on top and bottom wings, so sweep-back is built into wing peg boxes and dihedral into the wing pegs themselves. These peg boxes are wide to prevent breakage of pegs. The interplane struts are hinged in such a way that the top plane folds on top of bottom for transport.

The Undercarriage. The undercarriage is a structure of piano wire, faired with balsa. Every joint should be tinned first, bound with fine copper wire (fuse wire) and soldered solid. The rubber band shock-absorbers pass through two holes under the motor cowling to a wire saddle, located through two holes, at the bottom of bulkhead No.1. These rubber bands are tied with thick thread to their attachment loops on the undercarriage. Note - the holes under the cowling are much closer together than
their attachment loops, which causes the rubber to absorb much of its own backlash.

The wheels are my usual laminated paper structure (so is the pilot). A half model of the wheel is turned in wax or plasticine attached to a 1 in oversized disc of plywood, through the middle of which is a bolt to facilitate holding in the chuck of a lathe or twist brace. The brace, if used, is held in a vice and convenient sized boxes used as tool rests. When the half wheel is finished, a cardboard wall is stuck round the edge of the plywood.

Fine plaster of Paris is mixed; about 2-1/2 desertspoons to 2/3rds large cup of water, added by sprinkling into water. A film of plaster is brushed over the half wheel to prevent bubbles, and then the whole poured in. When set, remove from plywood and carefully remove model. With very slow heat, the mould should be dried out, painted, and when dry, greased. The pressing is made from five layers of newspaper, the first being soaked only in water, and the others in Gripfix. Press from the middle outwards and over the edge like a hat brim (all five layers). Gripfix the inside, press in second layer and Gripfix - third - fourth and fifth.

After three or four hours, temporarily fill back of pressing with plasticine and turn out and allow to dry hard. On no account use artificial heat. When dry, banana oil inside and out and cement thick celluloid washers inside and out of hub. Lay pressing on its 'brim,' 'crown' upwards, and with razor blade flat on brim, trim off.

Make and cement a balsa hub inside one of the pressings and allow to dry. Cement the edges and hub end and bring the two halves together. Thread on an axle, and, by twisting the pressings, adjust till wheel spins true. Edges can be pinned temporarily. Over the joint paste 1/4 in strip of newspaper and over that again a black bias binding tread, using 50-50, Durofix and banana oil. Give four coats black dope. Remember when making moulds or taking pressings, vaseline prevents sticking.

The Gearbox and Nose Block. The gear box and false nose are separate units, joined by powerful spring clipps. The propeller shaft is cut in halves in order that the whole false nose and airscrew can knock off in case of obstruction. The rear half engages the front half of the propeller shaft by means of a simple fork and T-piece. Gears are used to throw the rubber motor below the internal structure.

Step-up gears were tried but found a disadvantage. The lower shaft has 1/16 in (or more) forward travel and is spring loaded. The top of the spring is so shaped that it comes into contact with a curved T-piece on the end of the top shaft, as tension dies away, the curved ends of this locking plate allow the spring to ride over it for several revolutions.

The Rubber and 'Moore Diaphragm' (Patented). To overcome the necessity of ballast, I have evolved a method of installing the rubber so that a greater mass of rubber is in the front half of the motor. This is simply done by fixing a bulkhead or diaphragm, at right-angles to the rubber line, halfway between the front and rear rubber anchorages. In this diaphragm is a circular hole in which is located a circular plug, through the centre of which is a shaft running in a brass bush. This plug is free to dislocate and locate itself when winding and does so without help automatically.

A very much overlength motor is divided into two unequal skeins (ratio about two to one), but containing an equal number of strands. These skeins are pre-wound and attached to the plug, the long skein in front and the short behind. The attachment is by means of pig-skin (soaked in castor oil) stitched firmly to the plug shaft ends and similarly to gearbox and tail shackle. When wound and nose block is in place, the plug prevents the short skein pulling the long skein through the diaphragm: hence there is twice the weight in front of the diaphragm. The leather ends prevent all rubber bunching..."

Quote: "I have been looking for it and finally located it. The article was called 'A Tale Of Two Tigers' and came with both plans, republished in the April 1985 Aeromodeller... Have scanned them again at a high resolution and posted here to make the article more understandable. Both have a wingspan of 44 inches. Enjoy the 'Tiger' feast."

Note this plan was originally published in Dec 1946, this here is a later 1985 reprint.

Update 09/11/2018: Added article, thanks to RFJ.

Supplementary file notes

Article.

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