Free flight

Fundamentals of Model Airplane Building
A Complete Course for Beginners Who Wish to Become Expert. How to Build an All Balsa Twin-Propeller Pusher Model—Part No. 8
By EDWIN T. HAMILTON

This is the best way to launch the twin pusher

The completed all-balsa twin pusher ready to go places

AS OUR eighth airplane model of this series, Mr. Grant has designed the first twin-propeller pusherto appear in this course. As will be noted, we have kept solely to all-balsa models to date and so the one shown here continues that type of plane. This is done as part of a set program, to fully acquaint the beginner with all types of flying models of solid construction before taking him into the more difficult field of builtup construction. One of the most outstanding features of this model isits exceptional soaring ability which permits it to continue in flight long after normal propulsion by motor has ceased. On test flights, it has remained in the air over two minutes and flown a distance of two thousand feet. With these unusual flying qualities, it nevertheless is of such simple construction that the amateur can easily build it. The use of solid balsa

wings eliminates the tediousoperations of built-up framework, which necessitates a large number of ribs, intricate assembly and the covering of the structure with tissue. It represents the logical step toward contest models of like type and the beginner should find it a stimulating and interesting building problem without the usual expert workmanship being required. Flying the model will bring its builder experience whichwill prove not only valuable but absolutely necessary when tackling the launching, flying and handling of contest planes. It must be kept in mind that the whole worth of this course is to develop the rank amateur into a well grounded, well informed expert. The entire course has been laid out by your editor, Mr. Grant and the writer on this basis. Don't shirk ... don't "skip," and you'll find that wehave lived up to the usual

standards of UNIVERSAL MODEL AIRPLANE NEWS in giving its readers only the best.

A-Frame
In a twin-propeller model of this type, the fuselage is known as the "A-Frame." This is because it is built to the general lines of a capital "A." Such models are often referred to as "twin-stick pushers." They are essentially outdoor models and have set up some of the finestflight records known in the model airplane field. Two balsa sticks, measuring 1/4" square and 36" long, form the framework of the fuselage. These are joined together at the front end and spread apart at the rear or trailing end, by wire. Cut two sticks to this size, sandpaper each carefully and test to see that both are exact duplicates. A miter joint is cut at one end of the sticks, so that whenthey fit together, the trailing or opposite ends will be exactly 10" apart when measured from outside to outside of the sticks. This can be seen in the plans under "Top View." Lay both sticks in proper position and then cement their front ends together. Before applying the cement, squeeze the front beveled ends together and then measure the distance the rear ends are apart. If they are 10" fromoutside to outside,- or 9-1/2" from inside to inside, the beveled ends may be cemented together. Hold them in place with a model pin or a rubber band until the cement dries. Four piano wire braces are used to hold the frame in proper form. The two cross braces and the combination cans and center brace are all bent from 1/32" diameter wire, which is approximately a No. 13 piano wire. The trailingend brace because of added stress, should be bent from 3/64" wire. This is about a No. 21 gauge. If you cannot purchase wire of this diameter, do not use any of less diameter than a No. 16, which is .037". Bend the two cross braces, as shown in the plan under "Cross Braces." This plan is given full-size except for its length which had to be cut down. It is 71/2" long from bend to bend, as shown....