A model made on these lines will not need putting at any angle. It will assume its proper angle when left to itself by reason of its design and the way the weight is balanced between the supporting planes, and it will descend by partly gliding and partly parachuting at a steep angle but quite slowly. While, if the pilot so choose, he can, by raising the tail, increase the speed to a glide, which he can turn into a parachute action at any moment.
CHAPTER VI.
THE DESIGN WHICH FULFILS THE CONDITIONS.
In constructing any sort of machine it is usual to first obtain the most important device and then to build up the accompanying parts to that. We have now succeeded in evolving the thing we set out to look for, i.e., a plane which will fly and lift with the minimum of head resistance, and which is absolutely stable laterally and longitudinally by reason of its construction and without any interference from the pilot or the employment of balancing devices of any description. We have now to fit the propelling apparatus, car, and chassis on to this.
Fortunately, the design is one that lends itself easily to manipulation, which is not always the case with models. The short span of the planes, for instance, with the dihedral angle, at once suggests girder construction (see Figs. 29, 30), which is, perhaps, the strongest of all devices, being an M strut girder, familiar to us in numberless bridges.
Fig. 29. and Fig. 30.
The photo which forms the frontispiece of this book, and which, by the way, makes the car look much too large owing to its position nearest the camera, represents a 6-foot model which was exhibited at the Olympia Show, in order to show the construction of a full-sized machine made to the design of the paper model. This has since been considerably simplified, though the broad lines have been retained, by doing away with the struts and supports at the rear. The whole of the back plane is now supported by two curved members, which start from the girder of the leading edge and curve down to the T-section longitudinals which form the rigid part of the chassis. These longitudinals and the skids end at the leading edge of the back plane and the laminated skids and wheels are placed there. The machine is built without a wire and without a casting. It was made entirely of wood, but is so designed that it can be made entirely out of steel tube by using the ordinary screw connexions. If built of timber, the joints are made with strips of steel bolted and screwed on to the wood. The girders forming the leading edge of each plane have sockets formed in the upright struts of the M into which the ribs fit (see Fig. 30), and these are solid pieces on edge tapering to the trailing edge, where they are clipped to a slight spar which holds them together. This construction, while very strong, is yet sufficiently flexible to bend considerably before it reaches breaking point. Longitudinal rigidity is secured by means of the triangular duct which forms a complete girder from end to end. A sufficient number of uprights fill the space between the plane and the two T-section longitudinals which form the rigid bottom of the machine. On these latter the floor is placed and the car is built up, enclosing all the obstructions and putting the pilot in a place of safety, enclosed on all sides in the middle of the strongest part of the machine, with the strongest portion of that part between him and the ground. The centre of gravity is situated behind the pilot in the back of the car, near the floor, and here is space for the oil and petrol tanks. The engine is in front of the pilot, who is thus able to control it and watch it, and at the same time is free from the danger of having it fall upon him in case of an accident. As the machine turns horizontally and vertically on its centre of gravity, the front part of the car forms a sort of baffle or blinker for the rudder and elevator to act against. Both these are at the tail of the machine, where they have the most leverage, and these two are controlled by the one lever, which is pushed forward or pulled backward to raise or lower the elevator, and turned bicycle fashion to move the rudder. As the machine balances itself, there is no need for any balancing device either automatic or controlled.
