However, let us assume that a forty horse power motor is available, our 300 square feet of surface may be put into two planes, each having 150 square feet of surface, which would make each 5' by 30' in size; or, it may be decided to make the planes narrower, and proportionally longer. This is immaterial. The shorter the planes transversely, the greater will be the stability, and the wider the planes the less will be the lift, comparatively. RULE FOR PLACING THE PLANES.--The rule for placing the planes is to place them apart a distance equal to the width of the planes themselves, so that if we decide on making them five feet wide, they should be placed at least five feet apart. This rule, while it is an admirable one for slow movements or when starting flight, is not of any advantage while in rapid flight. If the machine is made with front and rear horizontally-disposed rudders, or elevators, they also serve as sustaining surfaces, which, for the present will be disregarded. Lay off a square A, Fig. 49a, in which the vertical lines B, B, and the horizontal lines C, C, are 5' long, and draw a cross D within this, the lines running diagonally from the corners. Now step off from the center cross line D, three spaces, each five feet long, to a point E, and join this point by means of upper and lower bars F, G, with the upper and lower planes, so as to form the tail frame. _Fig. 49a. Rule for spacing Planes._ As shown in Fig. 50, the planes should now be indicated, and placed at an angle of about 8 degrees angle, which are illustrated, H being the upper and I the lower plane. Midway between the forward edges of the two planes, is a horizontal line J, extending forwardly, and by stepping off the width of two planes, a point K is made, which forms the apex of a frame L, the rear ends of the bars being attached to the respective planes H, I, at their forward edges. _Fig. 50. Frame of Control Planes._ _Fig. 51. and Fig. 52._ ELEVATING PLANES.--We must now have the general side elevation of the frame, the planes, their angles, the tail and the rudder support, and the frame for the forward elevator. To this may be added the forward elevating plane L, the rear elevator, or tail M, and the vertical steering rudder N. The frame which supports the structure thus described, may be made in a variety of ways, the object being to provide a resilient connection for the rear wheel O. Fig. 52 shows a frame which is simple in construction and easily attached. The lower fore and aft side bars P have the single front wheel axle at the forward end, and the aft double wheels at the rear end, a flexible bar Q, running from the rear wheel axle to the forward end of the lower plane.