Some interesting experiments have been made by placing several vertical surfaces above the main stability plane. A series of four or six vertical rudders are sometimes spaced apart at equal distances, extending from the front to the rear edge, with a height of about half their length. In some cases the corners are rounded off, while others prefer to cut away the front edge sharply. In the Vinet monoplane, the vertical fin appears in an entirely new form. The fin is attached near the outer edge of the main plane and the upper edges curled inward, forming an arc of a circle. The theory of the curve is that it tends to keep the air from slipping off the ends, after the manner of the curtains of the Vaison biplane. As a rule, these curled fins are about three-fourths the depth of the plane and are attached with the front ends on a line with the entering edge of the plane. These curled planes may be stretched on frames of light wire or thin reed. As the model tilts to one side, the air striking the curved surface of the outer side of the fin meets with little resistance, while the fin at the opposite side, acting with its concave surface against the wind, offers considerably more resistance, thus tending to check the side motion and bring the aeroplane to an even keel. An effective form of aileron consists of an "L" shaped plane set closely against the rear corner of the main wing. These ailerons are made in pairs and hinged to a rear edge. The side should extend about half the width of the plane. The action of the hinged plane at the rear is, of course, familiar. The extension at the side, which should be kept rather narrow, not more than one-fourth the depth of the main plane, is likely to prove very efficient. If the aileron be turned too far either up or down it will offer considerable resistance. In one of the new English models, these ailerons are so connected that as one rises the opposite aileron is lowered. Here is a fascinating field for experiment in automatic control. The vertical rudder used on the new Bleriot, the result of an immense amount of experiment, suggests interesting possibilities for the model builder. The rudder is built in the form of a long triangle and is mounted by hinging one of its shorter sides to the upper surface of the rear plane, so that its corner will extend upward and outward. In this position it suggests a fish’s fin. The receding angle of the front edge offers very trifling resistance. The new Baby Wright racer depends for its lateral control largely upon a novel form of rudders known as "blinkers." These rudders are triangular in shape and extend out in front of and below the forward planes with their longer edges forward. They act much the same as the jib of a sailing vessel, and, because of their position well in front of the center of gravity, act with considerable leverage.