Model aircraft wing mounting Angle and pitch stability

The movement of the model aircraft around the horizontal axis (the imaginary axis of the center of gravity along the direction of the wingspan) is called pitch movement. The performance of the aircraft in flight that can automatically recover after being disturbed in the normal pitch state is called pitch stability. In normal aircraft aerodynamic study "pitch stability degree" is commonly used to reflect the pitch stability is good or bad, it is the plane pitching moment change with Angle of attack flight of an one ordered derivative of A function, its calculation and determine the many factors of involving the plane itself, and is very complicated, for ordinary model aircraft enthusiasts didn't have much practical significance, so we are commonly used in model aircraft pitch stability coefficient of A prone to reflect the plane: pitch stability A prone = S tail, tail L/S machine, b. In the formula, S tail is the horizontal tail wing area, S is the wing area, b is the chord length of the wing, and L tail is the distance from the pressure center to the center of gravity, which is called the tail moment arm, as shown in figure 1. In the figure, the distance from the pressure center to the center of gravity of the wing is represented by L engine. To avoid complex entanglement of theory, we will not enter the introduction of "aerodynamic center" is the concept of "focus", in order to make the discussion of the problem more intuitive simple, general airfoil wing, normal flight can be thought of pressure center in front of 35% to 40% of the position, Angle of attack flight reduced pressure center backward-shift, Angle of attack increases pressure center forward, while the aerodynamic center positioning on the wing surface from the front at 25% is a constant.

Why does a flat tail ensure stable pitching? The general explanation is that the plane's tail is far from the center of gravity and there is a long tail moment arm L tail. Once the plane raises its head, the Angle of attack of the plane tail increases and the lifting force increases. Under the coordination of the long tail moment arm, a lowering moment greater than the effect of the wing raising is generated, so that the plane can return to the original normal flight state. And vice versa. However, since torque is composed of force and moment arm, it is impossible to obtain sufficient recovery torque if the lift added by the flat tail is small. It can be seen that the stabilization effect of the flat tail is crucial because it should have a large enough increase in lift when the Angle of attack increases.

To make flat tail in the Angle of attack increases when can have a big enough, the addition of the lift, the key is must make the aircraft in flight wing's lift coefficient is large enough to lift coefficient, this is done by flying Angle of attack of the wing to the tail of the Angle of attack, and the Angle difference is installed by the wing Angle of big to end Angle guaranteed.