The relationship curve between control surface deflection angle, stick (disc) force or displacement, and related parameters in stable direct flight (flight with zero acceleration and balanced force and moment).
The balance curve includes the longitudinal lift or tail yaw angle at the full motion level, the relationship curve between the force or displacement of the steering rod (disc) and the speed of flight (or the speed of the head or the velocity coefficient). lift) and lateral aileron and rudder deflection when constant linear slip. angle or its control force and the bearing angle ratio curve, etc.
The trim curve is used to measure the static control characteristics of the aircraft and is closely related to the static stability of the aircraft (see aircraft dynamic characteristics). For a longitudinally stationary aircraft, the equilibrium curve of elevator yaw versus speed has a positive slope.
To increase speed on the original straight, in addition to increasing throttle to increase engine thrust, to maintain steady straight-line flight, the joystick must be pushed forward. At that time, the elevator trailing edge deflects downward (rudder deflection angle δ z ＞ 0), causing the aircraft to lower its head, the angle of attack decreases, and the lift coefficient decreases.
At the same time, the flight speed increases and the lift is still in equilibrium with gravity. On the other hand, when slowing down in the original straight line, the steering column must move back. These manipulation actions are in accordance with the physiological habits of the driver and are called normal manipulations.
For statically unstable airplanes, the slope of the equilibrium curve is opposite, and the action of controlling the control stick during acceleration and deceleration is opposite to the aforementioned law, which is called reverse control, which is not in accordance with the physiology of habits. The pilot.
To ensure flight safety, aircraft are generally not allowed to be designed for anti-control. For a neutral, static and stable aircraft, to accelerate or decelerate in the original straight line, it is not necessary to operate the control stick.
According to the rod displacement and force balance curve, certain indicators of static maneuverability and static stability can be checked, such as checking the rod force gradient, maximum and minimum rod force, etc. meet the requirements of the flight quality specifications (see aircraft flight quality).