Study of slat deflector geometric parameters effect on the aerodynamic characteristics of transport aircraft horizontal tail

Abstract

In modern aircraft, high-lift devices is widely used. It makes possible to improve maneuvering, take-off and landing aircraft characteristics, increase its payload and increase flight safety. The high-lift device of the wing increases the total lifting force, both by increasing the lifting force of the wing main part, and by the lifting force which is provided by elements of the high-lift device.However, powerful high-lift device of the wing can affect the work of the tail stabilizer. Slit retractable flaps increase the curvature and the area of the bearing surface of the wing. However, when applied, there is a fluctuation in airflow, resulting in a stream falling to a horizontal stabilizer at a certain angle, which in this case reduces the angle of attack of the stabilizer, and which may exceed the critical angle. The way out of the situation is the use of a slat deflector, which can ensure the elimination of the airflow breakdown on the stabilizer and increases the critical attack angle of the horizontal stabilizer.Slat deflector is an element of high-lift device of the front edge of the horizontal stabilizer. Deflector forms a slot, with the same principle of action, as in the regular slat of the wing. However, as a rule, a slat deflector of the horizontal stabilizer is designed to create a negative lift; the deflector slat is directed to prevent the breakdown of the airflow on the underside of the stabilizer.The effect is to increase the critical angle of attack. As a result, airflow breakdown on the lower surface of the stabilizer occurs at a larger angle of attack.In the closed position, the slat deflector should fit into the stabilizer profile to reduce the value of the drag coefficient. In the working position between the slat deflector and the forehead of the horizontal stabilizer, a profiled slot is formed. It provides an increase in the velocity of the steady airflow on the lower surface of the wing, resulting in the delayed development of the airflow breakdown, which occurs on larger angles of attack. That way we improve take-off and landing performance of the aircraft.The basis of the geometric parameters that most affect the aerodynamic characteristics of the slat deflector is the local chord of the deflector, angle of the deflection, relative height of the slot and overlap. During the research, the optimal geometric parameters of the slat deflector were selected, providing the maximum critical angle of attack.For comparison: the critical angle of attack of the stabilizer with the slat deflector is –19˚, while the same parameter for the profile without the use of the slat deflector is –11˚ with an insignificant increase in the drag coefficient. The difference is 8˚, so we can confidently say that the result exceeded expectations. Therefore, it is recommended to use an wind tunnel in the future, in order to confirm the results of computer calculations experimentally.One of the live examples of the aircraft, where the slat deflector can significantly improve the stability of the horizontal stabilizer to airflow breakdown is An-32 - Soviet military transport multipurpose aircraft.Upon modernization of existing aircraft, we will deal with restrictions on the size of the deflector. The size of the chord of the deflector is limited by the distance between the front longeron and the leading edge. On the other hand, in this case it is difficult to provide sufficient strength and stiffness of the construction at a large length with a relatively low height of the deflector profile. Prolongation of the slat deflector for the longeron can be implemented by reducing the height of the stabilizer longeron. However, this is undesirable.Thus, it can be assumed that the relative length of the chord of the slat deflector should not exceed 20% of the chord of the initial profile.The obtained results of the research can be applied by design bureaus in the creation of aircraft with powerful high-lift devices, as well as for the modernization of existing aircraft.