Static stability of a helicopter main rotor flexible blade at the parking affected by wind

Аuthors

Kargaev M. V.^*, Mironenko L. A.

National Helicopter Center Mil & Kamov, 26/1, Garshina str., Tomilino, Moscow region, 140070, Russia

*e-mail: kargaev_mv@mail.ru

Abstract

The article is dedicated to the topical issue of helicopter design, namely static stability of an unmoored main rotor blade of a parked helicopter under the wind impact.

The article considers a general case when the wind velocity is directed at an angle to the helicopter longitudinal axis. Velocities and angles of attack of the blocked main rotor's sections are being determined. The authors used experimental data on straight and oblique wings blow-down, as well as circular blow-down of the NACA 23012 profile while determining aerodynamic loads in the blade section, blown by wind flow.

The aerodynamic load, acting in the blade section, is a function of the blade curve, and changes according to the blade's rotation azimuth. Thus, while considering the issue of the blade static stability, the problems on determining the most insecure direction and maximum allowed wind speed of the unmoored main rotor blade under specified position of parked helicopter is solved.

The article considers the blade bending in the plane of least rigidity. The blade torsional deformations are not accounted for while loads determining. It is considered, that the helicopter has main rotor of a common type with hinge mount blades.

Firstly, the solution for the homogenous blade with constant stiffness and aerodynamic characteristics was obtained. The design equation determining the value of wind flow critical velocity in various azimuthal positions was derived. It was established the main rotor blade's stability loss under the wind impact was possible only with oblique blow-down with negative sideslip angles, i.e. when the blade tip position was directed against the wind flow. The wind flow critical velocity minimum value and its corresponding direction were determined. The authors suggest employing the wind coefficient of the blade as a generalized parameter characterizing the blade tendency to the stability loss under wind impact.

Further, the solution for the blade with inhomogeneous parameters was obtained. The value of wind flow critical velocities was obtained by two methods, such as method of straightforward iteration, as well as a method, employing the wind coefficient of the blade.

The article presents the result of the wind flow critical speed computation, performed for MI-8 helicopter main rotor blades, blown-down from the front and back edges.

Keywords:

main rotor blade, wind loading, static stability, critical velocity pressure

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