Stresses computing in the main rotor blade based on the nonlinear loading model under static wind impact

Аuthors

Kargaev M. V.

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

e-mail: kargaev_mv@mail.ru

Abstract

Wind is an important factor collateral to the helicopters operation. Due to a number of aeroelastic characteristics specifics, the non-rotating helicopter blades are sensitive enough to the wind impact. With this, the level of loads, acting on the blade, is commeasurable with the loads acting in flight. Traditionally, with high wind speeds mooring is employed to ensure the blades safety in parking position. It represents a flexible wire rope, which one end is fixed to the blade mooring unit, located as a rule at the blade tip section, and the other end is attached to the mooring node at the fuselage, or chassis of the helicopter. It represents a flexible wire rope, which one end is fixed to the blade-mooring unit, located as a rule at the blade tip section, and the other end is attached to the mooring node at the fuselage, or chassis of the helicopter.

The non-rotating main rotor blade according to its characteristics relates to flexible rods with deflections within the elastic deformations of the material commensurable with their length. This stipulates the necessity to consider the problem of the moored blade wind loading in a nonlinear formulation.

In this article, the parameters of the stress-strain state of the blade required for the mooring efficiency analysis are obtained based on a nonlinear model, which accounts for both geometric and aerodynamic nonlinearities. Computational algorithm for the initial nonlinear equation solution of the blade loading, developed based on the V.V. Petrov’s method of successive perturbation of parameters of was realized. The static loading is being considered as a process, developing at monotonous increasing of the loading parameter. The interval of load changing via its step- by-step application with small increments is split by steps, and for each step the linearized boundary value problem is being solved.

The blade deformed state, obtained in this manner at the current step, is assumed as the initial state for the next loading step. For error correction at each loading step, an iterative process is used, which allows performing calculations with a given accuracy.

The mooring effectiveness analysis was realized based on the computations performed for the moored and non-moored main rotor blades of the Mi-8 helicopter. The article presents the dependencies of critical gliding angles and limiting, under the strength condition, wind velocities values corresponding to them.

The article presents the dependencies of critical gliding angles and corresponding to them limiting, under the strength condition, wind velocities values. It also presents the dependencies of limiting velocities at the condition of a swaying absence condition on the characteristic section installation angle for the modes of blowing from both front and rear edges. The optimum installation angle, at which the range of safe wind speeds for the main rotor as a whole was the largest, was determined. This allows recommending to set the angle of the total step equal to the optimum one while a helicopter parking.

Keywords:

main rotor blade, wind loading, static strength, method of successive perturbations of parameters

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