Synthesis of the Blade Trimmer and Flap Individual Control Laws for the Helicopter Main Rotor Spin-Up and Deceleration under the Wind Conditions

Aeronautical and Space-Rocket Engineering


Аuthors

Kargaev M. V.1, 2

1. National Helicopter Center Mil & Kamov, 26/1, Garshina str., Tomilino, Moscow region, 140070, Russia
2. Moscow Aviation Institute (National Research University), 4, Volokolamskoe shosse, Moscow, А-80, GSP-3, 125993, Russia

e-mail: kargaev_mv@mail.ru

Abstract

The main rotor (MR) spin-up or deceleration under the wind conditions at the parking may cause damage of the helicopter blades or tail boom. The criterion characterizing the possibility of safely performing the specified modes of operation of the helicopter is the maximum wind speed, determined by the deflections of the blade end that occur during spin-up or deceleration. Two constructive ways for increasing the maximum wind speed may be distinguished. These are an increase in the stiffness characteristics of the blade in the plane of its lowest rigidity; and the application of the individual blades controls. The first method is traditionally employed in the vast majority of cases, though it leads to an increase in the weight of the blades. The second method is being related to the promising ones and requires solving a considerable number of scientific, design and technological tasks. 
The following means are usually considered as technical means for the blades individual control: controlled tips, flaps and trimmers; rods from a skewing machine with built-in drives; mechanical adders combined with a swash plate; piezoelectric sheaths, allowing to control the twist of the blade.
The presented article considers the similar problems of searching for the optimal control laws for the trimmer and flap of the MR blades. The desired control laws are represented in the form of linear splines, which parameters are being found by solving the identification problem. The vector of observations in the problems being solved corresponds to the deflections of the end of the blade, which occur during the MR spin-up or deceleration in the absence of the wind, and the model of the object is being determined by the equations of bending and torsional oscillations of the blades.
The author proposes to apply a controlled trimmer and a controlled flap in the design of the main rotor blade to compensate for wind disturbances during the spin-up or deceleration of the helicopter main rotor. Based on the adduced technique for synthesizing the individual control of the trimmer and the flap of the blade, a simulation spin-up of the MR under the wind conditions was performed at various values of the relative chords of the controls with a fixed limit on the maximum angle of their deflection.
The author demonstrates numerically that the controlled flap application while spin-up as a part of the model blade is 2.74 times effective for the Mi-171A3 type helicopter than the controlled trimmer application with the same relative chords. It allows increasing the limit wind speed from 18.6 m/s to 25.1 m/s (i.e. 35.1%) at the fixed limitation on the maximum deflection angle.

Keywords:

main rotor blade, wind loading, the main rotor spin-up and deceleration, controlled flap, controlled trimmer, maximum likelihood method, control optimization, modified Newton's method

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