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Comparison of stability and control characteristics of two twin-lift helicopter configurations

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Abstract

The stability and control characteristics of two twin-lift helicopter configurations are analyzed in this paper. In order to address the issue of configuration selection from a handling qualities viewpoint, their open-and closed-loop characteristics are compared. The two twin-lift configurations considered are the twin-lift with spreader bar and twin-lift without spreader bar. The nonlinear models describing the dynamics of these two configurations in the lateral/vertical plane are derived. The open-loop characteristics of the two systems are compared by linearizing the nonlinear models about a symmetric hovering equilibrium condition. The closed-loop characteristics of the two systems are compared using nonlinear controllers based on feedback linearization schemes. The performance of the resulting closed-loop systems in carrying out a typical twin-lift mission is evaluated through nonlinear simulation. Also, the effects of helicopter performance degradation and measurement errors on the overall system performance are discussed.

[B] Matrix multiplying the control vector in the nonlinear model

[B1] Matrix multiplying the control vector in the linear model

[C] Matrix defining vector of variables to be controlled

[C1] Damping matrix

CijElement of the damping matrix

e Parameter used in the linear model = M 1 h 1/I 1=M 2 h 2/I 2,/ft

{f} Vector independent of controls in the nonlinear model

g Acceleration due to gravity, ft/sec2

h1, h2Distance of tether attachment point to the center of gravity for helicopters 1 and 2, ft

h Parameter used in the linear model, =h 1=h 2, ft

h′ Distance between rotor hub and the helicopter center of gravity, ft

h h/l′

H Distance of the load from the spreader bar c.g., ft

H1, H2Length of tethers 1 and 2, ft

IRMass moment of inertia of spreader bar, slug-ft2

I1, I2Roll moments of inertia of helicopters 1 and 2, slug-ft2

k′ Non-dimensional hub control moment coefficient

KDDerivative gains

KIIntegral gains

KPProportional gains

[Ki] Stiffness matrix

KijElement of the stiffness matrix

l′ Parameter used in the linear model, =H 1=H 2, ft

L Spreader bar length, ft

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Authors and Affiliations

  1. School of Aerospace Engineering, Georgia Institute of Technology, 30332, Atlanta, GA, U.S.A.

    Manoj Mittal, J. V. R. Prasad & Daniel P. Schrage

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  1. Manoj Mittal
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  2. J. V. R. Prasad
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  3. Daniel P. Schrage
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Mittal, M., Prasad, J.V.R. & Schrage, D.P. Comparison of stability and control characteristics of two twin-lift helicopter configurations. Nonlinear Dyn 3, 199–223 (1992). https://doi.org/10.1007/BF00122302

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  • DOI: https://doi.org/10.1007/BF00122302

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