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Trim and Stability of a Twin‐Lift System in Forward Flight

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A detailed three‐dimensional model of a twin‐lift system has been derived. The system includes two helicopters, spreader‐bar, load and cables, connecting all the bodies. Nonlinear equations of motion of the entire system were used to obtain a system of nonlinear algebraic equations describing trim. Another system of linear differential equations described small perturbations about that trim. It is shown that the equations of trim form an undetermined system, and so additional conditions are required to define a single solution. This presents an interesting problem of optimizing trim. Stability analysis of the trim positions indicates that the root locus of the various modes is complicated and requires physical insight into the system's behavior. The flight of the system is complicated by unstable modes across the entire range of air speeds.

Document Type: Research Article


Affiliations: Faculty of Aerospace Engineering, Technion—Israel Institute of Technology, Haifa 32000, Israel

Publication date: April 1, 2005

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  • The Journal of the American Helicopter Society is the world's only scientific journal dedicated to vertical flight technology. It is a peer-reviewed technical journal published quarterly by AHS International and presents innovative papers covering the state-of-the-art in all disciplines of rotorcraft design, research and development. (Please note that AHS members receive significant discounts on articles and subscriptions.)

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