The potential of employing two or more helicopters for transporting payloads that are too heavy for a single helicopter is a well-addressed issue in the civil and military rotorcraft design arenas [37]. Overall requirements can be satisfied more efficiently with a smaller aircraft by using multi lift for infrequent peak demands. Hence the principal motivation for using multi lift can be attributed to the promise of obtaining increased productivity without having to manufacture larger and more expensive helicopters. A specific case of a multi lift arrangement, where two helicopters jointly transport payloads has been named twin lift. Figure P1.21 shows a typical "two-point pendant" twin lift configuration in the lateral/vertical plane. Develop the block diagram describing the pilots' action, the position of each helicopter, and the position of the load.

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Problems Helicopter I Helicopter 2 Aitachinent point Tether Load FIGURE P1.21 large load. Two hei copters used to lift and move a