1979-02-01

Multi Rotor Options For Heavy Lift 791089

This paper reviews some previous and current helicopters designed for heavy lift. Technology status is also reviewed and the problem of arrested development is shown to be in part due to the economics of insufficient utilization. Nevertheless, both military and civil needs are discussed and are projected to grow. A possible resolution of this utilization dilemma is suggested via tri rotor and quad rotor variants of the tilt rotor family of V/STOL aircraft. Multi (greater than two) rotor dynamic systems are projected to weigh less than twin rotor systems and are therefore a way of avoiding rapid design disc loading increases in an attempt to maintain productive vehicle weights. In addition, development risk, investment, and logistic costs are minimized if dynamic components are planned or in use on a smaller aircraft with high production potential. The current paper compares three and four rotor, tilt rotor V/STOL aircraft with an advanced tandem helicopter. All have four engines. The multi rotor V/STOL aircraft use turboshaft engines in the power class of the recent Navy subsonic V/STOL and Maritime Patrol Aircraft studies. Some design considerations discussed include: safety, aeroelastic stability, external noise, downwash effects, handling qualities and performance. New capabilities projected include lower-risk dynamic system development, payload-range characteristics and mainly, productivity impact. It is shown, for example, that the multi rotor option can service four times the revenue-producing territory (or theater of operations) per day than an advanced tandem helicopter. Recommendations are to pursue configuration research through design studies and analyses, scale model tests of aerodynamic interference, aeroelastic effects and dynamic load distributions. A potential subscale flight test with four XV-15 rotors and transmissions is suggested as a simulation of the development concept.

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