1273. Tilt Rotor – An Effective V/STOL Concept

Paper

Abstract

The objective of this paper is to answer the following questions:
– Where does the tilt-rotor aircraft fit in the spectrum of subsonic V/STOL concepts?
– What is a mission-oriented tilt-rotor aircraft like; how does it work?
– Why is the tilt-rotor V/STOL an effective concept; what can it do?
– How can an effective concept be turned into an effective operational system?
The approach used includes the following steps: 1) review the variation of hover efficiency, speed capability, and previously determined weight empty ratios for the helicopter, coaxial compound helicopter, the tilt-rotor, tilt wing, lift/cruise fan, and vectored thrust concepts to gain perspective, 2) describe a tilt-rotor design aimed at satisfying Navy/Marine subsonic V/STOL needs, 3) present the projected capabilities of this design to indicate the operational flexibility and efficiency that can be expected, and 4) describe examples of weight-oriented trade-off criteria that can be used to insure selection of effective technology for an operational system.
The results presented relate estimated performance capabilities during various modes of flight with useful mission elements. Flight modes include: hover, helicopter and conversion, airplane loiter, high speed and high altitude cruise, and short takeoff runs at overload weights. Mission elements include: search and rescue, transport of external sling loads between ships, low-level terrain flight, fuel-efficient loiter capability (ASW, AEW, or tanker), high speed airplane mode flight with or without external stores, and extended-duration missions with overload fuel.
Recommendations are that design investigations of operational tilt-rotor V/STOL continue and that technology tasks involving experimental investigations with the XV-15 tilt-rotor research vehicle, laboratory test rigs, and models be undertaken. Limitations of the applicability of the results shown herein can be expected if nothing is done toward meeting the technology levels assumed for the designs.
Graphs are presented as an aid for making trade-offs between tilt-rotor subsystem weights and performance parameters when alternatives exist among possible technology tasks. Such aids are useful to insure that limited resources be applied to the higher priority technology items.