This paper introduces a new idea of a centrifugally actuated variable span rotor. The rotor blade comprises a fixed inner section and a spring-restrained outer sliding (telescoping) section. No actuators are used to vary the blade length. Rather, the variation in centrifugal force on the outer sliding section (with variation in rotational speed) is exploited to get the blade to extend/retract in the span-wise direction. Situations in which it would be advantageous to use such a system are discussed. A proof-of-concept demonstration rotor was designed, fabricated and tested on a hover stand, and the extension was measured with variation in rotor RPM. A blade with a 14' unextended length extended by over 3.7' as the rotational speed increased from 0 to 245 RPM, and the extension did not show sensitivity to increase in rotor collective pitch. Simple analytical predictions of the extension agreed reasonably well with the test results and simulations were conducted to examine how extension over an RPM range varied with change in system parameters (mass, geometry, and spring characteristics). Some operational analyses were then conducted and it was shown that in space-limited areas it appears feasible to generate the required rotor thrust with a compact rotor, albeit at fairly high values of collective. Large increase in collective can be avoided if the rotor can be locked in the unextended configuration and its rotational speed increased (to match the tip speed of a nominal larger rotor). It was observed that a centrifugally actuated span increase does not yield power reductions expected with larger rotors due to higher tip speeds and dynamic pressures, relative to a baseline. However, if the centrifugally actuated rotor is extended, locked, and then slowed down to yield a larger span while keeping the same tip speed as the baseline rotor, substantial power reductions can be obtained. Based on the results in this paper it can be concluded that a centrifugally actuated variable span rotor is feasible, has clear benefits, and would further benefit from the development of a locking mechanism for certain missions.
A centrifugal force actuated variable span morphing helicopter rotor
Ein Hubschrauberrotor mit variabler Spannweitenänderung durch Zentrifugalkraft
2007
15 Seiten, 7 Quellen
Conference paper
English
A Centrifugal Force Actuated Variable Span Morphing Helicopter Rotor
British Library Conference Proceedings | 2007
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