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Modelling a helicopter rotor’s response to wake encounters
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Short Description: Modelling a helicopter rotor’s response to. wake encounters. G. R. Whitehouse and R. E. Brown. Department of Aeronautics. Imperial College, London, UK ...
Content Inside: THE AERONAUTICAL JOURNAL JANUARY 2004 15 Modelling a helicopter rotor's response to wake encounters G. R. Whitehouse and R. E. Brown Department of Aeronautics Imperial College, London, UK ABSTRACT In recent years, various strategies for the concurrent operation of R rotor radius fixed- and rotary-wing aircraft have been proposed as a means of S vorticity source, scaled by 2R2 increasing airport capacity. Some of these strategies will increase the t time, scaled by 1/ likelihood of encounters with the wakes of aircraft operating nearby. v velocity of flow surrounding rotor, scaled by R Several studies now exist where numerical simulations have been vc velocity at periphery of vortex core, scaled by R used to assess the impact of encounters with the wakes of large vi velocity normal to rotor disc, scaled by R transport aircraft on the safety of helicopter operations under such vP velocity parallel to blade section, scaled by R conditions. This paper contrasts the predictions of several vT velocity normal to blade section, scaled by R commonly-used numerical simulation techniques when each is used vvortex vortex-induced velocity field, scaled by R to model the dynamics of a helicopter rotor during the same vwake wake-induced velocity field, scaled by R idealised wake encounter. In most previous studies the mutually- blade section angle-of-attack induced distortion of the wakes of the rotor and the interacting blade flapping angle aircraft has been neglected, yielding the so-called `frozen vortex' 0 rotor coning angle assumption. This assumption is shown to be valid only when the 1s rotor lateral tilt angle helicopter encounters the aircraft wake at high forward speed. At the 1c rotor longitudinal tilt angle low forward speeds most relevant to near-airfield operations, rotor Lock number ac/I however, injudicious use of the frozen vortex assumption may lead blade feathering angle to significant errors in predicting the severity of a helicopter's 0 collective pitch control angle response to a wake encounter. 1s longitudinal cyclic pitch control angle 1c lateral cyclic pitch control angle rotor forward speed, scaled by R NOMENCLATURE rotor solidity Nc/ blade azimuth a aerofoil lift-curve slope vorticity of flow surrounding rotor, scaled by R2 A rotor disc area R2 blade flapping frequency, scaled by c blade chord scaled by R rotor rotational speed CL blade section lift coefficient CT rotor thrust, scaled by A(R)2 I blade flapping inertia, scaled by AR3 1.0 INTRODUCTION L distance from the vortex core to the rotor hub N number of rotor blades Innovative exploitation of the runway-independent nature of heli- r radial coordinate, scaled by R copter operations has been proposed as a means of maximizing the rc vortex core radius, scaled by R use of ground- and air-space at airfields(1) and thus of increasing Paper No. 2818. Manuscript received 4 December 2002, revised version received 1 March 2003, accepted 21 May 2003.
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