Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.486588
Title: The effect of aerodynamic interactions on helicopter flight mechanics.
Author: Fletcher, Timothy M.
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2008
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Abstract:
During the last 40 years many helicopters have suffered adverse effects on their performance and handling qualities as a result of various forms of aerodynamic interaction. These problems have tended to become apparent only after a substantial amount of development work has been performed and flight testing has commenced, leading to expensive re-designs. Aerodynamic interaction between the main rotor and stabiliser leads to pitch-up in low speed forward . flight, whilst interaction between the main rotor and tail rotor in a conventional helicopter is known to strongly influence the performance of the tail rotor. Consequently, poor handling qualities in response to loss of tail rotor effectiveness and dynamic characteristics such as tail shake can emerge. The capability of an advanced numerical model for the simulation of rotorcraft flows, the Vorticity Transport Model, has been demonstrated by investigating the circumstances in which these interactions occur, and used to expose some of the underlying fluid dynamic mechanisms. This dissertation shows that the origin of pitch-up lies in the impingement of the main rotor wake on the stabiliser of a helicopter, and that the characteristic pitch and roll moments on the vehicle are dependent on the helicopter geometry and the angle of sideslip. The characteristic effects of main rotor - tail rotor interaction are also a function of helicopter geometry, but are highly dependent on the flight trajectory and are sensitive to the sense of rotation of the tail rotor. In forward flight with a high angle of sideslip, the predominant effect is to change the steady thrust developed by the tail rotor. This is caused by a modification of the velocity field at the tail���· rotor which benefits tail rotors with a top-aft sense of rotation. In aft quartering flight, the predominant effect is of substantial unsteadiness in tail rotor performance, which is greater for a top-forward tail rotor, and is related to the dynamics of the helicopter wake.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.486588  DOI: Not available
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