An In-Flight Experimental Investigation of Helicopter Main Rotor/Tail Rotor Interactions

Ellin, A. D. S (1993) An In-Flight Experimental Investigation of Helicopter Main Rotor/Tail Rotor Interactions. PhD thesis, University of Glasgow.

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Experience had shown that the fidelity of the yaw control characteristics of the computer simulation models used at DRA Bedford and elsewhere was not up to the standard required for ACT control law development. It was therefore decided that the DRA model, Helistab, should be improved in this respect and a research activity initiated. In the absence of suitable published information or detailed data on the performance of the tail rotor, two experimental flight test programmes were conducted, the first with a Puma, the second with a Lynx AH Mk5. This dissertation describes the planning and conduct of the second experiment and the analysis of the data collected in both. Building on the DRA's considerable experience in main rotor research, the instrumented tail rotor blade for the Lynx was designed to make use of the Pressure Indicator Sensor technique which, provided that the local in-plane velocity is known, permits the local blade loading to be estimated from the pressures read at two points on the upper surface leading and trailing edges of the blade. The lack of this velocity information for the tail rotor presents problems, solutions to which are discussed. With the aircraft experimental installation completed, it was flown for fifteen hours, during which time data on over 1200 flight conditions were collected from within the Lynx low speed flight envelope. New techniques had to be developed to allow efficient analysis of this large database so that the information contained therein could be extracted. From the initial analysis of the data it was determined that the Lynx AH Mk5 low speed flight envelope can be sub-divided into six regions. In each of these regions, the mechanism of main rotor/tail rotor interaction is different. One or more flight conditions in each region were selected for in-depth analysis so that the detail of the mechanisms could be determined. Each interaction is covered in turn. Once the predominant mechanisms of the main rotor/tail rotor interaction were isolated, their respective effects on the yaw performance of the helicopter could be assessed and a decision taken as to whether or not they should be included in the model. The dominant interaction, that taking place in quartering flight, should be included in all tail rotor models. This effect has been modelled and, when included in Helistab, the trim results obtained show a marked improvement over those previously available. The remaining interactions are not so significant and their inclusion would depend on the detail required in the model and the purpose for which it was intended. The Lynx AH Mk5 experiment is seen as the first part of a comparative study: an additional trial with a Lynx AH Mk7, in which the tail rotor rotates in the opposite direction, is proposed as the second. The instrumented tail rotor blade designed for that aircraft includes an extra sensor that should enable the in-plane velocity to be determined. In addition to the model improvements, this research has suggested the use of cyclic control of tail rotor pitch to improve tail rotor efficiency. The use of this control technique has the potential to expand the low speed flight envelope, though it could only be incorporated as part of a helicopter ACT system. It is recommended that tail rotor cyclic control, and some other aspects of tail rotor performance highlighted by this present research programme, be more fully investigated in the future.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: R A McD Galbriaith
Keywords: Aerospace engineering
Date of Award: 1993
Depositing User: Enlighten Team
Unique ID: glathesis:1993-75364
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 19 Nov 2019 20:25
Last Modified: 19 Nov 2019 20:25

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