A single camera optical system for the measurement of helicopter blade track and elastic deflection

  • Alex J Palmer-Walsh

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)

Abstract

The purpose of helicopter rotor track and balance (RTB) is to reduce vibration levels in the helicopter airframe. During RTB, the tip height of each blade (the blade track) is measured. The objective is to reduce the difference between the highest and the lowest flying blades (the track split), resulting in a decrease in airframe vibration levels. This reduction in track split is achieved by altering the blade pitch change link (PCL) and trim tab.

Due to the fact that both tab and pitch change link (PCL) adjustment parameters are available for each blade and only a single track measurement is acquired, the system is undetermined unless data from multiple flight conditions are obtained. By detecting blade elastic deflection as well as track, a combination of pitch change link and tab adjustments can be determined from a single flight condition. The calculated PCL and tab adjustments reduce differences in the lift distribution between blades, resulting in a reduced track split for all flight conditions.

The research objective is to develop a single-camera photogrammetric system, capable of detecting blade elastic deflection. The developed system, named the Helicopter Optical System (HELIOS), is passive and functions without the need for any blade surface preparation. The photogrammetric method used is an extension of the Videogrammetric Model Deformation (VMD) measurement technique. A new iterative method of constraining the photogrammetric system is proposed and is shown to be more robust to error caused by blade deformation than the existing method. During a flight trial conducted on an AW109 helicopter, the PCL and tab adjustments acquired from the ground condition produced an expected 58% average improvement to the track split in ground and forward flight conditions.
Date of Award23 Jan 2020
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorNicholas A J Lieven (Supervisor)

Cite this

A single camera optical system for the measurement of helicopter blade track and elastic deflection
Palmer-Walsh, A. J. (Author). 23 Jan 2020

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)