Resonance avoidance for variable speed rotor blades using an applied compressive load

Robert Dibble*, Vaclav Ondra, Branislav Titurus

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

13 Citations (Scopus)
76 Downloads (Pure)


Varying the rotational speed of the main rotor is one method being considered to improve the performance of future rotorcraft. However, changes in rotor speeds often lead to resonant interactions between rotor blade modes and the rotor’s excitation frequencies which increase the vibratory loads in the rotor. This research investigates the use of a compressive load to reduce a blade’s natural frequencies and its potential to be used as a resonance avoidance technique by improving separation between the natural and excitation frequencies of a blade. The research presented herein describes and validates a model of a pretwisted rotating beam with non-coincident mass and elastic axes with an applied compressive load. The compressive load is applied at the elastic axis at the tip of the beam and is orientated towards the root of the beam. The beam model is then used in a case study to represent the rotor blade of a typical mid-sized civilian helicopter. The case study is performed to calculate the natural frequencies of a compressed blade for a reduction in rotor speed of up to 40% and evaluate the performance of the compressive load resonance avoidance technique. The results of the case study show that the compressive load improves the separation between natural and excitation frequencies over the full range of rotor speeds evaluated. The improved separation allows the rotor to operate safely with a reduction in rotor speed of up to 19%.
Original languageEnglish
Pages (from-to)222-232
Number of pages11
JournalAerospace Science and Technology
Early online date17 Mar 2019
Publication statusPublished - 1 May 2019

Structured keywords

  • Bristol Composites Institute ACCIS


  • Boundary value problem
  • Blade dynamics
  • Variable speed rotor
  • Compressively loaded beams
  • Modal tuning
  • Resonance avoidance


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