Analysing dynamic deep stall recovery using a nonlinear frequency approach

Duc H Nguyen*, Mark H Lowenberg , Simon A Neild

*Corresponding author for this work

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

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Abstract

Based on bifurcation theory, nonlinear frequency response analysis is a recent development in the field of flight dynamics studies. Here we consider how this method can be used to inform us on how to devise the control input such that the system transitions from an undesirable equilibrium solution – an aircraft deep stall solution in our case – to a desirable solution. We show that it is still possible to induce a large-amplitude oscillation via harmonic forcing of the pitch control device and escape the otherwise unrecoverable deep stall, despite very little control power available in such a high angle-of-attack flight condition. The forcing frequencies that excite these resonances are reflected as asymptotically unstable solutions using bifurcation analysis and Floquet theory. Due to the softening behaviour observed in the frequency response, these unstable (divergent) solutions have slightly lower frequencies than the value predicted using linear analysis. Subharmonic resonances are also detected, which are reflected in the time-domain unforced responses. These nonlinear phenomena show strong dependency on the forcing/perturbation amplitude and result in complex dynamics that can impede recovery if the existing procedures are followed. The proposed method is shown to be a useful tool for nonlinear flight dynamics analysis as well as to complement the rather thin literature on deep stall analysis – a topic of relevance for recent research on unconventional landing techniques in unmanned aerial vehicles. A full description of the aircraft model used, the unstable F-16 fighter jet, is provided in the appendix.
Original languageEnglish
Pages (from-to)1179-1196
Number of pages18
JournalNonlinear Dynamics
Volume108
Issue number2
Early online date21 Feb 2022
DOIs
Publication statusPublished - 21 Feb 2022

Bibliographical note

Funding Information:
The first author is partially supported by the University of Bristol?s Alumni Grant. We also would like to thank Prof. Tom Richardson and Mr Reece King for the F-16 model, as well as Dr Etienne Coetzee for his help with the DST software.

Funding Information:
The first author is partially supported by the University of Bristol’s Alumni Grant. We also would like to thank Prof. Tom Richardson and Mr Reece King for the F-16 model, as well as Dr Etienne Coetzee for his help with the DST software.

Publisher Copyright:
© 2022, The Author(s).

Keywords

  • frequency response
  • bifurcation analysis
  • deep stall
  • flight dynamics
  • harmonic forcing
  • resonance

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