Investigation of the effects of autorotative flare index variation on helicopter flight dynamics in autorotation

Paolo Scaramuzzino, Marilena Pavel, Daan Pool, Olaf Stroosma, Giuseppe Quaranta, Max Mulder

Research output: Chapter in Book/Conference proceedings/Edited volumeConference contributionScientificpeer-review

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Autorotation is a flight condition whereby the engine of a helicopter is no longer supplying power to the main rotor system, which is driven solely by the upward flow of the air moving through the rotor. For helicopters, autorotation is a common emergency procedure performed by pilots to safely land the vehicle in the event of a power failure or tail-rotor failure. In the classic analysis of dynamic stability of helicopters in powered flight, it is common practice to neglect the effect of variation of rotor angular velocity, as the rotorspeed is constant. However, this assumption is no longer justified in case of autorotative flight. Therefore, the rotorspeed becomes an additional degree-of-freedom in autorotation, giving rise to a new stability mode that couples with classical rigid-body modes. The present paper aims at understanding the role of the rotorspeed degree-of-freedom in modifying the stability characteristics in autorotation of rotor systems with different autorotative flare indexes. Results show that the helicopter dynamics are considerably affected in autorotation as a consequence of the fact that the rotorspeed degree of freedom couples with the heave subsidence mode. Therefore, autorotation requires a different control strategy by the pilot and should not be mistakenly considered only as an energy management task. Furthermore, the autorotative flare index, used to characterize the autorotative performance during the preliminary design phase of a new helicopter, provides only energy information. Indeed, this paper demonstrates that high values of this index, representative of good autorotative performance in terms of available energy over required energy, may lead to degraded stability characteristics of the helicopter in autorotation.

Original languageEnglish
Title of host publication45th European Rotorcraft Forum 2019, ERF 2019
Number of pages14
ISBN (Electronic)9781713805922
Publication statusPublished - 2019
Event45th European Rotorcraft Forum - Warsaw, Poland
Duration: 17 Sept 201920 Sept 2019
Conference number: 45

Publication series

Name45th European Rotorcraft Forum 2019, ERF 2019


Conference45th European Rotorcraft Forum
Abbreviated titleERF 2019
Internet address


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