Shipboard Helicopter Gust Response Alleviation Using Active Trailing Edge Flaps

Open Access
Author:
Montanye, Pamela L.
Graduate Program:
Aerospace Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
None
Committee Members:
  • Edward C Smith, Thesis Advisor
  • Christopher Rahn, Thesis Advisor
  • Stephen Clarke Conlon, Thesis Advisor
Keywords:
  • helicopter
  • rotorcraft
  • trailing edge flap
  • active rotor
  • flight dynamics
  • gust
  • gust response
  • shipboard
  • dynamic interface
Abstract:
Helicopter shipboard launch and recovery operations can result in high pilot workload due to the unsteady, turbulent ship airwake. Successful gust response alleviation could improve safety and potentially expand operational envelopes. The results of a feasibility study of using active trailing edge flaps as gust alleviation mechanisms are presented. Previous researchers have used the primary flight control effectors, including the swashplate and the tail rotor, to successfully improve the vehicle response and reduce the pilot workload. Other researchers have analyzed trailing edge flaps for the purposes of vibration control, noise reduction, and blade loads control. Until now, time-domain, non-harmonic controllers have seen little use in automated on-blade actuation studies. Additionally, using on-blade actuation is a novel method for gust alleviation. The benefits of on-blade actuation and previous gust alleviation control methods are combined in this study, yielding a system that uses trailing edge flaps for gust disturbance rejection while the swashplate provides primary flight control. The control architecture used in this analysis is comprised of two distinct controllers with separate actuators. The primary flight control system is a standard model-following controller (MFC) architecture that uses the swashplate and pedals to ensure that the vehicle follows a desired response to pilot inputs, based on handling qualities specifications. Separately, the airwake compensator rejects airwake disturbances with trailing edge flaps and a robust H2 controller. In this way, command tracking is decoupled from disturbance rejection. The controller is implemented in the GENHEL flight simulation code of the UH-60A Black Hawk with a CFD airwake solution for an LHA-class ship. Simulations are performed in hover. The size of the trailing edge flaps used in this study (fifteen percent blade span and twenty percent blade chord) is on the low range of the size of flaps studied for vibration control. Results indicate that trailing edge flaps are capable of alleviating the magnitude of the vehicle angular gust response in the roll and pitch axes. Roll response is significantly impacted in all cases, including a roll rate reduction of as much as ninety percent in specific wind-over-deck conditions. Pitch response sees a modest improvement in all conditions. Specifically, in a hover maneuver above a Landing Helicopter Assault-class ship with a thirty knot wind from thirty degrees from the bow of the ship, the maximum roll rate response of the vehicle is reduced by ninety-one percent. The maximum pitch rate response is reduced by thirty-two percent using a trailing edge flap controller designed for that flight condition. Varying performance and actuation parameters within the control synthesis has a strong impact on the magnitude and frequency of the required trailing edge flap deflections. Deflection requirements can be kept below current actuation technology stroke and rate limits while achieving the performance of a similar swashplate-based controller. The results of this study suggest that trailing edge flaps can be effective for shipboard gust alleviation.