Research of an Active Tunable Vibration Absorber for Helicopter Vibration Control

Abstract Significant structural vibration is an undesirable characteristic in helicopter flight that leads to structural fatigue, poor ride quality for passengers and high acoustic signature. Previous Individual Blade Control (IBC) techniques to reduce these effects have been hindered by electromechanical limitations of piezoelectric actuators. The Smart Spring is an active tunable vibration absorber using IBC approach to adaptively alter the "structural impedance" at the blade root. In this paper, a mathematical model was developed to predict the response under harmonic excitations. An adaptive notch algorithm was designed and implemented on a TMS320c40 DSP platform. Reference signal synthesis techniques were used to automatically track the shifts in the fundamental vibratory frequency due to variations in flight conditions. Closed-loop tests performed on the proof-of-concept hardware achieved significant vibration suppression at harmonic peaks as well as the broadband reduction in vibration. The investigation verified the capability of the Smart Spring to suppress multiple harmonic components in blade vibration through active impedance control

Actively Controlling Buffet-Induced Excitations

High performance aircraft, especially those with twin vertical tails, encounter unsteady buffet loads when flying at high angles of attack. These loads result in significant random stresses, which may cause fatigue damage leading to restricted capabilities and availability of the aircraft. An international collaborative research activity among Australia, Canada and the United States, conducted under the auspices of The Technical Cooperation Program (TTCP) contributed resources toward a program that coalesced a broad range of technical knowledge and expertise into a single investigation to demonstrate the enhanced performance and capability of the advanced active BLA control system in preparation for a flight test demonstration. The research team investigated the use of active structural control to alleviate the damaging structural response to these loads by applying advanced directional piezoelectric actuators, the aircraft rudder, switch mode amplifiers, and advanced control strategies on an F/A-18 aircraft empennage. Some results of the full-scale investigation are presented herein

Controlling Buffeting Loads by Rudder and Piezo-Actuation

High performance aircraft, especially those with twin vertical tails, encounter unsteady buffet loads when flying at high angles of attack. These stochastic loads result in significant stresses, which may cause fatigue damage leading to restricted capabilities and availability of the aircraft. An international collaborative research activity among Australia, Canada and the United States, conducted under the auspices of The Technical Cooperation Program (TTCP) contributed resources toward a program that coalesced a broad range of technical knowledge and expertise into a single investigation to demonstrate the enhanced performance and capability of the advanced active Buffet Load Alleviation ( ) control system in preparation for a flight test demonstration. The research team investigated the use of active structural control to alleviate the damaging structural response to these loads by applying advanced directional piezoelectric actuators, the aircraft rudder, switch mode amplifiers, and advanced control strategies on an F/A-18 aircraft empennage. Some results of the full-scale investigation are presented herein

Development and evaluation of hybrid seat cushions for helicopter aircrew vibration mitigation

This article investigates the use of novel energy-absorbing materials to reduce vibration transmitted through helicopter pilot seat cushions. A type of engineered material known as the hybrid air cushioning system was integrated into the design of helicopter seat cushions in addition to conventional foam materials. The prototype seat cushions were preliminarily evaluated as the bottom seat cushion on a Bell-412 nonarmored pilot seat through mechanical shaker tests. The promising cushion designs were further evaluated on a Bell-412 helicopter through extensive flight tests. The pilot whole-body vibration levels were assessed in accordance with ISO 2631-1:1997 standard. The flight test results demonstrated that the prototype cushions were able to reduce significantly the pilot whole-body vibration. Therefore, the integration of hybrid air cushioning system with Bell-412 seat cushion can serve as a low-cost solution to mitigate the vibration levels transmitted to helicopter pilots.Peer reviewed: YesNRC publication: Ye

Development and verification of real-time controllers for F/A-18 vertical fin buffet load alleviation

Peer reviewed: YesNRC publication: Ye

Development of adaptive helicopter seat for aircrew vibration reduction

The high level vibration of helicopter flight can cause physiological harm to the aircrew and may lead to occupational health issues. This article presents the development of an adaptive helicopter seat mount to reduce the vibration levels transmitted to the aircrew body. Flight test on a Bell-412 helicopter was conducted to measure the aircrew body vibration levels and vibration transmission through the seat structures. Experimental modal analysis on a Bell-412 co-pilot seat equipped with a mannequin was carried out to investigate the seat/aircrew dynamics and identify critical vibration modes. Based on observations from the configuration, an adaptive helicopter seat mount has been developed. Two stacked piezoelectric actuators were installed on the seat frame as active struts to provide effective control authority to the critical mannequin vibration modes. A proof-of-concept adaptive helicopter seat has been retrofitted on a full-scale Bell-412 co-pilot seat and the performance has been evaluated through extensive closed-loop control experiments. Test results demonstrated simultaneous suppression of the critical mannequin vibration modes and achieved significant global reduction of the body vibration levels, which verified the effectiveness of the adaptive helicopter seat mount concept for helicopter aircrew vibration reduction applications.Peer reviewed: YesNRC publication: Ye

Development of Smart Structure Systems for Helicopter Vibration and Noise Control

NRC publication: Ye

Identification of aeroelastic parameters for helicopter tail rotor limit cycle oscillation monitoring

The aeroelastic parameters of helicopter tail rotors are required in the monitoring and evaluation of rotor aeroservoelastic instability incidents such as limit cycle oscillations (LCO). However, in-situ measurement of these parameters on helicopters is generally difficult due to the need to transfer vibration data across a rotating interface. This paper presents a novel center frequency scaling factor relationship of the aeroelastic parameters between the rotating and stationary frames. Together with the stochastic parameter identification technique, this methodology enables real-time estimation and tracking of the critical aeroelastic parameters in the rotating frame during LCO events based on vibration information measured exclusively in the stationary frame. The methodology has been validated using flight vibration data measured from both the rotating and stationary frames of a helicopter tail rotor system during an LCO event. Moreover, this methodology has been applied to the analysis of vibration data measured from the teeter tail rotor system on the Canadian CH-149 Cormorant helicopters to derive the critical aeroelastic parameters during several LCO events.Peer reviewed: YesNRC publication: Ye

Smart Spring Impedance Control Algorithm for Helicopter Blade Harmonic Vibration Suppression

NRC publication: Ye

Canadian Contribution to the International Buffet Load Alleviation Program for F/A-18 Vertical Tail

Peer reviewed: YesNRC publication: Ye