Active rotor control for helicopters: individual blade control and swashplateless rotor designs

Abstract

Modern helicopters still suffer from many problems that hinder a further increase in their efficiency, acceptance and hence their market share. The high level of vibrations and the noise generated by the rotor are the most important reasons for this. Vibrations are problematic not only for pilot and passenger comfort, but also give rise to an increase in maintenance effort. The high noise level limits the acceptance of helicopters in the public, e.g. landing of helicopters on or close to hospitals during Emergency Medical Services missions. High noise levels also lead to an early aural detection during military missions. Further drawbacks of helicopters are the high fuel consumption in high-speed forward flight and hence low range, limited speed of flight, etc. To overcome these drawbacks, active rotor control technologies have been investigated for a long time. Many different approaches have been investigated and most of them are not being followed any more. First investigations started with socalled Higher Harmonic Control (HHC) which has been replaced by Individual Blade Control (IBC). In a previous paper motivation on active rotor control technology was recapitulated as well as achievements on HHC. This paper continues that work and gives a survey on IBC concepts and achievements. An outlook on the idea of the swashplateless helicopter concludes the paper.

Active rotor control for helicopters: motivation and survey on higher harmonic control

“…Later designs integrate the actuators into the blades. The various IBC concepts have been outlined in [13].…”

“…The very useful 2/rev frequency cannot be controlled by HHC for the 4-bladed rotor. This frequency turned out to be very valuable to reduce noise or required rotor power, see results in [13]. Since IBC can overcome this limitation arbitrary blade pitch motions can be superimposed to the pilot's controls.…”

“…Nevertheless, the relation of the three DOF of a swashplate and the IBC capability for up to three blades should be kept in mind. It will become important for so-called multiswashplate arrangements, see [13]. Another drawback of HHC becomes evident by Eq.…”

“…He concluded that dynamic characteristics of the blade would require careful adjustment to avoid torsional resonance. Later, the torsion response due to active control inputs of whatever kind was seen beneficial in order to assist in achieving the required air load, see [13] for more details. Like Steward, Payne concluded that the greatest angle of attack changes can be achieved for heavy blades or for very stiff ones.…”

A Time‐Domain Active Vibration Control Algorithm for Helicopter Based on a Prior Error Channel Identification Strategy

“…And most of all, the vibration control effect is not satisfactory. Active vibration control approaches for helicopter such as higher harmonic control (HHC), individual blade control (IBC), actively controlled flaps (ACF), active twist rotor (ATR), and active control of structure response (ACSR) can suppress unwanted vibration adaptively and make up for the weaknesses of passive techniques [6][7][8][9]. Among these approaches, ACSR has received considerable attention for its simple system components and stable performance and it has been used in helicopters such as EH-101, UH-60, and EC225/EC725 [10][11][12].…”