Control system tackles helicopter vibration

Excessive vibration on helicopter airframes can have detrimental effects not only on structures and components but also on the crew and passengers. Fuselage vibration can cause physical and psychological distress to people, while decreasing the operational abilities of the aircraft. Considerable time and money has been spent to develop systems that will control vibration, both for the comfort and health of the crew and passengers, and to ensure optimal operational performance.

Helicopter fuselage vibration is generated by the main rotor and the rotor blades during blade-pass. Aerodynamic loads, acting on the blades, transmit vibrations to the main rotor hub. If these loads are not decreased, they are transferred through the rotor shaft and main transmission into the aircraft. Controlling vibration at its source - the blades and fuselage - will prevent it from creating structure pulsations, thus protecting occupants, the helicopter structure, and equipment.

Controlling vibrations

Among the technologies that have been developed for helicopter vibration control are both passive and active control systems. Although passive-only systems have been effectively used to control vibration for decades, new and emerging rotorcraft designs that expand the performance envelope demand a new approach as passive technologies begin to display disadvantages that outweigh their many benefits. For example, passive technologies are designed to operate in a very narrow range of flight conditions and typically on helicopters with a single rotor speed. While passive systems perform adequately in these conditions to control vibration, they do not successfully control vibration in aircraft with variable rotor speeds.

In such applications, active vibration control systems (AVCS) were developed and have been proven to reduce vibration in helicopter fuselages generated by the main rotor over a wide range of aircraft speed and operating conditions. These systems control steady state and transient vibration, even during start-up and extreme flight maneuvers. AVCS-equipped aircraft are becoming the new standard against which helicopter manufacturers are beginning to benchmark expected performance.


Rotor craft design challenges

It is a very expensive proposition to redesign a helicopter from the ground-up. Mission requirements evolve and performance is enhanced in existing designs or design derivatives to meet new mission challenges. As existing designs are repurposed, helicopter manufacturers seek methods to evolve platform designs in order to better manage and control vibration. AVCS can be configured to adapt to the performance envelop of various aircrafts, and offer a vibration control solution that can accommodate the future advances in both mission and performance.

Specifically, an active vibration control system enables:
•    Reduced Weight – Eliminates heavy, passive-vibration absorbers,
•    Improved Performance – Enables expanded flight envelope within aircraft design limits and extended range,
•    Improved Comfort – Reduces occupant vibration levels in the cockpit and cabin, and
•    Reduced Direct Maintenance Cost – Lowered aircraft vibration levels result in less vibration-induced fatigue of structures and equipment.

One of the companies in the forefront of active vibration control system advances is LORD Corporation, a supplier of vibration, noise and motion control solutions. LORD has a strong history and legacy in noise and vibration control innovation. It has successfully worked with OEMs to reduce interior noise, mitigate structural vibration and lower vibration levels in rotorcraft.