BELL HELICOPTER and Allison Engine have started flight-tests on an AlliedSignal device which reduces rotor droop in helicopters.

Rotor droop is similar to power hesitation in a car, which can occur after the accelerator is quickly depressed. It occurs when the available torque of a helicopter's rotor blades is reduced and rotor speed momentarily drops.

The resulting droop lowers rotor speeds by as much as 8% and can cause problems when the helicopter is required to change altitude or attitude quickly.

The problem is being tackled with an accumulator staging valve (ASV), which changes the volume of the engine- control accumulator according to the power demands placed on the engine by the pilot. AlliedSignal believes that the ASV will be easily retrofitable.

The Allison/AlliedSignal/Bell team is flight-testing the ASV on a twin Allison 250-C20R-powered Bell 206L-4T TwinRanger.

"Following certification on the TwinRanger, ASV conversion kits will be developed for other applications, which will include LTS-101 helicopter engines and other Allison 250-series engines," says the company.

Certification is expected by the end of 1995.

Source: Flight International