DLR tests haptic sidestick controls

 - December 29, 2009, 9:06 AM

German aerospace research center DLR is testing sidesticks that provide force feedback and, on a more innovative note, touch cues to reduce crew workload. The pilot can feel stops or vibrations if the aircraft approaches a pre-defined limit.

The agency has been testing the right sidestick, which replaces the center stick that conventionally controls the cyclic pitch, since 2007. The DLR has tested several configurations, replacing part or all of the conventional controls. Unlike passive sidesticks, the active ones are equipped with an electric motor to generate the forces the pilot would feel with conventional controls.

DLR is now testing the left sidestick. It replaces both the collective and the pedals. For collective pitch control, the pilot moves the sidestick up and down, as with a conventional control. For tail-rotor control–and replacing the pedals–he rotates it.

But this is only part of the innovation. The sidesticks become an information channel, transferring important cues haptically (using the sense of touch).

The DLR has tested different kinds of haptic feedback to the pilot. One is for envelope protection. The computer takes over the task of monitoring different load or flight envelope parameters, such as engine torque, rate of descent or mast bending moment. “These limits are transformed back into limits in control deflection and brought to the pilot in the form of soft stops,” Max Abildgaard, a helicopter research engineer with the DLR, told AIN.

Another possibility is to use the haptic cues to guide the pilot along prescribed trajectories such as in a standard-rate IFR turn. Research engineers are also developing a warning before the helicopter enters vortex ring state. Information could be given to the pilot via soft stops or vibrations.

“We have found that using haptic cues can substantially reduce pilot workload,” said Abildgaard. As test pilot Herbert Kistler put it, parameters no longer appear only on the visual displays in the cockpit; they are also communicated via the controls as “boundaries that are felt.” This is especially relevant as a good proportion of helicopter flights are conducted under visual flight conditions and the pilot must continuously look outside, DLR engineers point out.

“We want to avoid visual channel overload,” said Antje Dittmer, a rotorcraft engineer at the DLR’s institute for flight systems in Braunschweig, during a presentation at the EASA’s rotorcraft symposium last month. The active sidesticks are part of a broader project called “assisted low level flight” (AllFlight). The flying testbed is a modified Eurocopter EC 135 with a certified quadruplex fly-by-wire/light core control system.

The DLR’s research is of little help to the pilots of current-generation helicopters, since its sidesticks are suited to fly-by-wire controls. “Retrofitting active sidesticks to non-fly-by-wire aircraft seems possible but probably expensive,” Abildgaard said. He does not see fly-by-wire controls being introduced on civil helicopters in the near future.

However, some helicopter manufacturers, including Eurocopter and Sikorsky, are studying fly-by-wire controls for civil applications.