Rotorcraft Technology: Fly-by-wire flight controls
Fly-by-wire flight controls are on the verge of making their debut in civil helicopters, decades after their introduction on fighters, airliners and, more recently, business jets. Eurocopter is investigating all-electric system architectures, including flight controls, hoping to have them in service in five to 10 years. In the U.S., Sikorsky has just flown a fly-by-wire H-92.
Fly-by-wire systems electronically link the controls inside the cockpit with the exterior actuators, eliminating the traditional mechanical linkage. So far, the only in production helicopters with fly-by-wire controls are the Kazan Helicopters Ansat, a light twin certified in 2004, and the Eurocopter/Agusta/Fokker NH90 military transport. Both have hydraulic actuators. The unique Eurocopter design will incorporate all-electric flight controls.
Fly-by-wire brings better function integration to the pilot, Marc Gazzino, Eurocopter’s design office head of electric system studies, told HAI Convention News. The autopilot can thus be more closely integrated with the controls. Such controls also offer improved handling qualities and precision. For the passenger they yield a smoother ride, said Philippe Antomarchi, another researcher at Eurocopter’s design office.
Maintenance also becomes significantly simpler. There is no longer a need for scheduled checks as there are with hydraulics. “The system monitors itself permanently and can anticipate potential problems so the maintenance is on condition,” Gazzino said.
As he suggested to HAI Convention News, the expense of validating the system’s reliability will be the main challenge. He also said that the business case for introducing such a system calls for starting with medium to heavy helicopters. “However, there is no consensus in the helicopter industry and some would rather begin with light rotorcraft,” he added.
Reliability testing will be done via a two-pronged approach, Gazzino explained. The first step involves computer analysis, followed by ground tests performed in degraded modes, with more demanding constraints than in normal operation. “We will work out an equivalent to a normal lifecycle,” Gazzino said.
There are also a number of technology enablers to validate. Eurocopter (Booth No. 631) is asking that suppliers work on fly-by-wire helicopter controls concurrently to speed development. However, the business case for the technology is not as straightforward as in the fixed-wing world because production volumes are smaller and implementation of electric systems is more difficult in helicopters. “Redundancies cannot solve as many reliability issues, so system reliability is even more critical,” said Antomarchi. Nevertheless, Eurocopter is seeking to exploit work already performed by Dassault, Alenia and Saab for fly-by-wire-controls in business and regional jets.
All are part of the More Open Electric Technologies (MOET) research program, funded by the European Commission. Although it mainly seeks to meet Airbus’s needs, manufacturers of smaller aircraft have found areas of common interest in MOET. The research program holds the promise of allowing bigger production volumes for some components and should therefore improve the business case for companies like Eurocopter.
Eurocopter researchers do not view the added cost of fly-by-wire systems as a main challenge. That is somewhat surprising considering that just three years ago then-CEO Fabrice Brégier was pointing to cost as the reason the company had “no particular plan” for fly-by-wire controls for civil helicopters.
On December 20 in Sikorsky’s development flight center in West Palm Beach, Fla., the first H-92 to feature fly-by-wire technology made its maiden flight. The
H-92 is the military designation for the civil S-92, a twin-engine helicopter in the 26,000-pound class. The next phase of flight testing is scheduled to start this year.
Company officials see the fly-by-wire H-92 as the first of a new generation of helicopters. They insist on the improved maneuverability, safety and effectiveness. However, they have not clarified yet when a fly-by-wire Sikorsky will go into production.
Two Sikorsky programs feature the technology–the latest version of the Black Hawk, the UH-60M, and the X2 demonstrator. The latter, which is expected to fly soon after Heli-Expo, is on display here at Sikorsky’s booth (Nos. 1543, 2046 and 1641).