Sikorsky’s prototype S-97 Raider coaxial-rotor helicopter flew for the first time May 22 at the company’s West Palm Beach, Fla., facility.
During the hour-long flight, Chief Pilot Bill Fell and co-pilot Kevin Bredenbeck put the Raider through what both called an “aggressive test card for a first flight for a helicopter.” After a 7 a.m. liftoff, the pilots took the aircraft through 97 test points.
“The aircraft was just rock solid and we’re excited to get to the next flight and open the envelope,” Fell said during a May 22 teleconference with reporters. “It flies very similar to another rotorcraft, the difference being that you have a phenomenal amount of control. You are able to very quickly make inputs in roll and pitch and the aircraft responds immediately to your control input.”
Sikorsky based Raider on its X2 technology, which uses coaxial, counter-rotating rigid main rotors, eliminating the need for a tail rotor. A pusher propeller at the rear is used for high-speed forward flight. It can be de-clutched for speeds up to 140-150 knots and engaged to fly up to 220 knots, much faster than conventional rotorcraft.
“This, we feel, was a really spectacular day for Sikorsky and for aviation in general,” said Mark Miller, vice president of research and engineering for Sikorsky. “It’s not every day you have a first flight and add on top of that you had a first flight of a very differentiated, compelling and new and innovative product like the S-97 Raider, that makes it even more special.”
Sikorsky developed X2 and Raider on its own dime, spending at least $150 million of internal research and development funding to engineer an aircraft that has the hover and maneuver capabilities of a helicopter and the fast airspeed of a fixed-wing airplane. X2, weighing in at about 6,000 pounds, was purely a technology demonstrator that last flew in 2011.
The S-97 scaled up the X2 technology by a factor of two and is meant to prove the design’s practical military application. It was initially pitched for the Army’s now-defunct effort to replace the OH-58D Kiowa Warrior armed scout helicopter.
Now the aircraft is being marketed as a special operations fast-insertion aircraft and as the light variant of the future vertical lift family of aircraft that will eventually replace all of the Army’s rotorcraft. It also is serving as a “risk reducer” and technology test bed for the SB-1 Defiant, which Sikorsky is offering for the Army’s joint-multirole helicopter technology demonstration program, which will inform FVL development.
Sikorsky advertised plans to fly Raider in late 2014, but purposefully delayed first flight to gather more data during tethered ground runs. Because there is no immediate customer for the aircraft, company officials chose a prudent and careful route to first flight, a cautious attitude the pilots and engineers will mirror as the Raider’s flight envelope is expanded, Fell said.
“Flight test is not a silk-scarf, hair-on-fire business,” Fell said. “It’s a methodical engineering process. We go out there and collect data at 10 knots in all the cardinal directions and we’ll go back and analyze the data and validate that what we thought we had in terms of an operating system is what, in fact, we measured in flight. Once we do that, either it was right on and we proceed to the next series of data points or we make adjustments to the system based on the knowledge we acquired during that flight.”
Friday’s test flight was originally scheduled for 30 minutes but stretched to an hour because the aircraft flew so successfully, Miller said. It included three takeoffs and landings, forward, rearward and sideways flight.
The pilots flew at only 10 knots during the maiden flight using a basic, degraded version of the Raider’s triple-redundant fly-by-wire control system. Fell said the controls flew better than traditional hydro-mechanical rotorcraft systems.
The pusher prop was spinning during the first flight but was not engaged, Miller said. The prop is needed for forward flights at higher speeds and will be tested in future flights after the flight envelope is opened. The flight test campaign is expected to last about a year. A second Raider, creatively dubbed Aircraft 2, or 972, is being assembled and should enter the campaign by the end of the year, Miller said. Aircraft 2 will primarily be used for customer demonstration flights.