The two pilots tasked with flying the experimental Sikorsky [UTX] S-97 Raider through a yearlong flight test campaign recently offered more insight into how the coaxial rotorcraft operates.
Chief Pilot Bill Fell and co-pilot Kevin Bredenbeck appeared in a short video posted online June 30 in which they answered questions from the public about the operation of the aircraft.
The Raider has side-arm flight controls rather than a conventional helicopter’s center stick control and side-stick collective control. But its stick controls are in the center of the aircraft, between the pilot and co-pilot seats, meaning one would hold the stick in their left hand and vice versa for the other.
It also features a fly-by-wire flight control system which will be unique among military rotorcraft. Raider first flew during an hour-long maiden liftoff on May 22.
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.
The pilots also discussed the Raider’s active vibration control that reduces vibration in the dual rigid rotor and airframe as the aircraft achieves higher speeds. The test pilots will measure the system’s effectiveness as they progress through the flight envelope and will fly both with it turned on and switched off, Fell said.
“We’ll know every step of the way that the system is helping,” he said.
Bredenbeck said the testing would include flying the aircraft as fast as possible with the AVC off “so we can get a base model from a vibration perspective in the airframe and the rotor system is fined tuned and then we overlay the AVC.”
Raider will eventually have a maximum airspeed of at least 220 knots, far faster than conventional rotorcraft. Depending on the external configuration of weapons and sensors, which create drag, the aircraft’s top speed will fluctuate, but 220 knots is the minimum maximum speed the company hopes to achieve, Fell said.
Differential torque between the upper and lower rotors gives the aircraft stability in forward flight at low speeds, as a tail rotor does on a conventional helicopter. Raider has no tail rotor, but features a pusher prop that provides thrust for high-speed flight.
“Differential torque during low-speed flight between the upper and lower rotor and as we accelerate out to speed, we phase that out and phase in rudder control in order to provide turn coordination-type features,” Fell said.
The concept, which blends the speed of an aircraft with the low-speed hover and maneuver capabilities of a helicopter, is being pitched 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.