Aviation Week is reporting that Lockheed Martin, which acquired Sikorsky in 2015, is continuing support for its S-97 prototype after the chopper suffered a hard landing at its development center in West Palm Beach, FL. The hard landing is being blamed on the digital flight control system. Sikorsky said the system unexpectedly transitioned from simple ground mode to augmented flight mode before the aircraft was took off.
Before the bad landing, the S-97 Raider was extremely close to achieving its goal of travelling faster than 220kt using the X2 technology. Sikorsky will continue development, and once the 220kt target is achieved, will look to add a weapons suite to the S-97 Raider.
Sikorsky was tantalizingly close to achieving its goal of exceeding 220 kt. with the S-97 Raider coaxial-rotor helicopter when the prototype made a hard landing on Aug. 2, after experiencing flight control problems. But Lockheed Martin, which acquired Sikorsky in 2015 when the industry-funded Raider program was well underway, has been quick to reiterate its commitment to the high-speed light tactical helicopter.
The incident at Sikorsky’s development flight center in West Palm Beach, Florida, came as the 6,000-lb. Raider was taxiing out to begin its 15th test flight, with the target of achieving 180 kt.—its highest speed yet. The goal of exceeding 220 kt. was planned for the next flight, its 16th. Achieving that objective will now have to wait until after the second prototype is completed and flown in 2018.
The fly-by-wire (FBW) Raider was taxiing to its takeoff position when the mishap occurred. The digital flight control system unexpectedly transitioned from simple ground mode to augmented flight mode before the aircraft became airborne. The crew lifted into a hover but, unable to stabilize the helicopter, quickly put it back on the ground, the Raider coming down heavily, upright and level on the runway. The two company test pilots powered down the engine and shut off the electrics before egressing. The Raider suffered substantial damage, but they escaped with minor injuries— the impact-absorbing landing gear, composite airframe and crew seats working as designed.
Investigation is ongoing with the National Transportation Safety Board (NTSB), but Sikorsky says its other fly-by-wire helicopters—the CH-53K and CH-148 Cyclone—are not affected, as implementation of the Raider’s triplex-redundant control system is different. But any lessons learned from the investigation are being shared with the Sikorsky/Boeing team developing the SB-1 Defiant Joint Multi-Role demonstrator. Expected to fly by mid-2018, the 30,000-lb. SB-1 shares the same coaxial-rotor/pusher-propeller X2 configuration and a similar FBW control system.
The NTSB has issued only a brief preliminary report, but the suspected cause is a flight-control software issue relating to the “complex interaction between the ground, the landing gear, the flight control system and the pilot,” says Chris Van Buiten, vice president of Sikorsky Innovations. The failure has been reproduced in the S-97 flight simulator, and software changes are being made “to ensure it never happens again.”
Damage to the first prototype is a setback for an industry effort that has slowed significantly since its launch in 2010 as a $200 million follow-on to the Sikorsky-funded X2 Technology Demonstrator, which reached a speed of 262 kt. that year. The Raider first flew in May 2015 with the goal of achieving its key performance objectives by the middle of 2016. But changing customer plans, technical challenges and Sikorsky’s integration into Lockheed all slowed the pace.
The mishap was not related to the coaxial rigid-rotor X2 configuration, says Van Buiten, and Lockheed’s leadership has committed to return Raider to flight once the cause is fully established. Aircraft 1 will continue to support the investigation, so the second prototype, assembly of which had been halted, will be completed and flown in 2018. Changes made to the first prototype as a result of 20 hr. of flight tests and 100 hr. of ground runs will be incorporated into Aircraft 2 before it flies.
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