As Sikorsky continues to inch toward first flight of the S-97 Raider demonstrator, company officials have outlined the scope and duration of the flight test programme for the high-speed, compound helicopter.
Sikorsky has identified three key performance parameters for the S-97 to achieve over a roughly 1.5-year long flight test programme, says Chris Van Buiten, Sikorsky’s vice-president of engineering.
The flight test programme will seek to achieve a manoevrability record for a rotorcraft: a 3g-turn at a maximum speed of 220kt, Van Buiten says in an interview.
“That’s something a helicopter has kind of never done,” Van Buiten says.
The second goal is to fly at 220kt while carrying a full weapons load, he says.
Finally, the S-97 will attempt to demonstrate a new level of hover efficiency for a rotory wing aircraft, he says.
There is an aerodynamic metric known as the isolated rotor figure of merit. A score of 100 means the rotor system is using the rotor’s power as efficiently as theoretically possible. Most helicopter rotor systems are unable to exceed a score of 75, Van Buiten says. Sikorsky declines to reveal the desired score for the S-97, but Van Vuiten notes the company has demonstrated a score of up to 80.
The higher the score, the greater the performance of the vehicle in hover. Sikorsky wants to demonstrate that the S-97 can achieve a hover with a full weapons load at 6,000ft elevation with a temperature at 35 degrees Celsius (95 degrees Fahrenheit), Van Buiten says. With a reduced load, the S-97 also should be able to hover at 10,000ft at the same temperature hevel, he adds.
Sikorksy first demonstrated the coxial-compound, rigid-rotor configuration with the Collier Trophy-winning X2 prototype, which flew 23 test flights. The number of sorties for the S-97 will be slightly higher to demonstrate the full envelope for the aircraft.
What happens after Sikorsky completes the S-97 demonstration is unclear. The aircraft is too small to compete for the army’s Future Vertical Lift (FVL) requirement. The army is also eliminating its armed aerial scout fleet as part of a broader restructuring of the aviation branch, although army officials say the requirement for such a helicopter remains.
“Our job is to demonstrate a super-compelling option and show that it’s possible to have FVL-level technology much sooner than you thought,” Van Buiten says.. “Raider serves as a great risk reduction for that technology.”