NEWS
Sikorsky Aircraft is betting its own money on a radical new helicopter design. The aircraft named, S-97 Raider will have a pusher propeller meant to send it zooming past the roughly 320 kmph top speed of conventional rotorcraft—and the company hopes to win Pentagon orders. The S-97 would have two pilots and six passengers, although the design would allow various sizes. According to the company sources, the proposed size has been picked up because the most likely replacement aircraft for the US military will be the Kiowa Warrior. Potential customers could include the US Marines, Army and Air Force Special Operations units.

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The S-97 Raider’s design will be based on Sikorsky’s revolutionary X-2 technology demonstrator, which features two counter-rotating rotors on a single axle, plus a pusher propeller mounted on the rear fuselage of the rotorcraft. The X-2 was essentially designed to prove to the world that it was possible to achieve sustainable forward velocity past the helicopter speed-barrier of 200 kts. Most helicopter designs limit the maximum cruise speeds in the region of 120 kts for utility helicopters and around 150 kts for attack helicopters with never exceed speeds (VNe) close to 150 kts and 175 kts for the respective types—the restraining factor being the complexities arising out of the rotor-tips nearing Mach 1 (speed of sound). The X-2 technology successfully demonstrated that with additional forward thrust being provided by a pusher prop like in a conventional fixed-wing propeller aircraft, a rotorcraft could be accelerated well past the 200-knot barrier. The X-2 has already flown at speeds up to 253 kts in level test flights and that was at just 70 per cent of power. With some modifications such as an appropriate axle fairing and a few more tweaks might allow the X-2 to reach hitherto unheard speeds of 280 kts (app. 600 kmph), as claimed by the project’s Chief Engineer, Steve Weiner. So impressive was the X-2’s concept and design that in 2010, it earned the Sikorsky Technology Demonstrator team the prestigious Robert J. Collier Trophy, awarded annually to recognise the greatest achievements in aeronautics or astronautics in the USA. But why so much fuss about the speed for the whirly birds? However, it is not the speed alone which matters for vertical take-off and landing (VTOL) rotorcraft, but also capacity and range.

The need for this was actually felt in the aftermath of the infamous and hugely embarrassing failure the US ‘Iran Hostages Rescue Mission’ in 1980, which called for an aircraft that could not only take off and land vertically but also carry combat troops, and do so at speed. This led to the ‘tiltrotor’ concept by the combined efforts of the Bell-Boeing duo which, after a long and tortuous design and development journey, was eventually operationalised in the V-22 Osprey avatar. Boasting a cruising speed of 271 kts at sea level, the V-22 can carry a respectable 4.5 tonnes (half its max payload) or 24 combat-equipped troops and travel a distance in excess of 900 nm. Though a revolutionary design and a technological marvel, the V-22—by its very technical complexities—has not only proven to be an expensive machine but also suffers from poor serviceability and low mission success rates with none too impeccable a flight safety record. Till date, there have been four Cat-1 accidents resulting in 34 fatalities.