Page 31 - World Airnews Magazine April 2021

FEATURE

noticeably quieter than a similarly sized So in the Raider, the engineers replaced must, since the rear prop eliminates the

conventional chopper.) the side-facing tail rotor with a rear-facing need to use the main rotor as a brake.

Pilots Bill Fell and Christiaan Corry propeller. That receives most of the power Speed, however, is only part of the

demonstrate fast braking, pitching the during forward flight, with the two main potential appeal to military users. Another

blades on that rear prop in the opposite rotors whirling just fast enough to maintain big benefit of the design is manoeuvrability.

direction from forward flight. And then lift, much like a wing. Conversely, the rear Test pilot Fell credits the aircraft’s flight

they show the aircraft’s key virtue, high- prop is nearly unpowered in low-speed capabilities to the rigidity of the rotor
speed forward flight. They make multiple manoeuvring while the rotors are given blades. “In other helicopters there’s a

passes across the field, reaching 218 mph all the power they need. (They’re able lag between putting the input in and

while sounding as much like a vintage to control the helicopter completely, getting the aerodynamic response,” he

World War II Spitfire as a 21st-century even if the rear propeller is damaged or said. “But with the rigid rotor it’s pretty

future flyer. destroyed.) instantaneous.” This manoeuvrability helps

On previous flights, they’ve reached 238 The company honed this system in its with the low-altitude, high-speed flight that

mph, and the Raider can likely go even experimental X2 helicopter from 2008 to Van Buiten says is crucial.

faster. By comparison, Bell's OH-58 Kiowa, 2011. The Raider started flying in 2015, Similarly, it can accelerate without
the Army’s current light scout and attack followed by the even faster and more pitching forward. All of this also means the

aircraft, tops out at 138 mph. powerful Defiant early this year. helicopter can point where it wants, when

Both the dual rotor configuration and the To ensure the two rotor blades don’t hit it wants, facilitating the crew’s aiming

rear pusher-prop contribute to the Raider’s each other, Sikorsky made them especially of weapons and sensors, use of rescue

fleetness of flight. The main rotors are rigid, so they don’t bounce and flex the way equipment, and whatever else they need

derived from Sikorsky’s Advancing Blade conventional helicopter blades do. (There to do.

Concept, a system that was conceived in have been other coaxial helicopter designs, Ultimately, the Raider will likely become

the early 1970s but until now has been mostly from Russian manufacturers, but one of Sikorsky’s first combat aircraft

stymied by costs and technical chal¬lenges. they use conventional flexible blades, as to widely incorporate autonomous (or

It uses two rotors spinning in opposite well as the more complex hubs to which to use the military jargon, “optionally-

directions, which neutralizes a conventional the blades attach.) piloted”) flight. That capability will derive

helicopter’s tendency to lose lift as its The rotors are also spaced a relatively fromSikorsky’s Matrix Technology system,

speed increases. wide 3 feet apart. which it’s currently testing in Black Hawks

Briefly: A helicopter moving forward Nevertheless, there was a flight test and commercial helicopters.

has blades that are always spinning in a accident in August 2017 in which the blades By the time it’s ready for wider dispersal,
horizontal circle and thus either advancing hit each other at low altitude, resulting in the Raider could be in full production.

or retreating. As the helicopter goes faster, a hard landing with no injuries to the crew. This assumes, of course, acceptance by

the retreating blades lose lift, or stall, The problem was traced to a software the defence department, in spite of stiff

relative to the advancing blades, since air is glitch that allowed the helicopter to roll competition from Bell, Boeing, and other

passing over the blade going forward at a much harder than it or any other helicopter manufacturers. But the aircraft also has

slightly faster rate. should have, according to Van Buiten. drawn significant interest from commercial

Having two rotor disks spinning in “It has been fixed and with additional and industrial customers, as well as foreign

opposite directions balances that effect measures to ensure nothing like it will governments. So one way or another,

and allows for much higher top speeds. happen again,” he said. “No hardware it should be rocketing across the skies

Because the counter-rotating rotors also changes were necessary at all.” sometime in the next decade. Q
negate the torque typically generated on Another of the Raider’s tricks is that it can
the fuselage by a single rotor, there’s no slow down quickly, and without pitching Article courtesy: https://www.wired.com/

need for a conventional rear tail rotor. the nose up, as conventional helicopters story/sikorsky-s-97-raider/

World Airnews | April 2021
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