WASHINGTON: When is a helicopter not a helicopter? The question arises because Sikorsky Aircraft’s new S-97 Raider got airborne for the first time the other day and company officials all but declared the dawn of a new age in aviation — or at least the birth of a new type of aircraft.
“This was, we feel, a really spectacular day for Sikorsky and aviation in general,” Mark Miller, Sikorsky’s vice president for research and engineering, told reporters on a conference call. “It’s not every day you have a first flight, and when you add on top of that a very differentiated, new and compelling product like the S-97 Raider, it makes it even more special.”
The S-97, based on Sikorsky’s Collier Trophy winning X2 technology demonstrator, uses two coaxial rotors and a pusher propeller to overcome rotor aerodynamics that have held helicopters to top speeds of no more than about 170 knots (195 miles per hour). Flown at West Palm Beach, Fla., the May 22 test was not a test of the aircraft’s speed or maneuverability. It consisted of little more than taking off and landing vertically and making a few cautious movements at 10 knots. It was a maiden flight, after all. But Sikorsky promises the Raider and its crew of two will someday carry six troops and external weapons at cruising speeds of 240 knots (276 mph).
Sikorsky also promises that the 11,000-pound Raider – about half the size and weight of the company’s UH-60 Black Hawk — will hover at higher altitudes, in hotter temperatures, and do it all with greater agility than any helicopter, thanks to its rigid coaxial rotors and other features. In fact, Miller said, the S-97 will do things helicopters “cannot even dream of doing in the future” and therefore “cannot be viewed as (simply) a replacement for a helicopter.” The S-97 “is a fundamentally different capability than what an Apache will give you,” Miller said.
Sikorsky is putting its money where Miller’s mouth is. The company is covering 75 percent of S-97 costs and 53 subcontractors are picking up the rest – a necessity since the Army cancelled an Armed Aerial Scout requirement the Raider was designed to meet. But if not just a better, faster helicopter, what is the Raider?
Roger Connor, rotorcraft curator at the Smithsonian National Air and Space Museum in Washington, said the answer “really depends upon who’s asking.”
When an aircraft uses one or two rotors to take off and land vertically, hover and provide all its lift and thrust, as Sikorsky’s single rotor Black Hawk and Boeing Co.’s tandem rotor CH-47 Chinook do, aviation experts call that aircraft a “helicopter.”
When a fixed-wing aircraft swivels wingtip rotors upward to take off and land like a helicopter and forward to fly like an airplane, as the V-22 Osprey made by Boeing and Bell Helicopter Textron Inc. does, that is a “tiltrotor.”
When an aircraft uses a rotor to take off and land and hover but adds not only an additional form of propulsion to fly faster than a helicopter but also a wing to provide lift, as Airbus’s X3 technology demonstrator does, it’s a “compound helicopter.”
The Federal Aviation Administration “would certainly view this as a helicopter,” Connor said of the S-97. “When the thrusting prop is not turning, it’s certainly a true helicopter.” But the Fédération Aéronautique Internationale (FAI), which verifies performance records, wouldn’t credit the S-97 with breaking helicopter marks because of its pusher propeller. At the same time, Connor said, the Raider isn’t exactly a compound.
“Typically, when you put wings on a helicopter, that is the definitive definition of a compound.”
Sikorsky may want to avoid the C-word anyway. Compounds have been out of fashion for some time, and have a chequered history.
Steve Weiner, the X2’s chief engineer, said the company itself has been flummoxed about what to call the Raider.
The Raider, Weiner said, “is a different animal. It performs like a helicopter. At speed, it performs with the performance of a tiltrotor or a compound, but there’s no wing to get in the way to help hurt the hover efficiency. If somebody held a gun to my head, I would say it’s a helicopter with aux propulsion. You can turn it off and you can operate it all day long right up to 170 knots, just like a helicopter. Once you add the aux propulser, you get quite a bit of additional operational envelope.”
What about “auxcopter?” Or “helispeedster?” Dear readers, what say you?