Hot-Rod Helicopters

There’s just no way to add 100 mph to the speed of a helicopter. Or is there?

Half-breed: Piasecki Aircraft has taken a Sikorsky helicopter and bolted on airplane hardware — a propeller (ducted) and a fixed wing — hoping the resulting X-49A SpeedHawk (top) will bust through the constraints that have kept helicopters slow. (Chad Slattery)
Air & Space Magazine

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John Piasecki, son of company founder Frank and now president, took the podium to thank the assembled uniforms, a Congressional delegation, representatives from other corporations, and Piasecki workers. Guests then filed out to check out the world’s only SpeedHawk. The aircraft, painted black, bore the red Piasecki logo, a two-legged triangle with a superimposed oval that presaged the insignia of the Star Trek crew.

Once the guests had assembled, the SpeedHawk embarked on a routine demonstrating high-G turns, quick takeoffs, and short stops. At this phase of research, a Navy rule limits speeds, so the flyby was capped at about 200 mph. (The company says the X-49A has reached 203 mph “in a slight descent,” and expects SpeedHawks to ultimately attain a maximum speed of 230 mph.)

The most striking feature was not the set of stubby wings (taken from an Aerostar FJ-100 business jet) but the Vectored Thrust Ducted Propeller. Tucked into the shroud are clamshell-like diverters that emerge in sections, projecting out of the shroud and forming a right-angle duct for sending the propeller’s thrust off to the side. During takeoff and slow-speed flight, the arrangement fills in for the typical tail rotor, which standard helicopters need to counteract the torque that the main rotor produces.

As the SpeedHawk accelerates to the point where less sideward thrust is needed, the duct retracts into the shroud. From then on, all directional control is exerted by a small rudder mounted inside the shroud. The main job of the propeller becomes providing forward thrust. (Attention, hotshot pilots: The ringtail’s push can also hold the helicopter at a steep nose-high attitude while hovering, a stunt that could be useful for a gunship tucked among the trees and waiting to bag an adversary. If an ordinary helicopter tried this, it would slide backward.)

The demonstration ended when the aircraft touched down tail-first, rolled up to face the crowd, and shut down for inspection.
Later, I spoke with Joe Cosgrove, director of program requirements, about some of the work that had preceded the demonstration. A helicopter is a delicately balanced machine with a minimum of extra hardware, so changing one thing usually triggers a long list of modifications and adjustments. Since the SpeedHawk goes unusually fast for a helicopter, explained Cosgrove, engineers decided to add a fairing around the rotor mast to cut aerodynamic drag. Another challenge was finding a place that was strong enough for the wing to attach to, and was very near the craft’s center of gravity. One possibility was immediately under the main rotor, but engineers chose an easier modification: the stout framing of the cabin floor. The final version, though, will have its wing mounted high, Cosgrove said, “and that will avoid troops climbing on it.”

The production version of the SpeedHawk will also stretch the cabin by almost four feet, replace the mechanical controls with digital ones, and replace the auxiliary power unit with a larger gas turbine, in order to deliver more horsepower to both the main rotor and the ringtail. The extra power should boost the speed and enable the craft to take off with more fuel, which increases range.

That’s if enough military money is rounded up to push the SpeedHawk upgrade kit through approval for manufacture and installation. The length of the procurement trail is a source of annoyance to John Piasecki. The standard procedure is broken, he says: “The procurement system is set up to motivate government program managers to eliminate competitive solutions, rather than create competition. Their job is to protect their program. But the responsibility of government is to leverage the innovative abilities of industry to get the best product for the expenditure of taxpayer dollars.” The military, he says, needs to look for solutions suited to the existing fleet, like the VTDP package. If it’s funded, the company hopes to have it ready for delivery in five or six years.

By contrast, the company’s closest competitor in the high-speed helicopter category, Sikorsky Aircraft’s X2, is an all-new design; Piasecki says that it will require many more years of work and hundreds of millions of dollars. “We’ve flown [the VTDP kit] full scale on an operational aircraft, the H-60, with a maximum weight of 24,000 pounds,” he says, whereas the X2, still in prototype, weighs only a quarter of that. “There’s no question that they [Si­korsky] could build a full-scale operational configuration, if sponsored by government. But they’d still face the timeline of a new-start aircraft.”

Several new-start military helicopter projects, despite having the great confidence of contractors and government backers, never made it through the whole developmental cycle: the AH-56A Cheyenne, a high-speed, heavily armed compound helicopter the Army commissioned during the Vietnam War; the Boeing/Sikorsky RAH-66 Comanche; and the Advanced Reconnaissance Helicopter.

By day, Sikorsky’s tom lawrence draws on 31 years of experience to advise on helicopter flight control systems, but by night, he is treasurer of the Sikorsky Historical Archives and a historian of vertical flight. On a recent trip I made to Sikorsky headquarters in Stratford, Connecticut, Lawrence invited me into his brown-walled cubicle, where he gave me a brief history of attempts to break through the limits of conventional VTOL flight.

Lawrence clicked through a slideshow of some of history’s more freakish vertical-flight variants: tilting jets, tilt-wings, ducted fans, tail-sitting airplanes, aircraft with rotors you could pack up and fold away. The Ling-Temco-Vought XC-142 tilt-wing created a downblast so strong it could throw rocks, knock people down, and uproot trees. Some models earned a few minutes of commentary, but others Lawrence dispatched with a single withering sentence: Of the Dassault Mirage III-V, which needed the thrust of eight jet engines to heave itself off the ground, he said: “Stand too close to this one and you’re French-fried.”

Sikorsky’s present innovation, the X2, is a helicopter with an aft propeller and what looks like an upside-down airplane tail. The X2 is Sikorsky’s second attempt to make a speed record breaker out of a coaxial helicopter (a coaxial has two main rotors mounted on one mast and turning in opposite directions; the arrangement maintains lift as speed increases). Sikorsky’s first attempt, the XH-59A prototype, flew for about 10 years beginning in 1973, but at high speeds it suffered from excessive vibration.

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