There’s just no way to add 100 mph to the speed of a helicopter. Or is there?
- By James R. Chiles
- Air & Space magazine, September 2009
(Page 2 of 4)
Piasecki Aircraft has developed a kit for compounding existing military helicopters with a Vectored Thrust Ducted Propeller—an eight-foot-diameter, tailboom-mounted, shrouded propeller, nicknamed “the ringtail.” The company hopes that the kit, along with a fixed wing from a business jet, will transform thousands of Sikorsky H-60 Black Hawk helicopters into SpeedHawks, bringing them into the fast lane, on a short schedule and a low budget.
On October 16, 2008, the company publicly debuted its single SpeedHawk, the X-49A demonstrator. The presentation took place at the New Castle County Airport, near Wilmington, Delaware.
The day was a mixture of celebration (this would be the last of the Phase I flights the Army contract required) and trepidation (Would the military cough up money for the next phase of tests?). Guests gathered to drink coffee and amble through exhibits and posters reprising Piasecki’s decades of research. Most pertinent was a SpeedHawk forerunner called the Pathfinder II, a turbine-powered compound helicopter with a ring-encased tail thruster, which in 1964 reached 225 mph. (It never went into production.) Later, Piasecki designed ducted-propeller upgrades for the Cobra and the Hughes AH-64 Apache; a mockup of the compounded Cobra and a poster of the modified Apache were on display.
Piasecki has a long history of developing vertical-flight variants. Though the company has manufactured no aircraft since 1955, it has developed and flown dozens of prototypes. Visitors at the airport got a look at the Air Geep, a two-turbine runabout designed for the Army and a magazine cover star of its day, and an unmanned Geep variant called the Air Scout. In the back lot of the company’s Essington, Pennsylvania headquarters, visitors can see remnants from the Heli-Stat, a heavy-lifting experiment in which a metal framework attached four H-34 helicopters to a blimp. (A crash ended the project.)
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.)