October 14, 2013
Credit: Karem Aircraft Concept
When the Pentagon set out its Future Vertical Lift (FVL) strategy to develop a family of advanced rotorcraft to replace its fleets of helicopters originally designed in the 1960s and '70s, one goal was to engage non-traditional suppliers to bring more innovation into the sector.
With the inclusion of two startup companies among the four teams awarded contracts for the U.S. Army's Joint Multi-Role technology demonstration (JMR TD), the Defense Department has taken a step toward that goal. Bell Helicopter and a Sikorsky/Boeing team may still be the favorites to fly two high-speed rotorcraft demonstrators in 2017, but they face real competition from two relative unknowns.
AVX Aircraft had already declared its hand, previously unveiling the 230-kt. coaxial-rotor, ducted-fan compound helicopter it is designing for JMR. But Karem Aircraft was not confirmed as a contender until Oct. 2, when the Army announced the four cost-sharing technology investment agreements for the $217 million JMR TD Phase 1 flight demonstration.
Karem Aircraft was formed in 2000 by Abe Karem, designer of the Predator unmanned aircraft and A160 Hummingbird unmanned helicopter, to develop his optimum-speed tiltrotor (OSTR) concept. Along with the other teams, Karem now has $6.5 million and nine months to complete preliminary design of its JMR demonstrator, the TR36TD, after which the Army will select two designs to be built and flown.
Karem is saying little about the design, except that the demonstrator will have two 36-ft.-dia. variable-speed rotors, powered by existing turboshaft engines, and that a production version would be capable of 360 kt. in level flight—faster than Bell's 280-kt. V-280 “third-generation” tiltrotor and Sikorsky/Boeing's 230-kt. coaxial rigid-rotor, pusher-propulsor design.
But some insight into the OSTR design is available from Karem's private-venture work on the 90-seat AeroCommuter and 180-seat AeroTrain commercial tiltrotors, and concept studies of a large cargo rotorcraft, the TR75, performed from 2005-10 under the Army-led Joint Heavy Lift project. JMR is a smaller rotorcraft, the precursor to a planned replacement for the Sikorsky UH-60 Black Hawk (see page 77).
The OSTR has long, light and stiff blades rigidly attached to the hub, which in turn is rigidly mounted to the nacelle—a lighter and less complex design than the articulated and gimballed hub on the Bell Boeing V-22. Instead of a swashplate and pitch links, the blades are individually controlled by electric actuators in the hub, saving weight and increasing reliability.