Attention has focused on Boeing teaming with Sikorsky to offer a high-speed coaxial-rotor compound helicopter, and Bell going it alone with a tiltrotor proposal. But they are not the only bidders for the US Army's Joint Multi Role (JMR) technology demonstration -- precursor to the planned Future Vertical Lift (FVL) Medium program to replace the UH-60 Back Hawk and AH-64 Apache. There are at least two others.
FVL-M Utility (Concept: AVX Aircraft)
One is small company AVX Aircraft, comprising mostly former Bell employees. Fort Worth-based AVX is proposing a compound helicopter (above) with coaxial rotors, small wings and dual ducted-fan propulsors. The rotor system is closely modeled on Kamov's coaxial design, down to the spacing between the two rotors, which is much greater than in Sikorsky's coaxial-rotor X2 configuration.
AVX says its design is capable of 230kt, the Army's threshold speed for the JMR flight demonstrators. The ducted fans provide the thrust, offloading the rotors, and at 230kt the forward and aft wings and fan ducts together produce 40% of the lift, with only 60% coming from the rotors.
FVL-M Attack (Concept: AVX Aircraft)
And, at 230kt, half the drag is from the fuselage and half from the rotor system. So AVX has been conducting windtunnel tests of a 50%-scale model of the coaxial hub in a bid to reduce its drag by a third. The rotor system has two composite-flexbeam hubs with drag-reducing aerodynamic fairings on the blade cuffs and the mast between the hubs.
Another bidder is only slightly bigger Piasecki Aircraft, which has a long association with compound helicopters. The company is emphasizing the "joint" in JMR with its PA61-4 Advanced Winged Compound (AWC) proposal. The 233kt full-compound Army variant (below) has Piasecki's signature vectored-thrust ducted propeller (VTDP), flown on the X-49A SpeedHawk, for propulsion and anti-torque and a long-span wing for lift. The wing pivots in pitch for addition flight control and to reduce rotor download in the hover.
Full compound Army FVL-M (Concept: Piasecki Aircraft)
Removing the wing, but retaining the VTDP, produces the 180kt "thrust compound" variant (middle, below), which is better suited to shipboard operations. If increased speed is not a requirement, say for external-lift or vertical-replenishment missions, the VTDP could be replaced with a lighter and cheaper conventional tail rotor to produce the 160kt helicopter variant (left, below).
Concepts: Piasecki Aircraft
The Army has funding to build two competing demonstrators, at most, with Sikorsky/Boeing's 230kt coaxial compound and Bell's 280kt "third-generation" tiltrotor currently leading the field. Eurocopter, through EADS North America, will have submitted a strong bid too, likely an X-3-style compound, so AVX and Piasecki would appear to be long shots.
Some suspect Karem Aircraft also may have submitted a JMR demonstrator proposal. Abe Karem designed the A160 Hummingbird with its optimum-speed rotor, and went on to work on an optimum-speed tiltrotor. Karem led one of the teams that worked on conceptual design of the Army's now-defunct Joint Heavy Lift large transport, so a JMR bid is not out of the question.