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Thursday, January 27, 2011

Carter Flies VTOL Hybrid

Plucky Carter Aviation Technologies has flown its proof-of-concept Personal Air Vehicle (PAV), which incorporates the slowed-rotor/compound (SR/C) technology that AAI has licensed for use in VTOL unmanned aircraft - and DARPA's Transformer (TX) flying Humvee.

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Photo: Carter

The PAV completed a 36-min flight in early January (and thanks to The Register's chief boffin-watcher Lewis Page for the heads up). Carter says the flight constitutes the first of eight milestones linked to release of funding under a $4 million economic-development incentive agreement signed with Wichita Falls, Texas, in April 2010.

For the initial phase of flight testing, Carter says, the PAV is being flown as an autogyro to refine the flight control system. This phase will include vertical take-offs and landings. For the second phase, Carter will add the 45ft-span wing and begin SR/C flight tests.

The first milestone flight (the PAV made its actual first flight back in December) is significant also for AAI, which has made a substantial bet on Carter's SR/C technology for its next-generation VTOL UAVs. Under the license agreement signed in November 2009, Carter is required to complete four new aircraft for AAI by the end of 2011.

AAI has ambitious plans for the SR/C concept, which combines the characteristics of an autogyro, compound helicopter and fixed-wing aircraft. In AAI's eyes, the SR/C is a fixed-wing aircraft that carries an unpowered rotor for VTOL capability, which makes it simpler and more efficient that a helicopter - conventional or compound.

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Shadow SR/C (Concept: AAI)

For vertical take-off, a drive system is engaged on the ground to enable the engine to spin the rotor up to take-off RPM. The drive is then disengaged and blade pitch increased for a "jump" take-off on the energy stored in the rotor. Once airborne, the same engine drives a pusher propeller to provide forward thrust. 

As speed increases, the rotor mast is tilted forward forward to slow down and offload the now-autorotating rotor, lift transferring to the more-efficient fixed wing. To land, the aircraft autorotates to a "zero-roll" touchdown using energy stored in the high-inertia rotor system, which has composite blades with heavy weights in their tips.

AAI has at least three projects under way using SR/C. The first is to modify a pair of next-generation Shadow tactical-UAV prototypes with the propulsor and unpowered rotor. VTOL capability will make the aircraft independent of the current Shadow's pneumatic launcher and runway recovery while increasing payload and endurance, says AAI.

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Cargo SR/C. (Concept: AAI)

The second is to fly a prototype of an unmanned cargo aircraft. This will be built by Carter and based on its PAV design, and will carry a heavier payload faster, and further, than an unmanned helicopter, says AAI. The Shadow SR/C and cargo UAV are to fly this year.

AAI's third project, for which a second license was signed with Carter late last year, is to design a four-seat "fly-drive" tactical vehicle for DARPA. This could lead to a protoype flying in 2015. AAI's TX design has folding rotor, mast and wings and uses a turboshaft engine to spool up the rotor and drive a ducted propulsor in "fly" mode, and to generate electricity to drive wheel motors in "drive" mode.

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Transformer SR/C. (Concept: AAI)

Carter, meanwhile, plans to offer the "2+2" PAV as a kitplane. The company calls the aircraft is its second generation of SR/C. In an...eventful...flight-test program between 1995 and 2008, the earlier technology demonstrator showed the aircraft can take-off and land vertically and cruise at 150kt with near fixed-wing efficiency.

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