Aviation Week – “Flying Humvees” being designed by AAI and Lockheed Martin have made it through to the second phase of DARPA’s Transformer (TX) program – but the sheer scale of the challenges in producing a fly-drive tactical vehicle is becoming clear.
Transformer is not simply a roadable aircraft – it is a four-seat vehicle that must be able to drive off-road, survive small-arms fire, and rapidly reconfigure into an aircraft that can take off and land vertically and be flown without pilot training.
Concept: Lockheed Martin and Piasecki Aircraft
AAI’s TX (below) is a 7,500lb vehicle with an unpowered rotor for VTOL, a fold-out wing for cruise and a ducted fan for propulsion. A single 1,200shp Honeywell HTS900 turboshaft generates power to drive the four electric wheel motors, spins up the rotor for a “jump” take-off and drives the 56in-diameter ducted fan in forward flight. Ground speed is up to 80mph; flight speed range is 50-155kt; maximum altitude is 10,000ft.
Using Cartercopter’s slowed rotor/compound technology, AAI’s TX is essentially an autogyro with wings. In forward flight, lift transfers to the wing and the 50ft-diameter rotor slows until it is rotating solely to provide stability. Compared with a conventional helicopter, this reduces rotor drag. Retractable suspension pulls the wheels up into their wells to further reduce drag in flight. To land, the vehicle autorotates, the high-inertia, tip-weighed blades storing enough energy to enable a “zero-roll” touchdown.
Lockheed Martin’s TX (below) is a 7,000lb vehicle with ducted fans that tilt from horizontal for VTOL and to vertical for forward flight. The 8.5ft outside-diameter fans are attached to a lifting-body center wing section mounted above the vehicle. This houses a pair of turboshaft engines that drive the fans and has a trailing-edge flap to increase lift at low speed. Flight speed is up to 130kt.
To convert from fly to drive, the outer panels of the 41.5ft-span wing fold inwards against the ducts and the complete wing/fan assembly rotates to lie along the length of the vehicle. A Pratt & Whitney EnduroCore heavy-fuel dual rotary engine then powers the four electric wheel motors. DARPA is aiming for a range – on the ground or in the air – of 250 miles on a tank of gas.
Phase 2 of the Transformer program is heading for preliminary design reviews at the end of the third quarter of fiscal 2012, after which DARPA will decide whether to select one team to proceed into Phase 3, which would culminate in prototype ground and flight demonstrations in mid-fiscal 2015. In addition to the objective “field vehicle” (FV) concepts shown above, the teams are designing prototype vehicles (PV). These would demonstrate the major features of their concepts, but would not be fully rugged and survivable tactical vehicles.
DARPA aiming for around $1 million a copy compared with $400,000 for a Humvee and $4 million for light helicopter.