Maverick TwinJet 1500 kit

First glance: Converted helicopter turbines power a mini-bizjet for piston money. By Howard Levy.

THE MAVERICK TWINJET 1500 is the world's first four- to five-place, turbojet, all-composite kit. Five are currently being built.

Designer Robert Bornhofen, a low-time private pilot, has an extensive background in mechanical and aerospace engineering. He began the programme three years ago. The plane was designed using CAD and 3-D modelling technology.

Initially, it was primarily in moulded pre-impregnated E-glass/honeycomb composites, with some carbon fibre composite in the wing spar and other high-stress areas. After flight testing the prototype, a number of changes were made. These included: more use of carbon fibre (all control surface skins and tail component structures); increasing the span of the flaps by one-third and deflecting flaps from 35° to 50°; removing wingtip fuel tanks; adding an inverted V-configured ventral fin at the tailcone; adjusting the C of G by moving the wing aft three inches and taking out the ballast and elimination of the inner landing-gear doors.

The modifications lightened the aircraft by approximately 500 lb while increasing its strength and improving performance.

In comparison to piston-engined twins of comparative class, the manufacturer claims the jet, with 200 to 220 mph cruise, is eighty per cent faster--and cheaper to operate.

The engines are General Electric T-58 1,200 shp turboshaft helicopter engines remanufactured and converted by Maverick Air to conventional, axial-flow turbojet powerplants. They are also derated to 750 lb static thrust--and redesignated MAT-58. The TwinJet's airframe is stressed to support engines up to 300 lb in weight and 900 lb thrust. The manufacturer is looking at afterburners as an option. Engine installation is a near-centreline thrust arrangement.

The prototype, N750TJ, flew in August 1999.

In January 2000 the right engine ingested a bird, but the engine maintained power and the airplane climbed out. In April 2000, during a high speed taxi test, the left tyre blew, a weld on the gear gave way, the gear collapsed, and the TwinJet skidded half-a-mile down the runway on wing and belly--all was repaired. Three months later, a TwinJet kit builder flew the same aircraft on a turbulent day. That, with wind-shear, resulted in a 6g landing, and when the gear appeared to be coming up through the wing, the engines were spooled up, and the airplane climbed out. It was decided to land the airplane on nearby Pueblo Airport's 10,500-foot runway rather than the aircraft's Penrose homebase. Both gears collapsed on touchdown.

In both the landing accidents the airframe stood up superbly.

In most moulded, composite aircraft, the shells are fabric