Bell D-292 ACAP
In February 1981 the US Army's Applied Technology Laboratory announced that Bell Helicopter and the Sikorsky Aircraft Division of United Technologies had both been awarded contracts for the design, construction, and initial flight testing of composite airframe research helicopters as part of the Advanced Composite Airframe Programme (ACAP). The programme is the development of an all-composite helicopter fuselage lighter and cheaper to build, per production airframe, than conventional machines. Bell and Sikorsky were each awarded contracts for the production of three machines; a tool-proof vehicle, a static test vehicle, and a flight test vehicle. Bell's ACAP machine, which carries the company model number D292, made its first hover flight on 30 August, 1985. By mid-January 1986 the aircraft had completed twelve of its projected fifty flight test hours.
The D292 was based on Bell's commercial Model 222 twin- turbine light helicopter and used that machine's Avco Lycoming engines, transmission, and two-bladed main and tail rotors. The ACAP's tailboom, vertical fin, and rotor pylon are almost identical in appearance to those of the 222, though the D292's entire elongated pod-and-boom airframe is constructed of glass-reinforced plastic (GRP), graphite, and Kevlar. The use of a particular composite material for a specific aircraft component is determined by the strength, flexibility or other primary characteristic required of that component. The D292's basic load-bearing structure is thus constructed primarily of graphite or graphite/epoxy, while the flooring and most of the craft's exterior 'skin' is made of a more ballistically-tolerant Kevlar/ epoxy or glassfiber/epoxy blend. The seats for the helicopter's two crew members and two passengers are of Kevlar/epoxy and are designed to absorb the high vertical loads of a forty-foot-per-second crash landing, as are the legs of the craft's non-retracting tailwheel landing gear.
In addition to 15 hours of ground running and 50 hours of flight testing, which were completed in October 1985, the D-292 was used for shake testing and controls proof loading. A five-phase militarisation test and evaluation programme (MT&E) began in 1985 and was completed in 1988, following evaluation of undercarriage crashworthiness, lightning protection system, internal acoustics and additional repairability demonstrations. This programme included dropping the helicopter airframe from 12m in September 1987 at the NASA Langley Research Centre to demonstrate the capability of meeting stringent military crash survivability requirements. This included a 15m/s impact velocity at an aircraft attitude of ten degrees roll and ten degrees nose up pitch without any apparent serious injuries to the four dummy occupants (this impact velocity was comparable to a free fall from a three-storey building). Another major advancement demonstrated by the Bell ACAP design during these tests was the fuel system which totally contained the fuel during the drop test, thus reducing the risk of post-crash fires. But the main purpose of the ACAP programme was to achieve the US Army's goal of reducing weight and cost, as well as improving military helicopter characteristics, by demonstrating the application of advanced composite materials. In this sphere, the Bell D-292 featured a weight reduction of 22% in the airframe structure, a 17% saving in cost, survivability in a vertical crash, and reduced radar signature. These comparisons were made possible because Bell and Sikorsky each also designed a duplicate aircraft of current conventional metal construction.
Engine: 2 x Avco Lycoming LTS 101-750C-1 turboshaft, 510kW
Main rotor diameter: 12.80m
Fuselage length: 12.32m
Take-off weight: 3395kg
Empty weight: 2615kg