BELL HELICOPTER

D-292 ACAP
(Advanced Composite Airframe Program)

Info: all-composite research helicopter

Powerplant: 2 x Avco Lycoming 510kW LTS 101-750C-1 turboshafts

Significant date: 30 August 1985 (first flight)

Under the Army's Advanced Composite Airframe Program (ACAP), Bell Helicopter Textron was one of the two manufacturers (the other being Sikorsky) awarded a contract to design and develop a prototype of an all-composite helicopter. Phase I of this programme, which consisted of the engineering design and design support testing, was completed by the end of 1982. The construction and testing of three airframes (Phase II), began in October 1982. The first airframe was a tool-proofing article (TPA) used for repairability demonstrations and ballistic testing, while the second airframe became the flight-test vehicle (FTV) and accomplished its initial hover flight on 30 August 1985, over a year after the initially scheduled date. This was caused by both a series of walkouts from Bell employees and a shortage of funds, which led Bell to ask the Government for extra funding.

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 program (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 program included dropping the helicopter airframe from 42 ft in September 1987 at the NASA Langley Research Centre to demonstrate the capability of meeting stringent military crash survivability requirements. This included a 50 ft/sec 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 per cent in the airframe structure, a 17 per cent 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.

Thus the ACAP programme proved successful in meeting its objectives to demonstrate the use of advanced composites in a fully militarized airframe. This fruitful experience was to be used in the development of the future LHX light attack/armed reconnaissance helicopter.

Much less known is the experiment that was conducted in 1986 by the Boeing Military Airplane Company as part of an $8.3 million US Air Force study on atmospheric electricity hazards. Using a Bell D-292 airframe provided by the US Army's ACAP program, the BMAC team investigated methods of protecting electronic equipment in all-composite airframes from lightning strikes. The lightning simulation was capable of producing 200,000A/1.6Mv. The study was completed in June of the following year.

Population: 3 [the flying article received Army serial 85-24371]

Specs:
Main rotor diameter: 42 ft (12.80 m)
Length: 40 ft 5 in (12.32 m)
Height: 11 ft 2 in (3.40 m)
Maximum takeoff weight: 7,485 lb (3,395 kg)
Empty weight: 5,765 lb (2,615 kg)

Crew/passengers: 4 (2 crew, 2 passengers)

A glance inside the D-292 ACAP helicopter's all-composite mainframe.