Country of origin:

United States of America

Description:

Commercial airliner

Power Plant:

Four 597 kw (800 shp) Pratt & Whitney PT6A-30 turboprops

Specifications:

History:

In about May of 1970 it was announced to the press that negotiations had been in progress for some time in relation to the possibility that the American-designed 36-40 seat GAC-100 feeder liner, powered by United Aircraft of Canada PT-6 turboprop engines, would be almost entirely built and assembled in Australia. It was thought at the time the Government Aircraft Factory (GAF) would be the prime contractor and that the Australian Federal Government would be involved to some substantial degree in funding the development of the aircraft, in addition to the American capital.

The President of the General Aircraft Corporation (GAC) of El Segundo, California was at the time Dr Lynn Bollinger, who was also president of Helio Aircraft. As part of the program he visited Australia to have discussions with the Australian Federal Cabinet. It was said the initial sub-contract came out of the blue when GAC, following an investigation of Australian Aircraft Industry facilities, offered GAF the wing manufacturing sub-contract. The award of the contract was jointly announced by Senator Anderson and the president of GAC on 7 February 1969. Senator Anderson stated he expected GAC would announce the go-ahead for production in about two months.

Pacific Airmotive Corporation of California had the prime contract to build the GAC-100 but withdrew some time before, in 1968, on the ground that, with other work, it did not have the capacity to meet the production requirement for eight aircraft a month. There was also the problem that at the time de Havilland Canada planned a competing aircraft, the de Havilland DHC-7, which was a high-wing aircraft of similar size with four engines, with Canadian Government financing. At the time a market survey showed considerable interest but no firm buyers amongst the American third level operators.

A visit was made to Australia in early 1968 by General Aircraft Corporation’s Senior Vice-President (Engineer), Mr Joe H Telley, and at that time Airfast Services Pty Ltd of Sydney, NSW was appointed as GAC’s sales adviser for the Australasian area. In May 1968 several senior staff from GAF left Australia to examine the technical and other details of the project, its potential – technically and economically – for GAF. They returned in June and their reports were submitted to the Australian Government for consideration and decision.

Initially the design was to have two engines – the Lycoming T-53 being initially selected – but this was not considered a suitable power-plant for commercial applications as it was essentially a military engine used predominantly in turboshaft form in the Bell UH-1 Iroquois series. It was also used in the Grumman Mohawk and the Canadair CL-84 tilt-wing experimental aircraft. As will be seen, the GAC-100 was similar in configuration to the French Potez 84 with Turbomeca Astazou X engines, which had already entered the market, and which did not succeed; and in its refined version, the Potez P-841, which also had PT-6 engines but was not produced in numbers.

GAC stated it was convinced that the GAC-100 design filled a substantial gap in the equipment picture and that there were good prospects for such a relatively economic, high-performance type at the short-haul, low-density end of the existing airline market. The sub-contract for GAF was reported to be worth $13,000,000 when announced. It was said Australian domestic airlines had shown a promising but non-committal interest in the aircraft, but had also shown interest in the DHC-7 and had already taken delivery of examples of the DHC-6 Twin Otter.

Reports of the time have varied but one report stated General Aircraft Corporation had designed a 32-seat turboprop transport aircraft aimed primarily at the third-level commuter and local airline market. It featured advanced high-lift devices (some under licence from Helio Aircraft Corporation) for low-speed operation from unimproved airstrips.

First flight of the prototype was scheduled for the second half of 1970 and type certification under FAR Part 25 was expected to be received by 1 January 1971. Production of all airframe assemblies was to be sub-contracted and Pacific Airmotive Corporation, Howmet Corporation’s Land Production Division, the Government Aircraft Factory, and the Commonwealth of Australia Department of Supply were named as sub-contractors.

Development of the design continued and the basic change to the design involved increasing seating capacity from 32 to 36, this being achieved by adding 43 cm (17 inches) to the fuselage length and by modifying the seat pitch, increasing gross weight from 10,660 kg (23,500 lb) to 11,567 kg (25,500 lb). The fuselage structure was a pressurised fuselage built in three main sections from 2024-T4 material. The main centre-section of the fuselage was to be constructed of external sheets stiffened with rolled or extruded longerons and formed channel section frames. The nose section incorporated formed external sheet panels, formed channel section frames, and rolled or extruded longerons. The aft section was to be of similar construction and was to have the fin built on to it.

The fin and tailplane structure were of conventional two-spar design with flat-webbed spars having extruded booms. The tailplane was to be built in left and right-hand panels attached to a horseshoe-shaped fuselage frame and the fin was constructed as an integral part of the fuselage structure. The wing was to have two spars, with spanwise panel stiffeners and chordwise ribs and bulkheads. The wing spars were to consist of extruded booms with sheet metal webs and extruded stiffeners. Ribs between the two spars were to have rolled or extruded stiffeners. Bulkheads formed the boundaries of the fuel tanks and were to be attached to and sealed at the spars and at the upper and lower wing skins. The wing was also to be covered with 2024-T4 aluminium alloy.

The wing contained two integral fuel tanks between the front and rear spars and provision was to be made for the installation an auxiliary fuel tank. Each Pratt & Whitney PT6-30 engine was to be attached to a forward ring with four mounting points. There was to be one fuel tank in each wing with a capacity of 1,249 litres (275 Imp gals), giving a total of 2,498 litres (549 Imp gals).

The undercarriage was designed for small airfields, including grass strips. It was a high-flotation undercarriage which had dual main wheels, and had twin nosewheels. The aircraft was able to make a 180 degree turn on a 14 m (46 ft) wide taxi-way. All three units retracted and extended hydraulically with mechanical latches. An anti-skid device system was incorporated in the brake system for the main wheels. All wheels retracted forward, the nose unit retracting into a fuselage well, whilst the main units retracted into the inboard engine nacelles.

Although very little had happened up to June 1981 in relation to the construction of a prototype, the aircraft was still considered to be proceeding, the manufacturer now becoming the Commuter Aircraft Corporation after General Aircraft Corporation went into liquidation. A new facility to build the aircraft was being constructed at Youngstown, Ohio, adjacent to the Youngstown Municipal Airport on a 94 acre site. An announcement was made that 1,600 jobs would be created in the Mahoning Valley to build the aircraft. At that time Kornel Feher was the president of Commuter Aircraft, having been the chief engineer for the GAC-100 project in the early 1970s , being credited with developing the idea of the aircraft.

By 1979 the United States was having problems with the economy, there having been 15,000 workers laid off as steel plants were closing across the country, and de-regulation of the airline industry was taking place.

An offshoot of the design was the GAC-100M for military use, this variant having a rear cargo door, which would have been able to accommodate a standard airdrop pallet, or up to 24 paratroops.

In 1981 Commuter Aircraft announced the aircraft was now to be known as the CAC-100, was a 50-seat commuter aircraft with a cruising speed of 560 km/h (348 mph), the prototype would be completed in late 1982 and the first scheduled production aircraft would roll off the production line in 1984.

One publication relating to the design in the early 1980s referred to it being an all-metal, fail-safe, semi-monocoque tubular fuselage pressurised and able to accommodate a flight crew of two, 50 to 60 passengers, a single stewardess, a coat compartment, galley and toilet, as well as a pressurised baggage compartment aft of the main cabin. By this time there was a reference to installing four Pratt & Whitney Canada PT6A-65R engines driving five-blade Hartzell constant-speed reversible propellers. First flight was set down for 1983.

One of the design features of the aircraft was that it would be a STOL aircraft, which has been referred to as a “short conventional take-off and landing aeroplane”, but there was no official FAA requirements for a STOL capability. The aircraft was to have a FAR 25 field length of 646 m (2,120 ft), increasing to 701 m (2,300 ft) on a 32.2 degree C (90 degree F) day. It would seem this STOL system, using Helio-developed leading-edge slats, would have been of little interest to airlines using the type and it may be this was one of the problems which led to the demise of the aircraft.

A British report relating to the design stated a technical novelty of the design was the high-lift system and associated lateral controls. Handley Page automatic slats extended over the entire leading-edge, and behind them were top surface flow intercepters which were operated by the aileron circuit (whenever the slats were extended) and were therefore expected to give increasingly precise roll control the higher the lift of the wing. Double-slotted flaps were to extend almost over the entire trailing-edge. In addition, there were full-span lift-spoiler air brakes. The article referred to the aircraft as very much like a scaled down Vickers Viscount and stated work had begun on the prototype, that it should fly during 1970, with deliveries to begin in late 1971 and early 1972. It also reported the Australian Government Aircraft Factory in Melbourne, VIC was considering taking a share in the airframe construction and several Australian operators had expressed an interest in the type, assuming it could be purchased for less than $1 million (£415,000).

But the aircraft was never built and another promising opportunity for the Australian Aviation Industry went begging. It seems no prototype was constructed and it is not known even if work commenced on the prototype or on a mock-up of the fuselage. In the end the design did not make it, the Government Aircraft Factory did not produce any wings, and it may well be it could not be manufactured at the right price to suit the market in the face of considerable competition arising for 50 seat aircraft around the world, most of which were twin engined.