de Havilland Gliders in the RAAF during WW2

Following the Japanese advance through Malaya and the Netherlands East Indies, and the bombing of Darwin on 19 February 1942, the Australian authorities were seriously concerned about the possibility of a Japanese invasion of Australia. The RAAF therefore considered that Australia needed its own troop-carrying glider capability, rather than depending entirely upon Britain or the United States.

In March 1942, the Department of Air issued a requirement for a total of 126 troop transport gliders and Specification 5/42 was issued for a small seven-seat glider.

The project was given to de Havilland Australia and it was particularly significant because the DHA glider was effectively de Havilland Australia’s first indigenous aircraft design. DHA had previously been assembling and manufacturing de Havilland designs under licence, including Tiger Moths and Dragons.

The glider was something different: an Australian design produced in response to an Australian military requirement. The chief designer was Martin Warner.

Because DHA was already heavily committed to wartime production, the glider project was undertaken using subcontractors and unusual manufacturing arrangements. The prototypes were constructed on the fifth floor of the Bradford Cotton Mills building at Camperdown, in Sydney.

The aircraft was essentially a large wooden box-like troop-carrying glider, but it was considerably more sophisticated than its rather simple appearance might suggest. Some of its characteristics were:-

The windscreen and window arrangement drew heavily upon the de Havilland DH.84 Dragon, which DHA was already manufacturing. The undercarriage was particularly simple: a single main wheel, with a substantial nose skid and tailskid. That was entirely appropriate for an aircraft intended to land on relatively rough forward strips.

The first prototype flew on 14 June 1942. It was initially tested at RAAF Richmond, with a Fairey Battle acting as the tug. The second prototype followed later in 1942.

There is some disagreement between some records as to the proposed use for this glider. One source indicated that the glider was intended to carry small groups of troops into areas threatened by Japanese invasion. Another source, which came from people involved with de Havilland, suggested a somewhat different role: namely carrying fighter-support equipment, engines, guns and personnel to forward fighter bases.

The DHA was far too small to be an Australian equivalent of the later American CG-4A or British Horsa. It could carry only six passengers plus the pilot.

Consequently, describing it simply as an “invasion troop glider” can give a misleading impression of its intended military usefulness. A more sensible interpretation is that it was a small tactical transport glider, capable of carrying a handful of personnel or a useful load of equipment into a forward area.

The RAAF subsequently ordered an improved production version of the glider which was designated DHA-G.2.

Six G.2s were built and assigned RAAF Serials A57-1 to A57-6. The G.2 differed from the prototypes in several ways.

Most importantly, its wing was redesigned so that it could be broken into three sections. This made the aircraft substantially easier to transport by road or other means to an operational area. The production aircraft also had a somewhat different fuselage and revised wing. The prototypes had approximately a 59-foot span, whereas the G.2 had a span of approximately 50 ft 6 in.

The six G.2s were constructed in Sydney in the Slingo & Williams building, which had previously been a toy factory. They were then assembled at Mascot.

The first production G.2 flew on 20 March 1943. It was delivered to the RAAF on 6 May 1943, with the remaining aircraft following in July 1943.

By the time the G.2 entered service in 1943, the immediate invasion threat had diminished substantially. This is probably the most important reason why the DHA glider never became an important operational aircraft.

At the same time, Australia was obtaining much more capable aircraft from the United States. The Douglas C-47 Dakota had already proven that it could transport considerably larger loads and could operate without the limitations associated with glider operations. The Americans were also supplying Waco CG-4A Hadrian gliders.

Consequently, there was little reason to embark upon mass production of a small Australian glider. Only six G.2s were ever produced.

This glider became by far the most historically significant aircraft. It ultimately became the GLAS II suction-wing research aircraft (see below).

The remaining five were delivered to No. 2 Aircraft Depot at Richmond in July 1943. In August they were transferred to No. 1 Air Observers School at Evans Head, where they were largely stored. Their subsequent histories demonstrate just how little the RAAF ultimately needed them.

This glider was occasionally flown behind C-47 Dakotas from Richmond, apparently continuing into the post-war period.

It was transferred to the CSIR Division of Aeronautics (CSIR-DA) for research purposes.

After the war, glider A57-1 was given a completely new lease of life. Australia had developed considerable interest in boundary-layer control and the possibility of using suction to maintain smooth airflow over an aircraft wing.

The concept was to suck air through extremely small openings in the wing surface. The objective was to delay flow separation and consequently improve the aerodynamic characteristics of the wing.

A decision was made in 1946 to use A57-1 for this work. The aircraft was rebuilt with an experimental Griffith-type suction wing.

The resulting aircraft became known as the GLAS II. This is an acronym associated with the Griffith/Glauert-type suction-wing research.

The modified A57-1 received a 96 hp Ford V-8 Mercury 59A engine. The engine did not primarily exist to propel the aircraft. Instead, it drove a centrifugal blower which generated the suction required for the experimental boundary-layer-control system.

So the aircraft effectively became a flying laboratory. Its engine was there principally to operate the aerodynamic experiment.

The GLAS II experimental wing had a span of approximately 48 ft 9 in (14.88 m). The wing incorporated very closely spaced slots through which air could be sucked from the boundary layer.

The idea was extremely ambitious. If the boundary layer could be kept attached to the wing, engineers hoped that aircraft could operate with:-

The Australian work was therefore not merely an experiment with the DHA glider. It was part of a much wider post-war investigation into boundary-layer control and laminar-flow aerodynamics.

Glider A57-1 with the modified GLAS II wing

Initial tests involved the aircraft being positioned behind the slipstream of an Avro Lincoln. Actual flight testing behind a Dakota began on 26 October 1948. The research program ultimately involved approximately 49 flights, according to Australian aircraft history sources.

There were considerable technical difficulties. One of the major problems was surprisingly mundane. Insects and other foreign matter contaminated the wing’s suction slots and disrupted the carefully controlled airflow. The experimental system therefore demonstrated both the potential and the practical problems of suction boundary-layer control.

The GLAS II experiment did not simply demonstrate that the DHA design was unsuccessful. Rather, the research showed that maintaining the extremely clean wing surface required by the suction system was a serious operational problem.

The contamination issue was particularly troublesome. Interest in the concept subsequently declined. Other much more ambitious Australian projects were being considered, including the GAD-4 suction-wing glider and even a proposed 72-passenger all-wing aircraft. Neither was built.

A57-1 continued in experimental use into the early 1950s. The GLAS II program was eventually terminated. The aircraft was offered for disposal on 17 December 1952. By then the DHA G.1/G.2 had disappeared completely as an operational aircraft type.

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