Profile – DHA Glas II Suction Glider

The task was not considered to be the number one priority; in fact, so busy were the aircraft manufacturers at that time that when de Havilland Australia won the contract they were instructed by the Government that the only staff allowed to work on the project would be a chief designer, an organizer and a stressing expert. In addition, no DHA equipment was permitted to be used for the glider project. (DHA were busy producing Tiger Moth and Dragon aircrew trainers. )

DHA selected Martin Warner as chief designer. Warner was not only an engineer, but a soaring enthusiast to boot. The other two DHA personnel were Steve Newbigin and Gordon Andrews. To overcome the problem of not being able to use any DHA equipment, the services of Slazengers (Australia) Pty Ltd were called upon, along with a small labour force of woodworkers. The aircraft was to be produced in the fifth floor of the Bradford Cotton Mills in Sydney.

Work started in March 1942 and only a matter of weeks after, the RAAF requested a second prototype; the intention was to soon after commence a production run of 126 aircraft.

The specification called for the gliders to be built entirely from Australian materials. The aircraft that took shape in the cotton mill were constructed primarily of wood. The high cantilever straight tapered wing had a wooden frame with plywood covering. All control surfaces were fabric covered. The fuselage was box-shaped in section, with the nose section modelled on the Dragon radio and navigation trainer. A single nose wheel and tail skid comprised the undercarriage. Seating was provided for the pilot and six passengers. The two DHA G1 prototypes were known as EG-1 and EG-2; ‘EG’ standing for ‘Experimental Glider’. The aircraft measured 17. 9m (59ft) in span and 10. 7m (35ft) in length and weighed 1,272kg (2,800lb) when loaded.

Flight Testing

EG-1 began flight testing on 14th June 1942, towed behind a RAAF Westland Wapiti. Test flying continued, with the Fairey Battle and late; the Spitfire also being used as tugs until EG-1 crashed after the tow rope snapped on a flight from Bankstown to Richmond. No-one was seriously injured, but the aircraft suffered considerable damage to the nose.

After EG-1 was repaired, it was joined by EG-2, which flew for the first time in November. After handing over to the RAAF, the two aircraft became A57-1001 and -1002 respectively.

Production

Meanwhile, the RAAF had altered the specification for the production gliders. Warner’s team were faced with the task of major redeslgn, including changing the wing from a single-piece structure to three parts (for easy transportation). An order for six production gliders was placed; these aircraft were to be known as DHA G2 gliders.

Before production even commenced, the tide of the war had turned and the invasion of Australia was appearing less likely. ln addition, the arrival of American equipment, including the Douglas Dakota and the Waco CG-4A 16-seat glider, had further reduced the need for the DHA gliders. Nevertheless, the six production G2s were completed and delivered to the RAAF between May and July 1943, to be numbered A57-1 to A57-6.

A57-1 spent the war as a trials aircraft with No1 Aircraft Performance Unit (APU), before being placed in storage. In 1946, this aircraft was earmarked for research work. The remaining five production gliders spent most of their lives in storage and were disposed of some years after the war (the last in late 1952).

The two prototypes ended up with No1 APU and were used for trials until late 1944. The two aircraft were then stored and disposed of in 1947.

The Second Life of A57-1

Had the story ended here, the DHA gliders would have earned no memorable place in history. However, A57-1 was to achieve some merit as the test bed for a weird ‘suction wing’.

After the war, the Commonwealth nations embarked upon an ambitious program of scientific and military research and experimentation. Amongst the Anglo-Australian projects that resulted from this postwar policy were the establishment of the Woomera rocket range, the atom bomb tests and later the lkara and Malkara guided missiles and Jindivik target aircraft. In June 1946, the Commonwealth Conference on Aeronautical Research was held in London to coordinate research activities throughout the British Commonwealth. One of the tasks discussed was the research and development of a Griffith-type suction wing and this was eventually allocated to Australia. The Council for Scientific and Industrial Research – Division of Aeronautics (later known as the Aeronautical Research Laboratories) were to work in co-operation with the Division of Aircraft Production – Beaufort Division (later to become GAF) in the testing of this wing on a modified DHA glider. OAP were responsible for construction of the wing and modification of the aircraft, while CSIR were to carry out wind tunnel testing, theoret-‘ ical calculations and flight testing.

Modification

On 15th January 1947, A57-1 was removed from storage and transferred to No1 APU at Point Cook. Before modification, a number of trials were carried out to provide before-and-after_ comparisons. In January 1948, the glider was transported to the GAF factories at Port Melbourne.

The wing under research was the GLAS II (Griffith Low-drag Aerofoil Section), a development of a proposal established in 1942 in Britain by Dr A A Griffith. This aerofoil employed the principle of boundary layer control by suction. ‘Laminar flow’ is simply a term describing air flowing over the wing and conforming to the shape of the wing, before becoming ‘turbulent’. On a normal smooth wing, the air stops being laminar and becomes turbulent at approximately one-third of the wing chord from the leading edge. Griffith believed the transition from laminar to turbulent flow could be delayed by applying suction at the trailing edge. He hoped to test this theory though an extremely thick wing which would rely almost entirely on suction, without which the huge increase in drag would cause the wing to be horribly inefficient. If such a wing proved practicable, the greater thickness would make it possible to house the crew, equipment, payload and engines all within the wing – completely redefining the purpose of the fuselage. This was essentially the basis of the ‘flying wing’ concept.

GAF set about the detail design and construction of the wing, under the project designation ‘A’. This was the first of the GAF project designations that would continue through ‘B’ (Jindivik) and onwards to the ill-fated Project ‘N’ (Nomad). The suction wing was built with the same platform as the original G2 wing and a Ford Mercury 59A VB car engine, mounted in the fuselage, was to provide suction. CSIR was to design the suction fan and fit the motor. The pop-up spoilers (or air brakes) of the conventional wing were replaced with shutters in the suction ducting which closed off suction to 1. 2m (4ft) of each wing to provide the necessary braking drag when required. Construction of the wing cost an estimated £6,500 (using 8,200 manhours and consuming.

Construction of the wing and modification of the glider proceeded through 1948. The modification to the fuselage involved structural changes to accommodate the Ford engine, fitment of a soundproof bulkhead and provision for a crew of pilot and observer forward of the bulkhead. The observer had all the necessary engine controls, switches for a recording camera and duplicate flight instruments. The pilot’s controls and instruments were standard, except for the provision of an emergency throttle override for the engine and a radio. An intercom system allowed the pilot and observer to communicate.

The recording camera was used to photograph another bank of instruments, with the observer using a connection board to allow pressures to be measured at up to 150 points on the wing and duct.

Flight Testing

After a trial assembly at Port Melbourne, the glider was transported to Laverton for reassembly and flight testing. The pilot was to be Sqn Ldr Gel Cuming, AFC, then chief test pilot with ARDU (the recently renamed No1 APU). Before a live tow, tests were conducted with the glider firmly tethered to the ground but wafting in the slipstream of a GAF Lincoln. This provided Cuming with a feel for the controls.

The first launch was made on 26th October 1948, with a Douglas Dakota acting as tug. It had been decided that initial trials would be with the engine in idle. During takeoff, the glider became laterally unstable and the pilot aborted, released the tow rope and landed straight ahead. A second attempt was made almost immediately, with the engine switched off completely. The launch proceeded and during the climb the pilot noted that the ailerons became ineffective at about 140 knots. Nevertheless, Cuming released from the Dakota and commenced testing. It was determined that the glider could be adequately controlled down to speeds of 60 knots with the engine off. When the engine was started, a violent porpoising resulted until the boundary layer adhered, whereupon the ailerons became extremely heavy. Cuming managed to land the glider with the engine running and almost entirely without aileron control.

After modification, the glider made two more flights, on 3rd December and 7th December. The latter flight almost ended in disaster when the aircraft entered a spiral dive from which recovery was made only after the engine was shut down. The time from release to touchdown was just 75 hair raising seconds!

Additional modifications and more flights ensued over the following year, when Cuming completed his 30th flight and handed the task over to another pilot in January 1950. Problems with lateral control had never been overcome but the cause had been determined: the humble insect. Insects collected by the wing during takeoff and climb had caused sufficient contamination of the leading edge to break up the laminar flow, unstick the boundary layer and degrade the lift and control of the wing. This problem afflicted all later attempts at boundary layer control by various countries and still hampers further development of the concept In spite of insects, sufficient data was collected to answer most of the questions about boundary layer behaviour around a GLAS II aerofoil. 17 more flights were made in A57-1 until the aircraft once again went into storage in July 1951, where it remained until its disposal in December 1952.

Conclusion

The GLAS II Glider was not the first aircraft to employ boundary layer control by suction; that honour fell to a modified Miles M. 8 Peregrine. Nevertheless, it was one of the most ambitious research programmes of its type and was extremely successful in proving the concept and discovering the major problem with the concept (insects). Later experiments with the Griffith wing included modifying Hurricane and Meteor aircraft with a much milder aerofoil.

Had the insect problem been overcome, the GLAS II glider would have paved the way for the proposed all-wing laminar flow airliner and thereby changed the course of aviation history. Although some ‘flying wing’ aircraft were developed, including the British Armstrong-Whitworth AW-52 jet and the Martin B-35 (piston) and B-49 Qet), the use of laminar flow as originally envisaged never occurred. The X-21 project saw the latest testing of boundary layer control by suction; two X-21A aircraft (modified WB-66 Destroyers) having been flown during the 1960s.

In spite of all the setbacks and dead-end projects, the field of laminar flow is continuing to be explored, with NASA identifying this technology as a key to any future supersonic airliners. That’s an awfully long way from the wooden glider built in a Sydney cotton mill in 1942