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Newsletter 17
Summer 2007
Updated on 28Jul2007
Contents
Editorial
Aces, Erks, Backroom Boys
Annual General Meeting
Dunsfold Wings and Wheels
EDO to Project Office
Eric Rubython
F-35 Lightning News
From Ribs to Retirement
Hawk News
Hawker Nimrod Query
Hawker People News
Hunters Still Active
Kingston Aviation Heritage
Members
Programme
Racing Gliders
Unlocking Potential
Upper Heyford Recollection
V/STOL Wheel of Misfortune
Why Pay More

Published by the Hawker Association
for the Members.
Contents Hawker Association

 
    The last talk of 2006 was given on the 8th November by aerodynamicist Afandi Darlington, a graduate of Imperial College, onetime employee of BAe, member of the British Gliding Team and president of the Imperial College Gliding Club. He also led Richard Noble's Farnborugh F1 design team and went with the project to the USA when it was taken on and built by the Gulf Aircraft Partnership as the Kestrel. His colleague, Peter Masson, was due to cover the competition aspects but, as he was indisposed, Afandi covered that as well as performance.
    The objective of glider design is to improve performance so that the aircraft flies faster and further, and climbs more quickly in thermals or waves. The key is low drag achieved by developing a clean airframe with laminar flow regions. A successful modern glider will demonstrate a lift:drag ratio (L/D) of up to 70; i.e. the glider will travel 70 miles for a mile of height. At low speed induced drag is dominant and this is reduced by winglets.
Racing Gliders And Optimising Performance

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    At high speed profile drag dominates, mainly from the wing, and this is reduced by achieving laminar flow and by careful design of profiles and the junctions between the wings and  tail and the fuselage. Water ballast is used to increase the wing loading which results in increased speed for the same L/D and yields an increased L/D because the operating Reynolds number is increased. The boundary layer can be laminar - thin and well ordered - or turbulent - thicker giving more drag. Glider wing sections are designed to achieve large regions of laminar flow with low drag and reasonable stalling behaviour.
    Afandi illustrated glider performance improvements by historical examples. The 'modern era' started in the 1930s with the German 'Wiehe', an 18 m span wooden design, which achieved a L/D of 29 at 41 kts and a minimum sink rate of 1.2 kts.
    The 'fs 24' Phoenix of 1957, a 16 m glass fibre design incorporating laminar flow technology, had a L/D of 40 at 43 kts with a sink rate of 1.1 kts. The equivalent numbers for the 'Nimbus' of 1971, a 20.3 m glass fibre design, were 49, 49 and 1.0.
     By 2000 the carbon fibre/glass fibre/Kevlar 31 m 'ETA' demonstrated 70, 59 and 0.9, the current 'state of the art.' By 2020 an L/D of 80 should be achievable by laminar flow control. It was laminar flow which gave the big jump in L/D post WW II.
    This is all put into perspective by Sir George Cayley's 1853 9 m span glider which had a L/D of 5 at 25 kts and flew 200 yds. In 1985 Werner Pfenniger designed a 32.4 m glider with a predicted L/D of 100 using a windmill to suck away the boundary layer. The honeycomb carbon fibre skin was laser drilled with holes of sizes which matched suction to local pressure and was successfully tested in a wind tunnel.
    The UK built 21 m  'Sygma' had a variable chord wing to be extended in thermals. Seal difficulties caused failure but the concept was later tried successfully in Germany. Also investigated have been the 15 m 'SB 13' flying wing and a variable span 19 to 30 m design with extension by hand crank.
    Current wing design tools include computational fluid dynamics and infra-red boundary layer visualisation in the wind tunnel; laminar flow is cool, turbulent is warm. Materials include Kevlar and carbon fibres aligned to tailor strength, using traditional wet lay-up methods or pre-impregnated cloth; 'pre-preg'. The latter reduces weight by 5% with increased strength but costs rise by 300%. Computer aided design and manufacture (CAD/CAM) techniques give accurate, smooth moulds allowing airframes to be hand finished to a mirror-like surface, aiding laminar flow.
    Modern gliders have safety cockpits, carefully shaped with high sills and made with a mixture of composites (70% Kevlar, 30% carbon or glass fibre) for peak energy absorbtion. They are equipped with electronic instruments including total energy displays and GPS. Some gliders have high powered, compact electric motors, the latest of which can take a glider from launch to 10,000 ft. The future holds the promise of stronger fibres, active boundary layer control, adaptive geometry, better instruments, fuel cell powered electric motors and weather information via datalink. Advances will probably spill across from military UAV (unmanned aerial vehicle) research.
    Turning to the sport of gliding, Afandi noted that the current distance record, which must be set in daylight, is 3009 km, the speed record is 247 km/hr over 500 km, and the altitude record is 49,009 ft, although Steve Fosset, in a flight yet to be homologated, has exceeded this wearing a pressure suit. Thermal, hill or ridge and wave lift are utilised but new records depend on the latter; wave lift is known to extend up to 100,000 ft in New Zealand.
    Competitions consist of nine races over nine days. Competitors launch when they choose, fly through the start line, then fly a triangular course back to the finish line. The United Kingdom is the top gliding nation!
    Afandi closed with a video of the Gulf Kestrel first flight and then answered questions from the floor. He encouraged the audience to go gliding, perhaps by a course at Lasham. (The Editor can thoroughly recommend this having done such a course in September.) The vote of thanks was given by Ralph Hooper, a once keen glider restorer and pilot who also worked with Afandi on the Farnborough F1.