Developed from the Kestrel 17, the 604 is often erroneously called a Kestrel 22 despite the company never giving it a formal name beyond its number designation.[2]
Design and development
The 604 was originally intended as a test aircraft for a proposed two-seat glider that was never built. The prototype did so well in competition that a ten-aircraft production run was completed, resulting in a total of eleven 604s being completed.[1][2]
Due to the aircraft's huge size, including its 22.0 m (72.2 ft) three-piece wing that weighs over 272 kg (600 lb), the aircraft picked up the nickname "the Jumbo". The wing centre section alone weighs 115 kg (254 lb), requiring a large crew in order to rig it for flight.[2]
The 604 is constructed from fibreglass. The wing employs a modified Wortmann FX 67-K-170 airfoil at the wing root, changing to a Wortmann FX 67-K-150 at the wing tip. The wing features six flaps, with the outer pair moving at a 2:1 differential ratio with the ailerons. For glidepath control, the 604 has wing top-surface spoilers and a tail-mounted drag chute. The aircraft can carry 100 kg (220 lb) of water ballast. The landing gear is a retractable monowheel.[1][2][3]
Operational history
The 604 prototype, flown by Walter Neubert, came in sixth in the 1970 World Gliding Championships held at Marfa, Texas, even though the pilot was lost overnight after a land-out during the competition and missed the following day. A 604 came second in the Open Class at the 1974 World Championships held at Waikerie, South Australia. The aircraft also set several world records between 1970 and 1974.[1][2]