In 1970 EFF began work on a turbojet powered version of the
FFA Diamant 18 sailplane. This, named the
Prometheus 1, first flew on 21 June 1971. It was initially powered by a
Microturbo Eclair II, later replaced by a
Microturbo TRS 25. The engine was mounted on a short pylon to the rear of the cockpit above the wing centre line. Apart from the addition of the engine and associated fuel tanks and accessories, the aircraft was essentially the single seat Diamant 18. The later Prometheus 19 of 1978 was a two-seat,
side-by-side configuration aircraft with a new fuselage, purpose built to contain the wider cockpit and the twin turbojets, a new,
mid-mounted wing with a different section and a span, in its initial form, of . The
all-moving tail of the Diamant was replaced by a conventional one. Design work on the
Prometheus 19 began in about 1971 and construction was started in 1975, leading to a first flight on 22 June 1978. Its wing had a single aluminium spar and was skinned with
plywood infilled with
glass fibre/
foam sandwich. It was fitted with
flaperons for lateral control and lift generation, combined with
DFS-type
airbrakes operating only from the upper wing surface. The forward
fuselage had a wooden structure skinned with glass fibre. The
cockpit, ahead of the wing, seated two side by side . Two
Microturbo TRS 18 engines were mounted behind the cockpit, fed from a pair of
dorsal intakes immediately aft of the glazing and exhausting over the rear fuselage a little behind the wing
trailing edge. This section of the fuselage and the
empennage were constructed from glass-fibre sandwich. The Prometheus had a tall, straight edged
fin with the narrow chord
tailplane and single
elevator on top in
T-configuration. It landed on a retractable
tricycle undercarriage. The mainwheels were sprung on rubber blocks and were fitted with brakes; the nosewheel had an oleo
shock absorber. The
Prometheus 12 was a variant with a span wing to improve the performance envelope and increase structural strength. ==Variants==