The EFF Prometheus was an unusual two seat motor glider powered by a pair of small

turbojet The turbojet is an airbreathing jet engine which is typically used in aircraft. It consists of a gas turbine with a propelling nozzle. The gas turbine has an air inlet which includes inlet guide vanes, a compressor, a combustion chamber, and ...

engines, designed and constructed in

Switzerland ). Swiss law does not designate a ''capital'' as such, but the federal parliament and government are installed in Bern, while other federal institutions, such as the federal courts, are in other cities (Bellinzona, Lausanne, Luzern, Neuchâtel ...

in the 1970s. Two versions with different spans were built, but it did not go into production.

Design and development

In 1970 EFF began work on a turbojet powered version of the FFA Diamant 18

sailplane A glider or sailplane is a type of glider aircraft used in the leisure activity and sport of gliding (also called soaring). This unpowered aircraft can use naturally occurring currents of rising air in the atmosphere to gain altitude. Sailplan ...

. 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 Tandem, or in tandem, is an arrangement in which a team of machines, animals or people are lined up one behind another, all facing in the same direction. The original use of the term in English was in ''tandem harness'', which is used for two ...

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 Plywood is a material manufactured from thin layers or "plies" of wood veneer that are glued together with adjacent layers having their wood grain rotated up to 90 degrees to one another. It is an engineered wood from the family of manufactured ...

infilled with

glass fibre Glass fiber ( or glass fibre) is a material consisting of numerous extremely fine fibers of glass. Glassmakers throughout history have experimented with glass fibers, but mass manufacture of glass fiber was only made possible with the inventio ...

/ 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 The fuselage (; from the French ''fuselé'' "spindle-shaped") is an aircraft's main body section. It holds crew, passengers, or cargo. In single-engine aircraft, it will usually contain an engine as well, although in some amphibious aircraft t ...

had a wooden structure skinned with glass fibre. The

cockpit A cockpit or flight deck is the area, usually near the front of an aircraft or spacecraft, from which a Pilot in command, pilot controls the aircraft. The cockpit of an aircraft contains flight instruments on an instrument panel, and the ...

, ahead of the wing, seated two side by side . Two

Microturbo TRS 18 The Microturbo TRS 18 is a small, low thrust turbojet designed and built in France in the 1970s. It was installed on both manned and unmanned aircraft. Design and development The TRS 18 was originally designed for self-launching motor gliders b ...

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 The empennage ( or ), also known as the tail or tail assembly, is a structure at the rear of an aircraft that provides stability during flight, in a way similar to the feathers on an arrow.Crane, Dale: ''Dictionary of Aeronautical Terms, third ed ...

were constructed from glass-fibre sandwich. The Prometheus had a tall, straight edged

fin A fin is a thin component or appendage attached to a larger body or structure. Fins typically function as foils that produce lift or thrust, or provide the ability to steer or stabilize motion while traveling in water, air, or other fluids. Fin ...

with the narrow chord

tailplane A tailplane, also known as a horizontal stabiliser, is a small lifting surface located on the tail (empennage) behind the main lifting surfaces of a fixed-wing aircraft as well as other non-fixed-wing aircraft such as helicopters and gyroplane ...

and single

elevator An elevator or lift is a wire rope, cable-assisted, hydraulic cylinder-assisted, or roller-track assisted machine that vertically transports people or freight between floors, levels, or deck (building), decks of a building, watercraft, ...

on top in T-configuration. It landed on a retractable

tricycle undercarriage Tricycle gear is a type of aircraft undercarriage, or ''landing gear'', arranged in a tricycle fashion. The tricycle arrangement has a single nose wheel in the front, and two or more main wheels slightly aft of the center of gravity. Tricycle ge ...

. The mainwheels were sprung on rubber blocks and were fitted with brakes; the nosewheel had an oleo

shock absorber A shock absorber or damper is a mechanical or hydraulic device designed to absorb and damp shock impulses. It does this by converting the kinetic energy of the shock into another form of energy (typically heat) which is then dissipated. Most sh ...

. The Prometheus 12 was a variant with a span wing to improve the performance envelope and increase structural strength.

Variants

;Prometheus 1:The first prototype, consisting of a Diamant 18 airframe powered by a Microturbo Eclair II, later replaced by a Microturbo TRS 25. ;Prometheus 19: The initial production configuration with a span of powered by 2 x

engines mounted behind the cockpit. Flown 22 June 1978. ;Prometheus 12: Span decreased to , wing area and the empty weight . First flown 17 September 1979. ;Promethus PV: As Prometheus 12, with tip tanks. No production intended.

Specifications (Prometheus 19)

References

{{reflist, refs= {{cite book , title= Jane's All the World's Aircraft 1981-1982, last= Taylor, first= John W. R. , year=1981, publisher= Jane's Information Group, location= London, isbn=0710607059, pages=588, 600–601 {{cite book , title= Jane's All the World's Aircraft 1982-1983, last= Taylor, first= John W. R. , year=1982, publisher= Jane's Information Group, location= London, isbn=0710607482, pages=618–9 {{cite web, url=http://www.minijets.org/index.php?id=41&L=3&cHash=eec8acf0b9, title=EFF Prometheus 1, access-date=26 October 2012, archive-url=https://web.archive.org/web/20160304103818/http://www.minijets.org/index.php?id=41&L=3&cHash=eec8acf0b9, archive-date=4 March 2016, url-status=dead

External links

Wortmann FX-67-170-17 airfoil
1970s Swiss sailplanes Aircraft first flown in 1978 Mid-wing aircraft T-tail aircraft Twinjets