The EFF Prometheus was an unusual two seat

motor glider A motor glider is a fixed-wing aircraft that can be flown with or without engine power. The FAI Gliding Commission Sporting Code definition is: a fixed-wing aerodyne equipped with a means of propulsion (MoP), capable of sustained soaring flig ...

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 Switzerland, officially the Swiss Confederation, is a landlocked country located in west-central Europe. It is bordered by Italy to the south, France to the west, Germany to the north, and Austria and Liechtenstein to the east. Switzerland ...

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 two or more animals, machines, or people are lined up one behind another, all facing in the same direction. ''Tandem'' can also be used more generally to refer to any group of persons or objects w ...

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 composite material manufactured from thin layers, or "plies", of wood veneer that have been stacked and glued together. It is an engineered wood from the family of manufactured boards, which include plywood, medium-density fibreboa ...

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 Foams are two-phase materials science, material systems where a gas is dispersed in a second, non-gaseous material, specifically, in which gas cells are enclosed by a distinct liquid or solid material. Note, this source focuses only on liquid ...

sandwich. It was fitted with

flaperons A flaperon (a portmanteau of ''flap'' and ''aileron'') on an aircraft's wing is a type of control surface that combines the functions of both flaps and ailerons. Some smaller kitplanes have flaperons for reasons of simplicity of manufacture, ...

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 language, French ''fuselé'' "spindle-shaped") is an aircraft's main body section. It holds Aircrew, crew, passengers, or cargo. In single-engine aircraft, it will usually contain an Aircraft engine, engine as wel ...

had a wooden structure skinned with glass fibre. The

cockpit A cockpit or flight deck is the area, on the front part of an aircraft, spacecraft, or submersible, from which a pilot controls the vehicle. The cockpit of an aircraft contains flight instruments on an instrument panel, and the controls th ...

, 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 Dorsal (from Latin ''dorsum'' ‘back’) may refer to: * Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism * Dorsal, positioned on top of an aircraft's fuselage The fus ...

intakes immediately aft of the glazing and exhausting over the rear fuselage a little behind the wing

trailing edge The trailing edge of an aerodynamic surface such as a wing is its rear edge, where the airflow separated by the leading edge meets.Crane, Dale: ''Dictionary of Aeronautical Terms, third edition'', page 521. Aviation Supplies & Academics, 1997. ...

. 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. F ...

with the narrow chord

tailplane A tailplane, also known as a horizontal stabilizer, is a small lift (force), 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 single

elevator An elevator (American English) or lift (Commonwealth English) is a machine that vertically transports people or freight between levels. They are typically powered by electric motors that drive traction cables and counterweight systems suc ...

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

tricycle undercarriage Tricycle gear is a type of aircraft undercarriage, or ''landing gear'', that is arranged in a tricycle fashion. The tricycle arrangement has one or more nose wheels in a single front undercarriage and two or more main wheels slightly aft of th ...

. 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 hydraulics, hydraulic device designed to absorb and Damping ratio, damp shock (mechanics), shock impulses. It does this by converting the kinetic energy of the shock into another form of energy (typic ...

. 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 Microturbo TRS 18 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