The SEPR 84 is a family of

liquid-propellant rocket A liquid-propellant rocket or liquid rocket uses a rocket engine burning liquid rocket propellant, liquid propellants. (Alternate approaches use gaseous or Solid-propellant rocket , solid propellants.) Liquids are desirable propellants because th ...

engines used as boosters for the

Dassault Mirage III The Dassault Mirage III () is a family of single/dual-seat, single-engine, fighter aircraft developed and manufactured by French aircraft company Dassault Aviation. It was the first Western European combat aircraft to exceed Mach 2 in horizont ...

mixed-power high-altitude interceptor aircraft of the 1960s. The engine was one of several similar developed by SEPR (

Société d'Etudes pour la Propulsion par Réaction The (SEPR) (in ) was a French research and manufacturing company founded in 1944 which specialised in the development of liquid-fuelled rocket engines during the 1950s, 60s, 70s and 80s. The SEPR 841 is a liquid-fuelled rocket engine used as an ...

SEPR 841

SEPR's auxiliary rocket engines were based on the

hypergolic A hypergolic propellant is a rocket propellant combination used in a rocket engine, whose components spontaneously ignite when they come into contact with each other. The two propellant components usually consist of a fuel and an oxidizer. The ...

fuel chemistry of

nitric acid Nitric acid is an inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but samples tend to acquire a yellow cast over time due to decomposition into nitrogen oxide, oxides of nitrogen. Most com ...

oxidiser and TX2 (tri-ethylamine xylidine) fuel. Unusually, the

turbopump A turbopump is a fluid pump with two main components: a rotodynamic pump and a driving gas turbine, usually both mounted on the same shaft, or sometimes geared together. They were initially developed in Germany in the early 1940s. The most co ...

for the engine was mechanically driven from outside. A mechanical drive shaft from the

accessory drive The accessory drive is a gearbox that forms part of a gas turbine engine. Although not part of the engine's core, it drives the accessories – such as generators, pumps for fuel and lubrication oil, air compressors, hydraulic pumps and engine st ...

of the main turbojet provided the needed at 5,070 rpm, provided that the engine was running at full speed. As the propellants are

, the engine can be ignited repeatedly simply by engaging the clutch drive to the pump. Bulk production of the engines was carried out by

Hispano-Suiza Hispano-Suiza () is a Spanish automotive company. It was founded in 1904 by Marc Birkigt and as an automobile manufacturer and eventually had several factories in Spain and France that produced luxury cars, aircraft engines, trucks and weapons. ...

SEPR 844

For simplicity of fuel supply, the TX2 fuel of the SEPR 841 was replaced with standard Jet TR-0 /

JP-4 JP-4, or JP4 (for "Jet Propellant") was a jet fuel, specified in 1951 by the United States Department of Defense (MIL-DTL-5624). Its NATO code is F-40. It is also known as avtag. Usage JP-4 was a 50-50 kerosene-gasoline blend. It had a lower fl ...

JP-5 Jet fuel or aviation turbine fuel (ATF, also abbreviated avtur) is a type of aviation fuel designed for use in aircraft powered by gas-turbine engines. It is colorless to straw-colored in appearance. The most commonly used fuels for commercial ...

(

kerosene Kerosene, or paraffin, is a combustibility, combustible hydrocarbon liquid which is derived from petroleum. It is widely used as a fuel in Aviation fuel, aviation as well as households. Its name derives from the Greek (''kērós'') meaning " ...

) in the SEPR 844.

Mirage

The

Mirage A mirage is a naturally-occurring optical phenomenon in which light rays bend via refraction to produce a displaced image of distant objects or the sky. The word comes to English via the French ''(se) mirer'', from the Latin ''mirari'', mean ...

and its distinctive

delta wing A delta wing is a wing shaped in the form of a triangle. It is named for its similarity in shape to the Greek uppercase letter delta (letter), delta (Δ). Although long studied, the delta wing did not find significant practical applications unti ...

planform In technical drawing and computer graphics, a multiview projection is a technique of illustration by which a standardized series of orthographic projection, orthographic two-dimensional pictures are constructed to represent the form of a three-d ...

began with the prototype

MD 550 Mystère-Delta The Dassault Mirage III () is a family of single/dual-seat, single-engine, fighter aircraft developed and manufactured by French aircraft company Dassault Aviation. It was the first Western European combat aircraft to exceed Mach 2 in horizonta ...

. This bore little relation, other than its name, to the

Dassault Mystère The Dassault MD.452 Mystère is a 1950s French fighter-bomber. It was a straightforward development of the successful Dassault Ouragan Development After the success of the Ouragan, Dassault was working on a more advanced machine which woul ...

; France's swept-wing fighter of the period. The delta aircraft was smaller, around two thirds of the Mystère's weight and was powered by two small

Viper Vipers are snakes in the family Viperidae, found in most parts of the world, except for Antarctica, Australia, Hawaii, Madagascar, New Zealand, Ireland, and various other isolated islands. They are venomous and have long (relative to non-vipe ...

turbojets and a SEPR 66 liquid-fuelled rocket. All three of these engines barely exceeded the thrust of the Mystère's

ATAR 101D The SNECMA ATAR 101 is a French axial-flow compressor, axial-flow turbojet engine built by SNECMA. It was derived from engines and design work carried out at BMW in Germany during World War II, and extensively developed though a progression of m ...

, although they also only weighed about half of the ATAR.

Mirage IIIC

The Mirage III adopted the more developed and afterburning ATAR 9. As the delta wing considerably increased the supersonic capacity of the aircraft, rocket power was retained. This was the first European aircraft to exceed Mach 2 in level flight. It was recognised that most mission profiles did not require the rocket and could not afford its fuel consumption. The original goal of intercepting high-flying bombers also seemed to be receding in favour of missiles, for both offence and defence. The Mirage's rocket was thus mounted as a removable pod which could be replaced with a jet fuel tank for additional range. Only the high altitude interception would still use it. To retain balance as rocket fuel was consumed, the rocket pack was in two parts. The

oxidiser tank was mounted directly ahead of the rocket engine. A smaller TX2 fuel tank was mounted just behind the cockpit, replacing the cannon pack. When in the rocket-powered interceptor role, the aircraft would only be armed with missiles. The fuel tank and rocket pack could be swapped in around 20 minutes by removing six bolts. Fuelling the rocket oxidiser was potentially somewhat hazardous and so it was carried out away from other aircraft, by groundcrew in protective clothing and with a fire crew standing by in order to flush away any spillage. Acid refuelling was carried out above a steel drip tray, with the acid flow and tank vent return through closed pipework with a sightglass to observe full tanks. Performance in training sorties achieved Mach 1.4 without the rocket and 1.8 with. Altitudes of could be reached in a zoom climb, or on rocket thrust. A typical training sortie duration of 45 minutes would be reduced to under 30, with high Mach and rocket use.

Specifications (SEPR 841)

References

{{Reflist, colwidth=35em, refs= {{Cite web , title=Mirage , author=James Hay Stevens , journal=

Flight International ''Flight International'', formerly ''Flight'', is a monthly magazine focused on aerospace. Published in the United Kingdom and founded in 1909 as "A Journal devoted to the Interests, Practice, and Progress of Aerial Locomotion and Transport", i ...

, date=22 April 1960 , pages=558–562 , url=https://www.flightglobal.com/pdfarchive/view/1960/1960%20-%200558.html , ref={{harvid, Flight, 1960 {{Cite web , title=Les Cigognes de Dijon , author= , journal=

, date= 5 September 1963 , pages=430 , url=https://www.flightglobal.com/pdfarchive/view/1963/1963%20-%201618.html , ref={{harvid, Flight, 1963 {{Cite web , title=The French Industry in Brief , journal=

, date=16 July 1964 , page=113 , url=https://www.flightglobal.com/pdfarchive/view/1964/1964%20-%202092.html {{Cite web , title=Aero Engines 1962 , journal=