The HWK 109-507 was a liquid-propellant

rocket engine A rocket engine uses stored rocket propellants as the reaction mass for forming a high-speed propulsive jet of fluid, usually high-temperature gas. Rocket engines are reaction engines, producing thrust by ejecting mass rearward, in accordanc ...

developed by Germany during World War II. It was used to propel the

Hs 293 The Henschel Hs 293 was a World War II German radio-guided glide bomb. It is the first operational anti-shipping missile, first used unsuccessfully on 25 August 1943 and then with increasing success over the next year, ultimately damaging or sink ...

anti-ship

guided missile In military terminology, a missile is a guided airborne ranged weapon capable of self-propelled flight usually by a jet engine or rocket motor. Missiles are thus also called guided missiles or guided rockets (when a previously unguided rocket ...

. It was produced by

Hellmuth Walter Kommanditgesellschaft Hellmuth Walter Kommanditgesellschaft (HWK), Helmuth Walter Werke (HWM), or commonly known as the Walter-Werke, was a German company founded by Professor Hellmuth Walter to pursue his interest in engines using hydrogen peroxide as a fuel. Having ex ...

(HWK). Like other Walter engines it used

hydrogen peroxide Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3%� ...

as a propellant.

Missile

The Hs293 has been variously described as a missile or as a boosted

glide bomb A glide bomb or stand-off bomb is a standoff weapon with flight control surfaces to give it a flatter, gliding flight path than that of a conventional bomb without such surfaces. This allows it to be released at a distance from the target rat ...

. It consisted of an

SC500 bomb The SC 500 (Sprengbombe-Cylindrisch bomb (disambiguation), Sprengbombe Cylindrisch) or ''cylindrical explosive bomb'' in English was a family of general-purpose bombs used by the Luftwaffe during World War II. Design They had three-piece draw ...

casing, fitted with wings, engine and radio control. Control equipment was housed in a rearward extension of the bomb casing but the motor was mounted in a separate housing beneath. It had originally been developed as an unpowered glide bomb, "Gustav Schwartz Propellerwerke", and the engine was added later. After flight tests, a visible tracking flare was also added, in a further rearward extension. As the engine was mounted below the missile fuselage, the exhaust nozzle pointed downwards at 30°, so as to align the

line of thrust The line of thrust is the locus of the points, through which forces pass in a retaining wall or an arch. It is the line, along which internal forces flow As it was intended for attacking lightly- or unarmoured targets, it did not require an armour-piercing high impact speed. The same engine was also used for the planned Hs 294, Hs 295 and Hs 296 missiles. As these larger missiles weighed twice the Hs 293, they used a pair of the engines, one under each wing root.

Development

This engine was a development of the

HWK 109-500 The Walter HWK 109-500 was a liquid-fuelled rocket engine developed by Walter in Germany during the Second World War. Description The 109-500 is a self-contained, modular monopropellant ''Starthilfe'' (take-off assist) engine in a pod, abl ...

''Starthilfe'' ( rocket-assisted take-off) engine. The 109-500 was pod-mounted and parachuted back to earth after takeoff. Engine pods were serviced and re-used. The 109-507 was developed from the 109-500. As a missile engine, it was only required to work once, and for a short duration. It was thus simplified in both its features and in its construction materials. Rather than the complex centrifugal

turbopump A turbopump is a propellant 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 purpos ...

s used for most Walter engines, a simple gas pressurisation system was used to feed the propellants. A wartime British report expressed surprise that the engine's

combustion chamber A combustion chamber is part of an internal combustion engine in which the fuel/air mix is burned. For steam engines, the term has also been used for an extension of the firebox which is used to allow a more complete combustion process. Interna ...

was made of mere

mild steel Carbon steel is a steel with carbon content from about 0.05 up to 2.1 percent by weight. The definition of carbon steel from the American Iron and Steel Institute (AISI) states: * no minimum content is specified or required for chromium, cobalt ...

, rather than anything more

refractory In materials science, a refractory material or refractory is a material that is resistant to decomposition by heat, pressure, or chemical attack, and retains strength and form at high temperatures. Refractories are polycrystalline, polyphase, ...

Engine

The engine's fuel chemistry used 80% high test hydrogen peroxide or '

T-Stoff T-Stoff (; 'substance T') was a stabilised high test peroxide used in Germany during World War II. T-Stoff was specified to contain 80% (occasionally 85%) hydrogen peroxide (H2O2), remainder water, with traces (<0.1%) of stabilisers. Stabilisers ...

'. This was a 'cold cycle' engine; the peroxide acted as a

monopropellant Monopropellants are propellants consisting of chemicals that release energy through exothermic chemical decomposition. The molecular bond energy of the monopropellant is released usually through use of a catalyst. This can be contrasted with biprop ...

and was decomposed by a catalyst into superheated steam and oxygen. The catalyst used was a consumable liquid solution of

calcium permanganate Calcium permanganate is an oxidizing agent and chemical compound with the chemical formula Ca(MnO4)2. This salt consists of the metal calcium and two permanganate ions. Preparation The salt is prepared from the reaction of potassium permanganat ...

or '

Z-Stoff Z-Stoff (, "substance Z") was a name for calcium permanganate or sodium permanganate mixed in water. It was normally used as a catalyst for T-Stoff (high-test peroxide) in military rocket programs by Nazi Germany during World War II. Z-Stoff was u ...

'. As this catalyst is consumed, the engine is regarded as a

bipropellant The highest specific impulse chemical rockets use liquid propellants (liquid-propellant rockets). They can consist of a single chemical (a monopropellant) or a mix of two chemicals, called bipropellants. Bipropellants can further be divided into ...

engine. Propellants are forced into the combustion chamber by compressed air, stored at in two steel vessels. This pressure is released through an electrically-fired cartridge that opens a valve with a blow-out disc. This is the full extent of the electrical control system. Once fired, the valve does not close again. A pressure regulator delivers air at , through a shuttle valve that pressurised first the catalyst tanks and then the propellant tank. This delay ensures reliable ignition in the combustion chamber. A non-return valve ensures that no catalyst can flow backwards into the air or propellant plumbing, with an explosive result. A rubber diaphragm, broken as propellant pressure builds, ensures that there is no backflow through the combustion chamber either. Z-stoff was known for problems of clogging injectors and so an inline filter was used. The propellant injector in the combustion chamber is a simple

light alloy Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 ter ...

casting, cooled by the propellant flow. The combustion chamber is single-walled mild steel, with no provision for cooling. A steel mixing cup is downstream of the injector, with the radial Z-Stoff 6mm pipe leading into it. One 3 mm diameter injector nozzle points into the cup, thirty smaller radial 2 mm nozzles deliver most of the propellant along the walls of the chamber. Helical swirl baffles in the chamber promote good mixing and decomposition of the peroxide. Thrust varied through the boost phase, as air pressure and propellant flow fell, dropping from 600 kgf to 400 kgf. The engine pod had a dry weight of 517 kg, carrying 68 kg of propellants when full.

References

{{Hellmuth Walter Kommanditgesellschaft aeroengines 109-507 Rocket engines using cold cycle hydrogen peroxide propellant