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A-8 - Hypergolic V-2

The A-8 was a projected development of the A-4. The A-5 was a small-scale A-4 used for experimental purposes in the development of A-4 and was designed and constructed before the A-4. The A-6 was a design study, never constructed. A-7 was a design study of A-5 with wings intended for launching from aircraft to secure scientific data. A-8 was a design study, never built, of a simplified, longer-range or heavier-payload A-4 with a 30-ton-thrust engine with a 90-second-duration level with nitric acid and kerosene / diesel oil as the main propellants, a hypergolic (self-igniting) and non-cryogenic propellant combination. It was strictly a drawing-board vehicle and none were constructed.

Transferring from Kummersdorf to the Peenemünde Army Research Center in the summer of 1940, Thiel became deputy director of the Peenemünde HVP Organization under von Braun. Before working at Kummersdorf, Thiel was a chemical engineer at the Heyland Works at Brietz near Berlin. Gauleiter of Berlin was Josef Goebbels Thiel also designed the motor for the Wasserfall anti-aircraft missile. Early in the Spring of 1941, Thiel began investigating nitric acid and diesel oil to be used as the fuel for the 30-ton-thrust A-8. On February 5, 1941, Thiel and von Braun inspected Helmut von Zborowski’s nitric acid/diesel oil rocket-engine development at BMW in Berlin-Spandau. That summer Thiel began his own testing of this propellant combination. The designation A-8, which probably had already been assigned to an improved A-4 concept, was reconceptualized as a simplified A-4 with a projected 30-ton-(66,000-lb)-thrust hypergolic engine of this type. Range could have been improved to 450 km (280 mi).

For nearly a year in 1941–42, Dornberger’s preferred solution was the A-8, a simplified, longer-range or heavier-payload A-4 with a 30-ton-thrust engine powered by nitric acid and diesel oil. The propulsion chief, Thiel, had begun investigating this propellant combination in the spring of 1941 and favored it as a way of getting rid of the problems of handling and manufacturing liquid oxygen. The alternative to the use of cryogenic oxidants for rocket propulsion was the use of hypergolic fuels that could be stored at ambient temperatures, such as a nitric acid/kerosene combination.

By the middle of August 1943, Thiel declared that the A-4 developmental problems precluded mass production, and recommended the project be abandoned. He resigned with notification he intended to lecture thermodynamics at a technical college. Thiel was killed days later, age 33, on 18-08-1943 in the Operation Hydra bombing raid on Peenemünde.

The A-8 fell out of favor because of questions about its aerodynamic stability at higher cutoff velocities, the pressing need to concentrate on the A-4, and Hitler’s lack of interest in the concept. The Führer’s reasons are unknown, but it is possible that Germany’s oil supply problems were a factor.

Claims that work was begun on the A-8, which had many features that were to be included in a trans-ocean missile, are little more than heavy breathing. The cliam that a preliminary plan for a piloted ground-to-ground rocket missile with trans-Atlantic capabilities (Amerkia Bomber) began with the A-8, is equally far-fetched.

Though not implemented for development of a new large common mixing head "Ofen" for the A-4 missile series C, this concept found appication in at least reduced dimensions for the "Wasserfall" anti-aircraft missile. "Wasserfall"was to have to stand ready for launching at a moment's notice, and it would have to stay fueled for possibly months on end, the liquid Oxygen/Alcohol fuel system of the A-4 could not be used.

It would be fair to say that this storable propellant design was the forerunner of post war tactical missiles, and the cryogenic liquid oxygen used on the V-2 was dead end.

Storable Hypergoli Propellants

Rocket engines can operate on common fuels such as gasoline, alcohol, kerosene, asphalt or synthetic rubber, plus a suitable oxidizer. Engine designers consider fuel and oxidizer combinations having the energy release and the physical and handling properties needed for desired performance.

Liquid propellants are commonly classified as either cryogenic or storable propellants. A cryogenic propellant is one that has a very low boiling point and must be kept very cold. For example, liquid oxygen boils at -297° F, liquid fluorine at -306° F. Personnel at the launch site load these propellants into a rocket as near launch time as possible to reduce losses from vaporization and to minimize problems caused by their low temperatures.

A storable propellant is one that is liquid at normal temperatures and pressures and may be left in a rocket for days, months, or even years. Hypergolic fluids are liquids that react spontaneously and violently when they contact each other.

A hypergolic reaction is defined as a material’s ability to spontaneously ignite or explode upon contact with ANY oxidizing agent; for example, a chemical reaction between nitric acid and oil. Combustion is defined as the burning of a gas, liquid, or solid in which the fuel is rapidly oxidized, producing heat and often light. Combustion falls into a class of chemical reactions called oxidation. Oxidation may be defined as the chemical combination of a substance with oxygen or, more generally, the removal of electrons from an atom or molecule. Oxidation reactions almost always release heat (exothermic). The fuels allowed a simple motor design with few moving parts, a rocket motor that was inherently reliable. Pressurize the tanks of acid and oil, squirt them to meet and automatically ignite in the firing chamber, "lift off."

The state-of-the-art in the field of bipropellant liquid rocket engines was at the level where straightforward engineering approaches would yield a reliable and operational rocket system with the use of a non-cryogenic propellent system. The problems associated with tankage for hypergolio propellents was the only risk area from the stand-point of eventual development of safe end reliable airframe design and operation, was primarily a specification problem involving myriad engineering details and is not associated with any basic physical phenomena other than the fact that hypergolic liquids are intensively reactive chemically and hence straightforward and rigorous means must be followed in the development of tanks required to contain the propellants.

The property of hypergolicity ensured acceptable combustion stability standards with relatively unsophisticated injector designs, meaning quality of propellent spray structure. In addition, the accumulation of fuel or oxidizer in the propellent chamber constituted less of a hazard. The use of hypergolio propellants admittedly constituted a problem from the standpoint of tankage and propellant handling equipment in confined volunes such as in en airframe fuselage. This, however, was an engineering problem which can be handled in an engineering manner, in comparison within stability problems in chambers using unsaturated hydrocarbon fuels or freezing problems in propellant handling equipment using cryogenic oxidizers. Consequently, it seemed apparent that liquid rocket engine systems seemed headed for the use of hypergolic, storable, non-cryogenic liquid propellants.

There was evailable the propellant system which experienced workers in the field recognized as the most effective system for bipropellant liquid rocket applications. This system is generalized as a large class of organic snd inorganio amine fuels with nitrio acid. The system which later showed the greatest degree of development potential or operational status was nitrc acid with either hydrazine or unsymmetrical dimethyl hydrazine.

Hypergolic fuels include hydrazine (N2H4) and its derivatives including; monomethyl hydrazine (MMH), unsymmetrical dimethylhydrazine (UDMH), and Aerozine 50 (A-50), which is an equal mixture of NA and UDMH. The oxidizer used with these fuels is usually nitrogen tetroxide (N2O4), also known as dinitrogen tetroxide or NTO, and various blends of N2O4 with nitric oxide (NO).

Nitric acid (HNO3) [aka Hydrogen nitrate; Aqua fortis; Azotic acid; Salpetersaeure is a colorless liquid that is used in the manufacture of inorganic and organic nitrates and nitro compounds for fertilizers, dye intermediates, explosives, and many different organic chemicals. Continued exposure to vapor may cause chronic bronchitis; chemical pneumonitis may occur.

Red Fuming Nitric Acid (RFNA) is a pale yellow to reddish brown liquid generating red-brown fumes and having a suffocating odor. Very toxic by inhalation. Corrosive to metals or tissue. Prolonged exposure to low concentrations or short term exposure to high concentrations may result in adverse health effects. Rate of onset: Immediate Persistence: Hours - days Odor threshold: ~1 ppm Source/use/other hazard: Used in many industries; Very corrosive to skin/mucous membranes as well as metals & other materials.

The industrial production of nitric acid by the Ostwald process ... involves three chemical steps: 1) Catalytic oxidation of ammonia with atmospheric oxygen to yield nitrogen monoxide: 2) Oxidation of the nitrogen monoxide product to nitrogen dioxide or dinitrogen tetroxide: 3) Absorption of the nitrogen oxides to yield nitric acid.

Nitric acid (HNO3) is a strong oxidant. It reacts violently with combustible and reducing materials, such as turpentine, charcoal and alcohol. The substance is a strong acid. It reacts violently with bases and is corrosive to metals. This produces flammable/explosive gas (hydrogen). It reacts violently with organic compounds.

Signs and symptoms of acute ingestion of nitric acid may be severe and include increased salivation, intense thirst, difficulty swallowing, chills, pain, and shock. Oral, esophageal, and stomach burns are common. Vomitus generally has a coffee-ground appearance. The potential for circulatory collapse is high following ingestion of nitric acid.

Approach fire from upwind to avoid hazardous vapors & toxic decomposition products. Use flooding quantities of water as spray or fog. Use water spray to keep fire-exposed containers cool. Extinguish fire using agent suitable for surrounding fire. Some foams will react with the material and release corrosive/toxic gases.

Keep unnecessary people away; isolate hazard area and deny entry. Stay upwind; keep out of low areas. Ventilate closed spaces before entering them. Wear positive pressure breathing apparatus and special protective clothing.