Walter RII-209
Walter HWK 109-509
Walter HWK 109-509.A-0
Walter HWK 109-509.A-1
Walter HWK 109-509.A-2

Walter's rocket motors decomposed hydrogen peroxide (T-Stoff) in a reaction with a catalyst to produce a large amount of thrust. The decomposition of the peroxide produced an exhaust gas flow, rich in oxygen. This gave ideal conditions for "burning" a fuel in the combustion chamber to radically boost the available thrust. The standard decomposition motor was known by Walterwerke as the "Cold" motor, in comparison to the fuel burning 109-509 motor which had a greater operating temperature, and was thus known as the "Hot" motor.

Introduction.

The new Me.163B, pictured on the left, was finally cleared for service following a number of development and production delays, designed to accommodate the new Walter "hot" motor.

The maximum thrust of the RII-203 motor of the Me.163A had been 750kg. By burning a fuel in the exhaust gases, the thrust of the new motor was increased to 1500kg.

Development.

The RII-203 motor used two propellant liquids, an oxidant and an oxidiser, pumped to the combustion chamber. To introduce a fuel to burn in the exhaust flow would require a three fuel system. Walterwerke produced a hot motor with a new fuel, 50:50 hydrazine hydrate and methyl alcohol with a dissolved copper salt to catalyse the decomposition of the peroxide. The hydrate promoted the auto-ignition of the fuel, and the alcohol was the fuel used to burn in the oxygen-rich exhaust. The development motor, labelled the RII-209 was associated with the Me.163B, but so far it's not clear if one was flown in an Me.163B airframe, or whether it was just bench-tested at Kiel.

The RII-209 had fuel drawn by a pair of serial fuel pumps for each. A slow running first stage pump was to keep good suction from the fuel tanks, feeding a high speed second stage pump.

Although the fuels were effective, the combustion chamber suffered from badly distributed and poorly atomised main flow at low thrust. In order to keep the combustion chamber alight, a pre-combustion chamber was used.

The pneumatic controls of the RII-203 were retained. Cooling of the combustion chamber was by using T-Stoff, as in Walterwerke's ATO "Starthilfe".

Description.

On the left is an early series HWK 109-509, mounted in an Me.163B. This picture has been published a number of times, without a definitive caption. It is partly disassembled, missing a steam generator and some of the connecting pipework. It shows the paint scheme which appears on other early motors.

From the development Walterwerke had done, the definitive Me.163B Komet motor was designated the RII-211, issued with the RLM number, 109-509. The RII-211 motor used hydrogen peroxide (T-Stoff) as the oxidant and a second propellant which combined a copper salt catalyst for the decompostion of the peroxide, and a hydrocarbon fuel and ignition promoter. This mixture was hydrazine hydrate and methyl alcohol in aqueous solution called "C-Stoff". Previous tests had shown that the 50:50 mixture was an ideal, but 30% hydrate by weight was just as effective and a cheaper option.

For a more detailed description of the fuels for the 109-509 motor, follow this link.

As you can see from the picture here, the new HWK 109-509.A (RII-211) was a single, discreet power unit; all of the motor systems were fixed to a single frame, which meant that motors could be power tested outside the airframe, and importantly for combat aircraft, serviced and changed easily.

A new single-stage fuel pump was implemented, which had an additional helical screw stage to draw fuel from the tanks. As the main pump was a centrifugal type, a type which can lack suction power, the helical screws boosted the suction for bringing fluids the distance from the tanks. The single, turbine-driven pump was divided into two halves, running on a common shaft, one half for each fuel. The whole pump was controlled indirectly via a system to regulate the generation of steam driving the turbine.

Propellant flow to the combustion chamber was controlled via a simple mechanical linkage to the pilot's throttle, making the motor easier to control and making its operation independant of the compressed air supply. The simplicity of the flow control system was the inclusion of a mechanical regulator to make sure the correct ratio of fuel to oxidant was used at all power settings.

Another major advance, was cooling of the combustion chamber by C-Stoff. In a short run ATO motor, T-Stoff cooling was effective enough. But over long periods, the heating of the T-Stoff made it unstable, and cavitation in the flow around the baffles in the lining space risked explosions.

The three-stage, progressive thrust system ensured better fuel atomisation at the low thrust settings, enabling the designers to eliminate the pre-combustion chamber and give a more reliable performance. The electrical starter system continued to give a good degree of reliability, and the use of the catalytic stones in the steam generator cut down on the amount of servicing required.

For a more detailed look at the individual parts of the Walter 109-509.A series motor, follow this link to the
Design Page.

The illustration above is a well known picture - it shows a standard Walter 109-509 motor. As in the illustration at the top of the page, the rear fuselage of the Komet has been removed to allow access to the motor. It is a still from a film made about Messerschmitt Komet operations.

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