Alexander Lippisch had designed a number of tailless gliders, the most successful of which was the DFS-194. The logical development from this was to become an aircraft from the drawing board of Willi Messerschmitt, a small, high performance, rocket powered interceptor, with a speed and climb to height which would outstrip every other manned aircraft of the day. It was the Messerschmitt Me.163A.

Introduction.

Walter had been developing his series of hydrogen peroxide motors, improving and refining the propellant delivery and the power control systems. His initial motors had burned liquids at a fixed rate for a limited time - the major development of this system being the 109-500 "Rocket Assisted Take-Off" pack as we would know it today, or "Starthilfe" as they were dubbed.

The development of the Me.163 is well documented elsewhere, safe to say that the Me.163A was designed to test the airframe potential, married to the powerplant. Walterwerke was already working on a better, more powerful motor for the production series, but the Me.163A was being used to train pilots on the flying characteristics of the small, very high speed "glider" and the eccentric and potentially dangerous rocket motors.

Description.

Previous Walter developments had produced a system of pneumatic fuel flow control, which could be effected by the pilot in the cockpit.

Starting, and more importantly, the in-flight thrust was controllable by the pilot, producing an aircraft with a much improved performance than the previous test units.

The Me.163.A used the Walter RII-203 motor. Hydrogen peroxide (T-Stoff) was used as the propellant oxidised by a potassium permanganate solution, known as Z-Stoff. Potassium permangante has a characteristic livid violet colour, and once the Me.163A was in motion, the exhaust plume of the motor was a purple trail.

Left is a diagramme of the RII-203 "controllable" motor, which is taken from a paper Hellmuth Walter wrote after the war. Compressed air from the bottle (1) drives T-Stoff from a reserve tank for starting (2), via a control valve (12) to the steam generator (9). Steam produced here is led to the turbine of the fuel pump (T) driving it round.

In the RII-203, both reactants were fed to the combustion chamber by a duplex fuel pump. The fuel pump was driven by the steam generator. On the RI-211 Me.163 prototype unit, at starting, compressed air was used to mix T-Stoff and liquid Z-Stoff in a reaction vessel to produce the steam needed. However over time, this caused fouling of the steam generator by maganese dioxide sludge requiring frequent maintenance. So by the time of the RII-203, only T-Stoff was fed to the steam generator, with catalyst stones being used to decompose it to steam.

The fuel pump (8) draws T-Stoff (P1) from the tanks and Z-Stoff (P2) to mix in the combustion chamber (4). Other features in the diagramme are the drains, fuel control valves and emergency trip valves necessary for a safe system.

The pneumatic system allowed the pilot to control the flow of propellants and so the power output of the motor. However, although experienced pilots were able to manage this system, it proved difficult for pupil pilots, who's coarse controlling movements led to hunting in the flow and poor performance characteristics. The compressed air system was also time consuming and costly to service.

In the illustration on the left, showing crews engaged in servicing an Me.163A, you can just make out the steam generator on the left, with the silver bolts holding the heavy steel lid in place. To the right of that is a small stainless steel or aluminium pressure vessel, which is probably the starting tank of T-Stoff. There are few other details visible.

Delays in the production of the "hot" motor, and the delays in production of the Model "B" airframe, led to the Me.163A and its motor continuing in training and service far longer than desired. Despite its problems, it was persisted with rather than developed, in the knowledge that a better alternative was due before long.

From the photograph of the Me.163A at the top of the page, you can see that the RII-203 reaction chamber has a very long exhaust gas tube, in order to keep hot gases clear of the airframe. This led to a lesser performance than could be expected from this type of motor.

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