Summary.

The Walterwerke designed a liquid peroxide fuelled rocket take-off assister and designated it the model RI-201. Once accepted for production, the RLM gave it the designation HWK 109-500.

Massed production was given to the Heinkel werke at Jenbach, who manufactured around 6,000 units during the course of the war.

HWK 109-500 motors were used on a wide variety of aircraft in a wide variety of theatres of operation.

The model illustrated here is preserved at the RAF Museum Cosford, in Shropshire England.

Description.

This is a diagramme of an HWK 109-500 motor which shows the main features.

The self-contained unit carries a series of compressed air tanks (1), which feed through a complex valve (2) to a reducing valve (3), which propels the peroxide from the T-Stoff tank (4) and permangante from the Z-Stoff tank (5), to the combustion chamber (6).

Operation.

The Allies captured a number of pieces of damaged and/or discarded HWK 109-500 in Sardinia in early 1944, and the parts were shipped back to the RAE at Farnborough for examination.

From this the Allies were able to accurately deduce the method of operation of the take-off pack, which was confirmed when other examples were captured intact by advancing troops later in the war.

The HWK 109-500 as fitted to the parent aircraft carries five compressed air bottles. At the start of the mission, the procedure was for the aircrew to run up the aircraft's main engines. When sufficiently prepared for take-off, a signal was given to the ground crew who then turned the rocket pack's master control cock to on.

The numbers on this picture have been added to correspond to the same parts on the diagramme above, for the sake of clarity.

The compressed air from all five bottles is fed through a complex valve (which the Allies' report calls the "Octopus" valve, because of the number of pipes which comprise it) to a single pressure reducing valve. From there the flow of air is held back by a solenoid operated valve.

At the point of take-off the pilot throws a switch in the cockpit which operates the solenoid in the valve in the compressed air line. Under resting conditions, the flow of compressed air is blocked to the fuel tanks by two pressure operated pneumatic valves. Through these valves, the air spaces in the T-Stoff and Z-Stoff tanks are vented to atmopshere.

When the solenoid closes, compressed air is fed to the two control valves which shut the vents to atmosphere and allow air to pass to the fuel tanks, giving them a loading pressure, casuing fuel to begin flowing.

The Z-Stoff passes through a filter and non-return valve, via a metering orifice (a common method of pre-setting the fuel flow in Walter motors) to an inlet in the side of the combustion chamber. The T-Stoff enters the combustion chamber through a spring loaded control valve built into the combustion chamber head. This valve has two inlets, a central pilot valve jet and a main mushroom valve which opens an annular orifice. Both valves are held shut by springs in compression, but when fuel pressure is admitted the pilot valve opens first, followed by the main valve. The effect of the valve system is to delay the arrival of the main flow of T-Stoff until there is an excess of Z-Stoff and the decomposition process has already been initiated by the pilot flow.

Within the combustion chamber the T-Stoff is directed into a shaped cup, within which is a small anvil onto which the Z-Stoff impinges. This causes both fuels to mix intimately, from where they flow into an annular trough at the head of the combustion chamber. There are two helical baffles in the combustion chamber, which is made of mild steel. The combustion chamber operates at a temperature of 700^o C.

As the fuel flows by means of air admitted through a solenoid controlled valve, the pilot could throw the cockpit switch and close the solenoid, shutting off the fuel flow and stopping the operation of the motor, if required.

Key References.

1. RAE Staff, RAE Tech.Note E.A.204
2. Topps J.E.C., Power Jets Report R.1065

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