Introduction.

Whatever its combat failings, there was little denying that the rocket powered Messerschmitt Me.163 had an incredible rate of climb, and a very impressive time to height for a small interceptor.

With the success of Walter's HWK 109-500 "Rocket Assisted Take-Off Packs", or "Starthilfe", for larger or heavily laden aircraft, it was almost inevitable that this technique should be used for providing the means of increasing the rate of climb for a conventional fighter.

The success of the Me.262 jet aircraft had led to the German high command investing most of their technical expertise in it as the primary air combat option. Being able to power a fully laden Me.262 from the smaller airfields and landing strips with which the Jagdgeschwader were being forced to contend, and to bring the Me.262s to combat height quickly, were attractive goals. The Walter rocket packs were a serious contender for this requirement.

The Starthilfern had only a limited duration and by the standards of the hot Walter motors, limited power output. The more sophisticated HWK 109-509 series offered greater endurance and greater power. The original Heimatschützer I development fitted the Walter motor within the fuselage of the Me.262. But as these rockets required a high degree of maintenance, and reduced the available space for standard fuel tankage, this proved to be an impractical solution. The Heimatschützer IV was a bolt-on rocket pack which could be serviced externally to the Me.262, fitted when required, and if not needed, not carried as an extra weight burden. In Spring of 1945, Walterwerke had produced a new design of their basic 109-509 series motor, calling it the "109-509.S2"

This Walter motor was a combination of parts from an HWK 109-509.A2 and an HWK 109-509.C with a compact arrangement. The weight of the unit was 140 kg, with thrust rated at 2000 kg.

Two 600 litre jettisonable T-Stoff tanks were slung externally on the bomb attachment points under the aircraft's nose, with the hydrazine hydrate (C-Stoff) carried in the rearmost converted fuselage tank. Fuel from the forward tanks was carried back to the Walter motor by flexible hoses,

History.

The new design was allocated the designation "Messerschmitt Me.262.C-3". Work on the prototype installation was begun in January 1945, and this project was retained in the emergency programme when others were cancelled following the directive.

Apparantly, tests on the T-Stoff installation encountered difficulties when the drop tanks were mounted lower than the motor, causing fuel feed problems.

The problems with the installation were not satisfactorily resolved before the factory at Jenbach was overrun by the advancing Allies in April 1945. None of the prototype aircraft had been completed, and it is presumed none had been flown under power.

Description.

The Walter 109-509 series motor was a bi-fuel rocket motor with a turbine driven fuel pump. The standard motor pack was already quite compact, but these basic elements were re-organised to fit the available space in a longitudinally streamlined housing, enclosed in a faired pack slung beneath the Me.262's fuselage.

As you can see from the illustration, the HWK 109-509.S2 is derived from the HWK 109-509.A-2 motor. There is no electrical starter; one can clearly make out, dead centre, the T-Stoff gravity starter tank, feeding directly into the steam generator. Just visible by the turbine pump is one of the fuel air ejectors.

The fuel outflow pipes from the fuel flow and pressure regulator are very short, and feed almost directly into the combustion chamber.

As the HWK 109.509.S2 pack is engineered to fit below the belly of the Me.262, the aim seems to have been to keep a minimum width. Seen in the picture on the right, the pack is not much wider than the width of the combustion chamber. This view also shows the motor's suspension hangers, for attaching it to the Me.262's fuselage.

Because of these dimension considerations, the steam driven turbine pump has been swung from its standard transverse position and fixed into a longitudinal orientation. This probably works well as a space saving measure, but one does wonder about the loads placed on the end bearing of the fuel pump during operating thrust. There is no indication that the WK9 turbine pump was modified in any way for this motor. As the unit's thrust is now directly down the length of the pump shaft onto the ball bearing at the T-Stoff pump end, through the sensitive seals and at ninety degrees to the axis of the turbine disk, it seems difficult to beleive that the HWK 109-509.S2 would have been able to run for the same length of time between overhauls as the standard 109-509.A1.

Preserved Motor.

Quite extraordinarily, there is a preserved HWK 109-509.S2 currently in store, awaiting restoration.

This photograph was taken in the RAF Museum's reserve collection store at Cardington. It shows the motor on its back, strapped to a pallet. The motor is stored inverted on its flat top, where it would have been fixed to the host aircraft. This is essentially a surface for placing the motor without damaging the pipework.

It is unclear how long this motor has been in storage at the RAF Museum, as research has shown that one very like it (and there are unlikely to be many) was in the Aircraftman's Hangar Museum at the RPE Westcott in the 1950s. The RAF Museum store at Cardington was closed in 2000 pending a move of the restoration team to a purpose-built restoration facility at the RAF Museum site in Cosford, and this photograph was taken during a visit by a preservation team looking for items of British rocket history. Items in store at Cardington have subsequently been moved, and currently reside in a closed storage facility at RAF Stafford.

As of Summer 2007, negotiations are being conducted to take this motor from store and move it to a restoration facility.

For more views of this motor, follow this link.

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