Walter 109-509 series motor
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.