The 109-500 is a self-contained, modular monopropellant Starthilfe (take-off assist) engine in a pod, able to produce 500 kg (1,100 lb) thrust for thirty seconds.

The T-Stoff monopropellant, stored in the large spherical tank within the Starthilfe module's forward end, needed to react with a catalyst to provide the boosting thrust for an aircraft on takeoff - this Z-Stoff sodium or calcium-based, alkaline permanganate-compound (in an aqueous solution) catalyst was provided in a small tank above the reaction chamber just forward of the exhaust nozzle, with compressed air from a network of five pressure tanks driving the monopropellant and catalyst together through the reaction chamber, which featured an internal, fixed helical "swirl baffle" to lengthen the period of time the monopropellant and catalyst were in contact for a more complete catalytic reaction within it, before the reacted T-Stoff exhaust exited the nozzle.

[1] It was "used extensively on a wide range of aircraft", especially the potentially underpowered (when heavily laden with external ordnance) Jumo 004-engined Arado Ar 234B,[1] with two of the units uniquely displayed as mounted operationally on the NASM's sole surviving, restored Ar 234B.

The HWK 109-501 was a higher-thrust variant (14.71 kN) bipropellant Starthilfe RATO booster unit[3], used on the Junkers Ju 287 prototype which proved to be unreliable over sustained periods.

Data from The race for Hitler's X-planes : Britain's 1945 mission to capture secret Luftwaffe technology,[1] Die Deutsche Luftruestung 1933–1945 Vol.4 – Flugzeugtypen MIAG-Zeppelin[4] Related lists