Heinkel HeS 40

Heinkel Strahltriebwerke (HeS)

Industry	Aerospace engineering
Founded	1940 (1940)
Founder	Adoph Müller and team
Headquarters	Germany
Products	Jet engines (experimental)

The Heinkel HeS 40 (abbreviated as HeS for Heinkel Strahltriebwerke) represented an experimental approach to constant-volume jet engine technology. Developed by Adoph Müller and his team at Heinkel around 1940 or 1941, it utilized the mechanical framework of the HeS 30. However, it distinguished itself by replacing the standard flame can combustion chambers with larger units equipped with substantial poppet valves that sealed each chamber during ignition. This constant-volume combustion process, analogous to the Otto cycle common in piston engines, offered significantly improved fuel efficiency compared to the conventional constant-pressure combustion found in typical jet engines.

Design

The HeS 40's development leveraged the HeS 30's architecture to facilitate parts interchangeability and simplify performance comparison. Key modifications included lowering the compressor's pressure ratio from approximately 2.8:1 to about 2:1 and introducing new combustion chambers of substantially increased size. Due to their larger dimensions, the number of burners was reduced from ten to six. The valve stems extended forward into aerodynamically shaped fairings located in the intake section behind the compressor.

Functionally, the engine's cycle resembled that of a standard six-cylinder piston engine, with the distinction that air compression was performed by the compressor rather than piston movement. The combustion chambers served solely for burning fuel rather than handling compression, combustion, and expansion as in a piston engine. Pressurized air—akin to that supplied by a turbocharger but at elevated pressure ratios—was sequentially directed into each chamber, which were then sealed by poppet valves before ignition occurred. Upon completion of combustion, pressure inside these flame cans rose substantially, although specific expansion ratios were not detailed. The resulting high-temperature gases exited to drive a turbine extracting mechanical power; unlike a piston engine where pistons convert pressure into motion, here most energy was expected to generate thrust in a typical turbojet configuration. The turbine primarily powered the compressor for continuous operation. Despite some inevitable charge loss during combustion reducing efficiency compared to an ideal Otto cycle, this design promised better fuel economy than traditional jet engines, albeit with added mechanical complexity.

History

The HeS 40 seems to have remained a conceptual project and was never physically constructed. Development on this design ceased by 1942, at which time the HeS 30 engine had already advanced significantly.