Truncated Annular Aerospike Nozzle

Standard bell nozzles are a rigid compromise—they only hit peak efficiency at one specific altitude, meaning they waste fuel everywhere else. The aerospike solves this by turning the engine inside out. The exhaust plume expands against the central spike on the inside and the atmosphere itself on the outside, automatically adjusting its own expansion ratio as pressure drops.

This is a functional model of an annular aerospike, heavily optimized for FDM printing. It uses a mathematically derived 1.5-power-law curve for the central plug, which efficiently redirects the radial flow from the combustion chamber into pure axial thrust.

Engine Specs

• Throat Gap: 2 mm annular clearance around the base of the spike.
• Truncation: The spike is cut at 80% of its theoretical ideal length. This flat base eliminates dead weight while retaining roughly 99% of the full-spike efficiency, thanks to base-pressure recirculation.
• Support Structure: 6 internal struts carry the outer cowl load across the combustion chamber.
• Printability: Fully print-in-place with no supports required. The base sits flat, and the steepest overhang in the combustion section is well within safe limits.