Cobra AERO and PteroDynamics have entered into an agreement to jointly develop a series hybrid-electric propulsion system for the P5 Transwing autonomous vertical takeoff and landing unmanned aircraft system.
The collaboration centers on the integration of Cobra AERO’s new A99HF-EPU (Electric Power Unit). This compact, liquid-cooled system generates 9 kW of electrical power at 120V and is specifically designed to maintain performance in “hot and high” or austere environments where air-cooled systems often struggle. The unit utilizes a straight-triple cylinder two-stroke internal combustion engine architecture, which is designed for low vibration, high power density, and the ability to operate on various military and civilian fuels.
The P5 airframe is optimized for this series hybrid-electric architecture. Utilizing the patented Transwing design, the aircraft uses a distributed array of propellers for both lift and thrust. This configuration allows the propulsion system to be optimized for efficiency by downsizing the prime mover and operating the hybrid system at its most effective points. Because the propulsion is distributed, the placement of the EPU within the fuselage is not restricted by propeller locations, allowing for cleaner airframe packaging and reduced drag.
Technical specifications for the A99HF-EPU include a fuel efficiency of 600g/kWe-hr, with a development roadmap intended to reduce fuel consumption by an additional 35% through improvements to the generator and combustion efficiency. The system currently targets a minimum time between overhauls (TBO) of 500 hours, with a projected pathway to 1,000 hours.
The development team includes several technical partners. Flighthouse Engineering performed the initial airframe and propulsion sizing analysis, while AllocorTech provided the Generator Control Unit. Power4Flight contributed to the engine and hybrid-electric system controls, and ePropelled is supplying the generator and propeller drives.
Sean Hilbert, President at Cobra AERO, commented, “Cobra AERO is excited to work with the PteroDynamics team in providing reliable, fuel-efficient electric power with low thermal and acoustic signatures for the P5. The A99HF-EPU will not only power this unique aircraft, but it will also power payloads, avionics, and communications.”
The integration is intended to support autonomous logistics, particularly in contested maritime environments.
Thomas Lewis, Lead System Engineer at PteroDynamics, stated, “Cobra AERO has been a key member of the P5 development team in advancing the aircraft’s hybrid-electric propulsion system. The A99HF-EPU provides a reliable, low-SWaP, heavy-fuel power solution that enhances the Transwing platform’s reliability, operational flexibility, and expeditionary capability. This partnership supports the development of a next-generation autonomous logistics capability for contested maritime environments.”
Current engineering activities are focused on system integration, controls validation, and test planning. The partnership expects to begin flight demonstrations of the integrated P5 platform in the fourth quarter of 2026.
