 It was based on the Me 309 but with the engine located behind a pressurized cockpit, much in a similar manner to the US Bell P-39 Airacobra.The engine was a Daimler-Benz DB 605B driving a three-blade propeller, and armament was to consist of two 13 mm (.51 in) MG 131 machine guns and two 20 mm MG 151/20 cannon.The tricycle landing gear from the Me 309 was retained, which worked better on the 509, due to the lower weight on the nosewheel - the Me 309's nosegear had collapsed during trials.