The aircraft was to be powered by four
turbofan engines buried in the wings, with the
bypass air feeding cold-air tunnels each side of the engines including a combustion chamber where additional thrust could be gained. The bypass air could be deflected though large slots on the upper and lower wings to act as aerodynamic
flaps or thrust reversers. Two engines could be shut down in flight to increase range. It was planned that the N-20 would carry its armament in a detachable weapons bay, capable of carrying large loads of cannons, rockets or bombs. It was initially planned that the aircraft's engines would be designed and built in Switzerland by
Sulzer. Sulzer only built a
turbojet though, the
Sulzer D-45, with a thrust of . Of these engines, D-45.01 was used in a test rig between 1950 and 1951 and the second engine, D-45.04 (of limited airworthiness) was used until 1955 in a test rig. The D45.04 is part of the Dübendorf museum N-20 display. For the development of the bypass-engine DZ-45 Sulzer expected a development contract worth 10 million swiss francs that never materialized. Aerospace engineer
Theodore von Kármán who worked on the similar Vought Cutlass when invited by
F+W Emmen for the N-20 project suggested a vertical stablizer for the aircraft. The
Armstrong Siddeley Mamba turboprop was then chosen as the basis for the N-20's prototype engines, with the
propeller reduction gear replaced by a low pressure compressor. This powerplant was named Swiss Mamba SM-1; the conversion was carried out in 1948 by EFW, with only six engines built (four fitted to the N-20 with two spares). One of the spare engines is today part of the
Swiss Museum of Transport, at the
Flieger-Flab-Museum Dübendorf. Flight tests of the engine began in October 1952 under a
De Havilland Mosquito. The proposed development into the SM-5 for the production aircraft was very similar to the DZ-45 proposed by Sulzer in 1947.
EFW N-20.01 Since Swiss industry still had no experience with the aircraft and aerodynamics of jet aircraft, several wind tunnel models were produced. In addition, a 3/5th scale wooden glider, the
EFW N-20.01 was built to allow testing of the novel wing shape; this flew on 17 April 1948. ==Specifications (N-20.10 Aiguillon)==