Fokker D.XXIII
The Fokker D.XXIII was a Dutch single-seat fighter prototype whose two engines sat in tandem in the fuselage, one driving a tractor propeller ahead of the cockpit and the other a pusher propeller behind it, so that an engine failure could not drag the aircraft sideways. Designed by Marius Beeling, it first flew on 30 May 1939. Rear-engine cooling problems dominated a short test programme of eleven flights; the undercarriage was damaged in April 1940 and the programme was abandoned when Germany invaded that May. The sole prototype was captured and scrapped in 1941.
Why It Mattered
Fokker designed the D.XXIII around a weakness of ordinary twin-engined fighters: with an engine on each wing, a failure on one side left the survivor dragging the aircraft off line. Mounting both engines in the fuselage, one pulling ahead of the cockpit and one pushing behind it, kept all the thrust on the centreline, where an engine failure could not swing the aircraft. Only one was ever built. The German invasion of May 1940 cut the programme off before any production version could prove whether the idea worked at squadron strength.
Design Notes
The design came from Marius Beeling, who had it drawn in 1937. His aircraft was a low, cantilever monoplane; the tail surfaces rode at the rear of two booms that ran back from the wing. The pilot sat in an enclosed cockpit between the engines, the front one driving a tractor propeller and the rear one a pusher. Power was a pair of Walter Sagitta I-SR engines, air-cooled V-12s built in Czechoslovakia and rated at 530 hp each. The landing gear retracted fully, and its nose wheel made the layout unusual among fighters of the day. The intended armament was two 7.9 mm machine guns in the nose and two 13.2 mm guns in the wings; the prototype flew with none of them fitted. Bailing out meant passing the rear propeller, so an ejector seat was studied and, as a stopgap, rails were fitted along the forward fuselage for the pilot to climb out on.
Operational History
Fokker built a full mock-up, engines included, and showed it at the sixteenth Paris Air Show in November 1938. Test pilot Gerben Sonderman made the first flight on 30 May 1939. There were just eleven flights in all, adding up to less than four hours in the air. The trials kept returning to one fault: the rear engine overheated, and its cooling was never put right. Fokker altered the rear fuselage panelling before the last flights in another attempt at a cure, and proposed Rolls-Royce or Daimler-Benz engines for production aircraft. On the eleventh flight, in April 1940, the undercarriage was damaged; a Dutch Fokker history site dates the accident to 11 April. The programme was abandoned the next month, when German forces invaded the Netherlands.
Afterlife
The captured prototype was not restored; the Germans studied its centreline engine arrangement and its nose landing gear, and then lost interest. They scrapped the fighter on 10 May 1941. Since only the one prototype had been built, the scrapping ended the type outright: no D.XXIII exists today. What survives is the record: photographs of the prototype, construction number 5614, wearing its test registration X-4 and later the pseudo-military number 998. A Dutch monograph on the design, published in 2012 under the internal designation D.23, keeps the type in the specialist literature.