Flight, December 1924

The Paris Aero Show 1924

THE FOKKER MACHINES

   Two machines are exhibited on the stand of the N.V. Nederlandsche Vliegtuigenfabriek (Fokker), one being one of the original Fokker monoplanes of 1912 or thereabouts. This machine is fitted with a Renault engine. By way of showing the progress made since those early days it would be difficult to imagine anything better than the placing side by side of this veteran and the latest Fokker single-seater fighter, the Fokker D.XIII with Napier "Lion" engine.
   The D.XIII is a development of the D.XII exhibited at Gothenburg last summer, and is of characteristically Fokker lines. The upper wing is large, of high aspect ratio and entirely constructed of wood, even to the wing covering, while the lower plane is of quite small dimensions, and serves mainly to steady the top plane against torsional loads, as, with the V struts running to the lower plane, any tendency to twist is resisted by the lower plane in drag. The top plane is carried on N-struts from the fuselage, and is braced laterally by a single outboard strut on each side. The lower plane, which, like the upper, is in one piece, slips into an opening in the sides of the fuselage and is secured in place by four bolts, as shown in one of our sketches. The fuselage is the usual Fokker welded-steel tube structure with wire bracing.
   The Napier "Lion" engine is neatly cowled in, the small overall size of the engine making this possible, and side radiators of a special type, capable of being withdrawn into the fuselage, leaving the nose free, enable a spinner to be used over the propeller boss. As the biplane wings are of the cantilever type, the V struts being, as already stated, for transmitting torsion mainly, the machine is very clean, and its excellent performance bears out the impression of efficiency. The particular Napier engine used, by the way, has a compression ratio of 5-8 to 1, and the performance figures given below apply to the machine thus equipped.
   The main dimensions of the Fokker D.XIII are: Length, o.a., 7.9 m. (25 ft. 11 ins.); height, 2.9 ms. (9 ft. 6 in.); span 11 m. (36.ft.); wing area, 21.47 sq. m. (231 sq. ft.); the weight empty is 1,180 kgs. (2,590 lbs.). The total useful load, composed of pilot, fuel for 2 1/2 hours, guns, ammunition, etc., is 430 kgs. (950 lbs.), and the total loaded weight is 1,610 kgs. (3,540 lbs.), giving a wing loading of 75 kgs./sq. m. (15.4 lbs./sq. ft.) and a power loading of 7.9 lbs./h.p. The top speed at ground level is 280 km./h. (175 m.p.h.). The machine climbs to 5,000 m. (16,400 ft.) in 12 minutes, and has a service ceiling of 8,000 m. (26,300 f t ). Its absolute ceiling is 9,500 m. (31,200 ft.). These figures are, we understand, those obtained on actual test flights, and not estimated figures, and if correct they are testimony not only to the power developed by the Napier "Lion" but also to the skill of the famous Dutch designer.