Flight, January 1935

A CONTINENTAL FEEDER-LINE TYPE
The "Gipsy"-engined Koolhoven F.K.48 Monoplane

   THE Koolhoven F.K.48 "Ajax" taken over by K.L.M. for their internal schedule should be interesting to readers of Flight, as England has given considerable attention to the feeder-line type of aeroplane carrying half a dozen passengers on 200-300 h.p.
   The Dutch machine in question is designed to provide room for rather more passengers than the average small single-engined aeroplane, and at a higher cruising speed than was previously considered sufficient.
   The wing is built up with box spars and plywood ribs, with a ply covering taking all internal and torsional loads in the normal manner. The wings are for the greater part cantilever, but struts run from the bottom of the fuselage to the engines, thus relieving both flying and landing loads. Advantage has been taken of this fact by reducing the wing depth and chord at the root to eliminate interference; at the same time, the result is very pleasing to the eye. The top of the wing remaining straight and the lower surface sloping up to the fuselage, it has been possible to obtain a much lower engine position than would have been the case had the wing been fully cantilever and placed on top of the fuselage. Moreover, tests with wool-tufts doped on to the trailing edge showed that the whole wing stalled at the same moment.
   The fuselage is a welded steel tube structure throughout, covered with fabric in the usual way. The section at the nose is elliptical, gradually shaping out to a rectangle at the front of the cabin. The pilots' compartment seats two, with duplicate controls and a very complete set of instruments. The windscreen is of the forward-sloping type, while an ingenious arrangement of slots prevents the air from breaking away over the top of the fuselage when the machine is pulled up at an angle near the stall.
   Normally the cabin seats six passengers. For joy-rides the number of passengers would number nine with one pilot, while as a private owner's or private charter machine the machine would be furnished with four or five very comfortable chairs and a lavatory aft. All cabin equipment can be easily taken out and freight carried.
   The tail unit is built up on a welded steel tube frame and sheet steel ribs, the whole fabric-covered. Trimming tabs are provided on elevators and rudder, this being considered a far simpler way to obtain correct trim than by the use of costly tail-trimming gear.
   The undercarriage has a very wide track, the oleo legs being attached to the front spar with axle and radius rod running to the bottom of the fuselage. A sprung tail-wheel, free to rotate through a complete circle, simplifies handling on the ground. Brakes and tyres are by Dunlop.
   The two "Gipsy Majors" are suspended in rubber blocks on a welded steel structure running from the front spar. One petrol tank is provided for each engine, and two pumps draw the fuel to the carburetters.
   As supplied to K.L.M. the F.K.48 is fitted with wireless, night-flying equipment and electric starting gear.

KOOLHOVEN F.K.48.
Two 120 H.P. "GIPSY MAJORS."
FEEDER-LINE OR PRIVATE CHARTER HIGH-WING CABIN MONOPLANE.

DIMENSIONS
   Span 50ft. 8in. (15,20 m)
   Length 33ft. 7in. (11,00 m)
   Height 8ft. 10in. (2,65 m)
   Wing area 346 sq. ft. (31,15 m2)

WEIGHTS
   Weight empty 2,580 lb. (1150 kg)
   Disposable load 2,020 lb. (1 000 kg)
   Total weight 4,600 lb. (2 150 kg)

PERFORMANCE.
   Maximum speed 130 m.p.h. (208 km/h)
   Cruising speed 118 m.p.h. (187 km/h)
   Landing speed 58 m.p.h. (95 km/h)
   Initial rate of climb 600 ft. p. min. (3 m/sec)
   Theoretical ceiling 14,000ft. (4 200 m)
   Service ceiling 11,300ft. (3 400 m)