Flight, November 1935

SOLELY for SURVEY
The Koolhoven F.K.4.9 for the Dutch Government: Dark Room on Board

   AN order has been placed by the Dutch Government with N.V. Koolhoven-Vliegtuigen, Rotterdam, for a twin-engined high-wing monoplane to be used for survey work.
   Its cantilever wooden wing is attached to the fuselage by four nickel-steel bolts, the wing itself being built up on two box spars with silver spruce flanges, plywood webs and plywood ribs, the whole being covered with plywood. Identical construction is used for the ailerons, which are operated differentially and are statically balanced.
   A fabric-covered structure, the fuselage is of welded steel tubes. The tail unit is built up from steel tubes with ribs of sheet metal, the covering being of fabric. A fixed fin and a trimming tab on the rudder are features and the tail plane can be adjusted on the ground. The elevator trimming tab is adjustable by the pilot during flight.
   Two Gipsy Major engines are fitted, these being built into the leading edge of the wing. The nacelles behind the engines are fabric-covered. Two welded aluminium sheet fuel tanks, each feeding one engine, are placed between the spars outboard of the engines. Each engine has two A.C. fuel pumps and all pipes are of the flexible type. Two oil tanks are placed behind the power units and are cooled by the air forced through the engine cowlings.
   The pilots are placed in the nose, permitting an excellent outlook. Windows of unbreakable glass are provided in their cabin, one of them being equipped with a sliding panel in case of bad weather. An electric windscreen wiper is also included. The commander, seated at the rear of the cabin, communicates with .the pilots by means of a telephone. A dark room is provided, the wall between the cabin and the dark room being fitted with a small lock which makes it possible to pass the plate holders without any daylight entering the dark room. Wooden panels form the floor, and the view-finder, the special drift indicator, and the cameras themselves can be placed in special openings which have appropriate coverings when not in use.
   At an all up weight of 4,673 lb. the F.K.49 has a maximum speed of 119 m.p.h. at sea level. Its service ceiling is 13,100 ft., and with full load the take-off run is 689 ft.