Flight, August 1936

THREE from ABROAD
Monoplanes for the Sportsman, Air Force and Navy: British Features

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The Koolhoven F.K.50B

   Although considered as a development of the Koolhoven F.K.50 commercial machine described in Flight of October 3, 1935, the new Koolhoven twin-engined bomber resembles that machine only in structure. Outwardly there is little which tells of its ancestry. From the military standpoint the type seems well planned and is blessed with quite an extraordinary performance; with two Bristol Mercury VI.S. engines it is claimed to be capable of 248 m.p.h.
   As the structure is generally similar to that of the F.K.50 the following description will deal mainly with the military features.
   The fuselage is arranged to accommodate a crew of four. In the nose is a transparent turret for a single machine gun, the angles of fire being 70 degrees to port and starboard and 50 degrees upward and downward. The bomb aimer, who also operates the wireless, is located behind the turret and is able to communicate directly with other members of the crew. The fuselage has been specially reinforced in order to avoid vibration of the bomb sight. If necessary the bomb-aimer can easily replace the pilot, whose enclosed cockpit is situated directly in front of the wing. The pilot has blind-flying instruments and emergency bomb releases.
   Aft of the wing are two further gun positions. The upper one has a collapsible top, which, when open, shelters the gunner against the pressures of the airstream, and the lower one can be operated by the same gunner, as the floor between the two posts does not cover the entire width of the fuselage. The lower gun can fire 90 degrees to the right and left and 90 degrees downwards. The bomb racks are located on the C.G.
   Unlike the commercial machine, the bomber incorporates a retractable undercarriage. This is fitted with Koolhoven oleo shock absorbers, low-pressure tyres and hydraulic brakes, and can be retracted by a single movement on the part of the pilot. A signal gives warning of the exact position. When raised the wheels are housed in the engine nacelles.
   The machine will take engines of about 700 h.p. the following performance figures relating to it as fitted with two 605/645 h.p. Mercury VISs, which are rated at 12,500 ft. Controllable pitch airscrews are specified.
   The main data are: Weight empty 7,165 lb., gross weight 12,787 lb., bomb load 2,200 lb., cruising speed at 15,580 ft., 223 m.p.h., landing speed with flaps and without bomb load 62 m.p.h., climb to 19,680 ft. 18 min., absolute ceiling 28,215 ft., range at cruising speed 710 miles.
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