J.Zynk Polish Aircraft 1893-1939 (Putnam)
Stefan Kozlowski, a young Polish automobile enthusiast in his early twenties, became increasingly interested in aeronautics and in the autumn of 1909 went to Germany to study aircraft engineering at the Fachschule fur Flugtechnik in Zahlbach and to learn to fly. While at this school, Kozlowski, consulting the Czech designer Skopik, evolved a detailed study for a tractor biplane, which, except for the powerplant arrangement reminiscent of the Wright system and the wing structure resembling Bleriot practice, was original in concept and layout.
Kozlowski returned to Warsaw on 25 January, 1910, and, with financial backing from Fraczkowski, at the beginning of the following month began construction of his biplane in the Wilczynski timber yard in Czerniakowska Street. With four craftsmen to help him, Kozlowski worked very quickly. In the middle of March the designer took delivery of an Anzani engine, airscrews, rubber-proofed fabric, wheels, tyres and other accessories from abroad, and by the end of that month all wooden assemblies and metal fixtures were ready. At the same time work began on a hangar in the nearby Siekierki meadows, and the airframe was moved there for final assembly early in April.
On 27 April, 1910, initial engine runs were made, and next day came the first taxi-ing run with Kozlowski in the pilot's seat but this revealed some shortcomings in the alignment of the wings. The fault was rectified and ground trials recommenced a few days later. Early in May. during the first take-off attempt, one of the transmission chains broke and the machine went back to the hangar for modifications, which included the replacement of the chains by specially impregnated hemp ropes, revision of the transmission system and engine mounting, exchange of the original pine interplane struts for stronger glued ash struts and improvement of the wing bracing in order to ensure better rigidity of the structure.
The improved machine, free from the vibration experienced earlier, resumed ground runs at the end of May, and early in June made its first short jump. During some 30 take-off attempts that followed, Kozlowski made six brief flights in a straight line, and according to his own statement these covered distances in excess of 30 m (98 1/2 ft) at a height of some 3 m (9.8 ft). However, the aircraft appeared to be tail-heavy and on occasions its tailwheel refused to leave the ground. Kozlowski intended to redesign the tail and add a tailplane and fin, but as his aircraft was to appear at the Aviation Day exhibition on Mokotow aerodrome in Warsaw on 26 June, he postponed this work until later.
Before transporting his biplane to Mokotow, the designer decided to make one more take-off attempt. This proved disastrous. The machine hit a dip in the ground and was severely damaged, while its pilot received cuts and bruises. This accident led to a row with his sponsors, who had hoped to profit by the aircraft's appearance at the exhibition and other future events and refused to provide funds for repairs. In the early autumn of 1910 Kozlowski advertised his biplane for sale, and financial difficulties forced him to abandon further aviation activities.
Despite its shortcomings and lack of satisfactory controllability, Kozlowski's biplane has a place of honour in the history of Polish design endeavour as the first indigenous aircraft to leave the ground under its own power in Poland.
Construction: Kozlowski's aircraft was a single-seat equal-span unstaggered multi-bay biplane of wooden construction. The wings, with a total gross area of 40 sq m (430.5 sq ft), were frameworks of pine, which consisted of three spars and curved lattice ribs, and were covered on both surfaces with Continental rubber-proofed fabric. The undivided upper wing was carried above the fuselage on two struts and connected with the lower wing by five single interplane struts on either side. The lower wing was attached to the fuselage lower longerons. Hinged flaps, which were mounted halfway between the planes on the two outermost struts on each side, acted differentially to operate as ailerons or independently (on one side only) to provide directional control. The rectangular-section main fuselage frame consisted of four longerons and nine frames, the whole trussed by diagonal wires with strainers, and its rear portion was covered with fabric. The pilot's seat was situated at the front of the frame. The forward nacelle, which was attached to the fuselage lower longerons at the front end of the main fuselage frame, carried the fuel tank, flight controls and a steel-tube cross-axle with two mainwheels, the axle being provided with rubber-cord shock-absorbers. The tail, supported by a castoring tail-wheel, consisted of elevators only. Power was supplied by an Anzani six-cylinder W-type air-cooled engine, with a maximum output of 60 hp at 1,300 rpm, which was fitted at the head of the main fuselage frame, above and ahead of the pilot's seat. Two Chauviere tractor airscrews, with a diameter of 2 m (6 ft 7 in), were driven in opposite directions by hemp-rope gearing from the engine shaft, one rope being crossed in a similar manner to that adopted on the Wright biplane. Data regarding the biplane, as supplied to the author by the designer, included a span of 10 m (32 ft 9 3/4 in), a length of 9 m (29 ft 6 3/4 in) and a loaded weight of 300 kg (661 lb).