The P.W.S.11 was a training aircraft similar in design to the P.W.S.10 fighter, but that didn’t enter production as the P.W.S.10 itself was only seen as an interim design which would soon be free to go to training units.
The P.W.S.10 was a parasol wing fighter that was developed in response to a Polish Department of Aeronautics request for a new fighter issued late in 1926, to be powered by 450hp Lorraine-Dietrich liquid cooled engine and with a mix of wood and metal construction.
Late in 1927 P.W.S. began work on a training aircraft to go alongside the P.W.S.10. This would have the same basic layout as fighter, but would be of all wooden construction, and use a 240hp Gnone-Rhone engine (eventually replaced with a 220hp Wright/ Skoda J.5 nine cylinder radial engine). The aim was to produce a training aircraft that was similar to fly but cheaper and less complex than the P.W.S.10.
The P.W.S.11 was developed alongside the P.W.S.10, but most of its elements were new – it had a slab sided wooden fuselage, an new tail, and a different engine mounting. The original version was to have a span of 31ft 2.25in and length of 22ft 4in, making it smaller than the P.W.S.10.
In the spring of 1929 P.W.S. was given a contract for two prototypes and a static test airframe of the P.W.S.11. The static tests were completed in October 1929 and the prototype made its maiden flight in November 1929, six months before the P.W.S.10. At this point the engine had no cowling, the fuselage had a rectangular cross section and it had the same design of wing as the first P.W.S.10 prototype, with a constant chord and thickness.
The initial trials shows that the aircraft was unstable and didn’t respond well to the controls. At first the tail was blamed, but several attempts to modify it didn’t help, and after some work it was discovered that the key problem was the impact of the combination of the un-cowled engine and the flat sided fuselage on airflow past the aircraft. The second prototype was thus given a cowling ring while the fuselage was faired to give it an oval cross section. This aircraft, as the P.W.S.11bis, began flight trials in the spring of 1930 and had largely fixed the problems.
During the rest of 1930 the aircraft was further modified, until by the end of the year it was an excellent aerobatic aircraft. However it was also no longer needed, as the P.Z.L. P.7 was emerging as a successful design which would soon replace the P.W.S.10 in the front line fighter units, leaving that aircraft free to go to the training units. However the P.W.S.11 was the basis of the two seat biplane P.W.S.12 trainer, which did enter production as the P.W.S.14 and the more advanced P.W.S.16
Engine: Wright/ Skoda J.5 nine cylinder radial engine
Span: 29ft 6.75in
Height: 8ft 0.5in
Empty Weight: 1,468lb
Normal Loaded Weight: 2,060lb
Maximum Speed: 130.4mph at sea level, 122.4mph at 6,561ft
Climb rate: 2min 44sec to 3,280ft, 10min 13sec to 9,842ft