Sk 10 - Raab-Katzenstein RK-26 Tigerschwalbe (1932-1945)
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Swedish Air Force Trainer Aircraft Sk 10 Raab-Katzenstein RK-26 Tigerschwalbe


In the autumn of 1930, Gerhard Fieseler, then World Champion of Aerobatics, visited the Air Force Flight Academy (F 5) at Ljungbyhed. Fieseler, who later designed the famous STOL aircraft Fieseler Storch (S  14), made an impressive show with his Raab-Katzenstein RK 26 Tigerschwalbe, an one-seated aeroplane designed for aerobatics. 

Gerhard Fieseler arrived to F 5 just at the right time. The Air Force Flight Academy needed badly an aircraft for advanced training. Fieseler had been invited to Ljungbyhed by the chief flying instructor Nils Söderberg, later Major-General (Air Vice-Marshal) of the Air Force.  

By recommendation of Nils Söderberg, the Air Board made an inquiry to the Swedish aeroplane manufacturer ASJA at Linköping. ASJA, which had secured the rights for license production, bought a German-built Tigerschwalbe. The aircraft were put into the civil register as SE-ACO and was rented to the War Flying School. At the school it was tested by the flying instructors, who found the aircraft suitable as the missing advanced trainer. 

In February 1932, ASJA got an order of 25 aircraft. The Air Force designation became Sk 10 and the individual aircraft got the Air Force numbers 521-545. The design was partly changed compared to the German Tigerschwalbe. The most important alteration was of course that the aircraft was changed to a two-seater with dual command. The original Tigerschwalbe was fitted with an 175 hp Armstrong Siddeley Lynx engine. The Swedish variant got an 260 hp Walter Castor 1A, of course stronger but also heavier. The wings were reinforced. Together with the heavier Swedish-made plywood, their weight increased by 60 kg. Also the tail part was reinforced. Totally, the ASJA-built Tigerschwalbe was  nearly 200 kg heavier than SE-ACO. This fact of course changed the flying performance. 

The 25 Sk 10:s were delivered from October 1932 to May 1934.  The Sk 10 became very controversial. Before the first half of the batch was delivered, two of the aircraft got into uncontrollable spin when flying inverted. This resulted in both cases in fatal crashes. These accidents started the ”Sk 10 Affair”, which engaged the newspapers of the entire Sweden. The Sk 10 was stamped as highly dangerous due to faulty design.. The Air Force was divided into two parties. An order which prohibited aerobatics was issued for the aircraft, but a commission of inquiry revoked this order. Charles Lindbergh, who visited Sweden in 1933, tested the Sk 10 and performed advanced aerobatics. His opinion was ”all right”.  One  Sk 10 was flown to the Royal Aircraft Establishment at Farnborough for tests. The report from 1934 brought it out clearly  that the aircraft was hard to handle, but as the British and the Swedish training programmes were totally different, the report was of little value. 

But as time passed, the Sk 10 were accepted  for its intended mission. It was a machine which separated the wheat from the chaff. Of the  25 delivered aircraft, 18 were written off due to crashes. 

One Sk 10, the only remaining Tigerschwalbe in the world, is preserved at Flygvapenmuseum (photo above). The aircraft was delivered in January 1934 and written off in December 1944. SwAF/n 536, c/n 20.   

As seen on the picture below, the Sk 10 could be equipped with skis. This photo below from the large archive of Lars E. Lundin, Västervik, shows a row of Sk 10 with SwAF/n 530 and 521 nearest to the camera. These aircraft from Ljungbyhed had just made a stopover at Malmen. The final destination is Grangärde in the province of Dalarna, where winter exercises will take place. 

Length: 6,55 m. Span: 8,40 m. MTOW 1.136 kg. Max. speed: 191 km/h.  


Swedish Air Force Trainer Aircraft Sk 10 Raab-Katzenstein RK-26 Tigerschwalbe

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© Lars Henriksson

Updated 2010-07-10