Project description FK131 Jungmann The FK131 ( C104FK) is a cooperation project between Co. B&F Technik GmbH Germany and Co. Podesva Air, Czech Republic. The aircraft design is widely based on the original Bücker 131A design, which was produced over longer times under Czech license named C104. The original Bücker 131A version was designed 1934 as a very light trainer and acrobatic aircraft (330kg empty) with a four cylinder 80hp HM60R Hirth engine. The concept of the FK131 is a replica coming as close as possible to the original, but been light enough to classify either as Experimental aircraft or as EU Ultralight. As the original airframe was very light there was no need to proceed significant changes in the way the structure is built. Basically it remains a steel tube fuselage with wooden wings. But instead of using the heavy original four cylinder Hirth engine the FK131 is powered by the today s version of the four cylinder air cooled aviation engine, the Walter Mikron. Both engines are having comparable cylinder capacity and same power. But the Mikron is made of modern materials and technology, saving a lot of weight compared to its original predecessor from 1934. In consequence the engine installation is coming very close to the original: Walter Mikron IIIC installation and engine cowl FK131 Jungmann - C104FK project descriptionrev. 15.10.2013 page 1
Scaling of the FK131project: left: FK131prototype right: T131 Jungmann (polish license production) The FK131 is coming as close as possible to the original outlines and dimensions of the Bücker 131A. Just a few corrections are needed to compensate for the lighter engine and to enable the owner to register the plane under the design regulation LTF-UL or US-LSA: Wing halfspan is shortened by 70 mm The wingsection is slightly redesigned to a more modern version to improve low speed characteristic and general performance These modifications are not obvious when comparing the FK131 versus an original Bücker131A. FK131 Jungmann - C104FK project descriptionrev. 15.10.2013 page 2
FK131 FK131 Jungmann - C104FK project descriptionrev. 15.10.2013 page 3
Structural design The lighter engine will reduce empty weight but also includes the need to correct CG position by building tailplane and rudder not in steel tube but in aluminum tube technology. Solid welded steel fittings bonded and riveted into the aluminum tube structure are connecting fuselage and tailplane. From outside this is in fact not evident and the basic design remains very close to the original. The fuselage structure is a welded steel tube frame using today s seamless steel tubes but based on the original geometry. The wings and ailerons are made in wood, also based on the original design. FK131 Jungmann - C104FK project descriptionrev. 15.10.2013 page 4
The stall speed is lower compared to an original B131A, making the plane more forgiving at landing and allows to fulfill EU LTFUL regulations. The FK131 Vne is at 253km/h and so less than the original B131A - but its stress calculations are based on the FAR23 acrobatic design regulation requirements. Additional tests should proof its capabilities for basic acrobatics in a later time of the project. FK131 Jungmann - C104FK project descriptionrev. 15.10.2013 page 5
Also cockpit interiors are done pretty much according to the original style of the 1930 s Jungmann. The outcome is a replica looking the same like its original predecessor. Even engine sound is very similar to a typical Bücker Jungmann A Version with Hirth engine! But instead of the original B131 A the FK131 features an up-to-date aircraft engine where parts are available and affordable, a ballistic emergency parachute system and the possibility to classify it as an Ultralight! This means having much less obligations and requirements compared to the operation and maintenance of an original Bücker FK131 Jungmann - C104FK project descriptionrev. 15.10.2013 page 6
Including the BRS ballistic parachute system the prototype came out well below 300kg, including all extras and options. The prototype of the FK131 made its first flight on October 24 th, 2012. Performance data are determined closer at present, but first results were coming pretty close to the original B131A specifications. A limited series of 10 ready to fly aircrafts is in production at present. Also a kit version will be available to qualify as an experimental aircraft. FK131 Jungmann - C104FK project descriptionrev. 15.10.2013 page 7
For more details address to B&F Technik Vertriebs GmbH Anton Dengler Straße 8 D-67346 Speyer info@fk-leichtflugzeuge.de FK131 Jungmann - C104FK project descriptionrev. 15.10.2013 page 8
original specification Bücker (brochure 1934) FK131 specification FK-Leichtflugzeuge 2013 FK131 Jungmann - C104FK project descriptionrev. 15.10.2013 page 9