FK Leichtflugzeuge entwickelt eine Bücker Jungmann Replika als UL & Experimantal

 

Die FK 131 "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 C131A 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 to have 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 is no need to do significant changes in the way the structure is built.

Basically it will remain a steel tube fuselage with wooden wings. But instead of using the heavy original four cylinder Hirth 

 

In consequence the engine installation is coming very close to the original:

The pictures are taken from a pre-serial plane built as 90% replica but having the full size engine compartment including the Walter Micron IIIC installation of the FK131 version.

 

 

The FK 131 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:

 

•   Fuselage tailboom is shortened by 120 mm

•   Wing halfspan is shortened by 120 mm

•   The wingsection is slightly redesigned to a more modern version to improve low speed characteristic and general performance

 

These modifications will not be obvious when comparing the FK131 versus an original Bücker131A.

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 are connecting the aluminium tube strcuture to the fuselage structure so 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. The outcome should be a replica looking the same like its original.

 

Even engine sound is very similar to a typical Bücker Jungmann with Hirth engine! But instead of the original B131 the FK131will feature an up-to-date aircraft engine where parts are available and affordable, a ballistic parachute system and the possibility to operate it as an Ultralight, means having much less obligations and requirements compared to the operation of an original Bücker.

 

The stall speed will be lower compared to an original B131A, making the plane more forgiving at landing and will allow to fulfill EU LTFUL regulations. 

 

The FK131 will have a Vne less than the original B131A, but stress calculations will be based on the acrobatic design regulation requirements and additional tests should proof its capabilities for basic acrobatics in a later time of project development.

 

The prototype of the FK131 is in construction since autumn 2011 . There will be 3 pre-serial aircrafts sold for special introduction conditions. Also a kit version will be available to qualify as an experimental aircraft. The FK131 will remain a limited production of 10 units.