Project description FK131 “Jungmann”

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
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Proportions and scale of the FK131project:
right: FK131 Jungmann
left: 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.
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FK131
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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.
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The stall speed is lower compared to an original B131A, making the plane more forgiving at landing
and allows to fulfill European LTFUL regulation.
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 envelope
requirements. Additional tests should proof its
capabilities for basic acrobatics in a later time of the
project.
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Cockpit interiors
are done pretty
much according
to the original
style of the
1930´s
The outcome is a replica looking identical to its original predecessor.
Even the 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 Jungmann.
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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 24th, 2012 . Performance data are
determined closer at present, but first results
were coming pretty close to the original B131A
specifications.
A small series of ready to fly aircrafts is in
production at present. Also a kit version is
available to qualify as an experimental aircraft.
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For more details address to
B&F Technik Vertriebs GmbH
Anton Dengler Straße 8
D-67346 Speyer
info@bueckerundfunk.de
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original specification Bücker (brochure 1934)
FK131 specification Bücker&Funk 2013
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