Pilot report - Bücker Jungmann
[Reprinted from Fliteguide / Imperial Aviation]
On one hand can be counted the world's light aircraft that when launched created a sensation. Sure, there are plenty of classics, amongst them Beechcraft's Staggerwing and Bonanza, Bellanca's Viking and the Meyers 200. These are fine aeroplanes with thoroughbred handling qualities but ever-so slightly compromised in execution. Two sensational aeroplanes come to mind immediately. One, Stelio Frati's magnificent Siai Marchetti SF-260 and Morovan's brilliant Zlin 50. There is perhaps a third; Carl Clemens Bücker's and Anders Andersson's oh soooo sweet Bücker Bü 131 Jungmann.
It is perhaps appropriate that all these three aircraft are fully aerobatic, two of them designed as trainers and the other, the Zlin 50, built with no other purpose than to provide Czech pilots with a competition-winning aeroplane. The SF-260 and Jungmann were cast to provide ab-initio training for military pilots and even today there are no other light aircraft that match their profoundly stunning handling qualities.
The Jungmann was born from unfortunate circumstance - to train pilots for war. The aircraft owes its existance to the close relationship established between Sweden and Germany during the inter-war period. It's a little known fact for instance, that SAAB (Svenska Aero AB) was a Swedish subsidiary of Heinkel. The Germans invested in Sweden to avoid far reaching restrictions placed on the manufacture of military hardware and the company was run for some years by Carl Clemens Bücker. In 1932 SAAB found itself in financial difficulties and was sold to Swedish company ASJA. Amongst the SAAB workforce was a local designer named Anders Andersson. Andersson had been busy working on Swedish Air Force Jatfalken bi-plane fighters during the early thirties and took up Bücker's offer of employment in Germany when it was clear the Swedish investment wasn't working out.
Bücker however, had little intention of returning to Heinkel. Knowing that Germany was about to rebuild its armed forces, he decided to start his own company and tender for one of the government's many requirements for training aircraft. He set Andersson to work immediately. Within six months, the prototype Jungmann was rolled out, flying for the first time in April 1934. The Reichsluftfahrtministerium were impressed and immediately ordered the diminutive little trainer for their Deutscher Luftsport-Verband or more commonly known as the 'DLV' - an ostensibly civilian national flying club which in reality was training military pilots for the future Luftwaffe.
Knowing the rigorous use to which his little bi-plane was to be put, Andersson had designed an aeroplane suitable for ab-initio training as well as aerobatics. The fuselage was steel using molybdenum tubing - which was unusual technology in the thirties, the wings were wooden and swept back to provide easy access for the front seat occupant. The interchangeable upper and lower wings had ailerons on all four surfaces which guaranteed sharp roll response. Hirth supplied a 80hp inverted, air-cooled, four-cylinder in-line engine.
The Jungmann was so well liked, the DLV wanted more and before 1934 was out, Bücker moved his Johannisthal factory to Rangsdorf, a little closer to Berlin. Shortly afterwards, Andersson produced the single-seat version, the legendary Jungmeister, which began to establish a reputation for itself amongst aerobatic competitors. As export sales were added to the DLV's requirements, Bücker decided to grant manufacturing licenses, the first of which went to German-owned, but Switzerland-based Dornier-Werke AG at Altenrhein on the shores of Lake Bodenzee. After 100 Bücker-built Jungmann's were supplied to General Franco's Spanish Nationalist air force, the country's Construcciones Aeronauticas SA, known today as CASA, were granted license production. By now the engine had grown from 80hp to 105hp and the Spanish installed their own 125hp powerplant, the ENMA 'Tigre' engine. Czechoslovakia's Tatra Wagon factory also obtained manufacturing rights and built ten airframes in anticipation of an air force order, which never materialised. The only other country to license-build the Bü 131 was Japan. Both the Watanabe Ironworks and Nippon Kokusai Koku Kgoyo companies produced versions of the Jungmann. These were powered by a 110hp Hitachi engine.
By the outbreak of World War Two, demand had begun to outgrow supply. The Yugoslavian air force ordered nearly 400 Jungmann's followed by the air forces of Bulgaria, Hungary and Rumania. 19 civilian aircraft were delivered to South Africa and these were commandeered by the SAAF at the beginning of World War Two. It is estimated that nearly 4,000 Jungmann's had been built worldwide by 1941. Anders Andersson returned to Sweden in 1939. He left having designed the Jungmann's replacement, the wooden Bücker Bü 181 Bestmann and was to continue his career as Design Office Chief until well after the war. Andersson's important influence in training aircraft design was celebrated by the 1945 launch of the SAAB Safir - an aeroplane that displays clear lineage to the Bücker trainers and itself, established a reputation for fine handling qualities.
There are a number of Jungmann's still flying. Brian Zeederburg at Syferfontein just outside Johannesburg is the owner of the oldest aircraft in existence and one of very few originally manufactured at the Rangsdorf factory. Zeederburg's Bücker was delivered new to the Swiss Aero Club in 1935. In '63 it was sold to the UK before eventually arriving in South Africa. The South African Jungmann's as well as the handful of Jungmeister's were sacrificed along with many other now rare and priceless Second World War aircraft. Every single South African Air Force example was burnt. Cynics suggest the aircraft were unacceptably 'German' and after the war were used for artillery practice before being given to an airfield fire department.
Almost every remaining Luftwaffe Bücker was broken up after the war having been butchered first by souvenir hunters who took a fancy to tearing away the fabric containing air forces crosses and swastikas. According to historian Charles Cain, the Hungarian examples were largely destroyed by the retreating German army. No Japanese-built aircraft survive. Apart from a few Czechoslovakian aircraft, most current survivors are from Spain and Switzerland, where the aircraft has a cult following. In a strange irony, the Czech air force, which before the war rejected the idea of purchasing Bückers, re-evaluated the Jungmann again in 1946 and ordered some 260 from the Tatra factory.
The Jungmann's license manufacturing history led to the installation of various engines. The original Hirth powerplant was distrusted by post-war operators. The engine, which had a roller-bearing crank, gained a reputation for throwing crankshafts, and whilst Spanish aircraft used a locally built Empresa Nacional de Motores de Aviacon (ENMA) 'Tigre' engine, and the Czech's used a Walter powerplant, it wasn't long before Hirth-powered owners started installing American engines. The favourite was the 180hp IO-360 Lycoming and aircraft so converted by Pilatus were called the 'Lerche' (Lark). It was unsurprising that Jungmann's would be sought after following the end of World War Two. During the fifties, aerobatic competitions were growing in popularity and pilots were seeking the best all-round aircraft to compete in. The Jungmann was a natural choice.
It was the Swiss who pioneered the engine modification. The Dornier factory on Lake Bodenzee had passed into the ownership of FFA and they installed a 170hp Lycoming into the airframe of a Bücker belonging to Albert Reusch. Reusch promptly took second place at the 1962 British Lockheed Trophy at Coventry - a result that raised many eyebrows amongst the European flying community. In '63 the aircraft came first in the Swiss National Championships and the following year another modified Jungmann entered the World's flown by Swiss pilot Arnold Wagner. In '64, the Communist Bloc entered in strength, bringing with them a formidable array of specialised aeroplanes. Their new Yak 18 and Zlin 226. Wagner managed an incredible 8th place.
The mid sixties was a short but sweet revival for the Jungmann in international aerobatics. In an attempt to keep the biplane competitive, the Swiss modified the wing by altering it's airfoil to enhance its inverted performance. Despite a fatal crash in 1966 following a low-level inverted loop, The enhanced aerodynamics enabled the Bücker to continue competing. In 1970 Eric Muller was placed 35th flying a Lerche version at Hullavington in England. This was the swansong for the Jungmann in international competitions, though the type was to be found flying in national events for a number of years afterwards.
Aerobatics were perhaps responsible for the type's longevity. Competitors continued play with the engine installation in an effort to obtain greater vertical performance. Czech Mira Slovak installed a 225hp Lycoming into one US-based Bücker and when the American's 'discovered' the Jungmann in the early sixties, many were promptly converted to 'flat-four' power. There are about 150 aircraft still around today. Many are Spanish-built CASA 1.131 versions as their air force only began disposing of them in the late seventies. Two of these arrived in South Africa in 1984, bought by EAA stalwart Peter Hengst.
Flying the Jungmann
The Jungmann is a tiny aeroplane, even by biplane standards - it's not a great deal bigger than a Pitts S2 and considerably smaller than a Tiger Moth. Clues to its legendary handling lie in the double-aileron configuration and Andersson's decision to use pushrod control linkages, leaving only the rudder-connect with a cable, guaranteed instant response. Construction quality is evident throughout the airframe. The control rods are located using self-aligning, double roll, ball bearings rather than deep grooved bearings. Moreover, although the wing area is nearly half that of a Tiger, each wing in uncovered form weighs a mere 15 kilogrammes. The highish wing loading, at least for a biplane, would suggest a 'hot' ship.
An 80 litre fuel tank mounted above the front pilot's knees feeds the Tigre engine and has a 'flop-tube' to allow for inverted flight. There is no inverted oil system, so whilst the engine will run for a couple of minutes upside-down, the engine will quickly starve itself of oil. This is more than adequate for hesitation rolls or a Half Cuban.
Either cockpits are a tight fit for larger occupants, the front being especially small. Entry, like a Tiger Moth, is helped by a pair of hinged doors which unlatch downwards. Two handholds on the top wing centre section and a strengthened skin area in front of the rear windscreen mean that once both feet have been swung inboard you can slide your bum easily into the reclined seat. It is not an especially comfortable place to be and those with long legs will find it almost impossible to raise their knees under the fuel tank and locate their feet onto the rudder pedals. The seating position appears to be rather high - a feeling accentuated by the curve of the top fuselage.
The panel layout at the front is simple. A single magnetic compass dominates the view and this is flanked by an airspeed indicator in knots, an rpm gauge and an altimeter. A sliding magneto switch is located to the left, though in an effort to reduce the risk of an inadvertent limb movement, the front switch knob has been removed. The throttle lever is mounted on the left and a trim lever on the right. The rear cockpit, which a student traditionally occupied, is far more comprehensively equipped. Here there's a mixture lever, radio, oil temperature and oil pressure gauge, fuel primer and 'g' meter.
Peter Hengst's two Jungmann's are both equipped with Tigre engines. However one is 125hp and the other is 150hp. ZU-UXB , in the colourful paint scheme of the Swiss air force, has the 150hp version. This engine was originally designed for Spain's indigenous 1943 INTA HM-1 trainer and the A.I.S.A. I-115 trainer of 1952. It nevertheless fits quite nicely into the Jungmann for a slight weight and thus C of G penalty. ZS-VIV, Peter's other Jungmann, is fitted with the correct 125hp Tigre G-IVB engine.
Spanish-built aircraft had a remote fuel primer tank bolted high up immediately behind the rear cockpit. The filler protrudes through a gap in the bulkhead and this needs to be topped up prior to starting the Tigre. German aircraft were primed directly from the main tank. Although 'UXB' is fitted with a starter, it has no battery to provide power - the wooden propellor therefore needs swinging by an able-bodied helper. The Tigre starts easily enough and settles into a wonderful war-movie rat-a-tat-rat idle. There's tailwheel steering via a rudder interconnect running within the rear fuselage. The original cable/drum brakes were notoriously ineffective - a problem with many wartime German aircraft, so Chalkie Stobbart, who helped Peter rebuild the Jungmann's, has installed a pair of powerful Cleveland discs - one of few modifications to the original airframe.
The wings look impossibly small from the cockpit - smaller even than those of Pitts. This is a mere optical illusion, as a Pitts' pilot view is dominated by wing sections and flying wires. On takeoff, the Jungmann displays few squirrelly tendencies. The view over the nose is restricted, though the narrow cowling goes a long way to aiding directional stability on the ground. The rudder is powerful enough to check any swing. At about 25 knots the tail comes up and the aircraft lifts off at about 60 knots - high for a thirties-era basic trainer.
Despite the cramped accommodation, it's plain to see why the Bücker Jungmann is a legend. Whilst the stick is placed so the top is level with the top of your thighs, control response is sweet and incredibly well harmonised. Each control input, whether it's rudder, elevator or aileron, requires the same amount of effort. Although the Jungmann's speed range rarely exceeds 120 knots, the controls remain light and highly responsive. UXB is at a slight disadvantage during aerobatic maneuvers because of the higher weight of its 150hp engine.
Although the Jungmann was never designed for advanced aerobatics, it nevertheless gets around a reasonable loop provided entry speed is sufficient to form a satisfactory parabola. A roll is pure delight. In its day, the aeroplane's six seconds taken to complete an aileron roll was sensational for a light trainer. Entry is done at about 105 knots followed by a pull up to 40 degrees; check forward on the stick and a crisp full aileron deflection. The aircraft recovers instantly with minimal height loss and with a beautifully sharp response when stopping the roll. Watching the world revolve between the wings, flying wires and centre section is pure song and dance.
The Tigre engine is limited to 2350 rpm - a speed it can easily exceed in a dive, so the rpm gauge is an important item to watch during aerobatics, especially as it lacks any form of red-line. Original Hirth engine's, with their roller-bearing crankshafts were built to withstand 3,300 rpm for two minutes - a factor which probably led to the engine's reliability problems. At the lower end of the speed range, the Jungmann's behavior justifies its reputation. The stall is very mild with little tendency to drop a wing with recovery instant. Although we didn't try a spin, According to many experienced Bücker pilots, the aircraft recovers instantly during this maneuver too.
Again with the extra weight of the 150hp Tigre, UXB is reluctant to do a full three-pointer. Moreover, a reasonable approach speed is necessary to avoid a high sink rate after the flare. 70 knots is about right for the Jungmann, and after a gentle round-out, the aircraft touches down with a good tail-low attitude. The brakes are extremely efficient and with the locking tailwheel, help to keep the landing roll-out very short.
Jungmann's are coveted collection pieces nowadays. Of the approximately 150 still flying worldwide, three are in South Africa, one being the oldest example in the world - Brian Zeederberg's ZS-BUC, construction number 20. This aircraft has had its original Hirth engine replaced by a unique Lycoming installation. Whilst purists may throw their hands up in horror at the appearance of Zeederberg's Bü 133, the original engine and its bearers and firewall have been preserved and stored so the aircraft can be re-converted again.
[END OF REPORT]
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