Max Kegel Segelflugbau
| Type | Single seat glider |
| Dimensions | Length 7,88 m , height 1,4 m , span 19,15 m , wing area 18 m2 , aspect ratio 19, Göttingen 549, max. wing chord 1,5 m , stabilizer 3,76 m |
| Weights | Empty 158,1 kg, loaded , max. take off weight 228,1 kg |
| Performance | Best speed ca 60 km/h, sink 0,71 m/sec., best glide ratio 20 |
| Type | Werk.Nr | Registration | History |
| On May 16, 1929, Robert Kronfeld exceeded 100 km in a straight line in a glider. Departing from the Rheine area, it landed in Dermold, 102 km from its starting point. Following the Teutoburger massif, he actually covered 145 km. Robert Kronfeld crossed the Channel and back on June 26, 1931 (Saint Englevert, Pas-de-Calais to Sangate then return the same day). Winner of the Rhön competition in 1929. Henri LUMIÈRE (son of Auguste Lumière, inventor with his brother Louis of the cinematograph) bought the Wien from Kronfeld around 1931-32, and flew it during meetings in the Lyon region. |
The Lippisch or RRG Wien was a high-performance glider designed by Alexander Lippisch in Germany in 1929. Owned and flown by Robert Kronfeld, it was one of the first sailplanes intended to exploit thermals. It set world records both for distance and altitude and demonstrated the practicality of long-distance cross-country flights.
Robert Kronfield was the overall winner of the 1928 Rhön Gliding Competition flying the RRG (Rhon-Rossitten-Gesellschaft) Professor. To remain competitive with the latest designs coming from the German universities, he asked Alexander Lippisch, the Professor's designer, for an improved version with better performance and handling. Lippisch's response was an elegant sailplane that Kronfeld named Wien after his home town. The Wien kept the layout of the Professor, with pylon-mounted single-spar wings braced with faired struts, but the span was increased by 3.0 m , raising the aspect ratio from 14 to 19.6. The fuselage was redesigned to have a smooth ovoid section, finer aft than on the Professor and fitted with a more aerodynamically refined fin and rudder.
Both designs used a plywood-covered D-box forward of the spar, with fabric covering behind, and their 2.50 m half span, parallel chord inner wing panels were similar, though close to the fuselage the Wien's wing was strengthened with full chord plywood skin. The V-form bracing struts linked the extremes of these panels to the lower fuselage. The extra span of the Wien was in the double straight-tapered outer panels, which continued out to finer, rounded tips. Ailerons occupied the whole trailing edge of these sections.
The Wien's open cockpit was ahead of the wing leading edge. There was no windscreen, and the instruments, including the still novel variometer, were displayed horizontally, inset into the fuselage immediately in front of the pilot. The undercarriage consisted of a single enclosed skid and a small spring tailskid. The rear fixed surfaces, ply covered, were very narrow, though the root of the fin was carefully faired into the fuselage. The tapered control surfaces were fabric covered.
The Wien was capable of utilizing both ridge lift and thermals. Kronfield used both methods in a series of ground breaking and often record setting flights between 1929 and 1931, learning much about thermal flying. On 15 May 1929 he made the first glider flight of more than 100 km , largely ridge flying but with some thermal soaring. This was followed by at least three world distance records, the last between the Wasserkuppe and Marktredwitz, a distance of 164 km flown on 24 August 1930. Some very significant though not record breaking flights of about 160 km (100 were made in August 1931 which used thermals alone and showed that on some days the distance that had to be flown between thermals was short. This was new information which, as it became widely known, opened up the potential of cross-country soaring.
Kronfeld also set two glider altitude records, the second flown on 30 July 1929 in thunderous conditions to a height of 2,560 m . At the invitation of the British Gliding Association he and the Wien made a series of demonstration flights on a tour of England in the summer of 1931. During it he flew over London along the Thames and also won a £1,000 prize donated by the Daily Mail for a cross Channel flight. The North -South crossing, followed by a return flight, was made in July 1931; these did not use thermals but were direct glides from about 3000 m after an aero-tow
Robert Kronfield was the overall winner of the 1928 Rhön Gliding Competition flying the RRG (Rhon-Rossitten-Gesellschaft) Professor. To remain competitive with the latest designs coming from the German universities, he asked Alexander Lippisch, the Professor's designer, for an improved version with better performance and handling. Lippisch's response was an elegant sailplane that Kronfeld named Wien after his home town. The Wien kept the layout of the Professor, with pylon-mounted single-spar wings braced with faired struts, but the span was increased by 3.0 m , raising the aspect ratio from 14 to 19.6. The fuselage was redesigned to have a smooth ovoid section, finer aft than on the Professor and fitted with a more aerodynamically refined fin and rudder.
Both designs used a plywood-covered D-box forward of the spar, with fabric covering behind, and their 2.50 m half span, parallel chord inner wing panels were similar, though close to the fuselage the Wien's wing was strengthened with full chord plywood skin. The V-form bracing struts linked the extremes of these panels to the lower fuselage. The extra span of the Wien was in the double straight-tapered outer panels, which continued out to finer, rounded tips. Ailerons occupied the whole trailing edge of these sections.
The Wien's open cockpit was ahead of the wing leading edge. There was no windscreen, and the instruments, including the still novel variometer, were displayed horizontally, inset into the fuselage immediately in front of the pilot. The undercarriage consisted of a single enclosed skid and a small spring tailskid. The rear fixed surfaces, ply covered, were very narrow, though the root of the fin was carefully faired into the fuselage. The tapered control surfaces were fabric covered.
The Wien was capable of utilizing both ridge lift and thermals. Kronfield used both methods in a series of ground breaking and often record setting flights between 1929 and 1931, learning much about thermal flying. On 15 May 1929 he made the first glider flight of more than 100 km , largely ridge flying but with some thermal soaring. This was followed by at least three world distance records, the last between the Wasserkuppe and Marktredwitz, a distance of 164 km flown on 24 August 1930. Some very significant though not record breaking flights of about 160 km (100 were made in August 1931 which used thermals alone and showed that on some days the distance that had to be flown between thermals was short. This was new information which, as it became widely known, opened up the potential of cross-country soaring.
Kronfeld also set two glider altitude records, the second flown on 30 July 1929 in thunderous conditions to a height of 2,560 m . At the invitation of the British Gliding Association he and the Wien made a series of demonstration flights on a tour of England in the summer of 1931. During it he flew over London along the Thames and also won a £1,000 prize donated by the Daily Mail for a cross Channel flight. The North -South crossing, followed by a return flight, was made in July 1931; these did not use thermals but were direct glides from about 3000 m after an aero-tow
Robert Kronfeld and his glider Wien
Following the rapid advances in gliding in the mid-1920s, the desire for a high-performance glider at affordable prices arose in many clubs – or for types that could be built within the flying groups themselves without major problems. Commissioned by Professor Georgii, head of the Rhön-Rossitten Society, Alexander Lippisch designed the Professor in 1928. The detailed design and construction drawings were provided by Hans Jacobs, who had been employed in the aeronautical engineering department of the RRG Research Institute since August 1927.
The aircraft, which as a prototype received the nickname "Rhöngeist," was indeed very simply constructed according to Professor Georgii's specifications, yet still quite suitable as a high-performance glider. It was a high-wing aircraft braced with V-struts and a wingspan of 16 meters. and a wing aspect ratio of 14. The wing with the Göttingen
profile Gö 549 was designed in three sections. The center section was rectangular in plan view, the outer sections trapezoidal. The main spar had the then already proven torsion leading edge, i.e., plywood skinning from the wing leading edge to the main spar; this construction method has not changed in wooden structures to this day! In the fuselage, the simple construction with the six-angular cross-section presented no particular construction problems. Initially, however, the aircraft was very treacherous to fly.
Lippisch not only aimed for a simple design during the construction – the professor was also expected to achieve the best flight performance. For a with the lowest possible sink rate and an optimal glide ratio in mind, Lippisch designed the glider with minimal washout on the pointed outer wingtips. It is therefore not surprising that the well-known glider pilot and author Peter Riedel called the professor's prototype a "tricky bird" that wanted to go into a spin at low speed during every turn. This is how P. Riedel describes it in his three-volume work "Erlebte Rhönge- Geschichte" (Experienced Rhön History). According to reports, fatal accidents occurred with replicas due to insufficient wing washout; therefore, the ailerons had to be modified for training and practice operations so that the outer wingtips had more washout.
Comparing the Professor with the gliders of the so-called "Darmstadt School" (Academic Flying Group Darmstadt) with their cantilevered, aerodynamically cleanest designs with
very good flight performance and the best flight characteristics for the time, one could retrospectively consider the Lippisch Professor design as a step backward in glider
construction.
It is probably only thanks to the gifted pilot Robert Kronfeld that the professor's prototype "Rhöngeist" was not forever remembered by posterity as a treacherous bird. Robert Kronfeld, a flight instructor on the Wasserkuppe not long ago, immediately got to grips with the somewhat demanding glider. He felt instantly familiar with the machine, had it completely under control, and flew it from success to success. Not entirely uninvolved in his flying success with the "Rhöngeist" and later in Vienna was, of course, an aircraft instrument that was newly discovered for gliding at that time and was installed for the first time in the "Rhöngeist." This instrument, the variometer, was not unknown, however, as balloonists had been using it for a long time before. But it was used here for the first time in a glider. This device, which displays the rate of climb and descent, was, besides the pilot and his aircraft, the most important prerequisite for the truly optimal use of thermal updrafts. We will return to the variometer later.
Before the Rhön competition in 1928 – instructed by Professor Georgii – Kronfeld completed at least one flight in cloud updrafts with the professor's prototype and tested tactical circling in the updraft area. During the Rhön competition, on August 6, 1928, Kronfeld also succeeded in finding a thermal area after a bungee launch. Always circling cleanly, gaining altitude.
This thermal flight lasted over three hours. This first publicly and successfully performed flight outside of the slope updrafts, with deliberate use of thermals, took him to the Himmeldunkberg, located about 8 km away, and back to the Wasserkuppe.
This 9th Rhön Gliding Competition was divided into three parts:Training, practice, and school competition. In the performance class, four pilots competed and completed 61 flights; the winner was "Bubi" Nehring in the Darmstadt. 21 pilots participated in the practice competition and completed 131 flights.
First place went to Robert Kronfeld with his "Rhöngeist." He became the overall winner of the 9th Rhön with his total flight time of 7 hours and 54 minutes.
Some imitated Kronfeld's flight tactics. Although they did not own a variometer, they were able to achieve beautiful results. Successes were achieved; Erich Bachem flew the Himmeldunkberg flight with his city of Stuttgart in a fabulous 33 minutes 7 seconds - Kronfeld needed 3 hours 3 minutes and 50 seconds despite using a variometer!
Conclusion of the Rhön competition 1928: Robert Kronfeld flew the first "conscious" public thermal flights, and all the others followed his example (without the advantage of the variometer).
Not as spectacular as the "secret" carrying of the variometer, but also not to be forgotten: Kronfeld is credited with being the first glider pilot to carry a parachute at all times, despite the scorn and ridicule of his colleagues. A few years later, this rescue device was fully established and could save the lives of many pilots.
Following Kronfeld's sensational successes, A. Lippisch designed a high-performance glider in 1929 based on the Professor's design, which was a completely custom-built aircraft. which was not intended for series production and was fully tailored to the young Kronfeld. This prototype glider received the type designation Wien. The calculations and design ideas were translated into construction drawings by Hans Jacobs (Wasserkuppe) and Emil Pohorille from Dresden. That the Wien is a further development of the professor's design is clearly evident when comparing photos of both aircraft – however, the Wien was aerodynamically refined considerably. The almost elliptical fuselage cross-section was tailored in the cockpit area to the physically short Robert Kronfeld. As with the predecessor model, the wing was mounted on a fuselage tower. The 19.15-meter wingspan wing was rectangular in plan view in the center section, while the outer surfaces were strongly trapezoidal. The Wien also still had the performance-reducing V-struts for wing bracing; designer Lippisch, however, believed that this disadvantage could be compensated for by using a thin airfoil with a low profile. At that time, it was not yet possible to achieve large spans with relatively thin airfoils without bracing to the fuselage using a cantilever construction method. As with the Professor, the tried and tested Gö 549 airfoil was used, but slightly modified, with increased camber and a thickened leading edge. Unfortunately, nothing precise is known about the airfoil modifications; airfoil drawings or coordinates were not preserved. - For the quality of the Gö 549 is, incidentally, evidenced by the fact that it was still used in wooden glider construction well into the 1960s. The wing profile was smoothed to an almost or completely symmetrical profile in the outer wing sections. No further details are available on this; it is also unclear whether, due to the bad experiences with the professor, a geometric twist was present in addition to the aerodynamic twist. There are no surviving reports on its flight characteristics; but we know that an exceptional glider pilot like Kronfeld could also cope with somewhat more "tricky birds". With a flight mass of 248 kg, the wing loading was very low at 13.8 kg/m². However, it fully meets the requirements that were placed on a high-performance glider at that time. The primary focus was not yet on great speed performance (which could only have been achieved with low camber and very low-drag airfoils), but rather on the lowest possible sink rate so that even the smallest thermals could be exploited. The goal was always to stay aloft as long as possible; distance could also be covered under these conditions – naturally, not by today's standards!
The Wien achieved its set goals. The achieved sink rate was 0.71 m/s, and the glide ratio was likely slightly over 1:20. The airspeed was relatively low; above 60 km/h, the optimal sink rate increased rapidly. Today, the Wien was described as a thermal glider, because Kronfeld was often still airborne with his aircraft when everyone else had long since landed. On May 15, 1929, Kronfeld achieved a world record with the Wien., which in those days was certainly just as sensational as the first 1,000 km flights 40 years later! On that day, Kronfeld flew from a 50-meter-high hill near Riesenbeck in the Teutoburg Forest to Horn near the town of Bad Driburg.
The first flight over 100 km (exact 102.2), a new world record in gliding. This flight took place predominantly in the weak slope lift of the long, low mountain range, the valleys were bridged by utilizing thermal updrafts. Such flights could only be accomplished with extremely light and slow aircraft, but also represent a remarkable flying achievement by the pilot. Nine years had passed since the first leisurely Rhön competition. In 1920, the 1st Rhön was still a holiday camp for aviation enthusiasts who spent more time tinkering with their unpowered aircraft than flying. The 10th Rhön competition, from July 18th to August 1st, 1929, was a huge success, especially for Kronfeld – he became the undisputed gliding champion of 1929. On July 20, during his first thunderstorm flight, he flew a distance of 143 km and reached an altitude of 2,281 meters – these were two world records. On July 30, two more followed with a distance flight of 150 km and an absolute altitude of 2,589 meters – thus, four world records were achieved within ten days. It was the Rhön competition of Robert Kronfeld and his Wien; by far he was the most successful glider pilot of 1929, and his Wien, built by the Kegel glider manufacturer, was the most successful glider.
In the same year, Kronfeld flew the Vienna in Austria on the Kahlenberg. Several photos of this flight in a snow-covered landscape are available, along with photos of the railway transport of the aircraft. Also in 1929, he was the pilot of the first RRG Alpine gliding expedition in almost polar cold on the rugged Rax Alps in Austria. At that time, neither the skid of his Vienna was faired nor did it bear any lettering; the flights must therefore have taken place shortly after delivery from the Kegel Gliding Aircraft Factory in Kassel. For the 1930 Rhön Gliding Competition, Kronfeld expected the completion of his Austria, the legendary machine with a 30-meter wingspan and "H-tail." This superb glider was at the Kegel Gliding Factory at that time. The Kassel gliding factory is under construction.
The Rhön competition (August 9-24) was hampered by the unfavorable weather on the one hand and the general economic hardship on the other. On 6 out of 16 days, the familiar "water-covered peak" prevailed – cloud fog and rain. Slope soaring was the order of the day; at times, up to 14 aircraft circled simultaneously in the spatially very limited updraft area of the western slope. Robert Kronfeld's cross-country flights were primarily conducted from slope to slope, utilizing the slope lift. On August 13, he achieved a difficult flight of 150.3 km to Rehau near the Czech border. The second cross-country flight during this competition was again a world record – 164.8 km to Marktredwitz. The flights still took place on the Wien; the expected Austria was indeed completed in time, but problems with the ailerons prevented its use.
Gerhard Fieseler, who took over the Kegel Glider Construction Company in Kassel in 1930 and was thus also responsible for the construction of this super glider, later criticized how inaccurate the drawings of the designer Dr. Kuppers were. Kronfeld was certainly disappointed to find the aircraft unairworthy. Regarding the Austria, only this much more:
The aircraft was a considerable challenge for aircraft construction – however, no significant cross-country flights were ever undertaken with this "super-ship".
In 1932, the Austria dismantled the aircraft over the Gersfeld Valley; Kronfeld was able to escape by parachute, the aircraft was nothing but a pile of wreckage. Insurance agent John from Frankfurt also stood speechless beside the wreckage. After all, he had persuaded his hesitant company to insure the glider, which cost 30,000 Reichsmarks!
Assembly of the pendulum-type glider at the "Vienna" site. On the damping fin of the side glider, the company logo can be seen, below it the company name: Kegel-Flugzeugbau Kassel. At the Rhön competition in 1930, a new design by Alexander Lippisch appeared again: the Fafnir, the legendary machine with pilot Gunter Groenhoff. The two professional glider pilots of the RRG, Groenhoff and Kronfeld, were also the only ones to fly with variometers in their aircraft at this competition. Despite the Fafnir not yet being optimal, It was clear that the young Groenhoff would one day become a master of his craft.
After his victory in the Rhön competition, Kronfeld was invited to his homeland by enthusiastic English glider pilots. He resigned from his position as a flight instructor at the Wasserkuppe and began assembling a "traveling circus" to demonstrate gliders.
Well, this brought him profit and was at the same time excellent advertising for the idea of gliding in Europe. Since Kronfeld was also a pioneer of winch launching, he used the car winch he had designed in his demonstrations and was able to encourage many gliding clubs at home and abroad to imitate this new launching method. (In June 1931, Kronfeld organized the first lowland gliding day in Mönster with the local flying club.) On June 20, 1931, Robert Kronfeld became the first glider pilot to cross the English Channel in both directions with his Vienna. The altitude gained was followed by aerotow. With this Channel crossing between Calais and Dover, he won the 1000-pound prize from the Daily Mail.
The 1931 Rhön was dominated by the enormous successes of the triumvirate of Groenhoff, Hirth, and Kronfeld. Robert Kronfeld achieved third place with a 165-km thermal flight in his tried and tested aircraft.Wien. The winner was Groenhoff with the Fafnir and a world record in cross-country flight with 220 km; and Wolf Hirth flew a distance of 192 km in his Musterle (built at the Kassel glider factory, formerly Kegel-Segelflugzeugbau) and thus became second winner.
The 13th Rhön competition in July 1932 was also the last for Kronfeld. In the performance competition, he did manage 3rd place behind Wolf Hirth and Hermann Mayer, but the flight performances were not impressive. His Austria broke apart in the air, and no great flights were achieved with the Vienna either. It was overshadowed, competition was ended by the fatal crash of Gunter Groenhoff in the Fafnir, one day after the crash of Kronfeld's Austria.
In 1932, the Wien was sold to France, flew there for some time, then its trail went cold.
The anti-Semitic policies of the Third Reich made it impossible for Kronfeld, as a so-called "non-Aryan," to continue being active as a glider pilot in Germany. In England, he found a new home, because the annexation of Austria to the Greater German Reich made a return to his birth country impossible.
He became a British citizen and served as an RAF officer in World War II. At the age of 44, he died in a flying accident while attempting to spin in a flying wing motor glider of his own design. The English glider pilots have erected an honorary monument to him with the Robert Kronfeld Club in London, and his name will always hold a special place in the history of the Rhön region. Due to a misguided political climate, he was no longer able to actively participate in the progress of German gliding in the later 1930s.
Following the rapid advances in gliding in the mid-1920s, the desire for a high-performance glider at affordable prices arose in many clubs – or for types that could be built within the flying groups themselves without major problems. Commissioned by Professor Georgii, head of the Rhön-Rossitten Society, Alexander Lippisch designed the Professor in 1928. The detailed design and construction drawings were provided by Hans Jacobs, who had been employed in the aeronautical engineering department of the RRG Research Institute since August 1927.
The aircraft, which as a prototype received the nickname "Rhöngeist," was indeed very simply constructed according to Professor Georgii's specifications, yet still quite suitable as a high-performance glider. It was a high-wing aircraft braced with V-struts and a wingspan of 16 meters. and a wing aspect ratio of 14. The wing with the Göttingen
profile Gö 549 was designed in three sections. The center section was rectangular in plan view, the outer sections trapezoidal. The main spar had the then already proven torsion leading edge, i.e., plywood skinning from the wing leading edge to the main spar; this construction method has not changed in wooden structures to this day! In the fuselage, the simple construction with the six-angular cross-section presented no particular construction problems. Initially, however, the aircraft was very treacherous to fly.
Lippisch not only aimed for a simple design during the construction – the professor was also expected to achieve the best flight performance. For a with the lowest possible sink rate and an optimal glide ratio in mind, Lippisch designed the glider with minimal washout on the pointed outer wingtips. It is therefore not surprising that the well-known glider pilot and author Peter Riedel called the professor's prototype a "tricky bird" that wanted to go into a spin at low speed during every turn. This is how P. Riedel describes it in his three-volume work "Erlebte Rhönge- Geschichte" (Experienced Rhön History). According to reports, fatal accidents occurred with replicas due to insufficient wing washout; therefore, the ailerons had to be modified for training and practice operations so that the outer wingtips had more washout.
Comparing the Professor with the gliders of the so-called "Darmstadt School" (Academic Flying Group Darmstadt) with their cantilevered, aerodynamically cleanest designs with
very good flight performance and the best flight characteristics for the time, one could retrospectively consider the Lippisch Professor design as a step backward in glider
construction.
It is probably only thanks to the gifted pilot Robert Kronfeld that the professor's prototype "Rhöngeist" was not forever remembered by posterity as a treacherous bird. Robert Kronfeld, a flight instructor on the Wasserkuppe not long ago, immediately got to grips with the somewhat demanding glider. He felt instantly familiar with the machine, had it completely under control, and flew it from success to success. Not entirely uninvolved in his flying success with the "Rhöngeist" and later in Vienna was, of course, an aircraft instrument that was newly discovered for gliding at that time and was installed for the first time in the "Rhöngeist." This instrument, the variometer, was not unknown, however, as balloonists had been using it for a long time before. But it was used here for the first time in a glider. This device, which displays the rate of climb and descent, was, besides the pilot and his aircraft, the most important prerequisite for the truly optimal use of thermal updrafts. We will return to the variometer later.
Before the Rhön competition in 1928 – instructed by Professor Georgii – Kronfeld completed at least one flight in cloud updrafts with the professor's prototype and tested tactical circling in the updraft area. During the Rhön competition, on August 6, 1928, Kronfeld also succeeded in finding a thermal area after a bungee launch. Always circling cleanly, gaining altitude.
This thermal flight lasted over three hours. This first publicly and successfully performed flight outside of the slope updrafts, with deliberate use of thermals, took him to the Himmeldunkberg, located about 8 km away, and back to the Wasserkuppe.
This 9th Rhön Gliding Competition was divided into three parts:Training, practice, and school competition. In the performance class, four pilots competed and completed 61 flights; the winner was "Bubi" Nehring in the Darmstadt. 21 pilots participated in the practice competition and completed 131 flights.
First place went to Robert Kronfeld with his "Rhöngeist." He became the overall winner of the 9th Rhön with his total flight time of 7 hours and 54 minutes.
Some imitated Kronfeld's flight tactics. Although they did not own a variometer, they were able to achieve beautiful results. Successes were achieved; Erich Bachem flew the Himmeldunkberg flight with his city of Stuttgart in a fabulous 33 minutes 7 seconds - Kronfeld needed 3 hours 3 minutes and 50 seconds despite using a variometer!
Conclusion of the Rhön competition 1928: Robert Kronfeld flew the first "conscious" public thermal flights, and all the others followed his example (without the advantage of the variometer).
Not as spectacular as the "secret" carrying of the variometer, but also not to be forgotten: Kronfeld is credited with being the first glider pilot to carry a parachute at all times, despite the scorn and ridicule of his colleagues. A few years later, this rescue device was fully established and could save the lives of many pilots.
Following Kronfeld's sensational successes, A. Lippisch designed a high-performance glider in 1929 based on the Professor's design, which was a completely custom-built aircraft. which was not intended for series production and was fully tailored to the young Kronfeld. This prototype glider received the type designation Wien. The calculations and design ideas were translated into construction drawings by Hans Jacobs (Wasserkuppe) and Emil Pohorille from Dresden. That the Wien is a further development of the professor's design is clearly evident when comparing photos of both aircraft – however, the Wien was aerodynamically refined considerably. The almost elliptical fuselage cross-section was tailored in the cockpit area to the physically short Robert Kronfeld. As with the predecessor model, the wing was mounted on a fuselage tower. The 19.15-meter wingspan wing was rectangular in plan view in the center section, while the outer surfaces were strongly trapezoidal. The Wien also still had the performance-reducing V-struts for wing bracing; designer Lippisch, however, believed that this disadvantage could be compensated for by using a thin airfoil with a low profile. At that time, it was not yet possible to achieve large spans with relatively thin airfoils without bracing to the fuselage using a cantilever construction method. As with the Professor, the tried and tested Gö 549 airfoil was used, but slightly modified, with increased camber and a thickened leading edge. Unfortunately, nothing precise is known about the airfoil modifications; airfoil drawings or coordinates were not preserved. - For the quality of the Gö 549 is, incidentally, evidenced by the fact that it was still used in wooden glider construction well into the 1960s. The wing profile was smoothed to an almost or completely symmetrical profile in the outer wing sections. No further details are available on this; it is also unclear whether, due to the bad experiences with the professor, a geometric twist was present in addition to the aerodynamic twist. There are no surviving reports on its flight characteristics; but we know that an exceptional glider pilot like Kronfeld could also cope with somewhat more "tricky birds". With a flight mass of 248 kg, the wing loading was very low at 13.8 kg/m². However, it fully meets the requirements that were placed on a high-performance glider at that time. The primary focus was not yet on great speed performance (which could only have been achieved with low camber and very low-drag airfoils), but rather on the lowest possible sink rate so that even the smallest thermals could be exploited. The goal was always to stay aloft as long as possible; distance could also be covered under these conditions – naturally, not by today's standards!
The Wien achieved its set goals. The achieved sink rate was 0.71 m/s, and the glide ratio was likely slightly over 1:20. The airspeed was relatively low; above 60 km/h, the optimal sink rate increased rapidly. Today, the Wien was described as a thermal glider, because Kronfeld was often still airborne with his aircraft when everyone else had long since landed. On May 15, 1929, Kronfeld achieved a world record with the Wien., which in those days was certainly just as sensational as the first 1,000 km flights 40 years later! On that day, Kronfeld flew from a 50-meter-high hill near Riesenbeck in the Teutoburg Forest to Horn near the town of Bad Driburg.
The first flight over 100 km (exact 102.2), a new world record in gliding. This flight took place predominantly in the weak slope lift of the long, low mountain range, the valleys were bridged by utilizing thermal updrafts. Such flights could only be accomplished with extremely light and slow aircraft, but also represent a remarkable flying achievement by the pilot. Nine years had passed since the first leisurely Rhön competition. In 1920, the 1st Rhön was still a holiday camp for aviation enthusiasts who spent more time tinkering with their unpowered aircraft than flying. The 10th Rhön competition, from July 18th to August 1st, 1929, was a huge success, especially for Kronfeld – he became the undisputed gliding champion of 1929. On July 20, during his first thunderstorm flight, he flew a distance of 143 km and reached an altitude of 2,281 meters – these were two world records. On July 30, two more followed with a distance flight of 150 km and an absolute altitude of 2,589 meters – thus, four world records were achieved within ten days. It was the Rhön competition of Robert Kronfeld and his Wien; by far he was the most successful glider pilot of 1929, and his Wien, built by the Kegel glider manufacturer, was the most successful glider.
In the same year, Kronfeld flew the Vienna in Austria on the Kahlenberg. Several photos of this flight in a snow-covered landscape are available, along with photos of the railway transport of the aircraft. Also in 1929, he was the pilot of the first RRG Alpine gliding expedition in almost polar cold on the rugged Rax Alps in Austria. At that time, neither the skid of his Vienna was faired nor did it bear any lettering; the flights must therefore have taken place shortly after delivery from the Kegel Gliding Aircraft Factory in Kassel. For the 1930 Rhön Gliding Competition, Kronfeld expected the completion of his Austria, the legendary machine with a 30-meter wingspan and "H-tail." This superb glider was at the Kegel Gliding Factory at that time. The Kassel gliding factory is under construction.
The Rhön competition (August 9-24) was hampered by the unfavorable weather on the one hand and the general economic hardship on the other. On 6 out of 16 days, the familiar "water-covered peak" prevailed – cloud fog and rain. Slope soaring was the order of the day; at times, up to 14 aircraft circled simultaneously in the spatially very limited updraft area of the western slope. Robert Kronfeld's cross-country flights were primarily conducted from slope to slope, utilizing the slope lift. On August 13, he achieved a difficult flight of 150.3 km to Rehau near the Czech border. The second cross-country flight during this competition was again a world record – 164.8 km to Marktredwitz. The flights still took place on the Wien; the expected Austria was indeed completed in time, but problems with the ailerons prevented its use.
Gerhard Fieseler, who took over the Kegel Glider Construction Company in Kassel in 1930 and was thus also responsible for the construction of this super glider, later criticized how inaccurate the drawings of the designer Dr. Kuppers were. Kronfeld was certainly disappointed to find the aircraft unairworthy. Regarding the Austria, only this much more:
The aircraft was a considerable challenge for aircraft construction – however, no significant cross-country flights were ever undertaken with this "super-ship".
In 1932, the Austria dismantled the aircraft over the Gersfeld Valley; Kronfeld was able to escape by parachute, the aircraft was nothing but a pile of wreckage. Insurance agent John from Frankfurt also stood speechless beside the wreckage. After all, he had persuaded his hesitant company to insure the glider, which cost 30,000 Reichsmarks!
Assembly of the pendulum-type glider at the "Vienna" site. On the damping fin of the side glider, the company logo can be seen, below it the company name: Kegel-Flugzeugbau Kassel. At the Rhön competition in 1930, a new design by Alexander Lippisch appeared again: the Fafnir, the legendary machine with pilot Gunter Groenhoff. The two professional glider pilots of the RRG, Groenhoff and Kronfeld, were also the only ones to fly with variometers in their aircraft at this competition. Despite the Fafnir not yet being optimal, It was clear that the young Groenhoff would one day become a master of his craft.
After his victory in the Rhön competition, Kronfeld was invited to his homeland by enthusiastic English glider pilots. He resigned from his position as a flight instructor at the Wasserkuppe and began assembling a "traveling circus" to demonstrate gliders.
Well, this brought him profit and was at the same time excellent advertising for the idea of gliding in Europe. Since Kronfeld was also a pioneer of winch launching, he used the car winch he had designed in his demonstrations and was able to encourage many gliding clubs at home and abroad to imitate this new launching method. (In June 1931, Kronfeld organized the first lowland gliding day in Mönster with the local flying club.) On June 20, 1931, Robert Kronfeld became the first glider pilot to cross the English Channel in both directions with his Vienna. The altitude gained was followed by aerotow. With this Channel crossing between Calais and Dover, he won the 1000-pound prize from the Daily Mail.
The 1931 Rhön was dominated by the enormous successes of the triumvirate of Groenhoff, Hirth, and Kronfeld. Robert Kronfeld achieved third place with a 165-km thermal flight in his tried and tested aircraft.Wien. The winner was Groenhoff with the Fafnir and a world record in cross-country flight with 220 km; and Wolf Hirth flew a distance of 192 km in his Musterle (built at the Kassel glider factory, formerly Kegel-Segelflugzeugbau) and thus became second winner.
The 13th Rhön competition in July 1932 was also the last for Kronfeld. In the performance competition, he did manage 3rd place behind Wolf Hirth and Hermann Mayer, but the flight performances were not impressive. His Austria broke apart in the air, and no great flights were achieved with the Vienna either. It was overshadowed, competition was ended by the fatal crash of Gunter Groenhoff in the Fafnir, one day after the crash of Kronfeld's Austria.
In 1932, the Wien was sold to France, flew there for some time, then its trail went cold.
The anti-Semitic policies of the Third Reich made it impossible for Kronfeld, as a so-called "non-Aryan," to continue being active as a glider pilot in Germany. In England, he found a new home, because the annexation of Austria to the Greater German Reich made a return to his birth country impossible.
He became a British citizen and served as an RAF officer in World War II. At the age of 44, he died in a flying accident while attempting to spin in a flying wing motor glider of his own design. The English glider pilots have erected an honorary monument to him with the Robert Kronfeld Club in London, and his name will always hold a special place in the history of the Rhön region. Due to a misguided political climate, he was no longer able to actively participate in the progress of German gliding in the later 1930s.
Technical Description
The machine depicted in our drawings was reconstructed using numerous photographs from the Szigeti archive and previously published drawings and sketches from the literature. Original drawing documents were no longer available for this single piece.Given the available documentation, the reconstruction could only be carried out to the best of our knowledge and belief.
Fuselage: Plywood construction with stringers and bulkheads. The cockpit was adapted to the body size of pilot Kronfeld, making it a true custom-made piece. The fuselage tube has elliptical cross-sections; the so-called fuselage tower accommodates the wing. Behind the small cockpit opening, the fuselage tower is slightly wider than the head. It widens slightly up to the main bulkhead and then tapers to a point at the rear. The nose of the fuselage is made of crimped aluminum, as is the fairing on the top of the fuselage tower between the cockpit opening and the wing leading edge. The main bulkhead serves to support the two wing halves and accommodates the two V-struts for wing bracing on the lower fuselage sides. Unusual for a glider is the control yoke for the ailerons, as is common in modern touring aircraft. The cockpit is accessed from the left after removing the small plywood cover.
Until 1931, only the altimeter was mounted on this cover. The airspeed indicator was on the fixed right side. The variometer was initially located in the fuselage; after 1931, it was moved in front of the altimeter. At this time, a small celluloid cover was installed in front of the instruments. This protected the pilot from the airflow, reduced turbulence in front of the wing, and also protected the instruments from external influences.The small damping fin of the vertical stabilizer is fixed to the fuselage and "grows" gracefully out of the upper fuselage. In the tail section, there is a particularly robust bulkhead for mounting the tube of the all-moving horizontal stabilizer.
The wingtips are mounted on the rear of the fuselage.
Wing: Two-piece construction conventional spar-rib design. Torsionally rigid leading edge through plywood sheeting up to the main spar; auxiliary spar in the rectangular center section of the wing from the root fairing rib to the aileron. 31 main ribs, with a shaping auxiliary rib in between each, on the center section only up to the auxiliary spar.
The large ailerons end shortly before the wingtip and are planked over 5 rib bays in the outer area. Plywood-planked, torsionally rigid leading edge with transverse ribs in the
first version, later with additional diagonal ribs, since the long rudder was probably not torsionally rigid enough; in the third and final version, probably with a completely planked aileron. Linkage of the ailerons with cables. One largely dimensioned segment lever almost at the height of the half-span of the rudder on the upper and lower surfaces behind the torsionally rigid leading edge.
The wing halves were attached to the fuselage frames above the fuselage conning tower at the main and auxiliary spars. A plywood covering conceals the gap. The V-struts were attached to the main and auxiliary spars at the level of the aileron start point, with the central attachment point on the fuselage being located at the main frame.
The steel fittings were covered with poplar or linden wood in a teardrop shape. A slightly modified Göttingen Gö 549 airfoil was used; from the outer wing sections to the wingtip, it was swept to an unknown symmetrical or semi-symmetrical airfoil. Whether geometric washout was also incorporated is unknown. Aerodynamic aids such as airbrakes or other features are not present. hand; this was not yet common at that time. Dive brakes and other landing aids were only used on gliders many years later.
Tailplane; Delicate construction of the empennage with torsionally rigid control surfaces, otherwise a structure of ribs and stringers. As with the wing, all unsheeted parts of the empennage were covered with fabric. Vertical stabilizer with large rudder compensation in front of the axis of rotation. The small damping fin, rigidly attached to the fuselage, was completely sheeted with plywood. The horizontal stabilizer was designed as a pendulum rudder; two-part design with tube spars mounted on the fuselage. The control surfaces were actuated by cables.
Landing gear: No wheel present; The takeoff and landing loads were absorbed by a stable skid. The large skid, elastically suspended by rubber, begins at the fuselage nose behind the aluminum fairing and ends at the wing trailing edge when viewed from above. After the initial flights, the skid was covered with leather. At the tail, there is a combined wood/steel skid with an attachment point for the ground crew's rope. The steel hook for the rubber launch rope is located on the leading edge of the skid.
Instruments: In front of the padded cutout for the pilot's head, the airspeed indicator is located on the right (in the direction of flight), and the altimeter is on the left, on the removable cockpit fairing. The variometer was located in the fuselage. Installed inside; possibly the instrument was also strapped to the pilot's hand. On the upper side of the fuselage nose, the Venturi tube is mounted; it is designed like a nozzle and thus directs the ram air to the airspeed indicator. Control is not achieved by the control stick usually found on gliders, but by a control yoke. The construction of the pilot's seat cannot be documented with a photograph. However, it may have been made of glued plywood. Seatbelts were present, and the aircraft was always flown with a parachute. From 1931 onward, the variometer was positioned in front of the altimeter on the fuselage hatch. In addition, the aircraft received a small Cellon disc over the instruments. Compass, turn indicator, and artificial horizon were not installed. That Kronfeld dared to fly blindly in the clouds with this meager instrumentation is quite astonishing today!
Finish: Kegel Aircraft Construction Kassel was famous for its excellent glider construction. So it is not surprising that Wolf Hirth also had his prototype built by this company. In an advertising brochure of the company, he and, of course, Robert Kronfeld praise the excellent workmanship of their aircraft. The finest and also the most stable woodworking was the company's capital. When reconstructing the prototype, Klaus Heyn had to realize that even with today's techniques it is hardly possible to execute the fine woodwork as it was done at Kegel back then. was done. After repeated sanding and varnishing, the aircraft, especially the Vienna, acquired a mirror-like surface.
The fabric covering was glued to the frame of the wings and tail surfaces using a special cold glue; this did not attack the fabric fibers, unlike normal cold glue. Upon request, the aircraft could also be finished with high-gloss varnish. So far, so good according to the brochure.
On both sides of the fuselage, between the pilot's seat and the nose, was the type inscription "VIENNA"; the acceptance stamp of the Air Police/Air Guard was applied using a stencil. The logo of the company Kegel was painted on both sides of the fuselage at the height of the strut connection, as well as on the damping fin of the vertical stabilizer. From 1931 onwards, a large "D" was painted on both sides of the fuselage at the level of the skid end. The respective competition numbers for the Rhön flights were located on the tail fin: 1929 No. 23, 1930 No. 1, 1931 No. 57 and 1932 No. 38.
The machine depicted in our drawings was reconstructed using numerous photographs from the Szigeti archive and previously published drawings and sketches from the literature. Original drawing documents were no longer available for this single piece.Given the available documentation, the reconstruction could only be carried out to the best of our knowledge and belief.
Fuselage: Plywood construction with stringers and bulkheads. The cockpit was adapted to the body size of pilot Kronfeld, making it a true custom-made piece. The fuselage tube has elliptical cross-sections; the so-called fuselage tower accommodates the wing. Behind the small cockpit opening, the fuselage tower is slightly wider than the head. It widens slightly up to the main bulkhead and then tapers to a point at the rear. The nose of the fuselage is made of crimped aluminum, as is the fairing on the top of the fuselage tower between the cockpit opening and the wing leading edge. The main bulkhead serves to support the two wing halves and accommodates the two V-struts for wing bracing on the lower fuselage sides. Unusual for a glider is the control yoke for the ailerons, as is common in modern touring aircraft. The cockpit is accessed from the left after removing the small plywood cover.
Until 1931, only the altimeter was mounted on this cover. The airspeed indicator was on the fixed right side. The variometer was initially located in the fuselage; after 1931, it was moved in front of the altimeter. At this time, a small celluloid cover was installed in front of the instruments. This protected the pilot from the airflow, reduced turbulence in front of the wing, and also protected the instruments from external influences.The small damping fin of the vertical stabilizer is fixed to the fuselage and "grows" gracefully out of the upper fuselage. In the tail section, there is a particularly robust bulkhead for mounting the tube of the all-moving horizontal stabilizer.
The wingtips are mounted on the rear of the fuselage.
Wing: Two-piece construction conventional spar-rib design. Torsionally rigid leading edge through plywood sheeting up to the main spar; auxiliary spar in the rectangular center section of the wing from the root fairing rib to the aileron. 31 main ribs, with a shaping auxiliary rib in between each, on the center section only up to the auxiliary spar.
The large ailerons end shortly before the wingtip and are planked over 5 rib bays in the outer area. Plywood-planked, torsionally rigid leading edge with transverse ribs in the
first version, later with additional diagonal ribs, since the long rudder was probably not torsionally rigid enough; in the third and final version, probably with a completely planked aileron. Linkage of the ailerons with cables. One largely dimensioned segment lever almost at the height of the half-span of the rudder on the upper and lower surfaces behind the torsionally rigid leading edge.
The wing halves were attached to the fuselage frames above the fuselage conning tower at the main and auxiliary spars. A plywood covering conceals the gap. The V-struts were attached to the main and auxiliary spars at the level of the aileron start point, with the central attachment point on the fuselage being located at the main frame.
The steel fittings were covered with poplar or linden wood in a teardrop shape. A slightly modified Göttingen Gö 549 airfoil was used; from the outer wing sections to the wingtip, it was swept to an unknown symmetrical or semi-symmetrical airfoil. Whether geometric washout was also incorporated is unknown. Aerodynamic aids such as airbrakes or other features are not present. hand; this was not yet common at that time. Dive brakes and other landing aids were only used on gliders many years later.
Tailplane; Delicate construction of the empennage with torsionally rigid control surfaces, otherwise a structure of ribs and stringers. As with the wing, all unsheeted parts of the empennage were covered with fabric. Vertical stabilizer with large rudder compensation in front of the axis of rotation. The small damping fin, rigidly attached to the fuselage, was completely sheeted with plywood. The horizontal stabilizer was designed as a pendulum rudder; two-part design with tube spars mounted on the fuselage. The control surfaces were actuated by cables.
Landing gear: No wheel present; The takeoff and landing loads were absorbed by a stable skid. The large skid, elastically suspended by rubber, begins at the fuselage nose behind the aluminum fairing and ends at the wing trailing edge when viewed from above. After the initial flights, the skid was covered with leather. At the tail, there is a combined wood/steel skid with an attachment point for the ground crew's rope. The steel hook for the rubber launch rope is located on the leading edge of the skid.
Instruments: In front of the padded cutout for the pilot's head, the airspeed indicator is located on the right (in the direction of flight), and the altimeter is on the left, on the removable cockpit fairing. The variometer was located in the fuselage. Installed inside; possibly the instrument was also strapped to the pilot's hand. On the upper side of the fuselage nose, the Venturi tube is mounted; it is designed like a nozzle and thus directs the ram air to the airspeed indicator. Control is not achieved by the control stick usually found on gliders, but by a control yoke. The construction of the pilot's seat cannot be documented with a photograph. However, it may have been made of glued plywood. Seatbelts were present, and the aircraft was always flown with a parachute. From 1931 onward, the variometer was positioned in front of the altimeter on the fuselage hatch. In addition, the aircraft received a small Cellon disc over the instruments. Compass, turn indicator, and artificial horizon were not installed. That Kronfeld dared to fly blindly in the clouds with this meager instrumentation is quite astonishing today!
Finish: Kegel Aircraft Construction Kassel was famous for its excellent glider construction. So it is not surprising that Wolf Hirth also had his prototype built by this company. In an advertising brochure of the company, he and, of course, Robert Kronfeld praise the excellent workmanship of their aircraft. The finest and also the most stable woodworking was the company's capital. When reconstructing the prototype, Klaus Heyn had to realize that even with today's techniques it is hardly possible to execute the fine woodwork as it was done at Kegel back then. was done. After repeated sanding and varnishing, the aircraft, especially the Vienna, acquired a mirror-like surface.
The fabric covering was glued to the frame of the wings and tail surfaces using a special cold glue; this did not attack the fabric fibers, unlike normal cold glue. Upon request, the aircraft could also be finished with high-gloss varnish. So far, so good according to the brochure.
On both sides of the fuselage, between the pilot's seat and the nose, was the type inscription "VIENNA"; the acceptance stamp of the Air Police/Air Guard was applied using a stencil. The logo of the company Kegel was painted on both sides of the fuselage at the height of the strut connection, as well as on the damping fin of the vertical stabilizer. From 1931 onwards, a large "D" was painted on both sides of the fuselage at the level of the skid end. The respective competition numbers for the Rhön flights were located on the tail fin: 1929 No. 23, 1930 No. 1, 1931 No. 57 and 1932 No. 38.
