A decade of research by
Fafnir - A mythical Dragon
The patterns of sailplane development had been dictated largely by the style of soaring which predominated at a given time. Through the 1920's and well into the 1930's ridge soaring was the predominant mode of flying. Designers, therefore, assumed that a glider would spend more time in lift than in sink, so their sailplanes were optimised for low sink speeds at low forward speeds, and with high maximum lift-to-drag ratio. Low wing loadings with thick highly cambered airfoils were considered necessary to achieve these desired low sink speeds. Even after the advent of thermal soaring, designers continued to employ low-speed performance in their sailplanes.
With increasing sophistication of soaring techniques came the realisation that not only low sinking speed and high glide ratios, but also high manoeuvrability about the pitch and roll axes were required to take full advantage of ridge (and later, thermal) lift. Rolling inertia was minimised by using a strongly tapered wing plan form and by mounting the wing on top of the fuselage, closer to the centre of gravity, rather than on a pylon. For the first time Alexander Lippisch had an airplane of large span designed with self-supporting cantilever wings. These two-part wings which were slender and strongly pointed, would connect to a middle section, which was part of the fuselage, using three fittings. The wing was built in a cranked (gull-wing) configuration, ostensibly to provide ground clearance on takeoff and landing, an advantage with off-field landings and for improved stability in turns, but aesthetics may have been as much a factor in this design decision as aerodynamics.This gave the main plane considerable dihedral, after which the wing remains horizontal to the tips giving the appearance of a seagull. Their disadvantage was the high construction cost and the weight for the necessary additional reinforced spars. The wing had two spars and later a third was fit. A main box beam at the one-third chord position, with an auxiliary 'I' beams fore and later one aft and with the leading edge being plywood covered.
Following experience of the "Professor", Lippisch included quite a large amount of aerodynamic twist . The wings used three profiles which gave progressively less lift towards the outer tip and all blended into one another, namely:
In order to preserve an accurate wing profile, particularly in the area of the leading edge, the ribs on the Fafnir were more closely spaced than on other gliders Several degrees of washout were incorporated and in this way aileron effectiveness at low speeds was improved and premature stalling of the wingtips was avoided. Aileron effectiveness was further improved by maintaining a constant aileron chord length over about 80 percent of their span from the inboard ends. With the highly tapered plan form this resulted in increased aileron / chord differential and thus increased aileron effectiveness toward the tips. Differential movement of the aileron was also incorporated after its successful application on the Wien.
It certainly was a remarkably sound machine and pleased it's producers enormously. Everyone was amazed with its high manoeuvring qualities, which was streets ahead of any other glider of the time. Although the Fafnir was decidedly on the heavy side, it showed itself to be a remarkably efficient machine with high manoeuvring qualities when in the hands of Groenhoff, the official test pilot at the Wasserkuppe who seemed very much at home in the machine, performing spectacular banked turns without any apparent loss of height.
The wing centre section was built into the fuselage with an elaborate curved fairing between the wing and fuselage made out of numerous small strips of plywood. This was to turn out to be a problem area for the Fafnir because of the potential for increased interference drag due to the proximity of wing and fuselage.
Previous designs of gliders had an open cockpit, but in order to reduce drag and protect the pilot from hail during meteorological research, a wooden canopy enclosure was constructed, being fared into the nose and wing roots. Portholes were included on either side to allow side vision only. Pilots of the time alleged that, one must "have the wind in your face", otherwise you are not gliding a superstition that would be weed out only slowly. The cockpit itself was tailor made to fit the small body of Groenhoff. The Fafnir also carried an external instrument for the measurement of humidity, in connection no doubt with the weather research work which was a big feature of the R.R.G. programme.
There was no landing wheel on the Fafnir, however the skid was cleverly sprung using a row of tennis balls trapped between the keel and the ash skid by wooden laths and around which was canvas or leather covering. Ground clearance all the way along the fuselage belly, and especially at the tail, was very small and this gave much trouble in service.
The Fafnir had quite a long oval fuselage covered in intricate plywood panels and had a rather small all moving tailplane set low down in the middle of the fuselage tail. This would later prove a problem to Groenhoff. The whole of the plywood paneling was finished in a high gloss varnish.
The Canopy and its' evolution
It was the opinion of a well-known German soaring pilot that no really successful thermal work could be carried out without a variometer. Bank indicators and longitudinal bubbles were fitted to several aircraft in addition to the more common compasses, thus making every provision in these machines for blind flying in clouds.
The instruments in the FAFNIR were manufactured by Askania and are worthy of special mention. In order to accommodate them all in the narrow space provided, types with narrow vertical scales were adopted where possible.
The FAFNIR also carried an external instrument secured to the outside of the fuselage below the starboard wing for the measurement of humidity, in connection with the research work which was a big feature of the programme of the R.R.G.
In this view on the left, the instruments are seen from the port side through the cockpit side opening. There is no actual 'panel', rather the instruments were mounted on a shelf above the pilot's knees. The layout of the instruments was staggered, those left of centre are set well back to allow placement of the compass, whereas right of centre they are positioned forwards, presumably to allow the two air canisters for the venturi to be fitted behind. The edge of one canister can just be seen in the photo to the right of the 'turn and slip'.
At the left is a liquid filled ball Compass and behind and to the right is the Turn and Slip indicator which has a spirit level to indicate bank angle at the bottom of the case and a needle to indicate the rate of turn. The instrument is linked to an air-driven gyro connected to one of the venturis on the starboard side of the nose.
Next to this is a Variometer with a large vertical scale. An Altimeter and an ASI were also installed, positioned out of site to the right and were driven from the second venturi.
On the photos below you can see the fixing point for the calibration instrument with the two venturis mounted in the nose. It also shows the final fairing of the fuselage-wing transition to overcome problems found on the first flights.
Flight Years of the Fafnir
The "Fafnir" was needed to be ready for the 1930 Rhön Competition at the Wasserkuppe and towards the end of its' build the craftsman Richard Mihm had to work day and night to get the glider finished in time.
The maiden flight was to prove a big disappointment. Following the launch, the glider proved to have no better glide ratio than that of a primary trainer. The problem was found to be the large fuselage to wing transition, coupled with the port holes which created strong eddies, allowing the airflow over the wing to tear off causing loss of lift and buffeting. According to Lippisch, the whole glider was shaking "like a lambs tail" and could even be seen from below by the spectators. Lippisch was under pressure from his friends to explain what was wrong with his glider, but he calmly brushed them off. However, the expressions on the faces of Lippisch's staff who stood around him, told him they urgently expected an answer to the problem
Lippisch went over to the workshop where the men were waiting for him and announced his cure. They were almost in tears when they had to cut apart again all the careful work they had done. The work was carried out over night to insert blocks of Balsa to re-contour the transition, and with all this effort, the bird would be ready to go again by the following noon.
On the next flight there was a noticeable improvement to the gliders performance. When it was bungeed off the slope in the second week of the 11th Rhön Competition, the Fafnir flew 15Km across the valley to Kreuzberg in 15 minutes and returned five hours later after fighting hard to sustain height on the way back to equal Kronfelds' world record set the week before. The Kreutzberg is a hill, 3,045 ft. (928 m.) high, 75 ft. (23 m.) lower than the Wasserkuppe, and is 9.5 miles (15 km.) to the south, with a lower hill, the Himmeldarlberg, lying between them.
On the 13th. April 1931, after trying the new style aero-tow start with Peter Riedel in the tow plane, Groenhoff flew 138 km to Bühl
On the 4th May 1931, Groenhoff flew a record flight of 278 km from Munich to Kaaden, but it was not officially recognised because aero-towing had not been recognised by the FAT for such purposes. The "Fafnir" had been specially designed to research flight before and during thunderstorms,. Despite its relatively high overall weight (200kg) the wing loading was also relatively high (16.9 kg/m2), and the aircraft with its transparent delicate covering performed well. During this flight, in stormy conditions, the wing was badly holed by hail and accumulated quantities of ice and water which sloshed around inside. On this occasion he flew on until after darkness and in the end landed using his electric torch, poked out of the barely adequate portholes, to make his landing.
In June the Fafnir joined an expedition to the High Alps in an area known as the Jungfraujoch (Top of Europe). The gliders were carried up the mountain on the railway from Lauterbrunnen to the nearest station and then had to be man handled to the launch point at an elevation of 3454 m (11333ft). Launches were to be made by bungee from deep snow on the slopes of the Jungfraujoch. Some difficulty was experienced in finding a suitable terrain for the start. Owing to the depth of the snow it was impossible for the starting men with the bungee to run, so it was decided to use ten men on each side of the double 40m. starting ropes, but even so, in the rarified air and hampered by the snow, the Fafnir on its first attempt was unable to reach flying speed.
Groenhoff found himself sliding down the slope toward the slope precipice. He endeavoured to pull it off but because the tail of the Fafnir lies close to the ground. it was extremely difficult to put a positive angle of incidence on the wings with the machine sliding down hill. It then ran through a snow wall and to the horror of the launching crew the sailplane toppled over the edge and as it did so tore off half the elevator on the snow wall. The damaged Fafnir dropped into space, but after falling vertically for about 100 meters without hitting anything, sufficient airspeed was attained for the controls to respond and Groenhoff was able to pull out of the dive away from the rocks and out over the open valley. On more than one occasion he thought he would have. to jump with his parachute, and he prepared his camera to take a picture of the Fafnir as she spun down, but the prospect of losing the machine and landing amongst crevasses on the ice where he might be hurt and unable to move, deterred him.The cockpit covering the Fafnir only provides the pilot with a 200mm aperture on either side of the totally enclosed cockpit so that he was unable to look back to see what had happened to the tail. Shortly afterwards it went on its nose again and Groenhoff decided to see if he could keep it there by pushing the stick forward. This he succeeded in doing and came to the conclusion that the elevator must be working to some extent and that therefore, the faster he flew, the more likely he would he able to control its flight, so he flew the machine at about twice its normal speed until he could reach the centre of the valley where there would be enough height for him to use his parachute. The sailplane behaved normally, provided the airspeed was maintained. Hating to lose his beloved Fafnir he decided after all to try to save it. After a flight of almost an hour, Groenhoff chose a large fiat meadow close to Interlaken on which he made a very fast touchdown. A wingtip caught in the long grass and a severe ground loop resulted. The Fafnir slid for twenty meters sideways, and came to rest without further damage.
Two days later, with a new tailplane sent from the Wasserkuppe, Groenhoff again flew the Fafnir from the Jungfraujoch, this time gliding down to a landing which, by comparison with his previous escapade, was something of an anticlimax. Several days of poor soaring weather followed during which snow banks were built around the glider to protect it from the winds. On his first flight after this, Groenhoff found had no rudder control, but was able to get safely down into the valley, where it was found that during the launch the wooden block at the rear end of the fuselage, where the hold-back hook for bungee launching cord was mounted, had broken off and taken the rudder fixing with it. This had taken with it the main rudder mounting and brought the rudder itself out of its bearings. Only four flights were made by the Fafnir from this lofty launching point. Two of them had been nearly disastrous. The fourth, when Groenhoff soared away to land at Bern aerodrome was successful.
On the 24th July during the 12th Rhön Gliding Competition Groenhoff achieved a record 220 km from a bungee launch at the Wasserkuppe winning him the Nehring--Gedächtnis-Preis of Bad Homburg as well as the Prinz-Heinrich-Rhönpreis for the greatest height gained (2,050 m.)
Groenhoff was to became only the third pilot in the world to gain the coveted Silver 'C' badge, after Kronfeld and Hirth.
At the 1932 Rhön Competition came disaster. Several machines were involved in serious accidents including the Austria, Luftikus, Senator and the Fafnir. On the 23rd July Groenhoff attempted a flight under very unfavourable tailwind conditions the low-set horizontal tail unit was to be damaged once more.. He was bungeed downwind by a powerful crew, but on account of the great weight of the Fafnir he succeeded only with difficulty in getting off. During the last bounce the fuselage hit some rocks which smashed the bottom hinge of the rudder and damaged the underside of the fuselage. The damaged rudder partially jammed the elevators, but nevertheless Groenhoff managed to continue in flight for a distance of about half a mile, when the rear of the fuselage severed, and caused the machine to dive. One wing-tip struck a tree, whereupon the machine span round and side-slipped to the ground, coming to rest among some trees and supported on one wing. One wing broke off close to the root and the fuselage was badly damaged. His death shook not only the glider pilots, but also the public who had taken great interest in him thanks to his results and his likeable appearance in the glider development
Groenhoff either jumped or was thrown out during the final spin round, and although the parachute opened, it was too late to save his life when his head struck a branch of a tree killing him instantly. It is generally believed that Groenhoff did not leave the machine voluntarily, and it is said that he was in the habit of flying without being strapped in, but at the same time it is difficult to account for the cockpit cover coming away unless he purposely released it to allow himself to be thrown clear. The condition of the sailplane after the accident made it appear very probable that the pilot would have escaped if he had been strapped in.1933
Georgii and Lippisch, director and head respectively of the technical division of the RRG, decided to repair the remains of the Fafnir. This time the cockpit was built large enough to accommodate pilots of average size and the old wooden canopy was replaced by a transparent one. Peter Riedel flew the rebuilt Fafnir 228 km from Darmstadt into France in June 1933. Riedel, later in the same year, won the XIV Rhön contest and was awarded the Hindenburg Cup.
A short video of a flight can be seen below
Hanna Reitsch (1912-1979), a pupil of Wolf Hirth and already on her way to become the famous German airwomen, flew the Fafnir in March 1934 with a 160 km flight from Darmstadt to Retlingen, a new course record for the women.
The same year, Peter Riedel, with the Fafnir, accompanied Georgii's, Hirth, Heini Dittmar and Hanna Reitsch on the expedition to Brazil and Argentina. The Fafnir achieved good cross-country soaring flights, the first accomplished in Latin America and on one occasion Riedel soared for seven hours over Buenos Aires. On return to Germany, the Fafnir remained in use far some years at Darmstadt, where the DFS, successor to the RRG, established its headquarters.
The Fafnir was retired and was finally destroyed during a bombing raid at the Deutsche Luftfahrtsammlung (German Aeronautical Collection) at Berlin in 1943 along with many other famous aircraft. Click the image below for an interesting pdf Brochure for the Museum