M.Simons The World's Vintage Sailplanes 1908-45
THE FAFNIR 2, SAO PAULO
At the University of Goettingen during the early 'thirties, H. Muttray performed a lengthy series of tests in a wind tunnel to determine the best shape for a fuselage in relation to the wing of an aircraft. Muttray
finally proved that the minimum additional drag, at least under wind tunnel conditions, resulted if the wing was mounted midway down the fuselage. Since the flow round a wing is curved, sweeping up ahead of the lifting surface and then down behind it, normal fuselages tend to break the flow, creating extra drag. Muttray argued that wing and fuselage should be designed together, the fuselage to conform as far as possible to the pattern of the flow over the wing. Alexander Lippisch designed the Fafnir 2 with these results in mind.
The general planform was similar to the Fafnir 1, but a new much less cambered wing profile was designed specially by Lippisch. The fuselage was calculated and plotted out, section by section, as if it were part of the wing. The thin trailing edge curved back to the rear and the wing leading edge bulged forward, the only break in the outline being where the cockpit canopy protruded. Even this was eliminated later, the canopy and nose being remodelled to blend smoothly. The form had to be built up carefully over numerous lofted cross-formers and laminated stringers, piece by piece, from strips of plywood scarfed together. The Fafnir 2 was neither the first nor the last aircraft to surprise its designer by turning out much heavier than expected. The error was 50 kg.
The Fafnir 2 became known as the Sao Paulo because German residents of the city of Sao Paulo in Brazil, where Georgii’s expedition had recently been breaking records, sent some cash to help the construction.
In its day the Fafnir 2 was the best sailplane in the world. Its flight performance was carefully measured. Compared with modem sailplanes it flew slowly, its best sinking speed occurred at about 53 km/h, and its best glide ratio of 1 : 26 at 67 km/h. This represented a marked advance on anything of its generation. At the Rhoen contest in 1934 Heini Dittmar set a new world distance record of 375 km, reaching Liban in Czechoslovakia. He was the third pilot to exceed 300 km, and with this flight broke Wolf Hirth's record of the previous day. The main prize of the year went to Dittmar. The Sao Paulo set no general fashion for such elaborate designs because the development of of such a form, in wood, was far too costly for production sailplanes.
The DFS, for political reasons, was excluded from the Rhoen contests after 1934, these becoming more rigidly organised and more closely associated with the Hitler Youth movement as time went on. Except for Dittmar’s victory in the Sao Paulo at the International Competition in 1937, when he flew a total distance of 1438 km in seven days, the Fafnir 2 did not fly much in competition. It continued in use at the Darmstadt HQ of the DFS where, in 1945, it was discovered intact by the advancing Allied armies. J. S. Sproule, a British sailplane pilot and designer who had worked for Slingsby, was in time only to rescue a few pieces of the aircraft before, acting under a blanket order to destroy all enemy aircraft, the troops of the RAF Regiment burned the Fafnir 2.
The figures given here are taken from W. Spilger’s report, published in 1937, of the DFS flight tests. The wing area stated is less than that given in other references, and accordingly the aspect ratio and wing loading figures are higher. Spilger calculated the wing area by the usual convention of projecting the lines of the wing straight through the fuselage, but ignored the exceptionally large root fairings of the Fafnir 2. Lippisch himself made an allowance for the broad fairings when he quoted the total wing area as 19 sqm and its aspect ratio as 19. (References; Lippisch, Luftfahrtforschung, October 1934, p 125. Spilger, Jahrbuch 1937 der DLF).
Fafnir 2: Span. 19.00 m. Wing area. 17.7 sqm. Aspect ratio. 20.4. Empty weight. 270 kg. Flying weight. 382 kg. Wing loading. 21.6 kg/sq m. Aerofoil. DFS Special. Best glide ratio. 1 : 26 at 66.5 km/h. Minimum sinking speed. 0.63 m/sec at 54 km/h. Sink at 100 km/h, 1.36 m/sec.
The Fafnir 2 in 1934. At this time the sailplane was clear varnished with the usual national flag colors on the starboard side of the fin and rudder and swastika on the other side. The cockpit canopy and nose show the original form. The ailerons had two horns each and contrary to some published drawings, did not taper to nothing at their root ends. Later, the nose was reconstructed to produce a smooth contour.
Heini Dittmar with the Fafnir 2 in 1934, at the time of his new distance record. On the original photograph the inscription on the fuselage nose may be partly deciphered. It read: Hersieller, DFS. Werknummer, 23. Baujahr, 1934. Zugelassen, Erpro..., durd..... (Manufacturer DFS, works number 23, construction year 1934, permitted uses? test flying?). The two discs on the fuselage beneath the wing root were detachable inspection panels.
The Fafnir 2 in its final form with remodelled nose and cockpit canopy, and painted overall. This is how it appeared at the 1937 Internationals which it won, flown by Heini Dittmar. The size of the crowd of spectators indicates the great interest shown by the German public in gliding at this time.