M.Simons The World's Vintage Sailplanes 1908-45
THE MU 13
The Mu 13 was a single-seat development of the Mu 10 Milan two-seater of 1934. In 1935 Kurt Schmidt and Tony Troeger, a friend, decided to build two similar sailplanes, each with a span of 16 metres but cheap and light. With help
from Egon Scheibe, who still presided over the Munich Student Flying Group (Akaflieg Muenchen), they worked hard to complete their aircraft for the 1936 soaring season. Troeger’s aircraft, named Merlin, was ready first; Schmidt's Atalante followed a few weeks later.
The fuselage was a steel tube framework with welded joints. After the fabric and dope had been applied, the whole fuselage weighed less than 50 kg. The undercarriage on the Merlin was made semi-retractable so that a motor and propeller could be fitted. Schmidt used a fixed wheel, but both aircraft had two wheels side-by-side on the axle. The tail unit was of the all-moving type with neither fixed fin nor tailplane. The wing, of wood with a Scheibe aerofoil, had flaps and ailerons with a fabric covered steel tubular frame. The flaps could be raised or lowered together to change the wing camber, but they could also be trimmed differentially for a left or right turn.
To retain balance, the seat was placed only slightly ahead of the centre of gravity, and with the wing mounted on top of the squarish, box-sectioned fuselage, the pilot's head came inside the wing root ahead of the mainspar. Windows were provided in front and just beneath the wing root, the canopy fairing neatly to the wing. Huge triangular windows were made on each side of the cockpit, through which it was possible to look downward.
At the 1936 Rhoen Competitions the weather was hot and few cumulus clouds appeared, lift being weak and winds light. The Atalante proved to be the ideal sailplane for such conditions. Schmidt won the contest, leaving behind the heavy, expensive but much more refined types like the Fafnir 2. He achieved the longest flight of the meeting, a 252 km goal flight to Trier.
Previously the sister ship, Merlin, took part in the world’s first sailplane tour, a 700 km round trip’starting and ending at Darmstadt.
In 1937 Schmidt added area to the aircraft's rudder and more dihedral to the wing. With production in mind, further changes were made to produce a more adaptable aircraft. The wing flaps were removed and the wing was given a very slight Sweepback to increase the centre of gravity range. Spoilers, and later airbrakes, were fitted, the double wheel was replaced by one wheel, and the cockpit canopy was improved. The ailerons, which on the prototype caused too much adverse yaw in turns, were provided with large Frise-type extensions under the wing, near the tips. By 1938 Schmidt himself was flying the Mu 13D, indicating that several versions had been tried out by this time. He was placed second in the Wasserkuppe contest that year, and the Mu 13D entered production at the Black Forest Aircraft Works. In the 1939 contests, 15 competed and production continued up to a total of about 150. The Mu 13D had a reputation for being difficult to fly accurately, mainly because of the adverse aileron drag, small rudder and short tail moment arm. At speeds only slightly faster than normal, the ailerons tended to become heavy and somewhat ineffective, though this was not at all uncommon on sailplanes of the period. Yet the Mu 13 would often stay up when every other aircraft had to land.
In 1943 a re-designed Mu 13 with a longer fuselage and larger tail unit, was produced. It was sometimes designated the Mu 13D/3. This had, instead of the square-sectioned rear fuselage, a triangular one, the lines being softened slightly by a light wooden lath along the side to lift the fabric covering off the steel framework beneath. These aircraft were easier to fly than the short-fuselage version, but the ailerons were not noticeably improved at high speeds.
Two of the old, short-fuselage Mu 13Ds survived till 1980, one in Germany and one, not airworthy, in Denmark. Several of the long-fuselage, Mu 13D/3, sailplanes are still flying, two of these in England and one in Canada. Post war, Scheibe produced a two-seater which was called the Mu 13E, later developed into the Bergfalke series. The true successors of the single-seater were the Spatz sailplanes from the same factory.
The performance figures and weights for the Mu 13D given here were reported in 1942 after the DFS flight tests.
Mu 13 Atalante and Merlin: Span, 16.(X) m. Wing area, 16.50 sq. m. Aspect ratio, 15.5. Empty weight, 145 kg. Flying weight, 235 kg. Wing loading, 14.25 kg/sq m. Aerofoil, Scheibe. Best glide, 1 : 24 at 60 km/h. Minimum sink, 0.58 m/sec at 45 km/h.
Mu 13D (Production model): Span, 16.00 m. Wing area, 16.16 sq m. Aspect ratio, 15.85. Empty weight, 180 kg. Flying weight, 260 kg. Wing loading, 16.1 kg/sq m. Aerofoil as for Atalante. Minimum sinking speed 0.62 m/sec at 54 km/h. Best glide ratio 1 : 24.8 at 62 km/h.
The late version of the Mu 13 series, the Mu 13D/3. This brightly colored example, named Moulin Rouge (Red Windmill), flies regularly in Britain. It makes an interesting comparison with the short-fuselage version.
Martin Simons in the cockpit of a restored Mu 13D/3 in Britain.
The only surviving airworthy short-fuselage Mu 13D, flown by Ernst Waiter at Sutton Bank in 1980. The cockpit canopy and nose had been completely modified. The name Merlin, painted in flowing script on the nose, is a reminder that the original design goes back to the first Mu 13, Merlin, of 1936.
A pre-war Mu 13D with NSFK registration.
An Mu 13D flown post-war by the RAF gliding club at Lubeck, hence the LU-23 registration. Note the slight sweepback of the wing, and the barely detectable change of taper on the trailing edge at the mid-span point.
Photograph of the Mu 13A which was flown in England by the RN Gliding Association. The canopy was greatly modified, the colors being cream with blue trim and naval pennant. The black tape under the wing root was only temporary.
Photograph of the Mu 13A which was flown in England by the RN Gliding Association. The canopy was greatly modified, the colors being cream with blue trim and naval pennant.
A Mu 13D/3 flown by the RAF Gliding Club at Scharfoldendorf (Ith) in 1947-50. Colors were clear doped fabric with dark blue wings and tailplane leading edges, and fuselage nose, with the RAF roundel on the rudder only.