The most successful Swiss performance sailplane

 by J.Spalinger. 

One cannot start any description of the S18 without turning back the pages to follow its development from Its origins. In March 1935 the original construction of the S18 was started, although some fairly concrete development work had been done the previous year with Its forerunner, the S17. The impulse for me to design a small performance sailplane came from my first thermal flights with the "Milan". Thermal flight is not so dependent on a theoretically good performance In straight flight, as on a good performance in turning flight. Therefore especially stability qualities play a dominant role, as every S18 owner knows very well. These points, a good flying performance In turning flight and good stability qualities have helped not a little to create a glorious record for the S18 in the story of Swiss gliding. 

Before we come to the technical part of our description, some historical dates of interest:


24/5/36          Test flying of the first S18 by J.Lemp, 

26/7/36          Test flying of the second S18 by J.Lemp, 

8/8/36            The Swiss S18 Team takes part in the Olympiad 1936 at Berlin-Rangsdorf 

14/7/37          First formation flight of seven S18 sailplanes behind three towplanes. 

26/9/37          Winning sailplane in the first Swiss gliding Championships. 

6/8/37            Crossing of Alps by H.Schrelber in an S18 Rochers de Naye - Simplon -Palagnedra 

17/7/39          Swiss Distance record of 216km by M.Schachenmann.

 19/8/39          Swiss Height record by H. Schachenmann : 3700m (Gain of height 2870m)

 18-19/6/42     World duration record by Eric Nessler in France in an S18 III of  38hr 22min.

 1943              Winning sailplane in the fourth Swiss Gliding Championships.

To give some idea of the widespread popularity of the S18, no less than 60% of the flights in the 1943 Swiss National contest were carried out on the type. The great popularity of the S18 was due to its effective construction and flying advantages that, until then, had not been advertised by the firm that built the machine, Bau A.G. Wynau. The firm have built four versions of the S18, the characteristics of which are listed below:~


  • S18 1 Olympiad 1936  13.3m span     Light metal wing fittings 
  • S18 K Aerobatics        11.7m span     Wing of great strength 
  • S18 II 1937 Champs.   14.3m span     Light metal wing fittings
  • S18 Ill World Record    14.3m span     Steel wing fittings A

This list Is not quite complete, because already in 1935 there was one S18 which was designed as a shoulder-wing sailplane but was finished with a midwing. Only one example of this machine was built. 




For 1944 the firm Bau A.G.,Wynau organised itself for series production and the following building programme was planned: 

S18 IlIm A development of the mid-wing version, the object of which was to Improve the S18 still further.

S18 IIIa Further development of the S18 shoulder wing version whereby Important progress could be made towards quality of production. The special characteristIcs were as follows:


  1. Complete Interchangabillty of all parts between sailplanes of the type.
  2. Refinement of construction details.
  3. Further Improvement for factory production quality, especially of metal parts which were mass-produced by a specialist firm.


Mass production allowed for the carrying out of various refinements without an appreciable cost Increase, which would have been Impossible In amateur construction. The news of a new cable back release, a more comfortable seating position, the lightness of the new controls and especially good visibility, gave much pleasure to S18 fans. 

The basic construction of the aircraft remained almost unaltered:



 Fish shaped, plywood fuselage of lenticular cross-section built on a keel on which all control, release and skid fittings were mounted. This layout was typical of all "S" gliders since 1925 and proved to be practical in all flying operations. A roomy cockpit enclosed by a light perspex canopy with very good visibility. 


This was a cantilever with a purposely generously dimensioned structure and attached to the upper surface of the fuselage at three points.


 Spalinger S-18 III


These were single-spar, cantilever, gulled and of near elliptical planform. Each wing was attached at three points to the fuselage with horizontal pins. This system was first developed by K.Flachsmann and has since been used with success for other designs, Including the S17, S18 and S22. 

The glider pilot when considering a sailplane thinks primarily of its gliding angle and sinking speed and believes these two factors are all that matters In his quest for progress. He overlooks the fact that often glider building firms publish figures for propaganda and make them look as good as possible. They are often only theoretical, "on paper". I am against this kind of advertising and believe that the qualities of a sailplane depend also on other factors. I have noticed that with a sailplane that is easy to fly one can expect many good performances from pilots which are not achieved by pilots flying machines of higher performance but which have worse control and stability characteristics. This Is the reason why during past years many young pilots without much experience have put up a whole series of good performances on the S.18, which have previously only been achieved by military glider pilots. It should not be overlooked that even the worst glider pilot might be able to obtain such a training In the course of military duty such as to enable him to put up a really first class performance. 

The true, tested performance figures for the S.18 are:


Flying speed                Glide Angle                  Sink speed
km/h                             ratio                             m/sec

45                                17                                0.75

50                                19                                0.72

55                                22                                0.75

61                                21                                0.85

70                                18.5                             1.05

90                                14                                1.60


The above figures show distinctly where the weaknesses and the strengths of the S.18's performance lie: this would become an essay If I were to give more details. 

What these honestly stated poor sinking speed figures mean Is that pilots should remember that In the past there have been many gliders with lower sinking speeds which are better for slope soaring. 

That this aircraft, in spite of Its slowness, Is not absolutely hopeless for racing Is evident from the Swiss National Contests of 1942 and 1943. While the Spahni - Schachmann dual (Moswey v S18) Is still fresh in the mind, the points difference between Spahni and Ehret In the 1942 Swiss Championships was even closer. Probably it has escaped the notice of many glider pilots that, at that time, an old S18 was treading very closely on the heels of the winner. Had Ehret been flying from the first contest day (he started flying on the third contest day) and had he not flown past the goal on the third contest day (1/9/42), thereby causing his disqualification and no score, then an S18 would have been the winning machine. A curve published In Aero Revue (12/11/42) with an Imaginary curve showing Ehret's flight from Grenchen to Olten. the goal, Instead of Grenchen to Aarau, shows that with his fine out and return flight Grenchen-Olten-Grenchen on 5/9/42, Ehret would have won the contest. In any case the flight on 5/9/42 made it clear that pilot and aircraft are not at all bad. 

I hope that my friends will Increase the success of the S18 In the future.

By Jakob spalinger,
the designer of the S18.

Translated from Hermann Rutschi's book "Segelflug" (Swiss Gliding) of 1944 by Chris Wills. 

The drawings used for this article were also taken from the book and were originally drawn by Henri Rutschi 

The book was kindly sent to Chris Wills by Willi Schwarzenbach. 

"Milan". We believe that this refers to the S17. This Is the third sailplane type named "Milan" that we have heard of. The other two are the Mü-10, and the 1949 French-built Weihe (VMA 200) "Milan" Is the French for Kite.