History of the glider

SL- 1 Akar glider was designed and constructed by students of WUT. SL abbreviation stands for the Polish name Sekcja Lotnicza (Aviation Section), Akar derives from the name  of the main designer- Mr. Adam Karpiński.

Building of the glider was a big challenge for the young adepts of aeronautical engineering. Not only they did not have enough experience but also gliding was only just starting in Poland and the airplane  designers were not so keen on it just yet. They decided to design a glider which would be as simple as possible but they did implement few latest innovative improvements such as quite thick modern profile that enables elimination of guy-wire connections and struts as well as the wing which reduces the air resistance. Apart from that, Akar was a classic construction made mainly as a students’ initiative so that they could  test their skills, especially because there was a good opportunity for it.

Akar was a phenomenon 1st Glider’s  Competition happened in Summer 1923 in Białka near Nowy Targ. Tadeusz Karpiński, the brother of the designer as well as Ryszard Bartel took respectively 1^st and 2^nd place. The winner managed to do the flight in 165 seconds. One year later, the same  pilot who steered Akar set up a record of Poland in the length of glider’s flight which was 4 minutes and  5 seconds.  After covering roughly 2km. distance during that time, the flight finished rapidly with a failure – the glider landed suddenly but safely and never got back to be flown.

Construction

SL-1 Akar is a twin-fuselage glider with the pilot’s seat located in the middle, before the wing. It’s got a cantilever, single-wing formation, wooden, covered with cloth as well as double, vertical stabilizers, single horizontal stabilizer, rudder with a balanced horn and a double-wheeled undercarriage with two landing skids.

Unladen mass of the vehicle is 80 kg., aerodynamic efficiency about 9 but it was most probably due to the pilot’s posture once seated on the flying plane. They tried to avoid complicated solutions as they were taking into account the character of the construction which was designed purposely for testing. It was a pioneering project on the scale of the whole country. When the glider was up in the air it reached about 45km/h speed which enabled a steady and safe flight.

Rebuilding

There are only very few original photos of the glider which portray it in such detail that the reconstruction was possible.

Most of the internal structure as well as the exact measurements of the parts, students had to design by themselves, bearing in mind the technical limitations that were available to the designers about 90 years ago. The foreign constructions of similar kind were a very valuable source of information and inspiration for the young designers. Students were looking into the books written on the topic of “gliders’ construction and design” during the days of Akar’s creation.

The deigning works was mostly done at the faculty of Power and Aeronautical Engineering. Part of the construction was made at the Glider Factory “Jeżów” in Sudety Mountains.

The construction of Akar required students to work at the University sometimes up to 14 hours per day and to sacrifice their weekends. In February 2015, the biggest parts of the glider were made. The flaps and empennage were made afterwards..

„As a tidbit, after the analysis of the photos, we realised that the vertical stabilizer was the only original element of Akar which was covered with cloth not plywood. Why was it this way we are not sure nevertheless, we have done it according to the original design” – says one of the constructors.

At the end of March this year, the glider ended up in Jeżów Sudecki where it entered another stage of finishing works. At the same time, students in Warsaw were occupying themselves with the main missing parts – pilot’s seat and the whole landing gear. In the second part of April, after a few more weeks of intense work, Akar was brought back to Warsaw in order to be assembled together.

The replica of SL-1 AKAR will be available for viewing during the Jubilee exhibition  ”On the wings of time – Warsaw University of Technology aviators and aircraft”, which will be organized in the Main Building of WUT between 13^th and 16^th May.

Acknowledgements

Students of WUT’s Students Aviation Association would  like to thank all involved in this project:

• Head of the Faculty of Power and Aeronautical Engineering and Mr. Stanisław Gradolewski the leader of the project for supporting it through&through
• Dr Roman Świtkiewicz and Mr. Bohdan Hernik – for historical and designer consultations
• the Glider Factory “Jeżów” – for cooperation and supervision of the glider construction process
• Companies: NB Composites and KOMO-furniture – for help and support