On Friday 05.07.2024 another flight test session took place. This time on the airfield of Luzern-Beromünster with grass runway.

 

Luzern-Beromünster airfield, towing by Scheibe Falke

Sören Pederson, experienced glider pilot and professional class 1 test pilot, head of flight tests at Diamond aircraft, did four flights with the glider. This time also me (Benjamin Meienberg) had the chance to do my first flight with the 1comet glider. The glider was already test flown about 10 hours before by Sören in different conditions.

 

Typical test flight:  duration was between ½ hour and an 1 hour per flight

The low mass of the glider let you feel every small lift. It has a very low moment if inertia, which gives an exciting flying experience. The glide ratio and the low sink rate are impressive. I didn’t like so much the hanging stick, since it is not intuitive (at least for me). Anyway, for the second prototype which will be ready for first flights soon, the design is changed to a side stick long time ago.

 

New stick: will replace the hanging stick 

 

Sören and Benjamin

Also part of the test was to check the efficiency of the retrofitted spoilers. The spoilers are designed by CFD to bring down glide ratio to about 7 when 90 degrees vertically up.

The spoilers work well and lead to a glide ratio of about 1:10 when they open to about 65°, as can be seen on the picture.

The second prototype has a different spoiler system, we will see which one suits better.

 

Spoiler at 65°

Sören also tested stall characteristics with side slip angle and during non-coordinated turns. The glider reacts in a predictable way, super docile stall, easily controllable.

Stall was below 40 km/h IAS, at full flaps, 17 kg/m2, CG at 400 mm. At full negative flap setting stall speed goes about 10 km/h up.

Minimum speed in turns:  45 km/h IAS at approx. 30 degrees bank, full flaps, 17 kg/m2.

The airspeed indicator from Winter was calibrated using the GPS in previous flights.

The indicator appears to give an accurate IAS at lower speeds. At 160 km/h IAS it is >10 km/h too low.

Also a trim tab on the horizontal stabilizer was once removed and once changed to a Gurney flap to see influence to elevator stick force and trim.

The thermal conditions on this day did not allow further performance testing. However, previous flights with prototype P01 in calm conditions in the early morning showed sink rates below 0.5 m/s at low speed and sink rates around 1 m/s at 100 km/h.

My former lecturer Prof. Dr. Leonardo Manfriani who has 30 year experience in flight testing and former head of the aerodynamic department of Pilatus Aircraft supported us with valuable tips on this topic, thank you Leonardo!

Debriefing: Sören, Donat and Leonardo

Special thanks also goes to Kilian Raemy who supported us with all the ground logistics for this day and to Christoph Meier, our towing pilot. Christoph Meier is also chief glider instructor at the gliding club Pilatus and examiner SPL and TMG.

Christophe Smith (SHV class 2 instructor) and Donat Bösch (founder 1comet, 500 h flight time on his 2 Swifts, former vice  European champion class 2)  were also present giving valuable inputs.

We will continue flying prototype P01. But specific flight tests will be done with Proto 02. Mayor modifications on Proto 2: We replaced the hanging stick and made the fuselage more streamlined.

 

Benjamin Meienberg