The JS design team was thrilled when Idaflieg approached them to test the JS3’s performance during their 2020 Summer camp.
Oftentimes, a manufacturer would be nervous at the idea that their glider’s published performance data may come up for scrutinizing and may even refuse to approve such a request at all, yet we see the importance of these tests; they provide the designer with direct feedback and the opportunity to calibrate their performance forecast models.
Chief Aerodynamic Engineer, Johan Bosman, reveals some insight regarding the JS3’s design.
“The aerodynamic design and analysis methods used for the JS-1 were nothing new at the time, and still an incredibly competitive glide ratio of 53:1 was obtained. In an article we wrote for the Technical Soaring (Refinement of glider aerodynamic design using CFD) Vol 37 #2, it was argued that flow regions on sailplanes where complex 3-D flow phenomena occur were not yet fully optimized.
These regions include the wing/fuselage junctions, winglets, fin/fuselage and fin/tailplane junctions, control horn fairings, wing and tail wheel fairings and internal cockpit ventilation. In order to extract additional aerodynamic performance it was proposed that these flow regions should be addressed – and that is exactly what we did! After conducting additional studies it was determined that the 18m sailplanes could potentially reach a maximum glide ratio of 58:1”.
“We incorporated CFD with transition prediction turbulence models in the design process of the JS-3, resulting in most of these complex flow regions being optimized.
A new high shoulder-wing configuration was implemented together with a highly contracted fuselage shape.
Control horns protruding from the surface for the rudder cables were removed completely and replaced with an internal push rod system. A new high-aspect ratio fin and fin-airfoil were designed for low drag and effective rudder control. These were but a few of the aerodynamic improvements that were made to the JS3 sailplane to get closer to that theoretical 58:1 magical number.”
Relative sink speeds at various flight velocities and flap settings were measured, with comparison flights wing-to-wing with their “holy cow”. From these measurements, a composite performance polar curve was obtained for the various flap settings.
The results confirmed the remarkable performance of the JS3, correlating very closely with the performance predictions of JS, with a maximum glide ratio touching the 57:1 mark.
“Now we have some work to do; update our brochures and website. ” Uys said smiling.
“These flight tests show that the design effort paid off and the bar has been raised for the next generation of sailplanes. A big thanks to the Idaflieg for doing such great research work and to Sturmi, giving us his ‘Black Forest Edition 55+2’ for testing. ”