Special Motor Glider – Flying Experiences with the “Twin Explorer IV” Motor Glider

The maiden flight of the “Twin Explorer IV” took place in July 2019 at the model airfield in Müswangen. The center of gravity and EWD were adjusted according to the Vortex simulation program. The butterfly settings were as usual (flaps at 60°, ailerons up 10°), along with aileron differential. The launch from the cart went off without a hitch. Hans Baumann, an experienced first-flight pilot, attested that the motor glider exhibited flawless flight behavior.

The model flies as steady as a board and is characterized by high stability and good gliding characteristics. Thanks to its lower wing loading, the “Twin Explorer IV” climbs rapidly in thermal tubes, while still allowing for tight turns. In the event of a stall, the model reacts very forgivingly: during normal straight-and-level flight and with the elevator pulled back, it tips forward. During simulated tight landing approaches at a safe altitude and low speed, the model tilted sideways; after a momentary pull on the elevator, it was quickly back under control. The “Twin Explorer IV” is not a high-performance glider in the modern sense, but rather a magnificent glider with captivating flight characteristics and excellent aerodynamics.

Thanks to the turbulators on the outer wing, the model exhibits very forgiving stall behavior: it remains controllable even if the inner wing stalls. If the turbulators are arranged across the entire wing, the stall speed generally decreases; however, controllability via the ailerons is no longer guaranteed: The model “loses control,” which is fatal near the ground (rest in peace, “Twin Explorer III”). I adopted the arrangement and geometry of the turbulators from examples in civilian sport aviation. I milled out the plastic plates (2 mm Graupner plastic sheet, white) and then secured them with white glue into the holes prepared using a drilling jig.

By using the Vortex simulation program, the desired characteristics of a model aircraft can be determined and optimized in advance. Based on positive practical experience, I decided to use the HQW-3012 airfoil profile for the inner wing throughout up to 66% of the wingspan and to transition from HQW-3012 to HQA-3010 on the outer wing. Additional dihedral on the outer wing set to -1 degree. The tried-and-true symmetrical NACA0010 profile is used for the elevator and rudder. Turbulators cannot be included in this program; however, the stall behavior in terms of controllability is significantly improved by the turbulators described earlier.

"Twin Explorer IV" is currently being replicated in Sweden, Germany, and Switzerland. All CAD files and a detailed, illustrated technical description serve as the basis for this project. All CAD files can be viewed using a free SolidWorks viewer. The cleaned-up *.dxf files serve as the starting point for a CNC milling machine. This replica project is recommended for experienced model builders.

www.solidworks.com
frankranis@gmx.de

www.ulmer-kunststoffteile.de
www.balsa.ch

www.mgmueswangen.ch

SolidWorks
CAD software, Frank Ranis, Vortex simulation software
, manufacturer of the canopy
, my wood supplier. Under “Customer Projects”: Twin Explorer III
, Müswangen Model Aircraft Club, “Pictures and Videos” from Q3 2019 and Q4 2019