Tests done on the Exulans

Free flight models and a 1:5 scale radio-controlled model were used for initial concept evaluations of the proposed tailless aircraft configuration. Stability and control properties, effect of flap and sweep changes and spin recoveries were tested.. The flight properties of this model were so good that they prompted the development of a full-scale prototype.

Besides wind tunnel tests, material tests and initial structural tests an intensive computational investigation of the aerodynamics was done.

The complete full-scale prototype was structurally tested in a special test frame. The so called whiffle tree allows the controlled application of a distributed load on the wing to simulate in-flight loads.

To verify longitudinal stability and control effectiveness, the full scale glider was mounted on a trailer test-rig with freedom to move about the pitch axis only. Flow visualization was done like in a wind tunnel. Pitch stability was studied at all angles of attack, flap and sweep settings. All tests showed excellent results

Tethered flights were performed on a vehicle mounted test platform. The glider was free to fly within safe constraints. Dynamic properties, transient behavior during take-off, flap extension, sweep changes and landing flares could be studied in this way. S-turns were also flown and extensive pilot training was gained

Launch options for the first untethered flight were considered carefully. To avoid the risk of ground proximity flight, an altitude launch from a hot air balloon was proposed. Although this imparts a higher risk of loss of the equipment, the pilot would have the option to abort during most of his flight by triggering the ballistic emergency parachute. Unfortunately RJ Huyssen had to make use of this option seconds after releasing from the balloon when the structure failed. He landed unharmed.

The results exceeded the expectations. Controlling the glider was no more difficult than flying a sailplane in aero-tow one meter above the ground. All involved with the project at the time easily managed to fly the Exulans even without prior experience (and everybody was exhilarated). Stall properties and pitch stability are comparable to those of conventional aircraft and the variable wing sweep produces the desired effect. In conclusion: the new aircraft configuration certainly holds great potential!