Wing Set for the "Cirrus" Fuselage

The elevator and horizontal stabilizer were carried over unchanged from the scale model, with the exception of the slightly enlarged rudder. The following characteristics were targeted: a wide speed range, good flight performance even in stronger winds—though not a true “storm model”—and forgiving stall behavior.

The main dimensions and wing construction are shown in the sketch. The conventional—though somewhat labor-intensive—construction method results in a very rigid airframe, which can be fully or partially covered with skin, depending on the builder’s preference. In the latter case, the rear skin panels are simply omitted, and instead, each rib is fitted with stringers. It is recommended to box in the main spar all the way to the wingtip. For the rectangular wing center section—the profile can thus be checked using a single template size—the E-392 profile from Eppler was selected. In the trapezoidal outer section, the profile is tapered to E-374. A corresponding root rib adapts the transition to the fuselage to the new profile.

During flight testing, a fairly significant shift in the pressure point was observed, resulting in a certain tendency to pitch up. This characteristic is greatly reduced if the center of gravity is not located further aft than approximately 30% of the wing depth. Since the model’s attitude relative to the lateral axis is usually very easy to discern during slope flying, you quickly get used to making slight corrections with the elevator. Entering an updraft zone is immediately evident from the corresponding reaction around the lateral axis, and the model is “sucked” into the updraft. Small thermal tubes can be flown out using very tight spirals.

Rolf Girsberger