fs32 – Aguila

Slotted Flaps for Low and High Speed Flight

Normally, a wing’s profile displays compromises for low and high speed flight performances. All the same, it’s possible to optimize the wing to different flight conditions by changing the geometry of the profile or the wing. Within the Idaflieg, there are some examples of this principle: Akaflieg Stuttgart fs29, Akaflieg München Mü 27, Akaflieg Braunschweig SB 11, and the Akaflieg Darmstadt D-40. The telescoping wing of the fs29 had a heavy mechanism and changing the wingspan required a lot of time and energy from the pilot. On the other hand, fowler flaps reduce the relative area of the ailerons, reducing maneuverability and increasing the induced drag coefficient.

With information from extensive tests, it was possible to develop a profile of the wing and flaps. With the flaps, it was possible to greatly increase the wing’s camber while only marginally increasing the wing area. Drag was reduced via a slot above the flap. Through this design, it was possible to achieve a high lift coefficient, which means that the fs32 can thermal slower and tighter around the center of the upwind where one can climb faster.

In its high speed configuration, the profile matches that of a modern racing class airplane and its performance isn’t inferior to the latter. In the low speed configuration, the flaps and ailerons are dropped down below the wing. The upper part of the wing’s skin is simultanously folded downwards, sealing the rear part of the profile.

The mechanism in each wing comprises of ca. 1500 parts which were manufactured with the help of the MBB trainee workshop in Donauwörth (milled parts) and MAN in Munich (CFK-torsion tubes). Therefore, there’s not a lot of space inside the wing. A further difficulty is that the wing had to be made stiff enough that the mechanism can run smoothly. The fuselage of the fs32 was built using molds from the Schempp-Hirth Ventus b, with the layout of the fibers optimized via the finite element method. The tailplane on the other hand was a new design. The rudder was made out of prepregs, which allowed for a high fiber volume proportion.


Construction1985 – 1991
First flight18 February 1992
Wingspan15 m
Wing area9,94 m²
Aspect ratio22,64
ProfileFX 81 K 144/20
Dihedral angle
Length6,62 m
Empty weight285 kg
MTOW500 kg