Akaflieg Stuttgart fs-29
A variable geometry wing offers the prospect of being able to vary the wing's area and geometry in flight to make the most of the soaring conditions encountered. A high aspect ratio could be selected for ascending in a thermal and a low aspect ratio (and hence a smaller area) for getting the maximum speed in cross-country flying.
The Stuttgart Akaflieg's solution to this problem in the high-performance single-seater FS-29 is a telescopic wing in which the span can be varied in flight from 43 ft 7.5 in to 62 ft 4in (13,3m - 19m) by outer telescopic wing sections sliding over fixed inner sections.
These outer wing sections are of glassfibre/foam/carbon-fibre sandwich construction and are extended and retracted manually by means of push-rods. A stub spar protrudes from each inner wing to provide a mounting for the guide rails on which the outer panels move. The inner wing is built up from a box spar of glassfibre/Conticell foam sandwich and is fitted with Schempp-Hirth air brakes on the upper surface which are only effective when the outer panels are extended. The plain ailerons are of similar construction to the outer wings. The fuselage is very similar to that of the Schempp-Hirth Nimbus 2, using the same landing gear and cockpit canopy, while the tail unit is the same as the Nimbus 2's.
Design work on the FS-29 began in 1972 and the problem of devising a wing which could be varied in span solely by manual power, and yet keep to the required aerodynamic and structural safety factors, meant that the first flight was not made until June 1975.
Akaflieg Stuttgart FS-29
Wing span: 43 ft 7.5 in to 62 ft 4 in / 13,3m - 19m
Length: 23 ft 5.75 in
Wing area:92.2 to 136.2sq ft
Aspect ratio:20.67 to 28.54
Airfoil: FX 73-170
Empty weight:787 lb / 365kg
Max weight: 992 lb / 450kg
Min sinking speed: 1.8ft/sec at 46mph
MinSink: 0.56 m/s @ 81 kph
Best glide ratio:44:1 at 62mph / 98 kph
No. of Seats: 1
No. Built: 1