The Project Without Construction
It’s not unusual, but not typical, that a project ends without an airplane being built.
Long before the end of construction on the fs33, a study was undertaken on the feasibility of the idea behind the fs34. A new idea was born out of this study, which was then given the name fs34 “Albatros” by the active members of the time. Complications with the flight tests of the fs33 along with personnel shortage and difficulties in planning the construction of the fs34 led to a stagnation of the project. By 2002, with all the original planners gone, the project was practically dead in the water. Attempts at passing on the project to the newer generation came to nothing due to the project’s complexity and feasibility, a lack of interest, and an overall low chance of success.
The need of a new group project, with which the whole group can identify with, led to the birth of the fs35 project. This spelled the end for the fs34 project.
The Original Idea of the fs34
Since the 60s, the idea of improving a sailplane’s flight performance through the use of variable wing geometry was thrown around a lot among Akaflieg members. The reason for this is the quite opposite requirements between low speed and high speed flight.
The first realization of such an idea in Germany was the Akaflieg Stuttgart fs29, which possesed a telescoping wing that could vary its wingspan between 13,3 and 19 m. Another example was the Akaflieg Braunschweig’s SB 11, which first flew in 1978. Its wings were equipped with Wortmann-style Fowler flaps and could increase its area from 10,56 to 13,2 m². With the latter, Helmut Reichmann could achieve his third world champion title in July of 1978. Other notable prototypes include the Akaflieg Munich’s Mü 27, a two-seater which was also equipped with Fowler flaps and first flew in 1979, the Akaflieg Darmstadt’s D 40 with its so called “pocket knife flaps” that first flew in 1986, and another Akaflieg Stuttgart prototype, the fs32, which was equipped with slotted flaps and first flew in 1992.
Experience
Sailplanes are equipped with flaps to allow for an improvement in climb performance by increasing the wing area without having to sacrifice high speed performance. It has been shown though that advantages gained in thermal performance can’t always be exploited as it’s not always possible to overtake or overclimb, so to speak, another sailplane safely. Furthermore, the commonly used method during cross country flight has changed, with the amount of thermalling being held to a minimum, using updrafts while flying straight ahead to stay in the air instead.
The Albatross
Based on experience with variable camber, the fs34 should have a better glide ratio with flaps retracting. With the ability to reduce wing loading by extending the flaps, the wings can be made smaller to optimize for high speed flight.
A 12,3% thick flap profile was developed and optimized, based on the SB 11 and modern racing class profiles. The fs34 was designed to be a 15 m racing class sailplane with a wing area being variable between 8 and 9,39 m². With the flaps retracted, the aircraft would have an aspect ratio of 28, very high for a 15 m wingspan, and a glide ratio of 50. To improve climb performance though, the fs34 is to be built as light as possible.
Past projects have shown that a plane’s performance during low speed flight, such as maneuverability and control surface harmony while thermalling, is more decisive than pure performance. Experience from the fs33 project should be considered when optimizing control surface harmony.
