VGC News/Newsletters - Lakes Gliding Club

In 1932 the Akaflieg stm·ted the development of che 0 28,
the subject of this article. The aim was to get good performance
even in poor weather conditions by building a relatively
small plane to the lowest possible weight. Iln this respect
the D 28 is unique stiB to this day; the empty weight was 54
kg (119 lb.) with a wing span of 12 m.
The main technical data:
Span 12,0 m
Wing Area 11,4 m2
Wing Aspect Ratio 12,6
Wing Profile
Gottingen 535 modified
Empty Weight 54 kg
Wing 27 kg
Fuselage 17 kg
Empennage 6 kg
Instruments 4 kg
Payload 75 kg
Maxil11l!Jm Weight 129 kg
Wing loading 11,3 kg/m2
LID (Measured at DFS 23,5 at 60,5 km/h
by Hans Zacher and R. Kreyser)
Minimum Sink 0,66 m/s at 52,0 km/h
Minimum Airspeed 43 km/h
dJ-- --;
Figure 2 : Rudder/Aileron Coupling Gear
~___ 5910-- - J
Figure 3: Semi-damped Fin and Rudder
Figure 1 : D 28 "Windspiel"
The main student designers were R. Schomerus and R.
Kosin. Rlidiger Kosin later played an important role as chief
aerodynamicist for the first jet bomber ARADO 234.
The one-piece wi1ng had one spar and a plywood torsion
nose box. The wing was attached to the fuselage by three duralumin
fittings. The full-span ailerons were operated in
common mode for airt{jil camber control and in opposite
mode for roll control. Rudder and ailerons were coupled by a
special gear, so with increasing rudder deflection the differential
function of the aileron was increased. This gear is shown
in the Figure 2. The fin and rudder arrangement of the D 28
was "semi-damped". The fin moved together with the rudder,
but only with 1f3 of the rudder deflection.
These special details were unique; they were never used on
other airplanes except the Darmstadt 0 30, which also had the
semi-damped fin and rudder arrangement. Personal comment
of Hans Zacher: "The manoeuvrability of the 0 28 at the low
speed of 60 krn/h was really exceptional due to the semidamped
rudder and the variable differential function of the
aileron. The LID of 23,S was remarkable compared to the DFS
Meise with 15 m span, a design which occured five years later.
I liked to fly the D 28 and moved it lively around the three
axes".
The front fuselage was a conventional wood structure; the
rear fuselage was a plywood tube over frames without
stringers.
The small weight was achieved by extremely careful
design and construction and exceptional skill in the workshop.
The D 28 was completely designed to the pre-war German
sailplane airworthiness specifications BFS and was even certified
for simple aerobatics. The following measures contributed
to the low weight:
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