corded directions of drift. Velocity and direc 
tion of the wind can thus be ascertained with 
an accuracy of +. 1 km or + V2 degree. 
The computation of the angle of crab for 
the go and return courses on the basis of the 
known phenomena of the wind triangle offers 
no difficulties. When the wind computer is 
used, all signs may be disregarded, as the cor 
rected courses may be read directly on the 
instrument. 
After the ground speed has been determin 
ed (with wind computer or direct reading of 
the (Lotfe) it will be practical to fix the length 
of the runs in minutes of time. In areas, such 
as deserts, jungle, Arctic regions etc., where 
the boundaries of the territory to be photo 
graphed are not defined by conspicuous land 
marks, e.g. shorelines or rivers, this is the 
only way for the determination of the ends 
of the runs. In any case, the previously com 
puted time for the end of the strip, which 
has been set on the index mark of the clock 
on the instrument panel, provides the entire 
crew with a reliable control for their various 
duties until the airplane turns around. 
2. Turning: 
a) We shall first discuss turning when the 
influence of the wind is eliminated. If the 
three turning speed stages of 1°, 2° and 3° per 
second provided by the Siemens automatic 
pilot system are used separately, they permit, 
with a certain air speed of the craft, to fly 
circles with 3 different diameters. Generally, 
the desired flight line spacings will not coin 
cide exactly with the diameters of these circ 
les. By combining various circle segments in 
to “compound turns“ any number of spacing 
combinations can be formed within certain 
maximum and minium limits. If the air speed 
is v, Fig. 5 permits to read the following data 
for the combination of turn segments of the 
two turning speeds 1° and 2° per second: 
q • v 
cx 1 0 + <%20 = 1800, r l0 = (? • V, r 2 0 = -j- 
s = r I o + r 2 o + (r 1 o-r 2 o) cosa 2 o- - © 
2 s „ 
COS (Xoo = 3 © 
ù Q-V 
or, converted in flying time: 
0^2° 
t jo = 180° — oc 2o , 1 2 o = —• • • ® 
The displacement of the strip terminals in the 
direction of the runs is: 
CC’ = • sin a jo @ 
Accordingly, the combination of the turning 
speeds 2°/3° per second is: 
r 3° 
cos «30 
q • v 
~T 
6 s 
V 
1 2 o = 90° — 
_ ut 3° 
cc 
Q • V 
— • Sin 0C 2 0 • . . 
• © 
• © 
• © 
B 
Fig. 5 
Turn composed of two circle segments with different 
radii 
The diameters of the half-circles which are 
flown only with one turning speed, repre 
sent the possible maximum and minimum 
flight line spacings. The combination of the 
turning speeds l°/3° per second would also be 
possible and include all possiblities both of the 
combination l°/2° and 2°/3° per second. For 
reasons of flying technique, however, it is 
practical to keep the stages for the variation 
of the turning speeds as low as possible so as 
to obtain smooth transitions free from bank 
ing. When going into a turn from a straight 
course, it will therefore be advisable to begin 
always with the low turning speed, accelerate