constitutes a valuable addition when the quality of the 
horizon pictures is limited, and also is useful in certain 
aerial triangulation techniques. 
A very important but often overlooked part of the 
mapping system is the static probe. This probe is necessary 
to provide an accurate source of static pressure for the 
height corrector of the APR and for the statoscope. A 
special swivel probe is installed near the tip of the wing, 
approximately two chord lengths forward of the leading edge 
of the wing. The probe consists of a set of concentric 
cylinders expanding rearward, always with a diameter less 
than one-tenth the distance from the tip. Holes are drilled 
at right angles to the surface. The swivel probe is supported 
at the center of gravity and carries a ring behind the centroid 
so that it will weathercock and keep a constant attitude to the 
air flow. 
The aircraft assigned to the task of obtaining mapping 
photography should be equipped as follows: 
- Wild RC.9 Aerial Camera equipped 
with super-infragon lens. 
- Wild horizon camera 
- Statoscope 
Static Probe 
Doppler navigation system