T-34C AIRCRAFT SYSTEMS FAMILIARIZATION
The AOA probe is located on the leading edge of the left wing. A rotary vane is attached to a
potentiometer located within the probe body. The vane is positioned by the relative wind
striking the leading edge of the wing. The potentiometer sends an electrical signal representative
of the AOA to the AOA electronic control unit.
AOA Electronic Control Unit
The AOA electronic control unit is a white rectangular box located in the aft cockpit on the deck,
right side. It is a solid-state electronic unit amplifying the AOA probe signal and sending it to
the AOA indicator pointer and indexer for display.
Accurate Display Indication Requirements
To display valid AOA information the aircraft must be airborne and in the proper wing flap
configuration; i.e., flaps full up (0%) or flaps full down (100%).
The AOA indicator is located in the upper left corner of the instrument panel in each cockpit. It
displays accurate AOA information in the form of arbitrary units. The indicator aids a pilot in
establishing the optimum aircraft wing AOA for a given airspeed. The display is comprised of a
pointer and a scale. The scale is graduated from 0-29 units in one-unit increments. Three special
indexes are marked on the scale at 20 units, 26½ units, and 29 units. The 20-unit index is the
optimum approach index. This is the most important, since it is used in the early stage of the
AOA landing approach to establish the aircraft on the correct airspeed at 20 units. In the T-34C
this will be approximately 80 KIAS with flaps down and 95 KIAS with flaps up. The 26½ unit
index is the stall warning index. The rudder pedal shakers, a physical stall warning feature, are
activated only in flight at or above 26½ units. Activation indicates the aircraft is 5-10 KIAS
above actual stall speed. On landing, the rudder pedal shakers are disabled by a safety switch
located on the nose landing gear. At 29.0 units, the aircraft is fully stalled. Should the pointer
move into the red OFF portion of the dial, it indicates the system has lost 28-VDC power. The
pointer is operated by an electrical signal that is developed in the AOA probe.