|Object Name:||Air Data Transducer|
|Part No:||1281AF 3A1B|
|Year of Manufacture:||Unknown|
|Location:||Main Object Store|
Air Data Transducer
RMT P/N 1281AF 3A1B
Impact Pressure Range (OC) 0 to 20in Hg
Static Pressure Range (PS) 0 to 32in Hg
+15V at 70mA. Max.
-15V at 70mA. Max.
Output Voltage: 0 to 10VDC
Protected by one or more of the following patents:
3,271,669 and 3,318,153
with other patents pending
Code Ident 04274
An aircraft airspeed unit measures the difference of pressure between the Pitot (or total pressure) and the Static pressure.
The Pitot pressure is obtained from the Pitot Tube and is a measure of ram air pressure (the air pressure created by vehicle motion or the air ramming into the tube). The Pitot tube is most often located on the wing or front section of an aircraft, facing forward, where its opening is exposed to the relative wind. When airspeed increases, the ram air pressure is increased, which can be translated by the airspeed indicator.
The static pressure is obtained through a static port which most often is a flush-mounted hole on the fuselage of an aircraft located where it can access the air flow in a relatively undisturbed area. Some aircraft may have a single static port, while others may have more than one. A Pitot-static tube effectively integrates the static ports into the Pitot probe. It incorporates a second coaxial tube (or tubes) with pressure sampling holes on the sides of the probe, outside the direct airflow, to measure the static pressure. When the aircraft climbs, static pressure will decrease.
This unit probably contains aneroid capsules with a conversion of the analogue movement of the diaphragm to an electrical output. This arrangement transmits the difference signal between the Pitot and Static pressure to a remote indicator for Indicated Air Speed and other functions such as Height Lock.
The identity label also contains the connector pin designation:
A- +15VDC Power
B- 15VDC Return
C- -15VDC Power
D- Case Ground
E- BIT Activate (if applicable)
F- PS Output Signal
G- Qc Output Signal
H- Signal Return
J- Not Used
K- Not Used