|Object Name:||Lightning Air Data Sensor Unit|
|Division:||Transport Aircraft Controls [TACD]|
|Year of Manufacture:||1965|
|Location:||Archive Object Store|
Marconi Collection Ref: 2101.
This Pitot-Static Transducer unit was believed to be designed for the English Electric Lightning but the box shape and finish are more like units used on Concorde but at present we cannot determine the aircraft it was designed for.
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 contains a simple aneroid capsule (or usually two capsules to magnify the movement) which is coupled to an arm sliding along a wire wound resistor. A small servo motor was used to further amplify the movement of the capsules to operate the internal gear train This simple arrangement transmits the difference signal between the Pitot and Static pressure to a remote indicator for Indicated Air Speed. The signal is also fed to a locking solenoid used in Height Lock mode to maintain barometric height.
This unit is unusual in having two Pitot and two Static inputs.
Although this unit has lost its formal ID marks it has a tatty cardboard tag tied to it that gives its identity.
It also has a maintenance label marked:
Reg. No. 12346