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Static Transducer Mk3

Technical Information

Catalogue No: C0131
Category: Air Data
Object Type: Sensor/Transducer
Object Name: Static Transducer Mk3
Part No: 13-006-01
Serial No: X004/70
Manufacturer: Elliott Bros (London) Ltd
Division: Unknown
Platform(s): Buccaneer , Lightning
Year of Manufacture: 1970
Dimensions: Width (mm): 165
Height (mm): 165
Depth (mm): 160
Weight (g): 4,100
Location: Rack RAA10 [Main Store]

Static Transducer Mk 3
Type No. 12-006-01
Ref. No.
Ser. No. X004/70
Code No.
Modification State -
GEC Avionics
Tag No 48
Part No
Ser No
Property of MoD
EBL 638 [inspection/repair stamp]


This Static Transducer unit was designed for and fitted to either the English Electric Lightning or the Blackburn Buccaneer.
The unit contains the pressure transducer which converts the Static pressure, from the aircraft sensor, to an electrical analogue. The static pressure system is open to the exterior of the aircraft to sense the pressure of the atmosphere at the altitude at which the aircraft is flying.
The difference between the Pitot pressure and the static pressure is called dynamic pressure. The greater the dynamic pressure, the higher the airspeed. So the Static Transducer working with the Pitot unit has the capability to provide an output of indicated airspeed, limits on the altitude and also to manage the maintenance of a specific altitude ; the height lock function. The Pitot and Static transducers will drive a cockpit instrument for indicated airspeed but will also feed into the Autopilot and automatically control the flying surfaces to maintain a pre-set speed or altitude.
The Differential Pressure Transducer within the box contains two aneroid capsules, or diaphragms, which expands and contracts with the pressure input from the Pitot tube. The case around the diaphragm is airtight and is vented to the static port. The use of multiple aneroid capsules is to multiply the movement. The movement of the diaphragm is mechanically coupled to a non-linear cam assembly with two rows of fifteen adjustable grub screws to set the desired profile. Within the casing is a wire wound resistor which is driven by the cam mechanism such that an electrical output of indicated airspeed is provided corrected by the cam profile for the non-linearity of the diaphragm movement. A small servo motor was used to amplify the movement of the capsules to operate the internal gear train.

This Static Transducer unit has been given an X Serial number indicating that it is an experimental or development unit. It was made in 1970 and is a Mk3 design. The Mk2 Type D was fitted to the Lightning so this may be a development for a later version of the aircraft. The relationship between ‘Type’ and ‘Mk’ numbers is not known but it would seem that ‘Type’ (in this case no ‘Type’ is given) can have incremental ‘Mk’ numbers; this being a ‘Mk3’.
This item was in the original Elliott Collection Ref: 2047

Air data systems provide accurate information on quantities such as pressure altitude, vertical speed, calibrated airspeed, true airspeed, Mach number, static air temperature and air density ratio. This information is essential for the pilot to fly the aircraft safely and is also required by a number of key avionic subsystems which enable the pilot to carry out the mission. It is thus one of the key avionic systems in its own right and forms part of the essential core of avionic sub systems required in all modern aircraft, civil or military.

The air data quantities; pressure, altitude, vertical speed, calibrated airspeed, true airspeed, Mach number etc. are derived from three basic measurements by sensors connected to probes which measure:

Total (or Pitot) pressure
Static pressure
Total (or indicated) air temperature

The total pressure, PT, is measured by means of an absolute pressure sensor (or transducer) connected to a Pitot tube facing the moving airstream. The Pitot pressure is a measure of ram air pressure (the air pressure created by vehicle motion or the air ramming into the tube). When airspeed increases, the ram air pressure is increased, which can be translated by the airspeed indicator.

The static pressure of the free airstream, PS, is measured by an absolute pressure transducer connected to a suitable orifice located where the surface pressure is nearly the same as the pressure of the surrounding atmosphere. 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. When the aircraft climbs, static pressure will decrease.

High performance military aircraft generally have a combined Pitot/static probe which extends out in front of the aircraft so as to be as far away as practicable from aerodynamic interference effects and shock waves generated by the aircraft structure. 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. Some civil transport aircraft have Pitot probes with separate static pressure orifices located in the fuselage generally somewhere between the nose and the wing.

From the measurements of static pressure PT and total pressure PS it is possible to derive the Pressure Altitude, Vertical Speed, Calibrated Airspeed and Mach number. Measurement of the air temperature is made by means of a temperature sensor installed in a probe in the airstream and from this a function called Total Air Temperature can be calculated.

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