Many of the instruments in the aircraft cockpit are based on the measurement of different air pressures outside the aircraft while it is in flight. The Air Data Test Set (ADTS) or Pitot Static Tester is a sophisticated system capable of testing aircraft flight instruments while the aircraft is on the ground.
Engineers create a simulated flight for the cockpit instruments by using a precision pressure controller to replicate precise flight pressures at the test points on the outside of the aircraft’s fuselage and verify that these critical safety systems are operating and properly configured, ready for the next flight. The Air Data Test Set simulates altitude, climb rate, airspeed, and acceleration rate. The ADTS can simulate flying the plane at any speed and ambient conditions.
The pitot-static device of an aircraft provides vital data to flight instruments such as altimeters, airspeed indicators, climb rate indicators, Mach meters, and air data computers. These systems can be checked and calibrated by Air Data Test Sets. These highly advanced pressure generation and measurement instruments are used both for leak testing of the pitot-static system of an aircraft and for testing and verifying the instruments of an aircraft by simulating the aircraft’s altitude and speed while it is still on the ground.
The Pitot tube
By converting the kinetic energy of the airflow into potential energy, the Pitot tube can help measure the fluid velocity at the stagnation point, situated at the entrance of the Pitot tube.
From the conversion of kinematic to potential transfer, a pressure higher than the free-stream or dynamic pressure is obtained. This static pressure is measured by comparing it to the dynamic pressure of the air with a differential manometer.
This differential pressure is converted to fluid velocity depending on the Pitot tube’s basic fluid flow regime.
How an aircraft’s Pitot system works
The Pitot tube’s forward opening point gets air at a higher impact pressure than the static pressure tube facing the side that detects the air in the free stream. The difference is known as the dynamic pressure between these two pressures and is proportional to the Indicated Air Speed of the aircraft, also known as Calibrated Air Speed. The free-stream air pressure is the same as the ambient air all around outside the aircraft. With rising atmospheric altitude, this ambient barometric pressure decreases. Static pressure is inversely proportional to the altitude of the aircraft.
A pitot-static aircraft system contains multiple sensors that sense the ambient air pressure affected by the aircraft’s forward motion known as the pitot pressure and unaffected static pressure. To provide indications of different flight conditions, these pressures are used on their own or in conjunction with each other.
Pitot Static System
- Altitude (Altimeter)
- Mach Number (Machmeter)
- Airspeed (Air Speed Indicator)
- Vertical speed (Vertical Speed Indicator).
The Pitot and static pressure are also used by other aircraft equipment, such as the Autopilot and the Cabin Altimeter.
Static pressure is measured by multiple vents at aerodynamically neutral points on the fuselage of the aircraft. On either side of the fuselage, vents are located and feed into a common tube; this has the effect of canceling errors resulting from the location of the vents to some degree.
In a pitot tube or pressure head, which is an open tube facing forward along the aircraft axis, pitot pressure is measured. The pressure measured in the tube is a combination of static pressure and pressure due to the forward speed of the plane.
Air Data Computer
Most modern aircraft have an Air Data Computer installed in it. It calculates the True Airspeed, Mach Number, Indicated Airspeed, Vertical Speed, Altitude, Outside Air Temperature, and Total Air Temperature, using inputs from the pitot-static system and temperature sensors. This data is supplied to aircraft systems in particular to the Electronic Flight Instrument System.
Connecting Air Data Test Sets to Pitot Tubes
The Static and Pitot aircraft ports are designed in many different ways, some of which may be unique to the type of aircraft. A special pneumatic link fixture or Pitot Static adaptor is normally required to make a piped connection to test the pitot device. If the two ports are combined into one probe, a combined port adaptor is used. The adaptor is driven with compression rings over the probe and locked in place. It includes precision seals to create partitions on the probe surface between the Pitot and static openings.
Air Data Test Sets provide aircraft operators and maintenance organizations with dependable and crucial support. They are designed to simulate the pressure conditions observed by aircraft during their flights which is required to calibrate the indicators for altimeter, airspeed, manifold pressure, and vertical speed. It also offers ways of leak monitoring the Pitot-Static mechanism of an aircraft. Accuracy of these parameters is critical for any safe flight.
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