没有传感器的时代 | The Era Without Digital Sensor

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Pitot-static instrumentsThe pitot-static system obtains pressures for interpretation by the pitot-static instruments. While the explanations below explain traditional, mechanical instruments, many modern aircraft use an air data computer (ADC) to calculate airspeed, rate of climb, altitude and Mach number. In some aircraft, two ADCs receive total and static pressure from independent pitot tubes and static ports, and the aircraft’s flight data computer compares the information from both computers and checks one against the other. There are also “standby instruments”, which are back-up pneumatic instruments employed in the case of problems with the primary instruments.Airspeed indicator Main article: Airspeed indicator
The airspeed indicator is connected to both the pitot and static pressure sources. The difference between the pitot pressure and the static pressure is called dynamic pressure. The greater the dynamic pressure, the higher the airspeed reported. A traditional mechanical airspeed indicator contains a pressure diaphragm that is connected to the pitot tube. The case around the diaphragm is airtight and is vented to the static port. The higher the speed, the higher the ram pressure, the more pressure exerted on the diaphragm, and the larger the needle movement through the mechanical linkage.[4]
Airspeed indicator diagram showing pressure sources from both the pitot tube and static port

Altimeter Main article: Altimeter
The pressure altimeter, also known as the barometric altimeter, is used to determine changes in air pressure that occur as the aircraft’s altitude changes.[4] Pressure altimeters must be calibrated prior to flight to register the pressure as an altitude above sea level. The instrument case of the altimeter is airtight and has a vent to the static port. Inside the instrument, there is a sealed aneroid barometer. As pressure in the case decreases, the internal barometer expands, which is mechanically translated into a determination of altitude. The reverse is true when descending from higher to lower altitudes.[4]

Diagram of an altimeter

Machmeter Main article: Machmeter
Aircraft designed to operate at transonic or supersonic speeds will incorporate a machmeter. The machmeter is used to show the ratio of true airspeed in relation to the speed of sound. Most supersonic aircraft are limited as to the maximum Mach number they can fly, which is known as the “Mach limit”. The Mach number is displayed on a machmeter as a decimal fraction.[4]

Vertical airspeed indicator Main article: Variometer
The variometer, also known as the vertical speed indicator (VSI) or the vertical velocity indicator (VVI), is the pitot-static instrument used to determine whether or not an aircraft is flying in level flight.[5] The vertical airspeed specifically shows the rate of climb or the rate of descent, which is measured in feet per minute or meters per second.[5] The vertical airspeed is measured through a mechanical linkage to a diaphragm located within the instrument. The area surrounding the diaphragm is vented to the static port through a calibrated leak (which also may be known as a “restricted diffuser”).[4] When the aircraft begins to increase altitude, the diaphragm will begin to contract at a rate faster than that of the calibrated leak, causing the needle to show a positive vertical speed. The reverse of this situation is true when an aircraft is descending.[4] The calibrated leak varies from model to model, but the average time for the diaphragm to equalize pressure is between 6 and 9 seconds.[4]

A vertical airspeed indicator

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