Altimeters are one of the most important instruments that can be found in the cockpit of an aircraft, allowing for a pilot to always be aware of their altitude or height above sea level. There are many reasons that a pilot would want to know their altitude, ranging from needing to remain high enough for ample performance to avoiding any possible collision with elevated terrain like mountain ranges. While many aircraft vary in the exact type of altimeter that may be present, almost all work in the same basic way. As any pilot will no doubt need to know their altimeter in and out to safely and optimally fly, we will discuss their functionality and importance below.
For aviation, the type of altimeter that is used is a barometric altimeter, and they rely on a wider assembly known as the pitot-static system for obtaining all their readings. The pitot-static system consists of a number of pressure-sensitive instruments and inlet ports, and it allows for readings to be made for airspeed, Mach number, altitude, and altitude trend. The altimeter itself only relies on the static port, that of which is a flush-mounted hole situated on the fuselage in an area where it can access airflow in a relatively undisturbed location. Pressure obtained from the static port is known as static pressure, and there may be multiple static ports for redundancy.
It is important to know that static pressure decreases as an aircraft climbs in the atmosphere, as well as increases when it drops down. This is because air becomes less dense the higher something is, and the change in static pressure generally follows a rule of 1 inch of mercury per 1,000 feet of climbing or descending. To ensure a standard set of readings regardless of the aircraft one is piloting, all altimeters should be calibrated to read pressure in terms of altitude above sea level, following the International Standard Atmosphere (ISA) model.
The altimeter itself will present either a mechanical or digital display for all readings to be conveyed, but this is not actually where the readings take place. Instead, they occur within an internal compartment that is filled up with static pressure directed from the static port. Also within the chamber is a sealed disc that is referred to either as bellows or an aneroid, and this element is designed to expand and contract in response to changes in static pressure within the instrument compartment. As an aircraft ascends, the aneroid will expand as it overcomes static pressure, and it will contract as pressure increases.
If a mechanical gauge-type altimeter is present, readings will be displayed on a dial with an adjustable needle that moves in accordance with changes in altitude. For the needle to correctly adjust, it is mechanically linked to the aneroid so that its expansion and retraction cause changes with the needle pointing to various markings on the dial. While modern glass cockpits have now replaced conventional gauges, the general method of conducting readings is roughly the same with a reliance on the pitot-static system. However, readings are now presented through digital means to make information more accessible and easier to access.
With a basic understanding of the altimeter, one can better see why they are a pivotal tool for safe flight. Here on Internet for Aviation, we provide customers access to over 2 billion new, used, obsolete, and hard-to-find parts that have been sourced from thousands of leading manufacturers that we trust. All of our listings are ready for purchase at any time, so whether you are in need of a magnetic circuit, electric motor, adapter transformer, aircraft wing component, or other such items, we have you covered! Get in touch with a team member at your earliest convenience and see how Internet of Aviation can serve as your strategic partner for all your various needs.
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