The pitot-static system is a very reliable set of instruments that measure air pressure and display airspeed, altitude and vertical speed to the pilot using that information. Continue reading “Flight Instruments: Pitot-Static System”
The Vertical Speed Indicator (VSI) displays the rate of climb or descent measured in thousands of feet per minute. It is considered to be a secondary instrument because it can generally be inferred from the altimeter. It is also considered to be unreliable in many circumstances because it has a delay.
Your height above the terrain and in relation to other aircraft is critically important. The altimeter is an amazing instrument that makes it easy to tell what your altitude is.
How to read an altimeter
There are 3 needles on this standard altimeter. The long needles pointing near the 7 moves the fastest and indicates hundreds of feet. The short needles pointing near the 1 indicates thousands and the thin needle pointing near 0 indicates tens of thousands. Continue reading “Flight Instruments: Altimeter”
Mach number is a measurement of the aircraft’s speed relative to the speed of sound. Mach 1 would mean the aircraft is flying at the speed of sound and Mach .5 would mean it is flying at half the speed of sound. The mach number itself is generally determined by an air data computer gathering pitot-static and temperature data. Continue reading “Flight Instruments: Mach Indicator”
How does the indicator work?
A basic airspeed indicator is a mechanical device that compares pressure from the pitot tube to pressure from the static port. The static port is mounted sideways with a hole the doesn’t face directly into the oncoming air. This way it gets a “static” measure of the air pressure. The pitot tube has a hole that does face into the airstream, so it has oncoming air forced directly into it.
The air from the pitot tube fills a diaphragm (like an accordion) and makes it expand. The air from the static port fills the gauge around the diaphragm and pushes it to contract. As the diaphragm expands and contracts it pushes a needle that we see on the instrument.
The airspeed indicator is very reliable but there are a few things that can go wrong.
Reading the airspeed indicator
The airspeed indicator is fairly self-explanatory to read. The most common mistake is not paying attention to units. Sometimes the instrument will measure miles per hour instead of knots. Always make sure you know which one you are looking at.
The indicator can also have some error, especially at high angles of attack. The manufacturer will often publish a calibrated airspeed table to help you determine the difference.