Aircraft speed - FlightGear wiki
The true airspeed and Mach number are calculated using the altitude information exemplary functional relationships and/or physical couplings between the. What is the relationship between the Indicated Air Speed (IAS), the Calibrated Air Speed (CAS) Relationship between IAS, CAS, EAS, TAS, Mach number M. Above approximately knots, the compressibility error rises significantly and TAS must be calculated by the Mach speed. Mach incorporates.
When filing your flight plan, make sure you use TAS in the airspeed block; air traffic controllers will sometimes use this speed to decide how best to handle your flight. Most of the time, the wind will not be a direct headwind or tailwind. In aircraft with an FMS, GPS, or other area navigation system, there should be a display of groundspeed somewhere in the cockpit.
Mach number Mach number is a speed derived in reference to the speed of sound. Mach 1 equals the speed of sound; most transport jets I guess all now that the Concorde has been removed from servicecannot cruise at Mach 1, but can cruise at a certain ratio of the speed of sound.
That ratio is known as the "mach number". At higher altitudes generally beginning around FLmost jets will fly a particular mach number instead of indicated airspeed.
There are two limiting speeds for aircraft capable of high altitude flight. One is an indicated airspeed; the other is a mach number. The mach number generally becomes more restrictive at altitudes above the mid-twenties.
At higher altitudes, pilots plan cruise speeds using mach numbers instead of using an indicated speed. At higher altitudes, controllers may assign speeds expressed as mach numbers instead of indicated airspeed. The phraseology should be something like, "maintain mach point seven four".
To determine mach number, most airplanes capable of high altitude flight use an air data computer which calculates mach number and displays it somewhere in the cockpit commonly using the notation "M. If you plan a high altitude flight, know where this information is displayed in your airplane. Obviously this is an important altitude to know. Light aircraft generally have no direct readout of AGL altitude.
Larger aircraft will have a radio altimeter sometimes called a "radar altimeter" which constantly measures the airplanes altitude above the ground directly below. Altimeter setting Because the atmospheric air pressure varies, altimeters incorporate a method to compensate for this varying air pressure called the "altimeter setting". Weather stations measure the air pressure and calculate altimeter settings which are available to pilots. This setting tells the altimeter where sea level would be.
Then the altimeter determines the actual atmospheric pressure outside the airplane and converts it to the actual altitude.
Obviously, it's important to know which one the country you'll fly in uses. If your airplane's altimeter does not use the same unit of measure as the altimeter setting provided, you can convert between millibars and inches of mercury by using a factor of To convert from inches of mercury to millibars, multiply by This altitude is called the "transition altitude", and it varies from country to country.
During descent, the altimeter setting is changed from standard Just like the transition altitude, this varies from country to country. To make things more complicated, the transition altitude and level aren't always the same.
The Airline Pilots Forum and Resource
In some cases like Germanythe transition level can vary from day-to-day and is passed to the pilot by the air traffic controller. Obviously, the specifics of the transition altitude and level vary greatly by region and country; consult your local VATSIM resources for more information. Altitude versus flight level This is one area that is commonly misunderstood. A Mach number above 1 indicates supersonic flight. The Mach number is critical because a number of phenomena take place just around Mach 1 transonic speedfor example a sudden increase in drag induced by shock-wave generation sonic-boom.
Aircraft that are not designed to fly supersonic will break up at Mach 1. The shape of the aircraft can cause parts of the aircraft being at or above Mach 1 while the fuselage is subsonic. Flying near Mach 1 can be quite dangerous, for most fast but subsonic aircraft Mach 0.
High flying aircraft, like passenger aircraft, can reach that limit easy while descending. The speed of sound changes with the compressibility and hence temperature of air, the Mach number is dependent on altitude as the air temperature drops at higher altitudes. The precise relation between TAS, Mach number and altitude is a complicated formulae and depends in essence on the local weather pattern determining the pressure and temperature gradients in the atmosphere.
Here a small abstract. Note that V speed definitions can depend of local Flight rules. Most V speeds depend on the aircraft configuration how much it weights etc. V speeds are used to compare aircraft performance and will be mentioned in the aircraft flight manual AFM. M speeds are expressed in Mach. This is where most corporate jets fly. In the example above, the tropopause starts at FL So what is happening with the chart above?
Relation between IAS and Mach number
The answer lies in how the true airspeed interacts with the Mach number. As the airplane climbs, at some point the crew will transition from using indicated airspeed to Mach speed.
Depending on the aircraft, that altitude may be different but almost always above FL Our original premise that true airspeed increases with altitude is absolutely correct but what is now changing is our indicated airspeed.