Outside air temperature
Encyclopedia
In aviation
terminology, the outside air temperature (OAT) or static air temperature (SAT) refers to the temperature of the air around an aircraft
, but unaffected by the passage of the aircraft through it.
, some of them being takeoff
performance, density altitude
, cruise
performance and go-around
performance. In most texts, the abbreviation, "OAT" is used.
or Fahrenheit
or both. The Kelvin
scale, however, is used for Mach number
calculations. For example, the speed of sound
in dry air is
where:
is the speed of sound in knots and
is the outside air temperature in kelvin
s
services, on the ATIS
or measured by a probe
on the aircraft. When measured by the airplane's probe in flight, it may have to be corrected for adiabatic (ram effect) rise and friction
, particularly in high performance aircraft.
Aviation
Aviation is the design, development, production, operation, and use of aircraft, especially heavier-than-air aircraft. Aviation is derived from avis, the Latin word for bird.-History:...
terminology, the outside air temperature (OAT) or static air temperature (SAT) refers to the temperature of the air around an aircraft
Aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...
, but unaffected by the passage of the aircraft through it.
Aviation usage
The outside air temperature is used in many calculations pertaining to flight planningFlight planning
Flight planning is the process of producing a flight plan to describe a proposed aircraft flight. It involves two safety-critical aspects: fuel calculation, to ensure that the aircraft can safely reach the destination, and compliance with air traffic control requirements, to minimise the risk of...
, some of them being takeoff
Takeoff
Takeoff is the phase of flight in which an aerospace vehicle goes from the ground to flying in the air.For horizontal takeoff aircraft this usually involves starting with a transition from moving along the ground on a runway. For balloons, helicopters and some specialized fixed-wing aircraft , no...
performance, density altitude
Density altitude
Density altitude is the altitude in the International Standard Atmosphere at which the air density would be equal to the actual air density at the place of observation, or, in other words, the height when measured in terms of the density of the air rather than the distance from the ground...
, cruise
Cruise (flight)
Cruise is the level portion of aircraft travel where flight is most fuel efficient. It occurs between ascent and descent phases and is usually the majority of a journey. Technically, cruising consists of heading changes only at a constant airspeed and altitude...
performance and go-around
Go-around
A go-around is an aborted landing of an aircraft that is on final approach.- Origin of the term :The term arises from the traditional use of traffic patterns at airfields. A landing aircraft will first join the circuit pattern and prepare for landing in an orderly fashion...
performance. In most texts, the abbreviation, "OAT" is used.
Units
Most performance and flight planning graphs and tables use either degrees CelsiusCelsius
Celsius is a scale and unit of measurement for temperature. It is named after the Swedish astronomer Anders Celsius , who developed a similar temperature scale two years before his death...
or Fahrenheit
Fahrenheit
Fahrenheit is the temperature scale proposed in 1724 by, and named after, the German physicist Daniel Gabriel Fahrenheit . Within this scale, the freezing of water into ice is defined at 32 degrees, while the boiling point of water is defined to be 212 degrees...
or both. The Kelvin
Kelvin
The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...
scale, however, is used for Mach number
Mach number
Mach number is the speed of an object moving through air, or any other fluid substance, divided by the speed of sound as it is in that substance for its particular physical conditions, including those of temperature and pressure...
calculations. For example, the speed of sound
Speed of sound
The speed of sound is the distance travelled during a unit of time by a sound wave propagating through an elastic medium. In dry air at , the speed of sound is . This is , or about one kilometer in three seconds or approximately one mile in five seconds....
in dry air is
where:
is the speed of sound in knots and is the outside air temperature in kelvinKelvin
The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...
s
Sources
Outside air temperature can be obtained from the aviation meteorologicalMeteorology
Meteorology is the interdisciplinary scientific study of the atmosphere. Studies in the field stretch back millennia, though significant progress in meteorology did not occur until the 18th century. The 19th century saw breakthroughs occur after observing networks developed across several countries...
services, on the ATIS
Automatic Terminal Information Service
Automatic Terminal Information Service, or ATIS, is a continuous broadcast of recorded noncontrol information in busier terminal areas. ATIS broadcasts contain essential information, such as weather information, which runways are active, available approaches, and any other information required by...
or measured by a probe
Probe
- Science and technology :* Medical equipment** Anal probe** Endoscope** Proctoscope* Atom probe, an atomic-resolution microscope* Hybridization probe or chemical probe, used in molecular biology...
on the aircraft. When measured by the airplane's probe in flight, it may have to be corrected for adiabatic (ram effect) rise and friction
Friction
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and/or material elements sliding against each other. There are several types of friction:...
, particularly in high performance aircraft.
See also
- Acronyms and abbreviations in avionicsAcronyms and abbreviations in avionics-A:*ACARS: Aircraft Communications Addressing and Reporting System.*ACAS: Airborne Collision Avoidance System.*ACP: Audio Control Panel.*ACS: Audio Control System.*ADAHRS: Air Data and Attitude Heading Reference System.*ADC: Air Data Computer....
- Density altitudeDensity altitudeDensity altitude is the altitude in the International Standard Atmosphere at which the air density would be equal to the actual air density at the place of observation, or, in other words, the height when measured in terms of the density of the air rather than the distance from the ground...
- Hot and highHot and highIn aviation, hot and high is a condition of low air density due to high ambient temperature and high airport elevation. Air density decreases with increasing temperature and altitude. Lower air density reduces the amount of lift generated by the wings or the rotors of an aircraft, which may hamper...
- Total air temperatureTotal air temperatureTotal air temperature is a term used generally in aviation. In other applications it is called stagnation temperature. Total air temperature is measured by a specially designed temperature probe mounted on the surface of the aircraft. The probe is designed to bring the air to rest relative to the...