Convert between Calibrated Airspeed (CAS), Equivalent Airspeed (EAS), True Airspeed (TAS) and Mach number (M) using the tool below. You need to specify the altitude at which you would like to perform the calculation every bit well as any one of the 4 airspeeds.

Distance choice is mandatory.

Select a temperature offset only if information technology differs from a Standard Atmosphere.

Altitude:

Temperature Showtime:

°C or K
Atmospheric Temp:

Select and input one speed below to calculate the remaining.

Calibrated Airspeed:

Equivalent Airspeed:

True Airspeed:

Mach Number:

Use the sliders to select an input speed and whether to employ a temperature deviation offset from the standard atmospheric value. The model is based on the United states of america Standard Temper of 1976.

Calculation Methodology

Indicated Airspeed

Indicated airspeed is the airspeed reading that the pilots sees on her airspeed indicator (ASI) and is driven by the pitot-static organization on board the aircraft. The system uses the departure between the total pressure level (measured past the pitot probe) and the static pressure (measured by the static ports) to determine the dynamic force per unit area which is converted to an airspeed reading.

The pitot-static system works on the principle of Bernoulli's equation which states that an increase in the speed of a fluid must simultaneously result in a driblet in the fluid's pressure, or a decrease in the fluid's potential energy.

bernoulli-equation

The total pressure (besides known equally the stagnation pressure or pitot pressure) is measured by the pitot probe. The moving air enters the probe and is brought to balance by the geometry of the probe.

The measured static pressure is the ambient pressure of the still air which is the barometric pressure level of the air at the aircraft's electric current distance. The static pressure is not only used to calculate the airspeed but also the distance (altimeter) and the vertical speed (VSI) during flight. The static ports are always installed affluent which ensures that the port opening is inside the boundary layer where the air is not moving.

The airspeed is therefore calculated as follows:
IAS_calculation

The density term in the denominator is not a constant and varies with distance and temperature. Yet, the airspeed indicator in the cockpit is ever calibrated to sea level density on a standard day. Thus the actual airspeed (truthful airspeed) will vary considerably from the indicated airspeed as the aircraft flies at higher altitudes and differing temperatures.

The big advantage of using IAS in the cockpit is that the aircraft will always stall at the aforementioned indicated airspeed (for a given aircraft configuration) regardless of the altitude or ambience temperature. This makes it much easier for a pilot to wing the aircraft as the critical speeds that ascertain the operating envelope remain the same regardless of the ambience atmospheric condition.

Calibrated Airspeed

Calibrated airspeed is the indicated airspeed corrected for instrument and position fault. This error is a function of both the quality of the pitot-static system used to calculate the dynamic pressure too as the location of the probe on the aircraft.

Positional errors outcome from the fact that the local velocity effectually an aircraft varies as a issue of the aircraft's changing geometry. For example, the local velocity over the upper surface of the fly is higher than below the wing in lodge for lift to be produced. In reality at that place exists velocity gradients all over the shipping, especially in regions where there is substantial curvature (forward part of the fuselage, windshield, wing surface).

Depending on the location of the pitot-static organization, the measured dynamic pressure measured may differ from the actual dynamic pressure due to local induced velocity furnishings. The offset between indicated and calibrated airspeed is usually published in the aircraft operating manual in the form of a tabular array. Here is an example of the calibration performed for a 2-seat light aircraft.

Calibration performed between Indicated Airspeed (IAS) and Calibrated Airspeed (CAS) for a two-seat shipping.

Equivalent Airspeed

Equivalent airspeed is the calibrated airspeed corrected for compressibility effects. It is likewise defined as the speed at sea level, under ISA conditions, that would produce the same incompressible dynamic pressure level that is produced at the true airspeed for the given aircraft distance. It is this definition that makes EAS a useful airspeed measurement for aeronautical engineers as it provides a convenient mode to summate loading on the airframe, or handling qualities as the dynamic pressure provided is an equivalent bounding main level pressure without the demand to correct for altitude or temperature.

Indicated and Calibrated airspeed is based on the formulation of Bernoulli's equation, which assumes that the fluid (air in this case) is incompressible. Bernoulli's experiments were performed in h2o where this assumption is valid, but compressibility effects in air start to become significant at Mach numbers above 0.3. Difference between CAS and EAS will be seen at speeds above 200 kts and altitudes above x 000 ft. CAS must therefore be corrected for compressibility effects to make up one's mind EAS equally an intermediate step to calculate the True Airspeed (TAS). Compressibility effects tin be deemed for through the calculation of the impact force per unit area, which is a function of the Mach number.

CAS_EAS_eqn

Truthful Airspeed

The truthful airspeed is the speed that the aircraft travels relative to the air mass in which information technology is flying. The truthful airspeed is equal to the footing speed in cases where there is no wind, and is used by and large for flight planning and when quoting shipping performance specifications. True airspeed can exist calculated from either the equivalent airspeed, or the Mach number if the outside air temperature (OAT) is known.

TAS_eqns

Mach Number

The Mach number is the ratio of the Truthful Airspeed to the sonic speed. The speed of sound in undisturbed air is a function only of temperature and not altitude every bit is often mistakenly assumed. Of course the ambience temperature will decrease as altitude is increased, leading to the reduction in the speed of sound as with increasing distance.

mach_eqn