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   Altimetry Help
   Equivalent Airspeed
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Using the Equivalent Airspeed Conversion Calculator

Note: If you are comparing the results with most flight computers you should uncheck this box.

Example 1:

You are flying at a pressure altitude* of 7620 ft, your temperature gauge which is corrected to show true air temperature (T), shows 4.6 oC. If your true airspeed is 220 knots, what is your equivalent airspeed?

*Note if you have calibrated altitude and the altimeter setting, you can calculate pressure altitude by using the pressure altitude calculator.

First let's list the information we have:

     1) PA = 7620 ft
     2) T = 4.6 oC
     2) TAS = 220 knots

We have three of the four variables for the calculator and therefore we have enough information to solve the problem. We will now enter the variables we have:

Begin by highlighting the field that corresponds to pressure altitude in ft.

Type in 7620.

Next, highlight the true air temperature field.

Enter the 4.6 value.

Highlight the true airspeed field.

Type in 220.

Press "Eval on the remaining field which is equivalent airspeed. Read the answer 195 knots (a).

The correlated variables section shows a few other properties that can be calculated using the data entered. In this case the calibrated airspeed (CAS) (b) was the same as the equivalent airspeed (a). This is because compressibility is not really a huge factor at this speed. Notice also that the speed of sound under these conditions is 649 knots (c). We are going to use this in the next example to show how there will be a significant difference at higher airspeeds.


Example 2:

Using the speed of sound and data from the previous example calculate the equivalent airspeed if the aircraft were traveling at the speed of sound (Mach 1) instead of 220 knots:


Begin by highlighting the field that corresponds to true airspeed in knots.

Type in 649 which is the true airspeed for the speed of sound.

We are going to leave the other information the same as in example 1. Press "Eval" on the equivalent airspeed field and read 574 knots (d) for equivalent airspeed.

Calibrated airspeed is 588 knots (e) compared to 574 knots of equivalent airspeed (d).

 
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