Scribd
Upload
224 views21 pages

Airspeed Measurement

The document discusses how an airspeed indicator determines indicated airspeed (IAS) through four main steps: 1. It measures the total pressure at the pitot tube, which is the stagnation pressure. 2. It measures the static pressure. 3. It calculates the dynamic pressure by subtracting the static pressure from the total pressure using Bernoulli's equation. 4. It calculates the IAS in knots by using the dynamic pressure in an equation that relates it to airspeed. The document also introduces concepts like calibrated airspeed (CAS) which corrects IAS for position and instrument errors, and true airspeed (TAS) which accounts for environmental factors like temperature.

Uploaded by

ykhamidi3889
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
224 views21 pages

Airspeed Measurement

The document discusses how an airspeed indicator determines indicated airspeed (IAS) through four main steps: 1. It measures the total pressure at the pitot tube, which is the stagnation pressure. 2. It measures the static pressure. 3. It calculates the dynamic pressure by subtracting the static pressure from the total pressure using Bernoulli's equation. 4. It calculates the IAS in knots by using the dynamic pressure in an equation that relates it to airspeed. The document also introduces concepts like calibrated airspeed (CAS) which corrects IAS for position and instrument errors, and true airspeed (TAS) which accounts for environmental factors like temperature.

Uploaded by

ykhamidi3889
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
You are on page 1/ 21

Airspeed Measurement p1

Overview
!! We are simply attempting to understand how an
airspeed indicator determines INDICATED airspeed

!! Need an understanding of Bernoullis principles of


pressure

!! We will look at the different types of airspeed and


the equations related to it.

Indicated is what you see. Note for cross country planning you calculate other types of airspeed first.

Measuring airspeed
!! In the air, given indicated airspeed IAS, how then do
we determine CAS, EAS, and TAS?

!! On the ground, given true air speed TAS, how then


do we determine EAS, CAS, and IAS?

Ice-T mnemonic

How airspeed indicator determines INDICATED Airspeed


!! IAS knots on airspeed indicator !! 1. Measure total pressure H. !! 2. Measure static pressure Ps. !! 3. Calculate dynamic pressure q from Bernoullis
equation q = H - Ps.

!! 4. Calculate KIAS from dynamic pressure,


!! V KIAS = !(295)q = 17.18 !q

!! *Note that the airspeed indicator does not measure


dynamic pressure!

1. Measure total pressure: Airflow on a Symmetrical Object

Free stream total pressure H = Ps + q. At the stagnation point, all kinetic energy or dynamic pressure q is converted to Ps. v=0

Definitions
!! Pressure at the forward stagnation point:
= H or head pressure = stagnation pressure = total pressure = ram pressure = Pitot pressure

!! The pressure at the stagnation point (total !! pressure) will be greater than the ambient static pressure by !! the amount of the dynamic pressure of the air stream

10

2. Measuring Static Pressure (p or Ps)

11

Calculating q=H-p

12

3. Calculate dynamic pressure q from Bernoulli


!! H = Ps + q !! q = H - Ps Airspeed indicators "subtract" Ps from H
to determine q.

13

4. Calculate KIAS from dynamic pressure

14

Converting H to KIAS

15

Now looking at CALIBRATED correction

16

Remember the ICE-T mnemonic

17

"Vi + "Vm
CAS is IAS corrected for installation (position) and instrument (mechanical) errors. CAS=IAS+Vi +Vm Possible errors in our IAS methodology:

!! Installation or position or error Vi. The

installation or position of the pitot tube and/or static port may induce errors.

18

Fuselage factor

19

!! Installation or position or error correction is


provided by manufacturer in the POH. and configuration.

!! Ps measured (and Vi) changes with aircraft speed

20

Mechanical Error:
!! Mechanical errors in the instrument. Airspeed
indicators must be checked and calibrated every 24 months. Usually considered to be zero.

21

You might also like