Atmosphere and Sound - Speed

8 important questions on Atmosphere and Sound - Speed

IAS CAS EAS TAS

CAS(IAS) = 1/2 R x V2

-IAS measure of dynamic pressure calibrated to ISA at MSl

-CAS is IAS corrected for instrument and pressure errors (also know as position or configuration error)

-EAS is CAS corrected for compressibility errors

-TAs is the actual speed of an aircraft through the air mass it is flying. TAS depends on air density. The higher the density, the greater the resistance to the motion, the lower the TAS. At a constant IAS, the TAS will increase with increasing altitude or temp beacuse of the reduction in air density.

Why use M at high altitudes

At around 26000ft the MN becomes the aircrafts limiting speed in preference to IAS. Up till FL260 an aircraft will climb at a constant IAS against an increasing MN. Then above FL260 the aicraft is flown at a constant MN with a decreasing IAS for an increase in altitude.


What happens to the MN in LRC as weight decreases

MN Decreases
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CAS/IAS if you descend at a constant TAS

CAS (IAS) will increase
-pressure increase with decrease in alt. Density increase with decrease in altitude; means that the CAS increases in a descent at a constant TAS

TAS if you climb at constant CAS/IAS

TAS will increase. Air density decreases with alt

MN if you climb at constant CAS(IAS)

MN will increase
TAS increase
LSS decrease

MN is a function of TAS/LSS

CAS/IAS/TAS if you fly constat IAS/CAS into warmer area.

IAS/CAS the same becasue unaffected by temperature
TAS will increase because of the lower air density (warmer)

2 a/c flying at different FL at the same MN, which a/c has the higher TAS/CAS(IAS)

Lower one, because the higher a/c will have to have a lower TAS to have the same MN.

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