Transonic Zone?

[Terry Perkins]

I have a question. I know the speed of sound is about 1123fps at sea level and 15 degrees C. When does the transonic zone start?

Terry P

 

[Terry Perkins]

Never mind, I found it.

 

[maynard]

Do tell. Inquiring minds want to know.

 

[Terry Perkins]

Since you asked...1.2 Mach and 0.75 Mach. About 1347fps and 842fps.

 

[WithoutWarning]

I like these interesting tidbit's,
so does anyone know what the speed
of sound is at say, 4500 ft, or a way
of calculating that ?
What kind of an effect does air density
have on sound velocity. .

 

[nairbg]

c = (k p / ρ)1/2
= (k R T)1/2 (3)
where
k = ratio of specific heats (adiabatic index)
p = pressure (Pa, psi)
R = gas constant
T = absolute temperature (oK, oR)
​

For an ideal gas the speed of sound is proportional to the square root of the absolute temperature.
Example - Speed of Sound in Air

The speed of sound in air at 0 oC and absolute pressure 1 bar can be calculated as

c = (1.4 287 273)1/2 = 331.2 (m/s)
where
k = 1.4
and
R = 287 (J/K kg)
​

 

[Terry Perkins]

I like these interesting tidbit's,
so does anyone know what the speed
of sound is at say, 4500 ft, or a way
of calculating that ?
What kind of an effect does air density
have on sound velocity. .

From what I have read recently...speed of sound is minimally affected by air density changes. It is most affected by temperature. Approximately 2 feet per second per degree of Centigrade.

 

[mbessey]

you will find that air density is greatly affected by temp, so wouldnt that mean it is affected by density?

maybe its altitude that its not affected as much by as it is temp?

I say this from flying experience.