On 20 Jun 2006 07:27:56 -0700, "Eunometic"
wrote:


Ed Rasimus wrote:
On 19 Jun 2006 07:50:02 -0700, "Don McIntyre" wrote:

While reading through Hans-Heiri Stapfer's "Walk Around MiG-21 Fishbed
Part 1" (Squadron-Signal), he makes mention of a temperature probe
mounted low on the nose on an MiG-21F-13. Why would a radar rangefinder
need to know the OAT?

Dunno about MiGs, but every high performance tactical aircraft I ever
dealt with had an OAT input to the Central Air Data Computer (or
whatever it was called on a particular system.) Air temp is a
component of density and that is a factor that impacts range of a
weapon.


AFAIK temperature determins the speed of sound all on its own. Air
density seems to have nothing to do with it unless you get to near
space. Air density of course would determin dymanic pressure.

Technically the speed of sound is the square root of the ratio of air
pressure over air density all multiplied by a constant known as adiatic
exponent of air. However as the ratio of pressure to density is a
constant at a specific temperature temperature is all that is needed.

Best look at it here
http://www.sengpielaudio.com/SpeedOfSoundPressure.pdf

You are correct, but irrelevant to the discussion of the relationship
between OAT and radar ranging. Mach is temperature dependent and since
the atmosphere gets colder as you rise, the speed of sound will
change.

But, while high performance aircraft do have mach indicators, they
operate on the basis of airspeed--which leads to an entirely more
complex discussion as we start to grapple with indicated, calibrated,
equivalent and true airspeeds as well as ground speed along with the
trigonometric impact of dive/climb angle relating to bombing.

Highly recommend you don't fly landing approach on mach.

Ed Rasimus
Fighter Pilot (USAF-Ret)
"When Thunder Rolled"
www.thunderchief.org
www.thundertales.blogspot.com