Scared of mid-airs

On Thu, 3 Aug 2006 06:54:23 -0600, "Jeff Crowell"
wrote:

As for KCAS versus KIAS in displays, I have no time in
F-16s, so I can't answer that categorically. But since
KCAS corrects for system error, it is more accurate than
KIAS, so why not? It would not surprise me if what's
displayed on the HUD, for example, and therefore
recorded by the tapes, is KCAS, since data displayed
there has been massaged by the aircraft's air data
computer (or some analogous system)...

Just a refresher for those who have been out of pilot training for a
long time:

ICE-T is the mnemonic for remembering the calculations involving going
from airspeed on the pitot-static gauge (Where's Tarver these days?)
to real, honest-to-God speed through the air.

Indicated airspeed is the uncorrected number of the pitot instrument.

Calibrated AS is corrected for "position error"--in the early days
pitot tubes often were placed conveniently for designers but that
resulted in either boundary layer distortions or plumbing errors along
the tubing to the diaphragm of the gauge. Modern aircraft (since the
'50s) minimize this error and for all practical considerations
Indicated is equal to Calibrated. As Jeff states, data processing
through the air data computer makes this computation.

Equivalent airspeed correct calibrated for "compressibility
error"--the fact that air is an elastic substance and at transonic
speeds creates molecule buildup at the pitot tube that distorts the
reading of the gauge. Typically Equivalent will be slightly lower than
Calibrated. At trans-sonic speeds the error spikes in a narrow regime
but then returns to small error less than Calibrated.

True airspeed is Equivalent airspeed corrected for air density.
Temperature and pressure reduce air density meaning fewer molecules
per cubic unit of atmosphere to register on the pneumatic instrument.
So, an indication is always lower than actual speed through the air.
Rule of thumb for standard day is 2% per thousand feet of altitude.
So, true airspeed is always higher than indicated and at high
altitudes is considerably higher.

This technical data should leave Larry calculating and seeking
further charts and documentation for weeks. When he returns I am sure
the speed of convergence will not be translated into TAS so that the
differentials are the maximum.


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