ASA Electronics cx-3 - AIRSPEED

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Solution: Press the key. Select the Airspeed
submenu and tap enter. Scroll to CAS, input and
tap enter for the planned CAS. Scroll to enter the
OAT:
and tap enter. Scroll to enter the PAlt:
and tap enter to enter 8,500 feet
PAlt.
The display will show 141.03 KTS TAS, 28°F TAT,
and 0.221 MACH.
Actual TAS
The Airspeed function can compute true airspeed
using information from instruments during an actual
ight. The inputs to this function are CAS, TAT, and
PAlt. The Airspeed function calculates TAS, OAT
(which can be used as an input to Plan TAS and Req
CAS functions), and Mach Number (MACH).
Problem: Compute the TAS at 6,500 feet PAlt,
+10°C TAT, at a CAS of 150 MPH.
Solution: Press the key. Select the Airspeed
submenu. Convert from knots to miles per hour by
scrolling down to CAS and by pressing , (you
will also need to convert TAT from °F to °C) then
press:
and tap enter to input 150 MPH, then
and tap enter to input 10°C TAT, then
and tap enter again to enter
6,500 feet PAlt.
The display will show 166.64 MPH TAS, 7°C OAT,
and 0.222 MACH.
Required CAS
The Airspeed function can compute the calibrated
airspeed required to achieve a given true airspeed
with the inputs TAS, OAT, and PAlt. The Airspeed
function calculates CAS, TAT, and MACH.
Problem: What is the required CAS or MACH to
obtain 150 knots TAS with 41°F OAT and 6,500
feet PAlt?
Solution:
Press the key. Select the Airspeed
submenu. Press:
and tap enter to input 150 knots
TAS, then
and tap enter to input 41°F OAT, and then
and tap enter to input 6,500 feet
PAlt.
The display will show 135.58 KTS CAS, 46°F TAT,
and 0.231 MACH.
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◗ STANDARD ATMOSPHERE
Since air pressure and air density are specied by
an altitude in a standard atmosphere, you may want
to nd the standard atmosphere for a given altitude.
The International Civil Aviation Organization (ICAO)
has established standard conditions for temperature
and pressure. You can enter an altitude (Alt) in
the StdAtmos function and obtain the outside air
temperature (OAT); pressure in inches of mercury (IN
Hg); and pressure in millibars (mb) for the standard
atmosphere. The StdAtmos function is valid up to
278,385 feet.
Problem: What are the standard atmospheric
conditions at sea level?
Solution:
Press the key. Scroll to Standard
Atmosphere and tap enter. You are prompted for
the altitude. Press:
and tap enter to enter 0 feet, or sea level.
The display will show 29.92 IN HG, 59°F OAT.
Problem: What are the standard atmospheric
conditions at 20,000 feet?
Solution: Select the Standard Atmosphere
function. You are prompted for the altitude. Press:
and tap enter to input
20,000 feet.
The display will show 13.75 IN HG, -12°F OAT.
◗ AIRSPEED
Planned and Actual True Airspeed (TAS) and Mach
number can be calculated and are dependent on
the temperature input. Planned airspeeds require the
use of outside air temperature (OAT), obtainable from
the preight weather brieng or from what you read
on a thermometer on the ground. Actual airspeeds
require the use of total air temperature (TAT), which is
obtained by a probe having velocity with respect to the
air (essentially, the thermometer in your aircraft). TAT is
warmer than OAT, because of kinetic heating due to
compression on the upstream side of the probe.
Planned TAS
The Airspeed function can compute the true airspeed
(TAS) for a planned calibrated airspeed (CAS) with the
inputs Planned CAS, OAT, and PAlt. It is important to
use the OAT and PAlt at the planned ight altitude.
OAT may be obtained from winds aloft forecasts.
OAT can also be determined from the TAT during
ight. PAlt is normally obtained from the Altitude
function. The Airspeed function calculates TAS, TAT
(which can be used as a cross-check with the in-
ight TAT), and Mach Number (MACH).
Problem: You plan to y 125 knots CAS, 8,500
feet PAlt, and 23°F OAT. Compute TAS and TAT.
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