Page 58 - EAA78.Newsletter.Archives.(February.2017-July.2021)

CHAPTER CHATTER, EAA Chapter 78 5

The normalized AOA is in use on Dassault’s Falcon 7X Quiz: How Much Do You Know About
and 8X, the Airbus A380 and nearly every jet produced These WWII Aircraft?
by Embraer.

Both AOA configurations consist of a heated wing
probe that looks similar to a standard pitot tube. Both
AoA versions also require an air-data computer and a
visual cockpit indicator.

The AOA tube is constructed with two tiny machined
holes to create differential pressure sources. One hole
is bore-sighted at the front of the AOA tube along the
longitudinal axis, while the second, located at the
bottom of the AOA probe, is pointed downward at a 45-
degree angle to act as a reference source.

Garmin’s normalized AOA includes an additional static-
air-pressure source to allow the air-data computer to
calculate airspeed and air density, important in
calculating precise AOA. The addition of the static-
pressure reference input makes the AOA indication Quiz: 6 Questions To See How Much
accurate regardless of the airplane’s weight, speed or You Know About Aircraft Systems
configuration. This comes in handy particularly in steep
turns when a pilot normally adds back pressure to
maintain altitude, something that also increases the
angle of attack and the airplane’s stall speed. In order
to ensure accurate data, each AOA must be calibrated
for the specific aircraft in which it is installed.

On a normalized AOA, air pressure passes from the
probe through flexible tubes in the wing until it reaches
three pressure sensors co-located with the air-data
computer’s microprocessor. It is here the translation
occurs to create the electronic signals sent to the
cockpit indicator.

The AOA indicator, in our example measuring
approximately 3.2 inches high by 1.4 inches wide, is
often mounted on the top of the glareshield, where it
can be easily seen through the pilot’s peripheral vision
during most flight conditions.

In cruise, the AOA is dark. As the angle of attack
increases, the AOA indicator (shown on the opposite
page)first illuminates the green bar near the display’s
bottom. As the angle of attack increases, additional
green bars light up until the green dot — called the
donut — illuminates, indicating the proper final
approach path angle. If the angle of attack continues to
increase, the green bars will turn yellow as a caution
and, finally, red as the wing approaches a stall.

One hurdle to widespread AOA implementation is the need for
CFI’s to understand and teach a useful tool most have never
actually used themselves.