Most pilots are introduced to the concept of angle of attack during
their initial flight training. However, as most GA aircraft do not provide
a way to directly measure this critical flight parameter, angle of attack
usually becomes an academic notion which is not thought about while flying.
Dynon Avionics was the first EFIS manufacturer to realize the importance
of angle of attack and offer an affordable, accurate, and useful way
to monitor it.
What is Angle of Attack, why is it important, and who uses it?
Angle
of attack is quite simply the angle between the wing chord and the oncoming
air that the wing is flying through. This is an important concept, as
aircraft wings stall when angle of attack gets too large, at a value
known as the “critical” angle of attack. As pilots
are taught in flight training, an aircraft can stall at ANY speed if
this critical angle of attack is exceeded. Hence, a great way to avoid
stalls is to not let the angle of attack reach critical, and the best
way to avoid critical angle of attack is to know what your angle of attack
is in the first place.
Dynon Avionics' AOA/Pitot Probe
Dynon Avionics was the first manufacturer
of affordable EFIS products to offer a way to measure angle of attack.
Through extensive wind tunnel testing, Dynon is able to offer an angle
of attack (AOA) pitot probe that measures both angle of attack and airspeed
when connected to any of our EFIS-based products.
|
Normal
Flight |
| |
|
Critical Angle
of Attack |
Principle of Operation
The concept behind Dynon's design is illustrated in the diagrams at
right. The Dynon Avionics AOA/Pitot probe performs two functions: airspeed
sensing and angle of attack sensing. These functions require having two
pressure ports on the tip of the probe. The normal pitot pressure port
is on the front face of the probe and is designed to be insensitive to
angle of attack. The second pressure port is located on an angled surface
just under the pitot port and is designed to be very sensitive to AOA.
The pressure from each port is delivered via separate air lines to the
instrument where they are compared to previously calibrated scenarios
specific to that aircraft.
Easy Installation and Calibration
Unlike other angle of attack instruments available to homebuilders,
the Dynon AOA/Pitot probe does not require you to drill special ports
in wing skins. It also does not have any moving parts such as vanes.
It is simply an AN5812-style pitot tube with an additional pressure port
to measure AOA. Simply use it as a normal pitot tube. The only difference
is a second plumbing line which runs back to the instrument for AOA calculation.
Once installed, the AOA/Pitot is calibrated to the individual aircraft
by running it through a series of pitch oscillations and stalls in various
flight configurations. All calibration procedures are performed via button
pushes on the instrument face.
Presentation
Angle of attack is indicated on the EFIS display as a vertical color-coded
tape with green, yellow and red areas. Once calibrated, critical angle
of attack will be indicated with the pointer positioned in the red area
of the tape.
An audio alarm can also be generated as AOA becomes critical. It can
be set as either a steady tone that sounds very near the critical AOA,
or alternatively as a beeping tone that starts as AOA gets high and increases
in frequency until it is a solid tone very near the critical AOA.
Heated AOA Pitot
The heated pitot includes a nichrome heating element that
is regulated by a separate pitot heater controller unit supplied with the
pitot. The controller actively monitors a temperature sensor embedded within
the pitot head and regulates the power to maintain a constant temperature.
This not only conserves energy but additionally prolongs the life of
the heater. The controller also outputs a signal that can be wired to
a warning light in the cockpit to warn the pilot anytime there is a malfunction
or that the pitot is turned off. |
Instruments - Pitot Tubes and Accessories - Dynon
