Avionics News July 2013 - 73

“These new products are designed by our dedicated
experimental engineering team, many of whom are pilots and
homebuilders, and they have created the kind of smart, costfriendly avionics that they want to have in their own aircraft.”
CARL WOLF, Garmin vice president of aviation sales and marketing

oped the G300 system, which developed into the G3X.
ing reference, and amplifies them to a level powerful enough
Garmin’s new G3X includes a sophisticated autopilot with
to drive a servo motor. The speed at which the servo motor
the ability to fly coupled approaches and coupled VNAV.
turns is critical to flight safety. This safety concern requires
The system includes flight-director cues and automatic trim.
traditional autopilots for normal or utility category aircraft to be
Builders may opt for the dedicated GMC 305 autopilot control
type specific and installed under a supplemental type certificate.
panel, which gives the pilot a dedicated interface to the autofliA particular make and model of autopilot might have several
ght system and additional functionality.
different servos or several different computer amplifiers – each
According to Garmin, the G3X uses GSA 28, “smart” autowith a different gain setting for a particular aircraft type. A servo
pilot servos, which are
designed for one type of
a new and lightweight
aircraft might cause a
design developed for the
catastrophic oscillation,
experimental market.
if it were installed in
Each GSA 28 weighs
another aircraft.
only 1.4 pounds, which
Garmin’s system,
makes them more than
including the “smart”
40 percent lighter than
servo, can change its
most
experimental
characteristics based
autopilot servos. Within
on software. In fact, the
The optional GMC 305 dedicated autopilot controller adds
each device, a gear train
G3X system does not
more features to the system.
with engagement clutch
require a line replaceand ability to back drive
able autopilot computer
the brushless DC motor provide multiple levels of protection
or amplifier. Each servo contains its own microprocessor. This
without the need to use a shear pin. Brushless motor technology
processing power allows the servos to connect directly to the
provides a higher level of reliability and longevity when comADAHRS unit and several other parts of the system via a data
pared to motors using brushes. Furthermore, the engagement
bus. Software allows Garmin to significantly reduce aircraft
clutch decouples the motor from the flight controls, minimizing
specific settings (gains). Although type specific customization
the friction the pilot will feel when the autopilot is off. Each
is still necessary at times, it has been able to fly very different
servo provides a built-in interface to drive a customer-supplied
aircraft well with a base set of autopilot gains. Servo software
trim servo. When the autopilot is off, the servo provides speed
updates are completed using the G3X SD card, eliminating the
scheduling for the manual trim commands. When the autopilot is
need to send the servo back to the manufacturer for updates.
on, the servo automatically trims the aircraft to constantly keep
Many builders may want to include the optional GMC 305
it in trim.
autopilot control panel. With the GMC 305, pilots will gain
One factor that adds to the cost of autopilots for aircraft
additional autopilot functionality, including airspeed hold, indecertified outside the experimental and light sport markets is
pendent flight director and an optional yaw damper, according to
type specificity. In the simplest sense, an autopilot is merely an
Continued on page 81
amplifier, which takes error signals from an attitude or rate sensavionics news

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Avionics News July 2013

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