Avionics News September 2022 - 47

THIS SYSTEM IS STANDARD EQUIPMENT ON
AIRLINERS, MOST BUSINESS JETS,
AND SOME TURBOPROPS,
BUT WHY NOT PISTON PLANES?
STORY
dvances in avionics technology traditionally trickles
down to general aviation from commercial/military
aviation and then corporate operators who have the
resources and operational opportunities to get a return on the
investment through improved efficiency and safety. Such has
been the path of communication, navigation, and surveillance
radios and the primary, multifunction, and auxiliary displays that
connect pilots to these systems.
A
And then there is the outlier in trickle-down
technology: autothrottle, also known as
autothrust.
Autothrottle reduces pilot workload
and increases efficiency and
safety by setting, within engine
limitations, power to provide
optimum performance for
the current phase of flight. In
rudimentary form, autothrottle first
flew in the later days of World War
II in the Messerschmitt Me 262 jet
fighter. In the 1950s, Safe Flight
introduced AutoPower on the DC-3
and Beech 18, the ubiquitous airline
and business aircraft of the day, before
continuing its pioneering efforts
with turbines. Today, autothrottle is
standard equipment on airliners, most
business jets, and some turboprops,
but why not piston planes?
Bill Stone, Garmin's senior manager
of business development, answers this
question with another: " When you think
BY SCOTT M. SPANGLER
of technology, first and foremost, what problem are you
trying to solve? "
Generally speaking, turbine-powered aircraft " have an
excess of performance, " meaning pilots have to throttle back to
maintain specific speeds. How do we fly with piston engines?
" Occasionally, you'll throttle back for best economy to stretch
your range, but for the most part, you fly with wide-open
throttle, " Stone said. " You pull back to 15 inches (of manifold
pressure) for approach to landing, drop the gear and
flaps, and you're at approach speed, so what kind
of problem are we trying to solve? Turbines,
with excess performance, they have
problems to solve. " A system that adjusts
the power to maintain a specific speed
reduces pilot workload by providing the
desired power within the engines specific
temperature and torque/power limits,
which precludes expensive overstresses.
The technology interface is the next
consideration, because most piston
general aviation aircraft have engines
initially designed in the 1940s. " You
have three levers, " Stone said,
" throttle, prop, and mixture, and
they are all interactive; you have to
manage all three. "
Courtesy of IS&S
IS&S designed small, light servos and
connecting rods that fit snugly in the King
Air's lower throttle quadrant.
In a turbine-powered aircraft,
the autothrottle system works with
one control input, the power lever
that, in most aircraft, is connected
Continued on following page
AVIONICS NEWS * SEPTEMBER 2022 47
Avionics News September 2022

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