Avionics News February 2015 - 30

certify at the end of 2015 or early 2016. With the system's
building block design, changing platforms was a matter of
removing the SCAS circuit board and replacing it with one for
elevator and auto trim. The pitch and trim servos are, naturally,
activated, Force Trim uses the parallel servos to hold the
platform specific, but all of them "are fail passive, as is the rest
cyclic in place. A force gradient system provides a "force feel"
of the autopilot," said Irwin, "which is a very high certification
as the pilot moves the control away from its position. When
standard."
the autopilot is engaged, the force feel system automatically
With the goal of designing, building and certifying
disconnects it when the pilot's control inputs override it.
helicopter autopilots and flight control systems, Irwin and
"Force Trim is a freebie with our autopilot systems,"
a small group founded Cool City Avionics at the turn of the
Irwin said. "But it is a good, low-cost stand-alone system for
century to meet the needs of a long underserved market for
helicopters that don't have autopilots because it gives pilots
low-cost helicopter-qualified autopilots. The name comes from
a short-term free hand to tune a radio, or look at a chart or
the small town outside of Mineral Wells, Texas, where Cool
checklist." In conjunction with SAS, the combination provides
City still has a fabrication facility and shop. Irwin moved to
a level of stabilization as well as cyclic holding.
the area when he started work with Mitchell in the late 1960s.
In flight, the stability and control augmentation system's
Falling in love with autopilots, he
contribution is relatively invisible to
developed a system for helicopters, and
the pilot. Sensitive and simple rate
"I had a chance to demonstrate it for
gyro sources drive the SAS's series
WITH THE GOAL OF
two high-ranking Bell (helicopter) guys,
actuators. They detect and attenuate
DESIGNING, BUILDING AND
including Bart Kelly, vice president of
aircraft motions not commanded by the
CERTIFYING HELICOPTER
engineering, and Joe Mashman," Irwin
pilot with proportional control inputs
AUTOPILOTS AND FLIGHT
remembered. "They liked the idea and
in the opposite direction, often before
CONTROL SYSTEMS, IRWIN
asked if we could package it and demo it
the turbulent bumps fully develop. The
AND A SMALL GROUP
again." Unmoved by Bell's interest "in
actuators operate 10-times faster than
FOUNDED COOL CITY AVIONICS
this thing that we'd cobbled together out
the servos, but they have limited travel.
AT THE TURN OF THE CENTURY
of two $900 autopilots," his boss said
"They can only take out the
TO MEET THE NEEDS OF A
"the world was not ready for a helicopter
perturbation requiring less than 10
LONG UNDERSERVED MARKET
autopilot."
FOR LOW-COST HELICOPTERpercent control authority," Irwin said.
Leaving Mitchell after more than 12
When activated, the autopilot
QUALIFIED AUTOPILOTS.
years, Irwin and his partners founded
detects and responds to the
S-TEC in 1978. Irwin resumed his
perturbation along with the SAS.
helicopter experiments in 1981 and was in a position to act on
Uniquely, one STC covers the six variations of Cool City
them, which led to the S-TEC helicopter project he began in
Avionics autopilots and flight control systems and all of their
1996. Part of the S-TEC sale in 2000, "the new owners didn't
subsystems. Cool City Avionics also holds STCs for the SAS
understand the helicopter market and put the helicopter project
and Force Trim systems.
on the shelf."
"We're flying the four-axis system now," said Irwin, who
Waiting until 2004, when he saw that the company wasn't
was a flight DER for more than three decades before retiring
going to do anything with it, Irwin decided to try again. He
to the office.
built a team of former S-TEC engineering and certification
It adds control of the collective to the three-axis system, and
folks and created a digital architecture that accommodates
he expects certification by the end of 2015. Makes and models
both helicopters and fixed-wing aircraft. The project started
so far covered are the Robinson R44 Raven, with the R66
with three people, and the company now employs 25.
Turbine and Airbus Helicopters AS350 in process at this time.
From the start in the 1970s, Irwin has clearly seen and been
"We just installed a three-axis system in an experimental
convinced about the rotary-wing market and its opportunities.
UH-1H," Irwin continued. "I haven't flown one since 1967. It
Optimism accounts for part of this, he said, but he's "spent a
was fun and exciting to have a Huey around."
lot of hours at the controls of a helicopter and knew what a
Cool City Avionics also is flying a fixed-wing version of
benefit an autopilot would bring to their operation." q
the autopilot in a Beech Baron, which the company plans to
COOL CITY OBSESSION
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Avionics News February 2015

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