Avionics News July 2021 - 40

AUTOPILOTS FOR HELICOPTERS
Continued from page 39
As Doyle explained, Garmin (or any other manufacturer)
starts by putting together a detailed flight test plan to show
that the system can do what they say it will do in any given
situation. These plans typically consist of three areas: basic
operations/maneuvers, various malfunctions, and pilot
interface demonstrations.
" In terms of these three areas, they're very similar to the
same things we demonstrate for a fixed-wing autopilot, "
he said. " There does tend to be more time spent on
the malfunction aspects of the helicopter unit, though.
And of course, we have to do them all in two types of
demonstrations - slow speed and hovering, which is its own
thing. And again, for forward, cruise flight. "
While the basic operations and pilot interface
demonstrations are all routine, will it hold a hover or track
a course, and are the buttons easy to understand and work?
The real fun - at least from a test pilot's perspective - is in
demonstrating how the autopilot responds to a variety of
malfunction situations.
" It starts with how the pilot will recognize that something
has gone wrong with the autopilot and then what the
response is to that malfunction, " Doyle said. " The FAA has
tighter parameters for the autopilot, and the reason for that is
the helicopter is unstable. So once the autopilot has stopped
flying, the pilot has a problem that they need to respond to
quickly.
" The helicopter autopilot does have a design that is
appropriate to what it's trying to do. The system has more
monitors that are set at tighter values than the typical
airplane's autopilot. So you need smaller deviation limits
when you have any malfunction, and the equipment is
designed to mitigate those issues. "
That means both the level of testing and approvals for
both the hardware and software are to tighter tolerances than
those of the typical fixed-wing system. As you may guess,
these are also significant factors in the final certification and
development costs of helicopter SAS/autopilot systems.
A big part of a typical FAA autopilot certification program
has to do with how the system and pilots recognize and
deal with a variety of malfunctions in an array of CG
configurations.
" For all of the malfunction demonstrations, what we
have to do is reach a point where the pilot would recognize
that the autopilot has malfunctioned and then wait a
set amount of time before we can provide control input
to recover, " Doyle said. " When we're in cruise flight,
we have to wait three seconds after the time the pilot
would have recognized a problem - it can be a long three
seconds. In hover situations, we have to wait one second. "
40 avionics news * july 2021
Doyle explained in the case of Garmin's GFC
600H autopilot, not all of the exciting flights involved
malfunctions. The new-generation GFC 600H is the
first autopilot to offer Garmin's automatic Level Mode
capability.
" What we do for the FAA demonstration is set the
autopilot's engagement limits, " Doyle said. " Those are set
to each individual helicopter. For example, on a helicopter
with a teetering rotor like a Bell, the autopilot engagement
limits are 30 degrees, nose up and nose down. On a nearrigid
rotor like an Airbus AS350, it may be 40 degrees up or
down. The roll limit is 70 degrees on all helicopter types.
" Then, as part of the flight test, we put the helicopter
in that maximum engagement situation and engage the
autopilot and let the system recover back to level flight.
We also do a rolling pitch-up where we start at low speed
and then accelerate and pitch the helicopter up into a roll
attitude. We engage the system and sit back and wait for it
to recover. It's some kind of ride. "
Doyle said that once Garmin has completed all of its
flight tests, which includes " hundreds of hours of flight
time, " it takes another 30 hours of flight time to complete
all the required FAA certification demonstration flights.
Do 'real' helicopter pilots want autopilots?
It's an odd question, but one you have to ask. Perhaps
many old-school helicopter pilots look at SAS/autopilot
systems the same way too many airplane pilots look at
airframe parachutes: " I don't need/want one of those. "
" I'd say since it's generally due to the fact that most pilots
haven't experienced just how important these systems can be
in a variety of situations, " McDougall said. " There are just
a lot of helicopter pilots who aren't familiar with what an
autopilot gives them. They don't train with autopilots in the
aircraft, so they've never been in a situation where they can
get a level of experience with the technology. "
" The majority of smaller helicopters are owner-flown,
and they just don't fly them on cross-country trips, " Bennett
stated. " They may see HeliSAS or another system as too
much or too expensive for their needs. But they've never
needed it. "
From his experience, Bennett added that's not typically
the case with professional helicopter pilots - or at least,
with newer-generation pilots.
" We've seen a lot of acceptance in the helicopter EMS
market for our HeliSAS system, " Bennett said. " They identify
this as a very valuable tool not only to reduce pilot workload,
but they typically fly for many hours a day and are doing a
variety of tasks. They want a system that provides aircraft
stability and helps alleviate some of their workload and stress.
That's what a helicopter stability augmentation system or
autopilot delivers. " q
Avionics News July 2021

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