December 1, 1999
Buying
with Bower
by Ron Bower
What’s in a Name?
THE HELICOPTER INDUSTRY, like the military and aviation in general, can be
an alphabet soup of acronyms. These acronyms are intended to simplify
day-to-day conversations among engineers, designers and other technical people.
However, for the rest of us non-techies, they can be a word maze that leadeth only to confusion.
One reader, a fixed-wing private pilot from Oregon who’s flying a Schweizer 300C while working on his helicopter rating, has
picked up on the industry’s tendency to create new names for systems that are
virtually, if not actually, identical.
The reader asks: What is the difference between an autopilot and an AFCS or
automatic flight control system? What system does a helicopter need to do
hands-off auto hovering? What do they call such systems? Who manufactures an
automatic hovering system, and can it be installed in a Eurocopter
EC-120 or
AFCS vs. autopilots
Those are all good questions. Here are my answers:
The difference between an autopilot and an AFCS is primarily in name. AFCS
usually indicates a "system" to include the autopilot plus other
devices and interconnections such has a GPS, VOR/ILS, HSI, and maybe even some
air data devices, which measure true airspeed.
An autopilot can be stand-alone, though they rarely are. As a stand-alone,
an autopilot might hold heading, maybe altitude, and control turns. Some
airplane autopilots are so basic that they have only a function called a wing
leveler.
Autopilots are primarily for back-up and assistance, although for some
next-generation systems that will be introduced early in the 21st century,
autopilots are likely to play an increasingly important role in maneuvering the
helicopter along highly precise approaches.
The auto-hover capability for a helicopter is very rare and typically found
only in the autopilots on large, expensive military helicopters. Like a human
pilot, an autopilot would need a lot of data to know how to have a stabilized
hover over one spot, correcting for varying wind direction and speed. I know of
no civilian helicopter autopilots that have an auto-hover capability.
As a result, there are no auto-hovering autopilots for the EC-120 or
The autopilot manufacturer must have some assurance that a market exists for
the autopilots that will cover its very expensive development and certification
costs and then return a profit. Neither
One from the military
The next question comes from a reader who is a chief warrant officer, second
class, with Task Force Hawk, the Apache force deployed to
I was wondering: Does the Bell 407 AFCS have a hover hold? We have an
altitude hold and hover hold on the Apache. Is the
AFCS similar? What control authority does it have?
Hover hold is way too expensive for civilian operations. Few commercial
operators would be willing to incur such an expense. I don’t know any
non-military helicopter types that have it.
Some civilian helicopters have a stability augmentation system, which
catches longitudinal and lateral movement with a potentiometer and corrects
that movement by adding a little opposite cyclic. It does stabilize the hover
some—you can see much less hand movement on the cyclic when hovering.
The HAS Corp./SFIM autopilot for the