The FAA’s certification rules do not require pleasing control harmony. There
are maximum stick forces specified that an airplane cannot exceed, and there are
phrases in the rules like “normal pilot strength” or “no unusual pilot skills,” but
ideal harmony among the control forces is not a rule. However, the rules do
require that stick force be positive, meaning it always takes more force on the
controls to increase the pitch, roll, or yaw rate.
Most certified airplanes—except for the smaller and lighter ones—end up
with some type of artificial force added in pitch in order to meet the rules for
positive stick force across the CG and operating airspeed range. The most common artificial force system is a spring that pulls the control wheel forward,
adding force when the pilot tries to pitch the nose up. The down spring would
almost certainly not be required when flying with a forward CG but is necessary
to keep stick force positive with the CG all the way aft.
Another technique for adding pitch force is the bob weight. A weight mounted
on a lever arm is attached to the down circuit of the elevator controls. The weight
applies a steady nose-down force, but its real function is to add stick force per g.
When the airplane pitches up or down, g-force amplifies the force of the weight
through the lever, increasing the nose-down or -up force the pilot feels through
Over the decades airplane designers have learned many techniques to tailor
control force and harmony. The pressure of the certification rules has been a factor, but more important is the competition of the market. A nice flying airplane is
simply more desirable and has a better chance to succeed.
I find it interesting that the one light airplane I have flown that comes closest to the perfect 2-4-6 control force harmony is the Cessna 162 Skycatcher. The
light-sport aircraft rules are the least stringent when it comes to flying qualities,
but Cessna engineers set their own standards and met them. With a clean sheet
design, and the experience of building thousands of two-seat trainers, the
Cessna people knew how to design the control system and the control surfaces
and where to locate the control hinges to achieve near perfection. Good flying
qualities are essential for safety, but also for learning. I think the 162 may be the
most effective trainer Cessna has ever built.
THE MOUNT MITCHELL RIDE
To get to the southeast coast and on to Florida and the Bahamas from our
still new home base in Muskegon, Michigan, I have to fly over the southern
part of the Appalachian Mountains. Actually, it is the
Black Mountain chain of the Appalachians, the
highest mountains east of the Mississippi River, that
are the issue.
Mount Mitchell is the star of western North
Carolina’s mountains topping out at 6,684 feet. Mount
Mitchell is just northeast of Asheville and is so special
that it is the center of an enormous state park, the first
state park in all of North Carolina. The peaks of the
Black Mountain ridgeline are pretty uniform, so it’s
sometimes hard to pick Mount Mitchell out from
other summits, several of which are only a few hundred feet lower than Mitchell.
Lots of people—probably most—love mountains.
But I hate mountains. Maybe if I didn’t fly, I would
come to love those big rocky lumps, but I do fly, and
mountains only mean one thing to me—turbulence
and bad weather. And Mount Mitchell delivers both.
To avoid flying over the mountains and on my way
southeast I file over the Spartanburg (SPA) VOR,
which takes me a little east of the direct course to
Savannah or on to the east coast of Florida. The route
usually keeps me out of the clouds that stick to the
Black Mountains most days, but the turbulence is
another matter. If the wind aloft is from the west,
there are going to be bumps, usually pretty big bumps,
as I pass the mountains.
Not long ago Stancie and I were cruising along in
nice smooth clear air headed southeast with the wind
blowing off the right wingtip and not doing much of
anything to our groundspeed. We had a good view of
the mountains as the cloud bases were above the
peaks, which is not often true. It seemed like we were
past the turbulence danger zone when I said something stupid like, “Guess there are no bumps today.”
Seconds later the airplane started climbing, the autopilot pushed the nose over to maintain altitude, and I
yanked the throttles back to keep airspeed under control. Then we hit the wake of the mountain. The
airplane shook violently for about 15 to 20 seconds
with stuff, and us, bouncing around the cabin.
Suddenly, the turbulence ended and we sailed on in
clear skies and a smooth ride.
Mount Mitchell is named for a professor from the
University of North Carolina who first determined
its elevation. Professor Mitchell died on the mountain when he fell off a cliff into a waterfall, was
knocked unconscious, and drowned. I plan to keep
an eye on that mountain and be ready for what it can
dish out. Maybe someday I’ll even get to fly past it in
J. Mac McClellan, EAA 747337, has been a pilot for more than 40 years,
holds an ATP certificate, and owns a Beechcraft Baron.