BTIZ wrote:

lets see.. wing leveler and heading control... sounds close to roll
and
yaw..

"Dave Butler wrote:

To me an axis is
roll-pitch-yaw. Unless the autopilot controls two of those, it's a
one-axis
autopilot... but I'm swimming against the tide.

Dave is correct here. The # of axes in an autopilot refers to how many
axes of _controls_ it has feedback for - i.e. one for roll/ailerons (for
wing leveling and/or heading via roll), two for pitch/elevator (for
altitude and/or climb/descent rate) and three for rudder/yaw. Almost no
small GA autopilots are more than two axis, and many are only one axis.

With one axis, you can easily control heading - when you're at cruise
speed in most small GA aircraft, and you change direction with the
ailerons in anything less than a 30 degree roll, you hardly use the
rudders at all (I said MOST). Now consider that the autopilot generally
will roll no more than 5-10 degrees, and you can see that rudder control
is not required.

Pitch as a second axis, however, is nice to have.....

--
Marc J. Zeitlin
http://marc.zeitlin.home.comcast.net/
http://www.cozybuilders.org/
Copyright (c) 2004