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THIS IS A VFR AUTOPILOT
Please remember that th& Navaid autopilot is not recommended for use in IFR
conditions. The components used in the kit are probably as reliable as any, but the system
has not been through the test regime that would be required of a type accepted piece of
equipment. Also, the installation was not done by a professional. These factors
necessarily result in a system of unproven reliability, so please do not bet your life that
this machine can carry you through a cloud.
COMMON PROBLEMS AND QUESTIONS
(1) If the autopilot is engaged while the airplane is on the ground, the stick shakes
continually. Why?
The servo has a very narrow dead zone in which the crank arm should stop. The problem
is that once a system with a fair amount of mass starts to move, it does not want to stop.
After the servo motor stops driving, system momentum carries the output arm through the
dead zone. Then the servo motor reverses, again overshooting the dead zone, and the
reversing process goes on repeating itself indefinitely.
The pair of interconnected sticks acts like a pendulum, or flywheel, that wants to keep the
system moving. The trick is to leave the dead zone as narrow as possible and still get the
servo to stop there.
Try placing a little side load on the stick with your finger while flying at cruise speed. If
this makes the stick stop oscillating, you can probably cure the problem by somehow
effecting a small trim change that would add an equivalent stick force. The explanation of
this is that, when the stick is moving against the finger force, it stops sooner than it
otherwise would and thereby stays in the dead zone.
(2) Why is there a bubble in the inclinometer?
The volume of the liquid and the internal volume of the glass tube changes with
temperature. The incompressible liquid would crack the glass if the air bubble were not
there to absorb the effect of these changes. The size of that bubble changes by a factor of
at least three over the expected temperature range.
You do not see the bubble in most regular turn coordinators. They have enough room
inside the instrument case to allow a stack, or vertical tube at one end of the inclinometer,
in which the bubble resides out of sight.
Summary of Contents for AP-1
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