Installing Engine Controls
What you need to know before you start
BY RICHARD KOEHLER
LAST MONTH WE COVERED the types of controls you can use for your
engine, but what about mounting these controls in your project?
First off, what length cable should you order? Length is critical
for a threaded-end control since it cannot be trimmed to fit. The best
way to determine length is to check what your kit/plans supplier
recommends, unless you are building a configuration different than
the standard or are doing a one-off. Then, if you must measure the
length, be sure to measure from the base of the panel mounting nut
at the instrument panel (or wherever the control is mounted) to the
end of the center wire or threaded end, with the control knob
pushed fully in. This translates to the position when the item being
controlled (throttle, mixture, prop) is in the fully on (or open, or
maximum) position. Put the control in this position and measure
from where the instrument panel mount nut will be.
It is easier to measure the distance if there is already a hole in
the firewall where the control will pass through. If not, you will
have to measure from the panel to the firewall and then from the
firewall to the actuator arm. This is usually not a straight line, but
sharp curves should be strictly avoided. A one-foot curve radius is
usually the maximum you want to bend a control cable for long life
and ease of actuation.
The best way I have found to estimate the cable run is to simulate it, ideally with old cable. If you don’t have a stock of old cables
lying around, you can use coat hanger wire or a larger safety wire
like 0.041.
The control cable should come off the
panel exactly perpendicular to the panel,
and then turn/curve as necessary to go
through the firewall and align at the control.
Within about 6 inches of the control arm in
question there must be a positive tab that
will allow mounting of a clamp for holding
the outer sleeve of the control. It should
allow a smooth straight line from the mount
tab to the control arm, and it should be in
the same plane of the actuation of the arm.
Route or bend the sample wire around for
the correct orientation, and then carefully
remove it and measure the length.
Again, a solid wire control can be
trimmed, but one with a threaded end,
which is preferred for throttle and prop controls, usually only comes in fixed lengths of
one-foot increments. Custom lengths can be
made, but they typically cost $20 to $40
extra, so using a standard length will pay off.
Putting a small piece of tape at one-foot
increments on the alignment wire will
quickly allow adjustment to see if a standard
length will work.
