Trio Avionics EZ Altitude Control - Manual (Page 15)

15
Note: A longer elevator crank radius dictates a correspondingly longer radius at the drive end.
The elevators must travel from elevator stop to elevator stop within the range of
movement allowed by the servo stops which limit crank arm rotation.
When the above conditions are met, the system usually performs best when the pushrod is
attached to the outermost hole in the servo crank arm. If your aircraft employs an elevator bell
crank, you should ideally attach the pushrod to the bell crank at a distance from its pivot point
equal to that of the servo crank arm radius (distance from crank arm pivot point to pushrod
attach point).
Again, never allow the servo to limit elevator travel.
6.3 Selecting a Site for the Servo
For most aircraft, it’s relatively easy to find a suitable site for locating the crank arm
servo. The length of the pushrod and, to some extent, the angle it makes with the driven
element are user selectable.
The rod end bearing allows
some misalignment, usually
about 8 degrees, between the
servo pushrod and the plane of
rotation of the crank arm. This
limit on angular displacement
often determines the minimum
pushrod length. Any side-to-
side movement must not jam
the rod end bearing. A suitable
hard point must be found, or
built, for mounting the servo.
The mounting place needs to be
as accessible as possible, and
there must be a means of
linking to the elevator control
system.
RV-6 Installation
The mounting place must be strong and rigid. If, for example, you need to mount the
servo on the skin of an airplane, it will be necessary to use additional bracing or a
“doubler” to provide appropriate rigidity. You do not want the push-pull of the servo to
fatigue the metal that holds it.
When mounting the servo, be careful not to drill
mounting holes into critical load bearing members.
It may be best to construct a mounting plate, place
and bond machine screws so that they will
interface with the case mounting holes, and then
secure the assembly into place. For a composite
aircraft installation, the bottom of the plate (shown
above) should be floxed and the holes in the plate
filled with flox before applying fiberglass layers
over it to secure it to the fiberglass structure.
NOTE - It is important that the servo mounting plate surface be flat and smooth. If it is not, this can
distort the servo frame when the servo is secured to the mounting plate.
Usually the servo pushrod will terminate on a control pushrod or a bell crank. If you are
connecting to a pushrod care should be taken to keep the pushrod from being free to
rotate. (To repeat, the pushrod should NOT rotate.) The reasoning for this is that as the
pushrod rotates there is “lost motion” in the system, i.e., movement of the crank arm does
not result in movement of the control system.