Navaid Devices AP-1 User manual

AP-1 AUTOPILOT
W/GPS COUPLER AND
S-2 SERVO
N AVAID D E V I C E S, I N C .
6 41 N o rt h Ma r k e t S t r e et
C ha t ta n o o ga , T N 3 7 4 0 5
Ph o n e : 4 23 ) 26 7 - 33 1 1
F A X : 4 2 3 ) 75 6 -6 1 5 4

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INTRODUCTION
Thank you for buying a Navaid Devices autopilot. We appreciate your business, and we
will support you in whatever way we can to make sure you get years of service from our
product.
We are quite confident that, after you read and follow the installation and checkout
instructions contained in this manual, your autopilot will become one of your most valued
flying tools. We like to think that you will soon come to regard it as one of your better
investment decisions. Experienced pilots often make go or no-go decisions on a trip
based on whether or not they have a working autopilot.
Should you ever change airplanes, you may want to use the autopilot in the new aircraft.
This can be done, but you may need to change it from 14 to 28 volt operation, or vice
versa. In this case the unit must be returned to Navaid for installation of the appropriate
motor and solenoid. Otherwise you just need new mounting hardware.
If you have any unresolved problems after reading this manual, give us a call. We do not
pretend to know all the answers, but we have been able to make the system work in every
type of airplane in which it has been tried so far. And we can usually refer you to
someone who has successfully installed the autopilot in a similar airplane.
Good luck. Give us a call if you run into a problem.

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1. THREE POSITION MODE SWITCH
RIGHT: Wing Leveler Mode. Keeps wings level by reference to the built-in gyro.
In this mode you can fly level, turn left, or turn right with the TURN CONTROL,
item 5.
MIDDLE: Turn coordinator. This position lets you fly without the autopilot, but with
the turn coordinator working.
LEFT: Track Mode. To track to or from a destination entered into a GPS, LORAN
or VOR.
2. TRIM CONTROL
Trims the ailerons for straight-line flight when the TURN CONTROL is set to a zero
turn rate.
3. RATE OF TURN INDICATOR
Electronically lighted bars indicate the rate of turn. The center reference bar stays lit.
Additional bars lit to either side of reference bar indicate turn rate: Vi degree per
second for each light.
4. MARKERS
Six lights out to the marker indicate a 3 degree per second standard-rate turn.
5. TURN CONTROL
When the airplane is in the Wing Leveler Mode, this knob turns the airplane left or
right.
6. TRIM POTS
These trimpots are used to match the autopilot to your aircraft. Once these pots are
adjusted (details in the owner's manual) further changes should not be necessary.
7. INCLINOMETER
Old fashioned "ball" coordinated turn or level flight indicator.

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HOW TO FLY WITH THE AP-1
(an overview)
1. Start the AP-1 by whatever switch connects it to the power buss. The gyro will
rev up. Have the MODE SWITCH in the center (TC) position and the TURN
CONTROL pointing straight up.
2. After the gyro is up to speed (about 5 seconds), turn the MODE SWITCH to
WING LEVELER. You are now flying on autopilot with the gyro keeping your
wings level. With the TURN CONTROL knob you can turn right or left to bring
the airplane to any desired heading. A greater turn of the knob gives a steeper turn
that will be shown on the electronic bar indicator.
Point the TURN CONTROL straight up to command a zero turn rate, and adjust
the TRIM knob to make the airplane fly straight and maintain a given compass
heading. Just watch for needed corrections, and of course observe your altitude.
3. If you have connected GPS, LORAN, or VOR, you can track to or from a
waypoint. The general rule is to fly to within 5 degrees of the VOR heading, or
2 miles of the GPS / LORAN track, to lock on. Do this by throwing the MODE
SWITCH leftward to TRACK.
After you are "hooked up" to your tracking signal, you can relax a bit. Just
monitor the flight, and stay ahead of the airplane.
4. TURN COORDINATOR MODE. When you wish to fly without the automatic
pilot, throw the mode switch to the mid position, and fly manually. The servo is
off and disengaged, but the electronic bars of the turn coordinator continue to
operate.
HOW TO INSTALL THE AUTOPILOT IN YOUR AIRPLANE
(an overview)
The entire job of the autopilot is to have the power driven crank arm, which is
linked to your airplane's aileron controls, push the stick left or right when you
request or require aileron adjustment. That's all. Further discussions simply relate
to ways to do this, and to tweaking the installation.
Begin by looking for a point where pushing or pulling a distance of 1.5 to 2.4
inches will do the job. Then find a place to mount the servo nearby to accomplish
this by means of the pushrod. You will mount the servo and pushrod so that the
ailerons are neutral when the servo crank arm is at mid position. That's it, aside
from carefully checking that the required range of aileron movement is transited
within the limits of the servo travel range.
Of course you will mount the AP-1 control unit in full view, and wire it with a
circuit breaker/switch (not supplied) to the power buss.

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INSTALLATION OF SERVO ACTUATOR - S2
CRANK ARM
The S-2 crank arm servo is easier to install than the capstan version and is suitable for all
but the largest homebuilt aircraft with heavy aileron loading. Because most installations
use the crank arm servo, information specific to the capstan servo is found in Appendix
A.
The S-2 crank arm servo uses a pushrod terminated by rod end bearings to link the servo
arm to the aircraft's aileron control system. We try to identify the type of rod end bearing
the customer needs for his intended installation and include it with his order. If it turns
out that your pushrod is not long enough (it must be trimmed to the correct length), or the
size of your rod end bearing is incorrect, please contact Navaid for parts exchange.
CONFIGURING THE CRANKARM
In your installation it may be more convenient to rotate the crank arm to a new
orientation that will give a neutral at +/- 90 degrees or 180 degrees from that as supplied
by Navaid. The servo crank arm is secured to a flange by four machine screws that can be
removed for indexing the crank arm +/- 90 degrees.
If you wish to rotate the crank arm 180 degrees, it is easier to just remove one of the stops
that limit crank arm rotation, rotate the crank, and replace the stop. It will be necessary to
change the indexing of the feedback pot after this, see RESETTING SERVO NULL
POINT, page 8.
In most cases the servo is installed with the bottom of the servo parallel to the ground, but
it operates equally well upside down or sideways
There are four holes in the crank arm that give operating radii with the combinations of
force and peak-to-peak travel listed in Table 1 below:
Crank Arm Max. Travel Force
Radius (peak-to-peak) (@ 30 in-lb)
1.0 in. 1.5 in. 30 Ib.
1.2 in. 1.8 in. 25 Ib.
1.4 in. 2.1 in. 21 Ib.
1.6 in. 2.4 in. 19 Ib.
Table 1
Choose the shortest operating radius on the servo crank arm that allows full aileron
movement (aileron stop to aileron stop) without driving the servo crank arm into its limits
(+/- 50 degrees).

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SERVO MOUNTING HARDWARE
The installation kit that Navaid offers for the Varieze, LongEZ. and Cozy is shown in
Fig. 2.
INSTALLATION KIT FOR RUTAN EZs
Fig. 2
Kits for other aircraft at least consist of a pushrod (cut to proper length by the user) and a
suitably sized rod end bearing for connecting to the airplane. When we are familiar with
the customer's aircraft type and know of a special requirement, we try to provide any
necessary special part that might be difficult for him to make.
SELECTING A SITE FOR THE SERVO
For most aircraft, it's relatively easy to find a suitable site for locating an S-2 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 limitation on angular
displacement often determines the minimum pushrod length. Any side-to-side movement,
such as may be caused by elevator action being mixed with the aileron movement at the
stick, must not jam the rod end bearing.
A suitable hard point must be found, or built, for mounting the servo. Of course, the
mounting place needs to be as accessible as possible, and there must be a means of
linking to the aileron control system.

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NOTE: A longer crank radius dictates a correspondingly longer radius at the drive end.
The ailerons must travel from aileron stop to aileron stop within the range of
movement allowed by the servo stops that limit crank arm rotation.
The mounting place must be strong and rigid-conceivably a lateral force of up to 50
pounds could be encountered. If, for example, you need to mount the servo on the skin of
an airplane, it probably 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.
Usually the servo pushrod will terminate on a control stick, a bellcrank, or perhaps a
lever sticking off of a torque tube. But in some cases (EZs, for example) it is more
convenient to terminate on an aileron control pushrod, in which case care should be taken
to keep the pushrod from being free to rotate. To do this, loosen the jam nut that secures
the rod end bearing in the pushrod, rotate the pushrod and jam nut in opposite directions
to remove any rotational slack, and retighten the jam nut. The reasoning for this is as
follows:
The servo pushes or pulls on a saddle bracket mounted on an aileron control pushrod, the
attach point being offset maybe an inch from the centerline of the control pushrod. If the
two pushrods are not perfectly aligned, the control pushrod may rotate instead of moving
sideways. Rotating, instead of moving, has the effect of putting play, or slack, into the
linkage, and the control movements in track mode are so small that it takes very little
slop in the system to make the airplane not track properly.
It will simplify installation adjustments if there is enough overhead clearance to allow
removal and replacement of the servo lid with the servo remaining in place. The servo lid
is secured by four screws at the side of the box. But, if it is more convenient, the lid may
be secured through holes in the top of the lid. There are two pots (potentiometers) and a
nut on the output shaft which should be adjusted with the lid off.
INSTALL THE CRANK ARM SERVO
Mount the servo without connecting the pushrod. See Fig. 3 on the next page and the
loose sheet showing how to solder the connector pins. The power and ground conductors
should be # 18 or larger. The servo signal wire carries little current and may be as small
as #24 stranded. If you also wish to hook up your nav receivers at this time, further
discussion starts on page 11.

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WIRING DIAGRAM FOR HAND-HELD GPS AND AP-1 WITH GPS
COUPLER
WIRING DIAGRAM
Fig. 3

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CHECKOUT
Do not use just a battery charger by itself to supply the power for testing your autopilot.
The voltage out of one of these has too much ripple. Connect a battery charger to the
aircraft battery and leave it on whenever using the servo. Otherwise the 1 amp drain of
the servo can pull the battery voltage below 12 volts and cause improper operation.
See Fig. 1 for a view of the AP-1 controls. Flip the Mode Switch on the AP-1 to the right
for Wing Leveler mode and turn on the aircraft master switch. The gyro should start to
wind up, and the servo should crank to a stop somewhere.
CHECK DIRECTION OF CRANK ARM ROTATION
CAUTION: The trimpots (item 5 in Fig. 1) to be adjusted in the following procedures
turn quite easily. If a pot resists rotation, do not force it—it probably is already turned as
far as it will go in that direction. The counterclockwise rotational limit is around 8 or 9
o'clock and the clockwise rotational limit is around 3 or 4 o'clock.
The GYRO NULL trimpot is factory set and should not need adjustment. But if you do
turn it by accident, just use a voltmeter to set the voltage between pins 10 and 11 on the
rear connector of the AP-1 to zero, or as close to zero as you can get it-the voltage may
wander a few millivolts. Make sure that your voltmeter—digital preferred—is set on its
most sensitive scale. Also, the cover of the AP-1 must be on (there is light sensitive
circuitry inside the instrument) and the AP-1 must be held still for this adjustment.
Set the SPAN trimpot fully clockwise. Rotate the TURN CONTROL for a right turn, and
note the direction of crank arm rotation. When the pushrod is installed, this rotation must
deflect the ailerons for a right roll.
If the aileron deflection is backwards, you must reverse the direction of servo rotation.
See Fig. 3 on the next page. Swap the motor wires at the motor. Swap end connections at
the FEEDBACK pot-these wires are white with red tracer and white with black tracer. If
necessary, reset servo null point.
RESETTING SERVO NULL POINT
When you turn the servo on after reversing the servo direction, or after changing the
orientation of the crank arm by 180 degrees, the servo may drive into its mechanical limit
and just keep grinding, slipping the clutch. This happens because the null point to which
the servo is trying to go has been moved to a position outside the range of servo travel.
To fix this, do the following:

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1) There is a nylon gear on the back end of the output shaft that engages another gear on
the feedback pot shaft. Loosen the set screw that secures the gear on the output shaft,
then slide it back so that it no longer engages its mating gear.
2) There is a U shaped gear engage rocker arm that the solenoid normally pulls up to
engage the gear train. Hold this down to keep to keep the gear train from engaging (it
does not hurt anything to let the crank arm hit the stop and grind, but the noise is
annoying), then turn on the autopilot. The motor will run continually.
3) Rotate the feedback pot-the motor will reverse direction at two points during a 360
degree rotation of the pot shaft. At one of the points, the motor abruptly switches from
full speed one way to full speed the other way. Find the other point, which is not really
a point but a very narrow range within which the motor can be made to a stop, or run
relatively slowly in opposite directions on either side of the stop. Turn the autopilot off
anywhere within this range.
4) Without rotating the feedback pot shaft any more than you help, re-index the gear on
the shaft so that the set screw is pointing straight up within, say, +/- 15 degrees. 5)
Point the set screw on the output shaft gear about straight up, engage the two gears,
point the crank arm where you want it, and tighten the set screw. Do not to use too
much torque tightening the set screw. You want to hold the gear firmly on the shaft,
but below, under SETTING SERVO NEUTRAL, you will need to force the gear to
rotate with respect to the shaft.
6) Turn on the autopilot. The servo should crank to a stop without moving very much.
SERVO MOTOR AND FEEDBACK POT TERMINALS
Fig. 4

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CHECK INDEXING OF TURN AND TRIM CONTROLS
Check the TURN and TRIM CONTROLS for proper orientation of the indicator. The
limits of rotation of each control should stop the indicator at points equally displaced
from 6 o'clock, in which case the indicator will point straight up at the center of rotation.
The TURN CONTROL has a dead zone, which is anywhere in the center 10 degrees of
shaft rotation. The dead zone is there so that the control does not have to be exactly
centered to command a zero turn rate. Point the indicator straight up to put it tin the dead
zone.
Center the TRIM CONTROL and TRIM RANGE trimpot. Now the AP-1 should think
the airplane is flying straight and level, and the servo is locked into the position that it
would hold for neutral aileron. The crank arm will be positioned properly for level flight
in the following segment
INSTALL THE SERVO PUSHROD
Cut the pushrod to the proper length so that, when the servo is at neutral, the ailerons are
also neutral. Do not worry about being exactly correct-the ailerons can easily be jinked to
a new neutral.
Choose the longest possible crank arm radius that accommodates a pushrod range of
movement equal to or exceeding that required for full aileron travel. Be sure that the rod
end bearings never jam due to misalignment as the pushrod angle is varied by different
combinations of aileron and elevator input. Put the stick in all four comers.
SETTING SERVO NEUTRAL
Find the FEEDBACK pot: it is mounted on the servo frame above the motor (see Fig. 4),
and it has a small gear mounted on its shaft. If you twist that gear, the servo will crank
until you let go, indexing the crank arm to a new position. You can use this feature to jink
back and forth until you get the neutral located exactly where you want it.
NOTE: if the small feedback gear is very difficult to turn, loosen the set screw in the
larger gear somewhat. The output shaft must rotate with respect to its feedback gear when
the crank arm is indexing to a new position. IMPORTANT: After this adjustment, check
the setscrew again to make sure that it is not too loose.
SETTING SERVO RANGE
Another servo adjustment is a small trimpot located on the printed circuit board. This is
the servo RANGE trimpot, and turning it clockwise increases the range over which the
servo operates.

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Set the SPAN trimpot in the AP-1 fully clockwise, then rotate the TURN CONTROL
from stop to stop and note the maximum obtainable aileron deflection. Adjust the servo
RANGE trimpot as necessary to obtain about 50 of full aileron deflection at the limits of
TURN CONTROL rotation.
SETTING SERVO OVERRIDE FORCF.
The servo TORQUE CONTROL nut (the locknut inside the servo on the output shaft)
sets the override force, which is the force you feel at the stick when the servo clutch
begins to slip.
Set the TURN CONTROL to neutral and then push the stick hard enough to override the
servo. Set the override force to a value that seems strong enough to give fairly good roll
authority, but not so strong as to be difficult to override. In subsequent flight tests, work
toward setting the servo slip clutch to the minimum torque necessary to give enough roll
control to handle a reasonable amount of turbulence.
If you tighten the clutch enough to exceed the 30 in-lbs maximum torque rating, you may
hear a loud clacking sound in the servo and the servo may disengage. This clacking
happens when the force pushing the gears apart exceed the solenoid's ability to hold the
gear train engaged. This is a redundant safety feature-just back off on the control nut a
little and recycle the power switch to re-engage the servo.
CONNECTIONS TO NAV RECEIVERS
Fig. 3 shows the autopilot interconnection wiring diagram. As stated earlier, the power
and ground conductors should be #18 or larger. The servo signal wire and push-to talk
switch wiring may be as fine as #24, or whatever heavier wire is convenient.
Use the supplied braided shield twin lead for the LORAN signal; do not use foil shield. If
you need extra, call Navaid Devices. Ground the shield on only one end (Fig. 3 shows
grounding at the AP-1 end). This shielded wiring is necessary only if you are connecting
to a LORAN—it prevents the gyro motor from lowering the signal to noise ratio.
When soldering the shield, be careful not to let the shield overheat the plastic and short to
the conductor. If you separate enough braid so that it can be held by a pair of needle nose
pliers while soldering, the heat from the braid will be soaked up by the pliers without
damaging the insulation.
The diode installed in series with the push-to-talk line, together with the wire connected
from the PTT switch to pin 7, are used to kill the signal to the servo while the PTT switch
is depressed. This prevents the servo from jumping around due to the presence of high
level RFI (radio frequency interference) on the power lines. The servo stays engaged
during the voice transmission, but it does not move until normal operation is restored by
releasing the mike button.

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We do not know all we would like to know about RFI, but we do know that the signal kill
wiring discussed in the previous paragraph is unnecessary in some cases. If you are using
shielded wiring in a metal airplane, RFI probably will not be a problem, and it may not be
a problem if you have shielded wiring in a composite airplane. But a composite airplane
with unshielded wiring usually needs the signal kill circuitry.
AUTOPILOT OUTPUT PINS ON NAV RECEIVERS
Your navigation receiver should have two output signal terminals to be used for driving
an autopilot or a CDI. Usually they are labeled '+ Left' and '+ Right', and they are to be
connected to the corresponding AP-1 terminals. If the labeling is ambiguous, as it is on at
least one fairly popular radio, just connect both wires without worrying about polarity
and check it out in flight test.
Many of the hand-held GPS or LORAN receivers, and a few of the panel mounted units,
have digital autopilot outputs that are not compatible with the analog (varying dc voltage)
signal required by the Navaid autopilot. If you have not yet bought your navigation
equipment, please check with the manufacturer—your receiver (GPS, LORAN, or VOR)
should be able to drive an external CDI, and this same signal is used to drive the
autopilot. If you are already driving an external CDI, just put the autopilot in parallel at
the same terminals.
MOMENTARY DISCONNECT SWITCH
In addition to the wiring shown in Fig. 3, you may wish to add a momentary pushbutton
switch in series with the servo power line. This switch would be located on or quite near
the stick, and it would disconnect the servo as long as the button is depressed. A lighted,
round switch that can mount in a 0.43 inch diameter hole is available (at the time of this
writing) from Mouser Electronics, phone [phone]. Use the two switch terminals
(of three) that are normally closed to interrupt the servo power wire.
Cap Color Part No.
Price
Red 10PL031 $11.08
Yellow 10PL033 $11.08
Green 10PL036 $11.08
Momentary Pushbutton Switch Options
Table 2

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CIRCUIT BREAKER/SWITCH
Instead of a switch and a separate in line fuse, you might want to consider a circuit
breaker/switch. Use a fast acting (NOT instantaneous) 3 amp magnetic circuit
breaker/switch (2 amp for 28V systems).
Carlingswitch (call [phone] for nearest distributor) makes a nice looking, gray
colored, lighted, 3 amp rocker switch that snaps into a rectangular cutout. The part
number is MF1-B-32-430-1-JC2-7-A. Each section of this long part number indicates a
different option—you might want to get a catalog and change, for example, just the color
of the light (this one has a green lens).
Or you may prefer the convenience of round hole mounting a similar sized black lever
switch available from the Airpax division ofPhillips Technologies (call [phone]
for nearest distributor, part number Tl 1-1-3.00A-OI-10A-V).
PREFLIGHT CHECK
Set the TURN CONTROL to midrange and make sure it is in the center dead zone. To do
this, set the AP-1 to WL mode (flip Mode Switch right) and slowly rotate the TURN
CONTROL from stop to stop at a constant speed. You will hear the servo pause as the
knob passes through the dead zone. If you do the same thing while you are flying, the
wings will momentarily stop rolling as the knob goes through the dead zone.
Set the TRIM and TURN CONTROLS to midrange. Set TRIM RANGE, LEFT CAL, and
RIGHT CAL trimpots to midrange. Leave the GYRO NULL trimpot alone. Set the SPAN
trimpot fully clockwise (Note: the servo range goes to zero when the SPAN trimpot is
fully counter-clockwise). Put a small screwdriver in your pocket for adjusting trimpots in
flight.
Put the autopilot in Wing Leveler mode (Mode Switch to right) while taxiing. Make a
right turn, and you should feel the stick move to the left, and vice versa. A right should
give left aileron. The servo must always work against whatever the airplane is trying to do
on its own.
BE DAMN SURE YOU CAN OVERRIDE THE SERVO ANYTIME YOU WANT!
Test the override by pushing the stick both left and right.
DISENGAGE THE AUTOPILOT BEFORE TAKEOFF.
The servo is disengaged only when the Mode Switch is in its center position. The turn
coordinator always operates, no matter what position the Mode Switch is in.

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TEST FLIGHT AND CALIBRATION
Take off, get some altitude, and set up a level cruise. If you have cockpit adjustable trim,
set it as necessary to achieve straight line flight.
Flip the Mode Switch rightward to the Wing Leveler position. The autopilot should take
control. The airplane probably will start a gentle turn indicating an out-of-trim condition.
If the system gain is set too high, the stick may feel jittery and the airplane may weave
back and forth.
SETTING SYSTEM GAIN
The autopilot should fly the airplane in a manner more or less similar to that of human
pilots. If the stick action feels too jittery for the weather conditions, or if the airplane is
continually hunting (oscillating) back and forth like a snake trying to follow a straight
line, the system gain is probably set too high for your aircraft.
Remembering that the trimpots should not be forced beyond their 9 o'clock and 3 o'clock
stops, you lower system gain by turning the SPAN trimpot counterclockwise. Decrease
the gain (turn SPAN trimpot counterclockwise) until the stick calms down, then increase
it to the point where the stick becomes jittery again. With your airplane operating at its
usual cruise speed, set the gain as high as possible without oscillation or jittery stick
movement.
If the SPAN trimpot ends up being set below 75 of maximum (full clockwise), the servo
RANGE trimpot is set too high and tracking performance may be degraded. The
following procedure increases servo resolution without changing system gain. Land the
airplane and measure (better write it down) the full range of aileron movement obtainable
using the TURN CONTROL with the autopilot in Wing Leveler mode.
Set the SPAN to about 90 of full clockwise rotation.
Adjust the RANGE trimpot on the servo printed circuit board to restore that same range
of aileron deflection.
TRIMMING THE AUTOPILOT
Do not touch the TRIM or TURN CONTROL now (they should already be at midrange).
Adjust the TRIM RANGE trimpot to make the aircraft fly straight. Note that you do not
adjust the airplane for wings level—sometimes a rudder out of trim makes it necessary to
fly with one wing a little low to achieve straight line flight. If you are flying in smooth
air, it should be possible to adjust the TRIM RANGE trimpot so that the airplane will
stay lined up on a distant target.

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If the TRIM RANGE trimpot does not have sufficient range, reset it to midrange. Then
use the TURN CONTROL to make the airplane fly straight. Leave everything as is, turn
the autopilot off, and land the airplane.
When the airplane is on the ground and the Wing Leveler is engaged again, the ailerons
will go to the correct level flight position. Mark this position. Now put the TURN
CONTROL back into the dead zone, which will move the ailerons away from neutral.
Then jink the servo FEEDBACK pot or adjust the mechanical linkage so that the aileron
is returned to the marked position.
TRIMMING FOR TRACK MODE
The autopilot should be set for proper aileron trim in WING LEVELER mode before
switching to TRACK. This is not a one time adjustment-you will probably have to check
the aileron trim every time you use the autopilot. Trim can change as a function of power
setting, fuel load imbalance, or trim tab adjustments. Aileron trim error shows up as a
tracking offset.
A common mistake is to leave in a TURN CONTROL input (turn control not in dead
one) while trimming the aircraft in Wing Leveler mode. This input drops out when you
switch to Track, which will introduce a tracking error if the TURN control input is
anything other than zero before switching. Therefore, always make sure that the TURN
CONTROL is in the dead zone while trimming.
With the TURN CONTROL in the dead (zero input) zone, adjust the TRIM control or
TRIM RANGE trimpot as necessary for straight line flight. If you are uncertain that you
are really in the dead zone, use the TURN CONTROL to roll the airplane back and forth.
Rotate the knob slowly at a constant rate, and you can detect a pause in the roll as the
knob goes through the dead zone at the center of rotation.
TRACK MODE
When you are first learning to use the autopilot to track a VOR, be sure you are within
ten degrees of the correct heading and no more than ten degrees off course, i.e., just
barely carrying full deflection of the CDI needle, before engaging the Track mode. In the
case of a LORAN, be sure you are within 10 degrees of the correct heading and no more
than 5 miles off course.
If you are using a VOR for making the following adjustments, try to stay within 1.5 to 15
miles of the VOR to be sure that the airplane responds to the adjustments within a
reasonable length of time. After each adjustment, the aircraft must fly to a new bearing
from the VOR before the CDI needle can stabilize.

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Head toward a VOR and flip the Mode Switch rightward to Wing Leveler. Zero the CDI
needle and, after a delay of about half a minute, flip the Mode Switch to the far left to
change to TRACK mode. The airplane should track in over a VOR.
The purpose in the delay in switching to Track mode is to allow the charge on some
capacitors in the AP-1 to stabilize. If the switch is made as soon as the needle is centered,
the machine will "remember" that the needle was off, "think" that it must correct, and
bank the airplane off course. If the airplane is improperly trimmed when Track mode is
initiated, the CDI needle will shift away from zero deflection as the autopilot flies the
aircraft as necessary to establish a stable off-course condition, a condition that generates
an error signal that cancels the trim error. If you are tracking a GPS or LORAN, the
aircraft settles on a course parallel to the desired course. If you are tracking a VOR, the
CDI needle settles down to a different radial from that selected at the OBS and still flies
over the VOR station.
The autopilot always makes the airplane follow the needle. If the CDI needle wanders
around, the airplane will too. This is a VOR problem that usually occurs at low altitude
over hilly terrain. If the cruising altitude is 4,000 or more feet AGL, the autopilot should
track the VOR without much S-tuming, or scalloping, back and forth across the track.
The autopilot works best tracking a GPS or LORAN because of the higher quality signal.
The error signal for a given distance off course stays constant in a GPS or LORAN, but a
VOR signal may scallop, and signal sensitivity varies over a wide range as a function of
the distance from the station.
TRIM WHILE TRACKING
The necessity for putting the TURN CONTROL in the dead zone has been discussed in
TRIMMING FOR TRACK MODE on the previous page. However the "dead zone" does
not necessarily command a perfect zero turn rate — but it is close. Therefore do not be
surprised if the airplane drifts off a little, probably less than a mile, after following the
foregoing procedure and switching to TRACK mode. This residual error, or any error that
later occurs as a result of a change of airspeed or uneven fuel loading in the wings, can be
corrected by turning the TRIM trimpot toward the error, i.e., turning the trimpot
clockwise to correct for a CDI needle that has shifted to the right.
Sometimes you may want to track with a parallel offset from a given line. If you are
tracking with GPS or LORAN that does not have this feature built in, just trim in the
direction of the desired offset.

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USER SELECTABLE GPS / LORAN SIGNAL GAIN
The standard error signal voltage for driving a CDI, which is also used for the autopilot,
is 150 mV at 5 miles off course (cross track error) for a GPS or LORAN. Some receivers
also have user selectable tracking gain that can be set to give a 150 mV error signal at
1.25 miles off course, and it may be called APPROACH MODE instead of CRUISE.
Another way of saying the same thing is that it may be possible to set your receiver
tracking sensitivity to 1/4 mile per dot instead of 1 mile per dot. If you have this feature,
try it—most customers prefer the increased tracking accuracy.
ADJUSTING THE SERVO SLIP CLUTCH - SAFETY VS. RESPONSE
The FAA requires autopilots for production aircraft to be set up so that a hard-over
failure will not cause the airplane to bank more than 60 degrees in the first 3 seconds
after recognition of failure. Since it takes about a half second to recognize a failure, the
time period might as well be 3.5 seconds.
For certified installations, the servo slip clutch is specifically set to meet this specification
for each aircraft model. A homebuilder, who is under no such obligation, may elect not to
perform the following test. Or he may perform the test and then deliberately increase the
torque setting to enhance performance under turbulent conditions. But he should at least
understand that there is such a thing as too much autopilot control, and that a fast
response to a hard-over failure can be dangerous. If you prefer a fast response, then you
should set conditions, such as minimum AGL altitude or formation flying, under which
the autopilot will not be engaged.
The worst case roll condition occurs at minimum speed and aft C.G. This could be a slow
airspeed if you are going to track the localizer. But we hope you just use the minimum
cruise speed—the autopilot is not required to work over as large an envelope, and you
can more gracefully afford a hard-over failure at cruise altitude and speed than at that
typically encountered while flying the localizer.
Check the maximum roll rate with the aircraft at aft C.G. and minimum speed. Disengage
the autopilot, then set the TURN CONTROL to full left mm. Hold the same airspeed as
you bank 60 degrees to the right, engage the servo, and measure the time it takes for the
aircraft to get to level. If the aircraft passes through level in less than 3.5 seconds, that is
too fast—the servo Torque Control nut on the output shaft needs to be loosened so that
the wind load on the aileron causes the clutch to slip sooner.
Before making a change to the servo, check for an adequate minimum roll rate with the
aircraft at maximum cruise and forward C.G. Rotate the TURN CONTROL back and
forth to see whether the aileron has adequate control. If the control is too weak, the servo
TORQUE CONTROL NUT needs to be tightened.

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Obviously, putting in a fix at low speed can adversely affect high-speed response, and
vice versa. It may be necessary to accept a compromise.
CALIBRATING THE DISPLAY
For your information, the RIGHT and LEFT CAL trimpots affect nothing but the number
of bars lit for a given rate of turn. Also, the direction is opposite of what you probably
would expect: clockwise rotation of these two trimpots causes a decrease in the number
of bars lit for a given rate of turn.
Disengage the autopilot and make a 360 degree standard turn to the right. Keep six bars
lit out to the white triangle and time the turn. If it takes less than 2 minutes to complete
the turn, set the RIGHT CAL trimpot halfway between wherever it is and fully
clockwise; conversely, set it half way to fully counterclockwise if the timed turn takes
longer than 2 minutes.
Make another timed turn, and correct as before but with only half as much correction, i.e.,
about 30 degrees of trimpot rotation. If that is not close enough, repeat the process again
using half the previous correction. Three or four successive approximations for RIGHT
CAL ought to get the time fairly close to the desired 2 minutes for a right turn. Repeat the
procedure on standard left turns, this time adjusting the LEFT CAL trimpot.
The accuracy with which one can fly a timed turn is limited by the resolution of the
display, which in this case is plus or minus 1/4 degree per second, as well as pilot
technique and turbulence. The above procedure calibrates the readout so that a six bar
rum gives a turn rate fairly close to 3 degrees per second, and the pilot is a component in
the feedback loop, so this calibration method is probably as good as any.
MEASURING THE MAXIMUM TURN RATE
The maximum turn rate that can be commanded with the TURN CONTROL cannot be
adjusted, but it is repeatable and can easily be measured. The measured value ought to
turn out to be a little less than 3 degrees per second.
Measure the time required for a 360 degree autopilot turn with the TURN CONTROL
fully clockwise. Divide the time, in seconds, by 360. The answer is the measured turn
rate. You may want to placard the instrument panel with the required number of seconds
for a 180 degree turn each way.