1. BELL MODEL 407 AUTOPILOT SYSTEM
Jake Hart
April 10, 2003

2. Helicopters & SFIM AFCS
Eurocopter
Puma, Alouette III, Gazelle
Super Puma mkI/II, Dauphin/EC155, Ecureuil
Eurocopter Deutschland
EC135, EC145
NHI
NH90 (Fly by wire)
Hindustan Aeronautics Ltd
Advanced Light Helicopter (ALH)
Module 11 Auto Flight Systems

3. Helicopters & SFIM AFCS
Bell Helicopter Textron
Bell 407, Bell 427
Mitsubishi Helicopter Industry
MH2000
Denel
Rooïvalk, Puma

4. System Supported by SFIM, Inc. Service Center
AP85 (AS-350/355, B407, EC120) : VFR
AP85 (AS-355) : IFR
CDV85 (AS-355, AS-365, AS332) : IFR
AP155 (AS-332, AS-365) : IFR
CDV155 (AS-365, AS-332) : IFR
AP16X (AS-332, ALH, Rooïvalk) : IFR
APM200x (EC135, EC145, EC155) : IFR

5. Future Projects Helicopter System Est. Date B 427 VFR 8/31/2003
S-64 Air-Crane VFR 1/31/2004
EC-130 VFR 6/30/2003
MD preliminary discussions
EC-130 SPIFR Late 2004*
* Depending on customer interest.

6. The SFIM PA85 Automatic Pilot System
Everything you ever wanted to know (and some things you didn’t) about the SFIM autopilot installed in the Bell Model 407 helicopter

7. OPTIONAL
N/A BH407

8. Primary Components AP CONTROLLER PITCH & ROLL SEMA TRIM COMPUTER
AXIS ENGAGE
AIR DATA SENSOR
AP COMPUTER
PTICH & ROLL TRIM ACTUATORS

9. Autopilot Control Panel
The AP control panel provides control of the autopilot system and annunciation of upper modes.
Control panels shown are the installed in Air Methods aircraft
AMC Panel

10. Autopilot Control Panel

11. Autopilot Control Panel

12. Autopilot Computer
AP computer is the heart of the system. It allows engagement of pitch and roll axes and operation of all upper modes.
The AP computer requires dc and ac electrical power as well as attitude data from the vertical gyro plus altitude and airspeed data from the BARAN.
The AP uses IAS data to execute standard rate turns in the HDG and NAV modes.
If one or more axes is terminated, the AP computer generates a flashing AP FAIL annunciation for 10 seconds to alert the pilot.
AP computer can be mounted either under the pilot’s seat or in the avionics area aft of the cabin.

13. Air Data Sensor (BARAN)
The BARAN utilizes data from the helicopter pitot / static system which is converted to electronic signals for use by the autopilot.
When the pilot selects ALT or A/S, a signal is simultaneously sent to the AP computer and BARAN. The BARAN sends error signals to the AP when the helicopter drifts off the selected airspeed or altitude.
The autopilot utilizes IAS data to determine bank angle required to approximate a standard rate turn during HDG & NAV modes.
The BARAN is located forward of the instrument panel on the right side of the extended console.

14. Smart Electrical Series Actuator (SEMA)
Pitch, roll and yaw SEMAs are controlled by the AP computer and perform all autopilot maneuvering of the helicopter. SEMAs:
are adapted to the control rods (pitch and roll are on the “long” rods in the vertical tunnel, yaw in the aft fuselage).
utilize brushless motors.
are self-monitoring. Command signal is sent to drive calculator and monitor calculator. Each makes calculation and if same result is not achieved, SEMA is shutdown and disengaged.
do not move the cockpit controls during operation.
self-center upon power-up
utilize non-contact Hall effect devices to monitor output shaft position and motor rotation.
have no gear train, motor shaft has acme screw onto which output shaft is mounted. Rotation of motor causes output shaft to extend or retract depending on direction of motor rotation.
replacement is on condition (no recommended overhaul).
authority is established based on helicopter response to hard-overs in each axis. SEMAs have the following authority:
Pitch mm ( inches) ~4.5% of control total travel
Roll mm ( inches) ~6.5% of control total travel
Yaw +8.0 mm ( inches) ~10% of control total travel

15. Trim Actuators
Pitch and roll trim actuators are controlled by the trim computer. Trim actuators provide the following functions:
When AP is engaged, they compensate for the limited authority of the SEMAs via the autotrim function. When a SEMA is operating off its midpoint, the trim motor is activated to move the cyclic in the appropriate direction and amount to cause the SEMA to return to its center position, restoring full authority.
Trim units, via an internal spring, provide artificial control feel to the pilot. This spring gradient allows the pilot to maneuver the helicopter when desired without deactivating the autopilot or any of its modes.
An internal microswitch signals the autopilot when the pilot executes a fly-through maneuver so the system will not oppose the pilot.
The control forces can be released via an internal clutch with the FTR button on the cyclic or overhead FORCE TRIM switch.
In the unlikely event of an internal jam, shear pins in the output shaft can be sheared by a strong pilot force on the cyclic.
The trim units are located under the copilot’s seat.

16. Trim Computer
The primary function of the trim computer is to control the action of the trim actuators for the automatic trim operation. The trim computer receives SEMA commands from the AP computer to determine SEMA position. Once a SEMA is operating off its midpoint, after a delay of ~3.5 seconds, it activates the appropriate trim actuator to allow the SEMA to re-center.
The trim computer sends a TRIM FAIL annunciation whenever the trim system fails to operate or if a trim actuator operates continuously for more than 4 seconds (an indication of trim runaway).
The trim computer is located under the copilot’s seat.

17. SEMA / Trim Relationship
Trim units are bolted to air-frame and connected to cyclic such that trim motion moves the cyclic.
The trim connection to the cyclic is between the SEMA and the pilot. The trim anchors the cyclic position so that SEMAs move the main rotor controls, not the cyclic.
The SEMA output shaft effectively shortens or lengthens the control rod on which it is located making the equivalent of small cyclic inputs to the rotor.
SEMAs are fast-moving with limited authority. Trim actuators move slowly, but have 100% authority. The combination of the two allows proper and safe operation and control of the helicopter by the autopilot system.
Generic drawing is used for simplicity. Bell SEMAs are located on rods in the vertical control tunnel.

18. SEMA / Trim Relationship

19. LET'S TALK FLYING !

20. Cockpit Checklist Additions
The following should be added to the interior check list:
If copilot’s cyclic stick is removed, check that the jumper connector is properly installed.
Overhead electrical panel:
AP related circuit breakers IN
FORCE TRIM switch - ON.
AUTOTRIM switch - ON.
After engine start:
GYRO FAIL annunciation - OUT
Prior to first flight of the day:
Trim test Check
Monitor Check
Immediately prior to takeoff:
pitch, roll, and yaw (if installed) switches - ON
FORCE TRIM switch - as desired.
Before or during climb, FORCE TRIM switch - ON.
After landing:
FORCE TRIM switch - ON
AP disconnect on cyclic - OFF

21. Prior to first flight of the day, perform the following checks:
Preflight Checks
Prior to first flight of the day, perform the following checks:
Trim Test: - pilot must avoid moving cyclic during test procedure.
FORCE TRIM switch - ON
AUTOTRIM switch - ON
GRYO FAIL annunciation - OUT
CYCLIC FRICTION - OFF
Pitch switch - ON
TRIM TEST switch - press & hold 7 to 10 seconds
TRIM FAIL annunciation - flashing
Check cyclic - slow aft movement
ATTD TRIM switch - FWD (observe main rotor tip path moves down)
- AFT (observe main rotor tip path moves up)
Pitch switch - OFF
Roll switch - ON
TRIM FAIL annunciation - flashing
Check cyclic - slow left movement
ATTD TRIM switch - LEFT (observe main rotor tip path moves down ON LEFT)
- Right (observe main rotor tip path moves down ON RIGHT)
Roll switch - OFF
SEMA monitor check:
Pitch & roll switches - OFF
TRIM TEST switch - P, R, Y* & MON illuminated
* “Y” only if yaw axis is installed

22. If Preflight Checks Fail
Trim Test:
The trim test checks for proper operation and annunciation of trim computer and trim actuators.
If trim test fails, system may remain functional. Pilot must utilize caution and carefully monitor automatic trim operation to ensure proper operation of autopilot.
If the pilot determines that one or both trim actuators or the autotrim system is inoperative, the FORCE TRIM switch should be turned off, thereby de-clutching the trim units from the cyclic. The autopilot now operates in the SAS mode and neither attitude hold nor upper mode coupling will function properly.
Monitor check:
The monitor check ensures proper operation of the monitor or fail safe  function of SEMAs .
If one or more monitor lights fails to illuminate, SEMAs will remain operational. Increased awareness by Pilot is required.
Note  Fail safe means free from possibility of SEMA hard-over - an uncommanded maximum authority output.
Note  The autopilot system, with or without the SEMA monitor intact, is not free from the possibility of a hard-over. However, hard-overs are extremely rare.

23. Overhead Electrical Panel

24. Autopilot Functions Attitude hold in pitch & roll with beep
Full-time pitch and roll SAS
ALT - Altitude hold
A/S - Airspeed hold
HDG - Heading select via HSI heading bug
NAV - GPS intercept and track (optional)
YAW - SAS (optional)

25. General Information
The autopilot is designed for full-time operations - on prior to takeoff; off after landing.
For proper performance, the AUTOTRIM switch must be on.*
Turning off the FORCE TRIM switch causes the autopilot to operate in the SAS mode thereby inhibiting coupling, but continuing to provide enhanced stability during “hand flying” of the helicopter. There is no annunciation of the SAS mode, and the upper modes will show engagement (the selected buttons illuminate), but the function will not perform properly.
Manual beep trim (via 4-way cyclic switch) and autotrim function are inhibited via the cross-tube “squat” switch when on the ground.
In flight, manual beep trim is inhibited when autopilot is engaged. With autopilot engaged in attitude hold (no upper modes selected), activation of 4-way switch modifies attitude memory of autopilot at approximately 4°/second in roll and 2 to 3°/second in pitch.
Engagement of upper modes(s) inhibits manual beep trim in the engaged axis or axes.
* The AUTOTRIM switch enables the motors in the trim units for manual beep trim and autotrim. Except for the rare case of trim runaway, this switch should never be turned off.

26. General Info (cont.)
When operating in the attitude hold mode, to establish or modify the attitude in the memory of the autopilot computer, either of two methods may be used:
The helicopter may maneuvered to the desired attitude with the force trim release (FTR) button on the cyclic depressed. Releasing the FTR button establishes the new attitude as the reference.
From an existing attitude, the pilot may “beep” the memory via the 4-way switch on the pilot’s cyclic. Activating this switch changes the memory at the approximate rate of:
in pitch, 2 to 3° per second.
In roll, 4° per second.
The yaw SAS provides excellent stability during hovering flight and requires no direct pilot action other than engaging the axis.
Yaw SAS does not provide turn coordination or side-slip control.
There is no trim actuator in the yaw axis; the pilot should keep his feet on the pedals.

27. General Info. (cont.)
Only one pitch and one roll upper mode can be engaged. When operating in a pitch and/or roll upper mode, selection of another mode in that axis, results in cancellation of the first and selection of the second.
Airspeed has a major effect on upper mode performance. When attempting to couple to a roll mode (HDG or NAV) at less than 75 knots, a slow roll oscillation or S-turns may be observed. As airspeed decreases, the oscillation will increase to an unacceptable level.
Attempting to maintain altitude (ALT) at less than 75 knots will result in performance that ranges from sluggish to unacceptable depending on airspeed.
The airspeed hold mode functions reasonably well down to 50 knots airspeed.
The performance of the attitude hold mode functions well throughout the airspeed envelope and is essentially independent of the airspeed.

28. Recommended Procedures
USE OF THE AUTOPILOT CAN SIGNIFICANTLY REDUCE PILOT WORKLOAD AND AID IN FLIGHT PATH ACCURACY.
IT PROVIDES FOR A SIGNIFICANT AMOUNT OF FLEXIBILITY. WHAT IS “RIGHT” FOR ONE PILOT IS NOT NECESSARILY RIGHT FOR ANOTHER.
THE FOLLOWING RECOMMENDED PROCEDURES ARE JUST THAT: “RECOMMENDED”.
EACH PILOT SHOULD DEVELOP AN UNDERSTANDING OF THE AUTOPILOT SYSTEM - WHAT IT CAN AND CANNOT DO, SO THAT HE CAN FORM INTELLIGENT PROCEDURES AND REDUCE HIS WORK EFFORT.

29. Recommended Procedures For Use of Force Trim
During short-term hovering prior to takeoff, it is recommended that the FORCE TRIM switch remain on. The may pilot hold-down the cyclic-mounted trim release switch to relieve the forces on the cyclic.
For prolonged hovering, the overhead FORCE TRIM switch may be turned off, but neither attitude hold nor coupling will function properly if the switch remains off once in forward flight.
During training or routine traffic pattern operations, it is often desirable to operate with the FORCE TRIM switch off. With the autopilot on and force trim off, enhanced stability will be provided by the autopilot, but attitude hold and coupling will not function properly.

30. Takeoff and Climb
Always check to see that the AUTOTRIM switch is on before liftoff to a hover.
Prior to transition from hover to forward flight or, at the latest, during climb, the FORCE TRIM switch should be on.
Climbs can be accomplished in either the pitch attitude hold or A/S mode.
Pitch attitude hold: At any point beyond 60 knots (with the roll axis coupled to HDG or NAV, if desired), adjust power as desired and maneuver to a pitch attitude approximating that required to maintain both the desired airspeed and rate of climb. Fine tune the attitude with incremental action on the 4-way beep switch. Remove hand from cyclic.
Airspeed hold (A/S): Once the desired airspeed is attained - 60 knots or greater - engage A/S. Power changes may result in small deviations from the selected airspeed. Remove hand from cyclic.

31. Takeoff and Climb Airspeed limitations Vertical Speed Limitation
60 KIAS or less pilot must keep his hand on cyclic
60 KIAS minimum speed for Airspeed Hold
75 KIAS minimum speed for Heading Hold
75 KIAS minimum airspeed for Altitude Hold
Vertical Speed Limitation
1,000 feet/minute rate of climb or more, the pilot must keep his hand on cyclic

32. Autopilot Safety Limits
An understanding of the pitch and roll safety limits can be important to the getting the maximum performance from the autopilot. Safety limits apply only when an upper mode is engaged:
The autopilot computer has internal limits for pitch and roll as a safety limit during autopilot maneuvering. The roll attitude is +20° and since the autopilot controls the bank angle to approximate a standard rate turn, the roll angle is always less than the safety limit; so there is no noticeable effect.
The pitch safety limit is imposed at +7° from the attitude at at the time of upper mode is engagement. During normal pitch maneuvers 7° is adequate. However, when making the transition from a high-climb-rate to level-off, it is possible to encounter this limit. The level-off performance can be significantly impacted. Seven degrees is adequate for climb rates up to 1,500 feet per minute, but at greater climb-rates, at execution of ALT, the nose will pitch down 7°, the climb rate will be significantly reduced, but the temporary altitude overshoot can exceed 300 feet.

33. Autopilot Safety Limits
After a AFCS failure to ensure Adequate control margins exist for takeoff and approach maintain the relative wind within +/- 35 degrees of the nose.
Adequate control margins exist while hovering sideward, rearward flight or crosswind and tailwinds to 17 knots with relative wind azimuths.

34. Climb to Level-off
Some thoughts on pilot technique during transition from climb to altitude hold (ALT):
As previously discussed, the pitch safety limit can restrict altitude level-off performance. To avoid this, the maximum climb rate should be limited to 1,500 feet per minute prior to engaging ALT.
The pitch safety limit has a greater impact on level-off from climbs than from descents.
A restrictor in the static line to dampen indicator vibrations, induces a lag in altimeter indication. This lag becomes evident at vertical rates of 1,000 feet per minute and increases as vertical rate increases. The lag-induced error can exceed 50 feet. Engaging ALT can result in actual level-off 50 feet or more above/below desired altitude.

35. SEMA & Trim Actuator Limitations
During the initial adaptation of an autopilot system in a new type helicopter, the first step is to determine the authority of the SEMA in each axis. This is done by inducing hard-overs (forcing the actuator to extend / retract its maximum amount) and evaluating the result. This is a tightrope between the maximum authority and failure characteristics. Since the SEMAs perform the autopilot maneuvering of the helicopter, the maximum possible authority is desired.
The function of the automatic trim system is to compensate for the limited authority of the SEMAs. However, when a SEMA is driven hard-over, if autotrim reacted immediately, the trim actuator would be driven in the same direction as the SEMA adding to the results. To avoid this compounding effect, the trim computer has a built-in delay of approximately 3.5 seconds.

36. SEMA & Trim Actuator Limitations
Another troublesome problem in certification is that of trim runaway. This is controlled to a major extent by reducing the speed at which the trim actuators operate to a rate that results in an acceptable failure response.
The combination of limited SEMA authority, autotrim delay, and controlled trim speed present a situation whereby the pilot can easily demand more than the autopilot can do as described in the following slide.

37. Cruise Performance and The Judicious Use of Power
All single-rotor helicopters have coupling between the collective and longitudinal axis. As power is changed, if unsuppressed, the pitch attitude follows the direction of the collective motion. Increased power results in pitch up and vice versa for power reductions.

38. Cruise Performance and The Judicious Use of Power
The Model 407 is different only in the degree of coupling - let’s call it significantly greater than the norm. This problem is most pronounced when cruising in the ALT mode. The coupling makes it incumbent on the pilot to exercise caution in the application of power. The SEMAs fly the helicopter, and they have extreme authority limits - roughly the equivalent of 3/8 inch of cyclic movement. The combination of autotrim delay and slow trim speed makes it impossible for the autopilot to keep up with major power changes. The pilot should endeavor to limit power changes during altitude hold to 10% torque. Then he should wait for a few seconds for the autopilot to catch up, then make additional power changes.
If major power changes are required, make them as necessary, and manually trim by depressing the FTR and moving the cyclic in the proper direction, then release the FTR. The resulting cyclic position may not be perfect, but the autotrim system will correct any position errors made by the pilot.

39. Instrument Approaches
The autopilot is limited to VFR operations, but it can be used during simulated approaches or inadvertent IFR. Consider use of the following procedure:
For GPS approaches, couple to the GPS, maintain a minimum of 75 knots until the FAF. Control the altitude with a combination of ALT and A/S (A/S for descents). At the FAF the GPS reaches it’s maximum sensitivity and the autopilot may end up doing a series of S-turns due to excessive sensitivity. Switch from NAV to HDG if necessary, and make small incremental heading bug changes to remain on course.
For an ILS approach, use HDG to maintain localizer and, at glide slope capture, switch from ALT to A/S and maintain the glide slope with collective changes. Keep power changes as small as practical. At approximately 500 to 400 feet above touchdown, the localizer and glide slope become increasingly sensitive and difficult to maintain. A little practice is required in anticipation and limiting overcontrol, but it is possible to get close enough to “save your bacon” should it becomes necessary.

40. Possible Future AP Control Panels
ALT
A/S
HDG
AUTOPILOT
TRIM
TEST
V/S
NAV
ALT P/S
ARM
PITCH
ROLL
P/N
P/N
P/N
AMC

41. NOW YOU KNOW EVERYTHING THERE IS TO KNOW ABOUT THE 407 AUTOPILOT
TAKE A NEW LOOK AT THE SCHEMATIC TO MAKE SURE YOU DO UNDERSTAND

42. OPTIONAL
N/A BH407

43. Trouble-shooting (or things to consider)
THE FOLLOWING IS PROVIDED AS AN AID IN TROUBLE-SHOOTING.
For initial engagement, the follow is required:
28 volts dc
26 volts ac (required for synchro reference)
A valid signal from the vertical gyro
If copilot’s cyclic is removed, jumper connector  must be installed
Assuming the first 3 requirements are met, the autopilot should never disengage, even due to extreme maneuvering.
Requirements for attitude hold and coupling of upper pitch modes:
FORCE TRIM & AUTOTRIM switches must be on.
Requirements for Heading Select mode:
Valid directional gyro
Requirements for GPS coupling:
Valid GPS signal
Note  Without the jumper, AP Disconnect and FTR switches (on cyclic) are open. The AP will not engage and the FTR switch will be inoperative (trim will not release).

44. Strange Problem
So that you will be aware, one problem that you may encounter is the following:
When the pilot selects ALT on the controller, a signal is simultaneously sent to the AP computer and BARAN signaling each that the selected mode is altitude hold. It seems that the autopilot always “gets the word”, but due (we think) to high resistance in the controller, the signal to the BARAN is marginal, and the BARAN does not know the autopilot is in the altitude hold mode.
It is the job of the BARAN to develop error signals that tell the autopilot when it is drifting off the “selected” altitude, but since it doesn’t know ALT is engaged, it doesn’t send the required error signals. No signals mean no correction. The result is the autopilot holds pitch attitude and makes no corrections when the helicopter drifts off the altitude.
If you recognize these symptoms, recycle the ALT button. Chances are that it will work. If you fly a 407 that occasionally exhibits this problem, please contact SFIM. See the last page for phone numbers.
A change is coming - in fact, two changes are coming: One is to change the value of a resistor in the controller; the second, is a new controller. Both changes require changes to the STC documentation and that always takes more time than it should.

45. When All Else Fails:
SFIM, Inc. is located in Grand Prairie, Texas. As the SFIM / SAGEM North American Service Center, all autopilot components except the BARAN (manufactured by Thales) can be repaired in this facility. The BARAN can be tested for proper operation, but must be returned to the manufacturer for repair.
Air Methods has spare autopilot components available.
Occasionally, a problem will occur that seems to defy all logic. If that happens, contact one of the following:
Don Shaw, AP Engineer
Jake Hart, Pilot
Don and Jake were involved in development and certification of the 407 autopilot. Most of the time they can help.