AVIONICS Irwin – The basic system will be available in the four
variants. The HFC-150 system has been designed for single pilot IFR at the TSO level. It provides independent SAS/ autopilot functions, integral gyro sensors and air data for redundant sub-systems. An altitude (ALT) mode, vertical speed (VS) mode and indicated airspeed (IAS) mode, along with other IFR features, are also provided. The system will also be available in dual versions using Moog Valve servo control actuation, with a later variant available using an integrated, partially-redundant electromechanical servo for medium-size helicopters. The dual system allows pilot selection of the active system or automatic transparent selection accompanied by annunciation in the event of a failure. Both systems are full-up, complete systems, with full navigation coupling and with the capability for redundant air-data and gyro sources, and each with their own integral back-up systems. Helicopter Maintenance – In describing the autopilot (AP) systems, you are also talking about modes that I normally associate with a fl ight director (FD). Are these modes part of the autopilots? Irwin – Yes, our autopilot systems combine the features of both an autopilot and what you refer to as a fl ight director in one digital fl ight guidance computer (DFGC). The DFGC does have a steering drive output to command FD steering bars, either single or two-cue types. Helicopter Maintenance – With respect to the fl ight
director, what lateral and vertical modes does it have? How many can be active at a time? Irwin – With the AP and FD functions fully integrated, functionally the diff erence is whether the AP servos are engaged. The FD is selected when the AP is “on” (engaged) simply using the controller-mounted AP on-off switch to switch the AP “on”. Deselecting AP (off ) with the controller switch will disconnect the autopilot and leave the existing modes for FD operation active and displayed. A second selection of the AP switch will remove (stow) the FD display and clear the modes. Disconnecting the AP with the remote disconnect switch will cancel and clear the modes and all functions, except SCAS. Helicopter Maintenance – Can fl ight director modes
be fl own manually in SAS? Irwin – Yes, the SAS function is completely independent of
the AP and will continue to operate with the AP disengaged. The SCAS function is not independent of the autopilot, because it uses AP servo control position feedback to tailor the SCAS response to reduce pilot control inputs in turbulence. If the AP position feedback fails, the SCAS will automatically revert to SAS functionality, and operate without the control feedback. SAS series actuator operations are transparent to the pilot,
moving only the aft control elements to the swash plate. They are very quick response, low-authority elements, while the AP operates with slower, parallel, full-authority servos. Both systems complement each other, but either system will operate without the other for redundant stabilization in the event of failure.
Helicopter Maintenance – What sensors does the system require?
18
HelicopterMaintenanceMagazine.com February | March 2014 Irwin – The basic system includes integral, solid-state
gyros and air-data transducers for all basic fl ight functions, but it will need a HDG bug and directional gyro input for the heading mode. It will also require navigation inputs for radio coupling — VOR/ILS/GPS modes. The system was designed as an “attitude” control system, with the integral gyros used as an IFR back-up safety system. As a result, system performance is improved when external attitude information is available. Autopilot use in hover fl ight requires attitude gyro references and heading references. However, all other modes and functions perform their intended functions regardless of the gyro sensor sources. Helicopter Maintenance – Must the sensor inputs be
digital?
System Controllers Irwin – No, the system will accommodate analog DC
synchro signals as well as ARINC 429 data. Helicopter Maintenance – Do you use “smart” servos (signal processing in the servo)? How about linear actuators? Irwin – The servos do not have internal processors.
However, they each provide integrity monitors that act independent of the DFGC during normal operation and failure modes, to determine proper servo command tracking and operation. The servos and actuators include motor controllers, direct position feedback sensors and integrity monitors that can stop errant servo/actuator operation, while also reporting servo operation back to the DFGC for system for evaluation and annunciation. Helicopter Maintenance – With so many uses of the
word digital being used in so many diff erent systems today, what does that word imply with regard to your system? Irwin – The system uses four digital signal processors and all control laws are executed in the processors. The DFGC is rack mounted, along with the air-data elements and the system confi guration module. They are mounted on the same rack and automatically connect to the installed DFGC when it is in the rack. All these components communicate digitally by design. The servos and actuators use stepper motors controlled by analog control signals and monitors. The controller is an analog switching device read by the computer at about 20 Hz.
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64