AVIONICS
HMM – Do you use “smart” servos? DuRall – If you mean, “Do the servos have independent
processors?”, then no. The HeliSAS uses two servos with digital stepper motors, clutches and feedback solenoids. HMM – Can the HeliSAS and, if installed, fl ight director
information be displayed on analog ADI and HSIs as well as EFIS?
DuRall – Flight director information is only displayed on the Genesys EFIS. The navigation and heading inputs can be displayed on other EFIS including the Garmin G500/600/1000 and Aspen PFD/MFD, or can be displayed on an analog HSI such as the Bendix/King KI-525A. HMM – If the HeliSAS is a digital system, exactly what does the term digital mean in this case? DuRall – The system is digital in the fact that any
analog input is converted into a digital signal inside of the FCC, and the FCC uses its two microprocessors to perform computations which are then converted into analog signals to drive the servos. Additionally, the FCC accepts digital data from external sensors typically using the ARINC 429 serial bus standard. The digital processing allows for a tighter, more accurate control of the entire system. HMM – How many LRUs are in the system, and what are their functions? DuRall – The HeliSAS can contain up to fi ve LRUs, depending on the confi guration installed with a maximum total weight of approximately 13 pounds. These sensors include the FCC, two servos, an external attitude source and an optional HeliSAS control panel (HCP). The “brains” of the system is the FCC which contains
three-axis accelerometers and rate sensors, pitot and static pressure sensors, and two independent processors that continuously compare both internal and external sensor data. The processors calculate control laws and compare the results between each other. If there is a diff erence, the FCC will shut down. The FCC includes a stick-rate monitor that senses excessive movement of the fl ight controls and shuts the system down if detected.
Genesys ADAHRS The servos are connected in parallel with the aircraft Flight Control Computer
The HCP is installed when autopilot coupling is desired. This includes heading, VOR, localizer, glideslope and GPS steering. The HCP is the mode controller for the HeliSAS and contains six push-button switches with multi-colored LEDs to quickly identify the modes of operation in use. When an SAS-only confi guration is installed, the HCP is replaced with a SAS on/off switch.
controls, and the servo clutches are set for approximately nine pounds of force. Paralleling the servos allows for a lighter, less expensive servo that can tailor the force-feel characteristics without the mechanical tension that occurs with series servos, and eliminates servo saturation in turbulent air. The low clutch setting allows the pilot to “fl y through” the servos if needed with minimal force to reposition the aircraft controls as required.
HeliSAS Control Panel An external attitude source is needed to provide
redundancy comparison of the internal sensors in the FCC. The attitude source can be analog from an attitude indicator (ADI) with autopilot pick-off s, or an ADAHRS, such as the Genesys ADAHRS or Garmin AHRS with the G500/600/1000 EFIS.
Castleberry ADI
Pitch or Roll Servo 14
HelicopterMaintenanceMagazine.com December 2014 | January 2015
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