AFCS Flashcards
System Description
Electrohydromechanical system that provides inputs to the flight control system to assist the pilot in maneuvering and handling the helicopter
Major Subsystems
- Stability Augmentation (SAS)
- Stabilator System
- Advanced Flight Control Computer (AFCC)
Each operate independently but all compliment each other
All Features
- Pitch, roll and yaw stability augmentation
- Stabilator control
- Cyclic, collective and pedal trim
- Pitch and roll attitude hold
- Airspeed hold
- Heading hold
- Barometric altitude hold
- Radar altitude hold
- Pitch and roll hover augmentation/gust alleviation
- Turn coordination
- Maneuvering stability
- Automatic approach to hover
- Hover coupler
- Automatic depart
- Crew hover
- Blad fold assist
- Automatic preflight check
- Diagnostics
- Cable angle hover
AFCC
Commands SAS actuators and trim actuators in all four channels
Provides self monitoring, fault isolation and failure advisory
Two types of control: inner and outer loop (both can be overridden by pilot input)
Inner-loop Control
Employs rate damping to improve dynamic stability
Fast in response, limited in authority and operates without movement of flight controls
Routed to SAS actuators
Outer-loop Control (Autopilot)
Provides long-term inputs by trimming flight controls to maintain selected flight regime
Capable of driving controls through full range of travel (100% authority) at a limited rate of 10% per second
Routed to TRIM actuators
Stabilator System
Primary purpose: eliminate nose-up attitudes caused by rotor downwash impinging on horizontal stabilator during transition to a hover and low-speed flight
Optimizes trim attitudes for cruise, climb and autorotative flight, and provides redundant pitch stability augmentation to compliment SAS
Automatic fly-by-wire control system with manual backup slew control
Stabilator TEST Button
Operational below 50 KIAS, tests automatic mode fault detector
Jackscrew Actuators
Two screws, each provide 1/2 input to position stabilator and controlled by redundant stab amplifier
Any system malfunction caused by difference in two actuator positions results in auto power shutdown to both actuators
Stab travel restricted to 35* if actuator fails in full-down position or 30* if actuator fails in full-up position
Stabilator Inputs
- Collective position
- Lateral acceleration
- Airspeed
- Pitch rate
Stability Augmentation System
Senses acceleration rate in the pitch, roll and yaw axes and applies control input to damped out sensed rate
Inner-loop system with two independent channels: SAS 1 and SAS 2
