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Frasca's
Electric
Control Loading (ECL)
Allows for elaborate and realistic control
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Frasca's Electric Control Loading (ECL) system
is an advanced design that accurately simulates the forces acting on the aircraft control
surfaces in both static and dynamic conditions. The ECL system provides realistic levels
of resistance and inertia to the control stick and rudder pedals during all phases of
operation by representing the static "feel" of the controls while the aircraft
is stationary on the ground. The dynamic pressures act on the control surfaces during
taxiing, take-off, landing ground roll, and through entire range of the aircraft flight
envelope.
The ECL system provides a loading simulation
of all the forces acting on the three major axes of the primary flight controls. In the
case of a system failure, either the student or the instructor can immediately halt the
system.
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ECL Actuator
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ECL Actuator
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Each primary flight control axis (elevators, ailerons, and rudders)
connects through a precision mechanical linkage to a separate electrical actuator. A
single, highly integrated digital controller governs the three actuators through
independent servo-feedback loops to ensure highly accurate and stable operation of the ECL
system. In order to determine the appropriate control forces, the controller receives the
following information from the host computer:
- current aircraft configuration
- flight and environmental conditions
- Control system status.
The electrical actuators are self-contained electromechanical
assemblies mounted in the vicinity of the controls. Each actuator assembly includes the
following:
- electrical drive motor
- mechanical drive train
- position sensor
- Load sensing cell.
The digital ECL controller provides the ability to tune the
characteristics of the ECL system through a series of adjustable control system
parameters. Factory-set adjustments match these ECL system parameters to the aircraft
control system characteristics.
Design
The ECL system models the entire aircraft flight control system on a
one-for-one basis; that is, every significant element and aspect of the aircraft flight
controls (such as cable stiffness) is included in the model.
Since none of the control system parameters are combined together, the
control loading system has the same number of state variables as the aircraft flight
control system. In this way, the "feel" of the control loading system can be
accurately matched to the "feel" of the aircraft flight controls under both
static and dynamic conditions.
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ECL Panel from Cessna
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The ECL system accounts for all of the forces acting on the aircraft
controls to accurately simulate control "feel". These include but are not
limited to the following:
- Inertia
- Trim effects
- Static friction
- Cable stretch
- Control stops
- Stall buffeting
- Rate Damping
- Breakout force
- Coulomb friction
- Angle of attack effects
- Aerodynamic gradient
- Backlash (or deadband)
- Control force vs. control deflection for a given flight condition
- Control deflection vs. surface deflection
Electronics
The majority of the electronics for the ECL system are included in the
digital controller. In addition to a microprocessor-based control computer that handles
data communications with the host computer and calculates the appropriate control forces,
the digital controller includes output amplifier boards for each control axis and I/O
boards to drive the electrical actuators and monitor the servo-feedback loops.
The digital controller includes specialized hardware to monitor the
following ELC parameters:
- system status
- analog and resolver to digital conversions
- Digital–to-analog conversions.
Software in the digital controller performs the following functions:
- compute control forces
- monitor safety aborts
- Close the force feedback servo loop to drive the control actuators.
Each individual ECL actuator includes the following:
- interface hardware
- abort electronics
- motor amplifiers
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