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Functions of the Stabilator
SCALP
- Streamlines with rotor downwash at low speeds (<30 knots) (A/S & Air Data Transducers)
- Collective Coupling to minimize pitch attitude excurtions due to collective inputs (Coll. Pos. Transducer)
- Angle of Incidence decreases above 30 KIAS to improve static stability (A/S & Air Data Transducers)
- Lateral Sideslip to pitch coupling to reduce susceptibility to gusts. Up - nose right, down, nose left. (LatAccelerometers)
- Pitch Rate Feedback to improve dynamic stability. Dampens pitch excursions (Pitch Rate Gyros)
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Funtions of the ECU
NOT THIS
- Np reference set by Pilot (96-100%)
- Overspeed Protection (Np overspeed 106%)
- TQ matching Load Sharing. TQ will increase to share, but not decrease (3% above reference)
- TGT Limiting (843 + or - 9) Except during start, comp stall, and ECU lockout
- History Recorder signals
- Isochronous Np Governing. ECU will maintain Np reference set by pilot. Trims HMU through TQ motor
- Signals to the Cockpit (Np, TGT, TQ)
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Alternator
ANIE
- Ng signal
- Ignition power to exciter boxes
- ECU power
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Fuel Flow
PFHLP
- Pump (Engine Driven Fuel Pump)
- Fuel Filter
- HMU
- Liquid to Liquid Cooler
- POU
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Funtions of the POU
MOPS
- Main fuel sequencing for starting and engine operation
- Overspeed Protection (Np) solonoid activation from ECU to limit fuel flow (106 +or- 1%)
- Purges Start and Main Fuel on shutdown to prevent coking
- Sequences Start and Main Fuel for engine start
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Functions of the HMU
PM CAN VETO
- Pumps fuel at high pressure (400-832 psi.)
- Meters fuel to POU in response to PAS, LDS, TQ motor from ECU & ENG variables
- Collective
Pitch Compensation through the LDS- Accel
/Decel fuel flow limiting to prevent compressor stall, flameout & ENG damage (Ng)- Ng
limiting - Limits max TQ available under low temp conditions- Variable
Geometry Postioning of the inlet guide vanes for optimum performance- ECU
Lockout - PAS Override & Control- Torque
Motor to trim Ng output. Fine tune engine output (Np Governing)- Opens
Vapor Vent for manual HMU priming to remove air from HMU
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Mechanical Mixing Unit
- Collective to Pitch - Compensates for rotor downwash on stabilator
- Collective to Roll - Translating Tendency
- Collective to Yaw - Torque Effect
- Yaw to Pitch - Lift component of the Tail Rotor
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TRIM
- Provides a gradient force
- Maintains position of cyclic and pedals
- Provides muscle for FPS
- 2 Electromechanical actuators (Roll & Yaw)
- 1 Electro-Hydro-Mechanical acuator (Pitch)
- Boost required for operation
- Slip clutch requires 80 lbs of force in yaw and 13 lbs roll
- Hard-over causes caution/advisory lights and can move cyclic 1/2 in and pedals 1/4 in
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Electronic Coupling
- Collective to Airspeed to Yaw
- compensates for TQ effect in addition to Collective to Yaw mixing
- Function of the Trim Card
- Provides 100% below 40 Kts to 0% at 100 kts
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FPS (Basic Autopilot)
- Enhances Static Stability
- Long-term rate dampening in pitch, roll, and yaw
- 100% control authority when coupled with Trim
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These systems must be on and operational for FPS to have 100% control authority
- SAS 1 and /or SAS 2
- Boost
- Trim
- Stabilator (helps, but not required)
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FPS functions below 60 kts and above 60 kts
- Below 60 kts Above 60 kts
- Att Hold Pitch Att Hold/AS Hold
- Att Hold Roll Att Hold
- Head Hold Yaw Head Hold/Turn Coord
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What does SAS do?
- Enhances dynamic stability through short-term rate dampening in pitch, roll, and yaw
- 5% control authority each (electrical limit)
- 10% total (mechanical limit)
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SAS 1
- Brain is SAS amp in avionics compartment
- 5% control authority
- Inputs to SAS 1:
- Pitch - #1 Stab amp
- Roll - pilot's vertical gyro
- Yaw - SAS 1 amp
- Airspeed - A/S transducer
- Malunction indicates by erratic movement of helicopter ( no lights)
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SAS 2
- Brain is SAS/FPS computer under center console
- 5% control authority
- Inputs:
- Pitch - #2 Stab amp
- Roll - roll rate gyro (nose)
- Yaw - yaw rate gyro (nose)
- Airspeed - air data transducer
- Malfunction indicated by SAS 2 failure advisory light on AFCS panel
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During hover, rotor blades move large amounts of air through the rotor system in a downward direction. This movement of air also introduces another element—induced flow—into relative wind, which alters the AOA of the airfoil. If there is no induced flow, relative wind is opposite and parallel to the flight path of the airfoil. With a downward airflow altering the relative wind, the AOA is decreased so less aerodynamic force is produced. This change requires the aviator to increase collective pitch to produce enough aerodynamic force to hover.
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Ground effect is the increased efficiency of the rotor system caused by interference of the airflow when near the ground. Ground effect permits relative wind to be more horizontal, lift vector to be more vertical, and induced drag to be reduced. These allow the rotor system to be more efficient. The aviator achieves maximum ground effect when hovering over smooth hard surfaces. When the aviator hovers over such terrain as tall grass, trees, bushes, rough terrain, and water, maximum ground effect is reduced. Two reasons for this phenomenon are induced flow and vortex generation.
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The benefit of placing the helicopter near the ground is lost above IGE altitude. Above this altitude, the power required to hover remains nearly constant, given similar conditions (such as wind). Figure 1-50, page 1-36, shows OGE hover. Induced flow velocity is increased causing a decrease in AOA. A higher blade pitch angle is required to maintain the same AOA as in IGE hover. The increased pitch angle also creates more drag. More power to hover OGE than IGE is required by this increased pitch angle and drag.
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