DECU / EDECU Flashcards
T2
Compressor inlet temp
P3
Compressor discharge pressure
HMU responds to Collective position through LDS for what
Coordinates Ng speeds
HMU responds to PCL through PAS for:
Fuel shutoff Engine start fuel glow w/ automatic acceleration to ground idle Setting Ng up to permissible max Fuel Priming DECU override (Lockout)
HMU responds to T2, P3, Ng for
to control variable stator vanes and anti-ice / start bleed valve position and max/min flow
Feedback signal from HMU to decu
through LVDT (Linear variable displacement transducer) to null torque motor servo and stabilize metering valve
Ng overspeed valve trips at ____
110 +_2
Spring loaded ball valve ports fuel pressure cuasing the minimum pressure valve to secure flow
PAS sets max available Ng, and gives engine power more than required for 2 reasons
- Fail safe to high power, torque motor reduces power normally, but if electrical power to torque motor is lost it returns to the highest so you can adjust with the PCLs
- Power available with OEI
HMU provides
Rapid engine transient response through collective compensation
Acceleration Limiting - Rapid PCL movement won’t damage engines
Ng overspeed protection 110 +_ 2
Ng governing through T2, P3, Ng
Automatic fuel for engine start
Flameout and compressor stall prevention through anti-ice/start bleed valves
What opens the shutoff valve in HMU to ODV
PCL moving to IDLE
Four functions of ODV, overspeed drain valve
Traps fuel upstream which keeps fuel/oil heat exchanger full so that priming is not necessary
Returns fuel back to HMU if Np overspeed is energized or hot start
Main fuel flow to 12 fuel injectors
Purges main fuel manifold overboard after shutdown to prevent coking
DECU control parameters
Np sensing (governing)
Np overspeed and torque sensing
TGT monitoring
Inputs to DECU from cockpit
ENG SPD Trim switch
CONTGCY PWR switch
ENG OVERSPEED TEST A and B
Inputs to DECU from helicopter
Torque demand from other DECU
Np demand
400 hz backup power
HMU (LVDT)
Signals from DECU to cockpit
Torque
Np
TGT
C power
DECU functions
400 hz Np overspeed protection Np governing Np overspeed test Ng auto decay relight feature C-power Hot start prevention Engine load sharing Fault diagnostics TGT limiting Auto-ignition Signals Transient droop improvement Eng spd trim DECU lockout
Np governing
Actual Np is compared to a reference Np
Np Overspeed protection
actuated at 120 Np, signal to ODV, diverts fuel to HMU causes engine flameout
W: ENG OVSP circuit breaker shall not be reset in flight, may result in engine failure by inititiating overspeed
TGT limiting
When TGT reaches 851 IRP or 878 MRP EDECU prevents increase in fuel flow.
839 +_ 10 IRP
866+_10 MRP
______ will be sacrificed to protect the engine against overtemperature
Np governing
Engine load sharing
Compares torque signal from other DECU, increases power on lower engine
Engine Speed trim
INCR / DECR
Controls Np between 96 and 101 percent
Contingency power
Allows TGT to increase to 903
CRP limiter will prevent further fuel flow at 891+_10
EDECU auto C-power enabled for OEI when one engine is below 50% trq, advisories will no illuminate
Np overspeed test
Np overspeed limit is re-referenced to 96 percent
DECU lockout
PCL manually controls Ng and Np
Lose TGT limiting, Np governing, and load sharing
IDLE then fly to regain
Hot start prevention
When TGT exceeds 900 with Ng below 60 and Np below 50, stops fuel flow by tripping ODV
Fuel flow restored when TGT less than 300 or 25 seconds
Can be disabled by holding OVSP TEST A and B
Fault diagnostic system
Codes
Can be suppressed and recalled by pressing either OVSPD test
Cleared and verified after engine at FLY
400 Hz airframe power
Decu powered by either engine alternator or 400 Hz aircraft power via ENG OVSP circuit breaker
Transient droop improvement TDI
Anticipates signals from TDI Nr sensor on left accessory module and collective position sensor in the mixing unit
Auto-ignition
Np overspeed, when Np drops below 120 the system closes the overspeed valve and turns on the igniters for 5 seconds
Continues to cycle until Np/Nr is controlled
Yaw kcik may be felt each relight
Ng decay relight feature
Auto ignition if engine flames out, turns on igniters for 5 seconds
Relight feature disabled below 62% Ng
