ENGINE CONTROL SYS Flashcards
What type of engine do we have?
T700-GE-401C front drive turboshaft engine
How can ambient air be heated via the anti-ice system in the inlet cowling?
air can be heated via the inlet anti-ice valve or via the inlet surface which is perforated with small slits to allow 5th stage bleed air to heat the inlet surface
What type of compressor do we have?
5-stage axial, single-stage centrifugal
What type of combustion chamber do we have? How many ignitors and fuel injectors?
flow-through annular combustion chamber with 2 igniter, 12 fuel injectors, and 1 exciter
What type of turbines do we have?
dual stage coaxial turbines (Np lives inside Ng)
Where is TGT measured?
between the Ng and Np turbines using 7 thermocouples
What does the Ng turbine drive?
the compressor and the accessory gear box
What does the Np turbine drive?
the power turbine drive shaft
The power turbine drive shaft extends through the front of the engine and connects to the high speed shaft which connects to the input modules
Explain the breakdown of airflow in the engine. (Think %)
30% of the total airflow through the engine is used for combustion
70% is used for: compressor inlet air temperature (T2) compressor discharge air pressure (P3) combustion and turbine cooling engine oil seal pressurization
Name the five major components of the engine control system.
HMU, ODV, EDECU, engine-driven alternator, fuel flow control valves
Name the three inputs to the HMU.
- Mechanical (PAS / LDS)
- Electrical (torque motor servo to trim Ng speed)
- T2, P3, Ng (control variable geometry vane and anti-ice valve position during start)
Name the functions of the HMU. (RANFAN)
R - rapid engine transient response through collective compensation. (LDS)
A - automatic fuel scheduling for engine start (PAS)
N - Ng overspeed protection (110+/-2%)
F - flameout and compressor stall protection (variable geometry vane)
A - acceleration limiting
N - Ng governing (T2, P3, Ng to sked fuel flow)
What does the variable geometry vane servo do?
using fuel tapped from the HMU, the servo opens the anti-ice / start bleed valve preventing compressor instability
the valve opens at 88% Ng and closes at 90% or 94% with OAT > 15C
What is the relationship between the torque motor servo and the metering valve?
the metering valve schedules engine fuel flow commensurate to the current power demand
the torque motor servo trims fuel flow by the the metering valve in response to the EDECU
What does the linear variable displacement transducer (LVDT) do?
provides a feedback signal to the EDECU to null the torque motor servo input therefore stabilizing the metering valve and preventing engine oscillation/hunting
What does EDECU stand for?
enhanced digital electronic control unit
What inputs does the EDECU take from the cockpit?
engine speed trim switch
contingency power switch
engine overspeed test A/B
What inputs does the EDECU take from the helo?
torque from the other EDECU
Np demand
400-Hz backup power
HMU (via LVDT)
Name the functions of the EDECU. (4N CHEF TASTED)
N - Np governing
N - Np overspeed protection
N - Np overspeed test
N - Ng decay relight feature
C - Contingency power
H - Hot start prevention
E - Engine load sharing
F - Fault diagnostic system
T - TGT limiting
A - Auto-ignition system
S - Cockpit Signals
T - Transient droop improvement
E - Engine speed trim
D - EDECU lockout
Np governing
Np sensor located on left side of the power turbine sends signal to EDECU
actual vs. a reference Np is compared to compute a speed error
Np overspeed protection
when Np > 120%, a signal is sent from EDECU to ODV, diverting fuel to the inlet of the HMU therefore causing a flameout
Np overspeed test
activated via A/B, pressed together Np overspeed limit is re-referenced to 96%
Ng decay relight feature
if the engine flames out and exceeds Ng deceleration rate, the auto-ignition system will turn on igniters for 5 seconds in an attempt to relight the engine
this feature is disabled below 62% Ng
Contingency power: Manual, Auto, Dual-Eng
Manual - switch allows TGT up to 903C, max contingency range power limiter will prevent further fuel flow at 891+/-10C
Automatic - enabled in OEI conditions when torque of one engine < 50%, TGT limit reset from 866+/-10C to 891+/-10C (light will not illuminate)
Dual-engine auto - TGT up to 891+/-10C if the following exists: 1) Np < 96% 2) >3% droop between reference and actual Np 3) >5%/sec. Np droop with Np < Np reference
Hot start prevention
detects a hot start when TGT > 900C with Ng < 60% and Np < 50%, fuel flow is stopped.
fuel restored when TGT < 300C or after 25 seconds.
Engine load sharing
torque matching system will increase torque of the lower Q engine
Fault diagnostic system
displays fault codes on startup/shutdown, can be suppressed with A/B
TGT limiting
fuel flow stopped at 866+/-10C so that TGT does not exceed 878C.
Np/Nr will droop and Ng governing will be sacrificed to protect against an overtemp.
Auto-ignition system
triggered at Np = 120%, overspeed valve in the ODV opened to reroute fuel to HMU
when Np < 120%, valve closes and turns on igniters on a 5 sec. time to relight the engine. this will continue until Np/Nr are controlled
Cockpit signals
Np, TGT, and Q signals are sent to the cockpit display
Transient droop improvement
uses anticipator signals from the TDI Nr sensor and collective position
fuel flow increased via torque motor servo at low torque settings when collective demand increases rapidly
Engine speed trim
increase/decrease switch controls Np of both engines simultaneously between 96-101%
EDECU lockout (what do you lose and retain?)
Np and Ng with PAS and LDS positions only, torque motor servo is disabled (loss of TGT limiting, Np governing, and load sharing)
Np overspeed protection retained
Where does the engine anti-ice valve live in the engine?
Within the swirl vanes in the IPS
What does the inlet particle separator (IPS) consist of?
Swirl vanes which impart rotation to airflow and throws particles outward to the collection scroll. The dirty air in the collection scroll is thrown overboard with the blower assembly. Clean air is sent through the deswirl vanes with remove rotation and provide smooth airflow to the compressor.
Name the four main functions of the ODV.
“Provides, Purges, Traps, Returns”
- Provides main fuel flow to the 12 fuel injectors during engine start and operation.
- Purges the main fuel manifold overboard, after engine shutdown, to prevent coking of the fuel injectors.
- Traps fuel upstream, which keeps the fuel/oil heat exchanger full, so that system priming is not required prior to the next start.
- Returns fuel back to the HMU if the Np overspeed is energized or if the EDECU hot start preventer is activated.
