Engine Operation and Ground Running
TURBINE ENGINES Engine Operation and Ground Running Running
Specify the general precautions and prepre-start -start checks prior to ground running a gas turbine engine: ~ The aircraft should be facing into wind and securely chocked . ~ The visual and free movement of both compressor and turbine should be checked, and the engine air engine air intake examined for loose articles. articles. ~ The areas to the front and rear of the aircraft should be checked for loose articles and spilt fuel, which could cause a hazard to the aircraft during the run. ~ Prior to starting the engines all personnel involved must be made aware of their responsibilities and responsibilities and role during the run.
Describe general procedures procedures for starting, ground run runst opping a gas turbine engine: run-up -up and stopping ~ Starting procedures will vary depending on aircraft type and installation hence, the AMM must always be referred to. to. ~ a typical starting sequence is as follows: (1) rotate the compressor with the starter until a prescribed rpm is reached; (2) turn on the ignition; and (3) open the engine engine fuel valve, either by advancing advancing the aircraft throttle throttle from Off Off to Idle or by moving a fuel shutoff valve, or switch, depending upon the type of engine. up. ~ Look up the EGT rise as a first sign of engine light up. ~ Also look for rise in oil pressure (extinction of “oil low pressure” light), RPM, Fuel Flow and other parameters. ~ After engine running for maintenance checks requiring high power setting, engine is brought to idle power and run for a few minutes for cooling (a five-minute cooling period at Idle is usually desirable prior to shutdown). shutdown). engine by closing the main ~ Turbine engines are shut are shut down by the simple expedient of cutting off fuel to the engine by fuel shutoff valve, either with the fuel shutoff lever or switch, or by retarding the aircraft throttle to Off. ~ This is followed by switching off the aircraft aircraft fuel boost pumps. pumps.
Define what is meant by selfsustaining achieved: self --sustaining sustaining rpm and how this is achieved: ~ this is the minimum the minimum speed at which the engine can run unassisted ~ once above self-sustaining speed the starter and ignition will cut out automatically, automatically, and the engine will accelerate accelerate to ground idle
Describe the cycle of engine operation as the power lever is is advanced from ground idle to full power and back to ground idle:
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Engine Operation and Ground Running
Specify the indications, effects and remedial actions for the the following defects: a. Hung Hung start ~ After light up the engine RPM does not increase to ground idle, but remains at some lower value. ~ Hung starts are often caused by insufficient power to the starter motor, or the starter cutting out too soon. b. Hot Hot start ~ These occur when the EGT exceeds the manufacturers specified limits. ~ They normally result from too rich a fuel/air ratio. ~ The engine should be shut down immediately. c. Wet Wet start ~ Where the engine is being started with a quantity of fuel already pooled in the engine (perhaps the result of a previous failed start) or the pilot delays ignition beyond what is normal and allows fuel to pool in the engine before ignition. ~ Wet starts can result in a fire plume or a loud bang, and may damage the engine. ~ Makes a nice bang. ~ The most dramatic damage will be to the turbine blades due to pressure and heat failure. d. Poor acc acceleration eleration up to sustainable rpm ~ same as hung start ~ N2 fails to spin up sufficiently for fuel flow to be introduced. ~ Each start has a time limit and the start will be aborted. e. Over Over temp ~ If there is insufficient flow through the engine is enough to spin the N2 compressor prior to light off, the engine can quickly over temp and be damaged. ~ It is especially important to abort this kind of start as soon as an abnormality is detected. f. Compressor Compressor stall ~ Normally the flame doesn't go out, the engine just coughs. ~ If you are running an engine and it stalls, just quickly throttle back and it should recover. g. Compressor surge ~ complete stoppage of airflow or reversal of airflow ~ action same as compressor stall h. Lack of ignition ~ Fuel flow is introduced but light off has not occurred in a proper timeframe. ~ Fuel is building up in the engine and if light off does occur, it can be damaging. ~ The start is aborted and dry motoring is performed to clear the engine. i. Tail pipe fire ~ A tailpipe fire is caused by an excess of fuel in the combustion chamber, the turbine or the exhaust nozzle that ignites. ~ It can result in significant flames coming out of the engine exhaust or in smoke from either the exhaust or engine inlet. ~ Abort the start (or continue with the shutdown) to stop the flow of fuel to the engine. ~ Dry crank the engine to extinguish the flames and remove the remaining fuel from the engine.
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Engine Operation and Ground Running
j. Overspeed (Runaway N1 or N2) ~ If the FADEC isn't managing fuel flow properly, the engine may not settle but continue to spin up. ~ Abort the start. k. Over torque ~ Where the engine torque has exceeded the maximum allowable for a given operating condition or time limit. ~ Over torque can cause internal damage to an engine. ~ On some engine installations an overtorque limiter is installed to limit maximum engine output torque to a preset value. l. Bleed band or bleed valve stuck in the open or closed position ~ This will usually require an engine shutdown to remedy.
State the purpose of and describe the procedure of the following performance runs: a. engine engine trim ~ A maintenance procedure in which a turbine engine fuel control is adjusted. ~ The idling speed and the high-end performance are adjusted to cause the engine to produce the required EGT or EPR at the RPM specified by the engine manufacturer. ~ An engine should be re-trimmed anytime there is a decrease in engine thrust, or after maintenance action. b. power assurance ~ A test run made of a gas turbine engine to determine the way its performance compares with its performance when it was new or freshly overhauled. ~ Charts are followed to allow operators to monitor the condition of their engines and the results of maintenance actions. c. data data--plate speed che check ck ~ a check to see if the engine will run up to the specified rated RPM, EPR, EGT, etc. ~ performance specifications are recorded by the manufacturer or overhauler and recorded on the engine data plate d. torque check ~ turboprop and turboshafts ~ test run to ensure engine produces the specified torque at specified speeds and power settings e. trim trim balance
State the source of ambient data used during an engine run: ~ Where should ambient temperature be measured when trimming a turbine engine? ~ In a shaded area as near to the inlet as possible.
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Engine Operation and Ground Running
Interpret engine power output and limitation limitation charts and determine adjustment adjustment and rectification requirements: ~ see chart below for typical example of an engine test run
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Engine Operation and Ground Running
Describe the effects of antianti-ice system operation on engine performance for the various types of gas turbine engine and how this this would be shown in the cockpit: ~ The de-icing system on most turbine aircraft uses bleed air from the engines, that is it extracts some air from behind the (low pressure stage of the) compressor. ~ This air is therefore not ejected from the nozzle and not producing thrust , so the thrust is reduced, or fuel flow rate increased if thrust levers are advanced to compensate & fuel consumption increases. Describe the effects of high altitude operation on turboturbo-prop and turboturbo-fan engines with multiple or split compressors: ~ The fall of pressure reduces the air density and hence the mass airflow into the engine for a given engine speed. This causes the thrust or s.h.p. to fall. ~ For any given power setting the high-pressure compressor speed (N2) is held fairly constant by the fuel control. ~ The low-pressure compressor (N1) will speed up or slow down with changes in engine inlet conditions, ie. atmospheric changes and altitude, etc. ~ Altitude increase = less resistance = N1 RPM increase ~ This effect in some ways compensates for the reduced mass airflow through the engine by adding an increased ‘supercharging’ effect to the core engine as altitude increases.
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