Gas Trubine Control And Operation Flashcards
Engine start sequence
~ignition commences
~air start velve opens
~min fuel is delivered into the primary zone (HPSOV)
Types of the starter motor
~air pneumatic starter :driven by compressor air and controller by an air start valve
~electrical strter/genrator : use don More electric a/c
~during strat ac electric spins motor truning the accesory gearbox
~once at ground idle,the sys flips to genrator mode
Start malfunctions
It may be that 15 min its needed between each cycle of starting an engine to allow the starter motor to cool down
Abnorml, ~dry start ~hung start >>( ~hot start ~wet start
In addition may result in a tailpipe fire
~this will not illluminate an eng warning
~it may or may not be indicate through a high EGT
~the eng should be shut down ,any fire extinguisher and eng should be examined for damaged
Dry strat
~low rpm
~no egt rise
~no fuel flwo
~maybe malfunction of the HPSOV
Hung start
Low and stagnating rpm
High egt
Low fuel flow
~low bleed pressure
~engine failing to reach self sustaining speed
Hot strat
~normal increase in rpm
~rapid excessive egt rise
~normal fuel flow
~possible following a previous failled strat attempt
Wet start
~low and stagnating rpm
~no egt rise
~some indicated feul flow
A dry run (clow trhough) should be carried out
Mutpi spool eng start
~at ground idle ther will be a marked difference in rotational speeds between N1 and N2
~n1 20/25%
~n2 50/60%
~flight idle only availble in fllight is a higher idle setting allowing the eng to respond to any speed increase quicker
Airborne relight
Starting mean sin the ground
Relighting means strating in the air
~starter motor circuit will not be required as the eng will be windmilling
~altitude and airspeed must be considered into account
Usually below 25000ft and 250kts
Thrust indications
~max take off : this is the max allowed ,usually time limited
~max continuous :the maximum thrust that can be used continuosly
~go around: might have have different N1 or EPR values
~max climb: used for routine all engines climb
Epr and thrust indications
~engine pressure ratio
~accurate method to indicate pressure thrust
~copares the pressure in the intake
~if sensors beomecs unavailble the eng revert to N1 trhust settings
N1 and thrust indications
~n1 thust setting
~thrust set by a percentageof fan rpm
~Fadec will rotate N2 to a desired value in order to provide an N1 rotation and given thrust setting
Turbo pro p torque indications
~percentage of maximum ,torque
~usually measured using oil pressure or an elctric wheatstone bridge
~in take off or high power conditions percentage may exceed 100% fro a limited time
De rate and flex thrust
~in order to maximise engine life
~the eng will provide thrust in a worst case scenario,high altitude and high take off mass
~under all other conditions,especially cold and sea level enviroments the engine will perform better than required
~under these conditions the crew can legally plan a reuduced power take off
~two methis possibile
De rate
Felxible(flex) thrust
De rating
~de rating reduces the thrust available from the max value
~for instance
If the produces a maximum of 264000lb of thrust
Its possibile to set 24000 via the fmc
~this has the effect of imposing a lower thrust limit on the engine
The Vmcg and Vmca speeds will change and are available through the performance manual
~the disadvantage of this system is full thrust is not available should it be required
Flex tresut
~is another alternative mens to reducing eng trhust on take off
~the most common method is to use an assumesd temperature method
~benefit of this method id that if full thrust required the thrust levers can be set to TO/GA to disregard the flex configuration.as full thrust is available ,Vmcg and Vmca msut be calculated based on full thrust settings
Thrust in flight ,low by pass
~as altitude increase outside air become less dense ,this cause a change in availble thrust
~as the mass flow of air decreases ,fadec or barometric controller will adjust the fuel flow accordingly
~ a fall in temperature will cause an increase in density ,mass flow will increase and thrust available will increase
~in the clim,the combines effects will cause
High by pass
In a high pass things are broadly the same
~however ,the reduction in thrust as speed increase can be more pronounced
~this is due to lower ram effect in the by pass duct
~ram effect ,increasing mass flow as tas increase,raises the static pressure within the intake to improve compression ratio
~ as fuel consumption isproportional to temperrure ,in the cruise the high by p[ass trubofan becomes more fuel efficent
Thrust can be reduced
Fuel will be reduced
Engine vibration indication
~piezo electric crystal is used to detect vibration
Engine seizure
Engines one or both spools stop rotating
Lack lubrification
~failure of the compressure
