Question about airliner engines

[Guest]

When they pull up to the gate the fan blades come to a stop, but how does the engine keep running? I always thought the compressor blades were linked right to the shaft, so I don't see how they can stop while the engine remains active...Thanks

[StoneC0ld 5]

I'm 99.8% sure they all do shut down the engines when parked at the gate, always.. Otherwise it would be too hazardous for ground crews working behind the engines as they'd be working in the jetwash to load the baggage, etc....They may run the APU (a small jet turbine in the tail) to power the aircraft and give it bleed air for the air conditioning (as well as air to start the engines) while parked, but I don't really know of a time when they'd leave the engines running at the gate...

[Guest CRJ700FO]

>When they pull up to the gate the fan blades come to a stop,>but how does the engine keep running? I always thought the>compressor blades were linked right to the shaft, so I don't>see how they can stop while the engine remains active...>>Thanks For jets:The blades are physically connected (via the N1/N2 shafts) to the turbines in the back of the engine. The turbines are not physically connected to the engines. The blades you see in a modern turbojet engine are connected via the N1 shaft. Once ground power is connected or the APU is turned on then the engines are shut down at the gate.The blades sometimes you will see spinning at the gate is simply caused by wind either coming in the front or back of the engine. They are simply free turning at that point. The actual blades themselves are fairly loosely connected to the shaft at low rpm (centrifugal force at higher rpms locks them into place) and when the N1 shaft is free turning it rattles quite a bit due to the blades not being locked in. This is also why vibration values vary for every engine start as the blades lock in at different times. If some don't quite balance out, a higher vibration generates.http://en.wikipedia.org/wiki/TurbofanFor props:In general, if a prop feathers upon shutdown (Saab 340, Beech 1900, Dash 8) then the prop is not physically connected to the engines. The props can free turn and not affect the engine. If a prop does not feather at shutdown, it is connected to the engine (Jetstream 31). Typically a prop will have a prop sock to hold the prop in place on overnights (a simple sleeve put on the prop and connected to the engine case / exhaust pipe / etc to keep it from spinning freely).http://en.wikipedia.org/wiki/TurbopropHope this answers your questions.