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A beginner's doubt on jet engines



 
 
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  #21  
Old December 24th 04, 05:34 AM
Cockpit Colin
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10 Points to Bob, who got it first

Merry Christmas everyone.


"Cockpit Colin" wrote in message
...
For what it's worth, a 757 at ground idle produces around 3000 pounds

thrust
per engine - you can back them using the reversers, but you can't go full
power as the re-ingest the exhaust gasses.

And when you're backing you must always use forward thrust to stop, and

not
the brakes - anyone guess why?


"Ramapriya" wrote in message
oups.com...
I know that a car's engine needs to be mated to the transmission for
propulsion. This I know isn't the case with an aircraft with a jet
engine; if the engine is turned on without the brakes applied, the jet
of air leaving the engine will hurl the craft forward.

My doubt is, why does this forward motion effect not occur during
push-back, when the engines are normally turned on? Is it because at
low revs the engine would lack the punch to initiate the forward motion
of a heavy aircraft? If not, I'd imagine the push-back becomes a bit of
a tiresome affair by the time it's over...

Sorry if this is infuriatingly elementary, but I need to ask somewhere


Ramapriya






  #22  
Old December 24th 04, 08:59 AM
Marty
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"Cockpit Colin" wrote in message
...
10 Points to Bob, who got it first

Merry Christmas everyone.


Tail strike was my first thought only because I did it in my TriPacer when a
friend got over zealous pushing me back into a tiedown. We had just got back
from OSH and the back seat & cargo was full of gear tho. ;-)

Merry X-Mas to all,

Marty



  #23  
Old December 24th 04, 03:33 PM
Greg Faris
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Never seen jets do this. I have seen turboprops do it at one airport
(Southhampton UK). I would think airport ops would be worried about loose
tools, articles debris (like ramp agents) getting thrown through the
terminal's picture windows if heavier aircraft start doing this!

G Faris

"Jay Beckman" wrote in message
news:3buyd.350$yW5.320@fed1read02...
"Ramapriya" wrote in message
oups.com...
I know that a car's engine needs to be mated to the transmission for
propulsion. This I know isn't the case with an aircraft with a jet
engine; if the engine is turned on without the brakes applied, the jet
of air leaving the engine will hurl the craft forward.

My doubt is, why does this forward motion effect not occur during
push-back, when the engines are normally turned on? Is it because at
low revs the engine would lack the punch to initiate the forward motion
of a heavy aircraft? If not, I'd imagine the push-back becomes a bit of
a tiresome affair by the time it's over...

Sorry if this is infuriatingly elementary, but I need to ask somewhere


Ramapriya



Sometimes they don't even need a tug to get away from the gate...

I've been on American Airlines MD80s that have pushed back under their own
power via their reversers.

Jay Beckman
PP-ASEL
Chandler, AZ




  #24  
Old December 24th 04, 04:10 PM
Bob Moore
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"Greg Faris" wrote

Never seen jets do this. I have seen turboprops do it at one airport
(Southhampton UK). I would think airport ops would be worried about
loose tools, articles debris (like ramp agents) getting thrown through
the terminal's picture windows if heavier aircraft start doing this!


Yes...here in the US, the FAA grants permission for "Power-Back"
operations at specific gates and specific aircraft. Pilots
receive special training before they are allowed to conduct
Power-Back operations. I did Power-Back operations in B-727 a/c.

Bob Moore
ATP B-707 B-727
PanAm (retired)
 




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