propilot83
Posts: 618
Joined: Sat Jan 27, 2001 2:41 am

Thrust Reversers

Fri Mar 27, 2009 5:52 am

I had a question for anyone who is a commercial airline pilot. My question is "do the engine blades inside of the engines turn counter clockwise during reverse thrust at touchdown? and "during thrust reversal, where does the air intake flow through the engine or does air flow into the engine during thrust reversal? I understand that the engine exhausts are directed to blow forward instead of aft during thrust reversal, however during thrust reversal does the engine suck in any air or not? Thanks!
 
vikkyvik
Posts: 11764
Joined: Thu Jul 31, 2003 1:58 pm

RE: Thrust Reversers

Fri Mar 27, 2009 6:06 am



Quoting Propilot83 (Thread starter):
I had a question for anyone who is a commercial airline pilot. My question is "do the engine blades inside of the engines turn counter clockwise during reverse thrust at touchdown? and "during thrust reversal, where does the air intake flow through the engine or does air flow into the engine during thrust reversal? I understand that the engine exhausts are directed to blow forward instead of aft during thrust reversal, however during thrust reversal does the engine suck in any air or not? Thanks!

The engine continues rotating the same direction. Instead of the engine actually reversing direction, the airflow is ducted around and expelled forward.

So basically, air is still going into the engine inlet, and instead of all of it blowing out the back of the engine, some (or all, depending on the engine) of it is ducted to point forwards (usually at an angle - generally not directly forwards).

Here's an example in which all of the engine exhaust air is redirected (737-200):


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Photo © Wolodymir Nelowkin



And here's an example (much more common these days) in which only the bypass air is redirected (A340-300 - the core flow still exhausts out the back of the engine):


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Photo © JX Ren



Those flower-petal like flaps that are open on the engines are the exhaust for the reversed bypass air.
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rwessel
Posts: 2448
Joined: Tue Jan 16, 2007 3:47 pm

RE: Thrust Reversers

Fri Mar 27, 2009 6:06 am

The engine itself does not reverse direction because you've engaged reverse thrust. Whether it's rotating clockwise or counterclockwise is up to the engine manufacturer, but it goes the same way all the time (at least when running - on a windy day the fan of a stopped engine is often spun gently in the wrong direction if the wind is from the back of the aircraft).

The reversers work by "bending" the stream of air coming out of the back of the engine to point forward. This can apply to the whole stream, or just the fan section, depending on the design, but the net effect is to get more thrust going forwards than backwards. Usually there's some sort of scoop or clamshell that sticks into the exhaust stream. Several decent pictures at:

http://en.wikipedia.org/wiki/Reverse_thrust

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