Victor Hotel
Topic Author
Posts: 289
Joined: Fri Aug 25, 2000 8:29 pm

Thrust Reverse

Sat Nov 18, 2000 2:22 pm

For thrust reverse on turbofan engines, do they bleed pressure from some of the compression stages and direct them forward. Can someone explain how they work properly for me, keeping it simple? Thanks.
VH
 
242
Posts: 495
Joined: Tue Oct 24, 2000 1:10 pm

RE: Thrust Reverse

Sat Nov 18, 2000 3:19 pm

It just depends on what type of reverser the engine has.

A clam-shell, or bucket style reverser, like on DC-9s and 737-200 JT8-D engiines, both the hot stream (core exaust) and cool stream (fan exaust) are deflected forward.

On larger engines, like the GE CF-6 and P&W 4060, the cascade type reverser slides backward, pulling panels closed via linkage in the cool stream duct and exposing the cascade screen to deflect only the fan exaust forward. The hot stream is not affected.


 
JT8DJET
Posts: 196
Joined: Fri Jul 07, 2000 12:28 am

RE: Thrust Reverse

Sat Nov 18, 2000 3:35 pm

Forward thrust

Click for large version
Click here for full size photo!

Photo © Colin K. Work




Thrust reverser deployed exposing the cascade vanes.

Click for large version
Click here for full size photo!

Photo © AirNikon




 
Victor Hotel
Topic Author
Posts: 289
Joined: Fri Aug 25, 2000 8:29 pm

RE: Thrust Reverse

Sun Nov 19, 2000 12:45 pm

thanks people.
VH
 
TOP
Posts: 250
Joined: Wed May 10, 2000 5:22 am

RE: Thrust Reverse

Sat Nov 25, 2000 3:18 am

I think I've a photo of a dismantled reverser unit...
Are you interested in it?

 
Guest

RE: Thrust Reverse

Sat Nov 25, 2000 4:54 am

TOP: I don't know if Victor Hotel is, but I am very interested in that picture.
 
TOP
Posts: 250
Joined: Wed May 10, 2000 5:22 am

RE: Thrust Reverse

Sat Nov 25, 2000 7:41 am

I'll send them to you next time!

stephan.tophoven@t-online.de
 
Guest

RE: Thrust Reverse

Sat Nov 25, 2000 10:10 am

Something to remember is that the thrust is NOT directed exactly forward (i.e. 180 degrees from the reverse axis). Once the aircraft touches down, electrical switches on the landing gear enable the thrust reverse control system to engage. The pilot brings the engines to forward idle, and pulls up on a set of smaller levers forward of the actual throttles. This causes the "buckets" or "sleeve" (see below), to swing back into the engine's thrust stream. Once the pilot sees that all engine thrust reversers are engaged, through a set of indicator lights, he advances the normal engine throttles to bring the engine power up and the reverse thrust force higher.

On the T-Tail aircraft, thrust reversers are large "buckets" of metal that mechanically swing back and "clamshell" into the exhaust stream of the engine, deflecting the thrust maybe 10-20 degrees max forward. These "buckets" are actuated either pneumatically (using air bled from the engines) or hydraulically (using a self-contained hydraulic system).

On underwing engines, the principal is the same but you really can't see the reversers working. Usually a sliding sleeve on the engine slides aft, which closes off the buckets inside the tailcone, deflecting the exhaust to the sides and forward, but nowhere near directly forward, more like 10-20 degrees....

Some of the myths of thrust reversers are:
(1) the engine stops, and spins in reverse, directing thrust forward (NO! not even close)
(2) the compressor blades in the engine are pivoted to direct the thrust forward (NO! although some engines do have variable stator vanes, these are used to schedule the airflow through the engine)

Hope this helps!

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