lugonza_2001
Posts: 310
Joined: Tue Oct 30, 2001 4:31 am

How Does Reverse Thrust Function?

Tue Jan 06, 2004 4:29 am


Hi!

How does reverse thrust function? i see that engines open the cowlings and... is the air blown in opposite direction and that´s it? Through the blades?

 Smile/happy/getting dizzy
 
FredT
Posts: 2166
Joined: Thu Feb 07, 2002 9:51 pm

RE: How Does Reverse Thrust Function?

Tue Jan 06, 2004 4:41 am

The actual mechanisms vary quite a bit from implementation to implementation, but the basic mechanism is to turn all or part of the airflow forward. So far you are right. However, it does not go back through the blades. It is diverted around the outside of the engine on its way forward.

Do a search for "clamshell reversers" on google, and you will probably find a lot of good explanatory pictures.

Cheers,
Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
Staffan
Posts: 3879
Joined: Tue Mar 18, 2008 9:21 am

RE: How Does Reverse Thrust Function?

Tue Jan 06, 2004 5:06 am

On the CFM56 for example, the rear part of the cowling is moved back. I think it's called a cascading reverser or something. There are latches all the way around the bypass duct that are mechanically linked to the cowling, se when it moves back, the bypass air is deflected and let out forward in the gap between the forward and aft part of the cowling.

In the second picture I think you can see one of the linking arms in the bypass duct. It's the thin dark thing at the 11 o'clock position between the inner and outer walls in the duct.


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Staffan
 
air2gxs
Posts: 1443
Joined: Mon Jun 18, 2001 1:29 pm

RE: How Does Reverse Thrust Function?

Tue Jan 06, 2004 6:16 am

Basically right. On a fan air reverser, the translating sleeve (the part that moves back) operates the blocker door links. These links are connected to the blocker doors which rise up and block the fan air (or bypass air) from moving down the bypass duct. This air has to go somewhere. When the sleeve moved it exposed the cascade vanes. These are "panels" that are installed on the engine through which the bypass air is now routed. The vanes direct the airflow forward and away from the engine.

Hope that makes sense.
 
IMissPiedmont
Posts: 6200
Joined: Wed May 23, 2001 12:58 pm

RE: How Does Reverse Thrust Function?

Tue Jan 06, 2004 1:27 pm

All the answers, though somewhat corrrect, are not how it actually works.

In essence what happens is that a massive amount of draf is produced . The true angle of airflow from the engines is something near 45 degrees, all out of the tailcone. For a test put your hand level out your car window at 60 MPH then turn it 135 degree to the left or right and see what happens.

The wall of air will move your hand backwards quickly.
The day you stop learning is the day you should die.
 
vafi88
Posts: 2981
Joined: Sun Apr 08, 2001 10:32 am

RE: How Does Reverse Thrust Function?

Tue Jan 06, 2004 1:36 pm

In simple terms: When the engines are at standard, the air blows backwards and thrusts the aircraft forward, when the air is deflected to shoot forward, the aircraft wants to "go back" or slow down.
I'd like to elect a president that has a Higher IQ than a retarted ant.
 
MITaero
Posts: 485
Joined: Mon Jul 28, 2003 8:00 am

RE: How Does Reverse Thrust Function?

Tue Jan 06, 2004 5:43 pm

>All the answers, though somewhat corrrect, are not how it actually works.

I think the most concise way to explain how reverse thrust works is conservation of momentum.

Using a simple control volume around the engine, and integral momentum equations, you can calculate thrust as well as reverse thrust. But here's a tangible analogy, since I'll get yelled at for that..

Imagine being on a boat. Someone standing outside the front of the boat (fore) tosses you rocks very slowly. You throw the rocks back at him/her with a much higher velocity. Here, airflow is simplified to be many little rocks. The net difference in momentum is what creates a force backwards. To create thrust forward instead, just throw the rocks backwards with high velocity. The key to understanding the concepts behind propulsion is momentum, not drag.

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