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How Does Reverse Thrust Function?  
User currently offlineLugonza_2001 From Spain, joined Oct 2001, 315 posts, RR: 1
Posted (10 years 10 months 4 weeks 1 day 21 hours ago) and read 3152 times:


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

6 replies: All unread, jump to last
 
User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 1, posted (10 years 10 months 4 weeks 1 day 20 hours ago) and read 3135 times:

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.
User currently offlineStaffan From , joined Dec 1969, posts, RR:
Reply 2, posted (10 years 10 months 4 weeks 1 day 20 hours ago) and read 3110 times:

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


User currently offlineAir2gxs From , joined Dec 1969, posts, RR:
Reply 3, posted (10 years 10 months 4 weeks 1 day 19 hours ago) and read 3079 times:

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.


User currently offlineIMissPiedmont From United States of America, joined May 2001, 6332 posts, RR: 33
Reply 4, posted (10 years 10 months 4 weeks 1 day 12 hours ago) and read 3002 times:

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.



Damn, this website is getting worse daily.
User currently offlineVafi88 From United States of America, joined Apr 2001, 3116 posts, RR: 17
Reply 5, posted (10 years 10 months 4 weeks 1 day 11 hours ago) and read 2991 times:

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.
User currently offlineMITaero From United States of America, joined Jul 2003, 497 posts, RR: 8
Reply 6, posted (10 years 10 months 4 weeks 1 day 7 hours ago) and read 3023 times:

>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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