Thrust Reverser

Tue Jun 20, 2000 11:49 am

Hi guys,
I would like to know a bit more about thrust reverser on jets. I know some works with some kinds of buckets like the 737-200 (I think) but what about the others?. Is it just the fan blades changing the side of rotation or is it something more elaborate?
Once on a US Airways 737-400 I was sitted right next to the engine and i watched closely the engine when the pilot started to reverse the thurst and I notice some kind of door opened which was green inside? Could someone tell me about that?

Thanks a lot
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RE: Thrust Reverser

Tue Jun 20, 2000 12:27 pm

There are two types of jet thrust reversers, the "bucket" type, like on the 737-200, and the cascade type like you saw on the 737-400. The cascade type has the diverter vanes located just aft of the compressor and actuates the doors on the engine cowling to move out of the way and sends the reverse thrust out that way.
Stop drop and roll will not save you in hell. --- seen on a church marque in rural Virginia
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RE: Thrust Reverser

Tue Jun 20, 2000 3:42 pm

Hi, I think that the "bucket" type is quite old now, and that new jet have "cascade" type, as this 737-400: you can see that his reverse are opend (correct me if I'm wrong)

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RE: DesertJets

Wed Jun 21, 2000 1:58 am

Cascade type reversers actually use fan air not compressor. The reverser sleeve slides back, pulling the blocker doors closed and exposing the cascade vanes (the green components) which diverts the fan air forward.

RE: Thrust Reverser

Wed Jun 21, 2000 5:39 am

Well thanks a lot guys. I find this very interesting, In fact I didin't know how cascade type worked.

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Thrust Reverser,Three Types

Tue Jun 27, 2000 12:31 am

Thrust is (gas) massflow multiplied by speed.

We know about the 'bucket' or 'target' type reversers, the cascade reversers and the 'petal' type reversers.
target type reversers were mainly used on single flow and low by-pass engines reversing the complete gasflow of the engine ( military engines, B707, DC 8, Fokker 28 ..) at the exhaust.
Cascade reversers reverse the fan duct flow only. The fan flow being blocked by blocker doors moving into the stream with the cascade cover sleeve moving back. The cascades are rows of vanes directing the flow to the outside front to create reverse thrust.
Petal type reversers are further simplyfied blocker doors which block the fan duct and at the same time direct the fan duct air flow to the outside front to create reverse thrust (A320/CFM56-5, A330/RR Trent).

Thrust reverser efficiency is about 30 to 40 per cent, that means for a given gas flow, they produce in reverse about 30 to 40 per cent of the same gas flow's direct thrust.
have fun,
your F-WWAI

F-WWAI (Confused)

Tue Jun 27, 2000 5:54 am

So, as you put it, an a/c with the petal or cascade type reversers produces 60-70% forward thrust and only 30-40% reverse? Wouldn't that mean acceleration?
Also- I don't think Fokker 28 has thrust reversers. I do believe that F70 and F100 do.
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RE: Not Confused

Tue Jun 27, 2000 6:18 am

I understand F-WWAI the way that max reverse trust is 30-40% of max forward trust.
If you have a 20,000lbs trust engine, then you can count on a reverse trust of somewhere between 6,000 and 8,000lbs in reversed mode.
Always keep your number of landings equal to your number of take-offs
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RE: F-WWAI (Confused)

Fri Jul 07, 2000 6:28 pm


You're right. The F28 doesn't have thrust reversers. Nor does the BAe146.

Reverse thrust is probably about 30% of the forward thrust. Although this is not much, the crucial thing is that it "destroys" the residual idle thrust (remember, you taxi a plane on literal idle thrust, eg 23N1 for a 320.). It is most effective at higher speeds, but it can also cause directional stability problems.

Ultimately, your brakes are the ones that count.



I Learned Something Today!

Fri Jul 14, 2000 1:52 am

For one thing I knew was that the Fokkker 28 and the Bae-146 did not have thrust reversers! They have a kind of air brake on the aft fuselage. I knew how the bucket type of thrust reveser worked but I had no idea how the cascade type worked! A few weeks ago I flew from Charlotte to Chicago (ORD) in a USair 737-400 and it was my first encounter with the cascade type of thrust reverser.

OH! I have a question??


Best Wishes 727 Rules!  


Fri Jul 14, 2000 1:58 am

I have a good question for you all?

What are winglets used for? I have heard that they are used on some airplanes to reduce drag and to conserve fuel. Can anybody tell me how do this little things REDUCE DRAG?

oh and also! Why dosen't the 777 have winglets! The MD-11 Does The 747-400 does. And what is the Big Deal in putting this little things onm 727's I"ve seen some private owned 727 with wingletts!!      


727 RULES!   
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RE: Thrust Reverser

Fri Jul 14, 2000 4:00 am

Winglets reduce induced drag which is a by product of the amount of lift a wing is creating. Hopefully you know how a wing creates lift (low pressure area on top, high pressure area below - in a short sentence).

Without getting to technical (though I can if you wish). The lower high pressure air under the wing is trying to get to the low pressure on top of the wing. One way it tries to do this is by spilling over the wingtip. Air under the wing moves outbound (from root to tip) and air on the top moves inbound (tip to root) - This is induced drag in it's basic form. This also has the effect of creating vortices behind the wing (the two spanwise flows meet at the trailing edge of the wing and a swirling pattern of air is produced).

When the wing is producing maximum lift (during high speed cruise and when configured for approach) the spanwise flow is at it's greatest - induced drag is at its greatest - and wingtip vortices are at their greatest. In order to alleviate some of this induced drag and minimize wingtip vortices a means of preventing or hindering this high pressure air on the lower surface of the wing and the low pressure air on top of the wing has to be used. Having done this, a by product of reducing induced drag and wingtip vortices is that less fuel needs to be burnt to produce a certain amount of lift. This fuel saving actually amounts to the figures of 3-4% that Boeing and Airbus quote so often.

There are various ways in which this can be done, Winglets (Boeing & Airbus), wingtip fences (Airbus), wingtip fuel tanks (Cessna, Bombardier) are ways in which aircraft manufacturers have been able to do this. Winglets are a preferred method because they also provide a means of increasing the wingspan, thereby producing more lift and still allowing the aircraft to use gates designed for aircraft with smaller wingspans.

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727 Thrust Reversers

Fri Jul 14, 2000 4:38 am

The earlier 727s had cascade-type reversers, with the vanes on the upper and lower portions of the exhaust. Later versions had clamshell-type reversers. Correct me if I'm wrong.

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