Topic Author
Posts: 172
Joined: Fri Apr 13, 2001 6:38 am

High-Bypass, Clamshell Reversers

Sat Aug 10, 2002 9:13 am

I have a question about high-bypass jet engines.

Has there ever been a cowling for an engine that extends over EVERYTHING such that a "clamshell" reverser could be installed (not like the A-320s). The cowling would cover the tailpipes, etc. Also, is it possible to get a high-bypass engine to do "full reverse" such that no forward thrust is created, and all thrust is directed forwards, such as with the engines on MD-80s, etc.?

Posts: 180
Joined: Thu Feb 22, 2001 8:04 am

RE: High-Bypass, Clamshell Reverser

Sat Aug 10, 2002 11:12 am

The BR715 on the 717 is a high-by-pass engine with clamshell reversers.

Ejay MD-11

RE: High-Bypass, Clamshell Reversers

Sat Aug 10, 2002 1:51 pm

Dear Ngr -
With the old 747, they first came with fan reversers as well as turbine reversers... the turbine reversers were worthless, created problems and were deactivated in most instances... Later, even only fan reversers "only" were installed, forget the turbine reversers...
The "nice feature" of reversers, is to "cancel the residual thrust" of the engine at idle... I personally often land, just deploying the reversers and not using any power "in reverse" actually, combination of slight aerodynamic braking (nose high) and "idle reverse"... the only time I touch the brakes is at reduced speed (30-40 kts) to steer off the runway...
Reversers are NO part of the landing distance equation for transport airplanes in any case, they are just "extra help" to stop the plane. If you look on a landing distance problem, airplane "x" requiring a "5,000 feet runway" means that this airplane will fly over the runway threshold at 50 feet AGL, touch down, and using brakes and spoilers/speed brakes only - NO REVERSERS - stop in a 3,000 feet distance from the threshold...
Transport airplanes must be able to stop on 60% of the landing distance available... brakes and spoilers only - NO REVERSERS again...
... And yet I still have to tell little old ladies that planes are extremely safe, yet they dont believe me. I feel I am preaching in the desert... c'mon Abigail, sit on the jump seat, remove these cherries from your hat, and the net from your face, and watch what we do, these planes are super...  Wink/being sarcastic
(s) Skipper
Posts: 2166
Joined: Thu Feb 07, 2002 9:51 pm

RE: High-Bypass, Clamshell Reversers

Sun Aug 11, 2002 12:18 am

An interesting fact is that when you turn on the autobraking on the B744 (and probably most other planes/models) it will actually use enough brakes to give you a deceleration proportional to your autobrake setting. IOW, the only thing which the reversers do is help reduce brake wear - they won't help you slow down faster.

Whether you use more than idle reverse thrust or not is up to airline SOPs and what they think will be the safest/most economical.

I thought I was doing good trying to avoid those airport hotels... and look at me now.
Posts: 835
Joined: Fri Sep 14, 2001 8:30 am

RE: High-Bypass, Clamshell Reversers

Sun Aug 11, 2002 9:15 pm

Didn't the original L1011's have clamshell reversers on the tail monuted s-duct engine??? Those would have been RR RB211s...I have seen pictures of this a/c with clamshell reversers...Can someone add the more technical information...Thanks Ry
Posts: 3549
Joined: Tue Oct 26, 1999 11:34 am

RE: High-Bypass, Clamshell Reversers

Mon Aug 12, 2002 12:40 am

the only thing which the reversers do is help reduce brake wear - not with carbon brakes. The T Revs delay the time it takes for the brakes to reach their optimum temp and this in turn increases brake wear.

It has now been proven that it is cheaper all round not to use the revs if it is possible. It saves brake & engine wear.
Posts: 2166
Joined: Thu Feb 07, 2002 9:51 pm

RE: High-Bypass, Clamshell Reversers

Mon Aug 12, 2002 3:08 am

Thx VC-10, an additional piece in the puzzle. Not familiar with carbon brakes on airliners, I'm afraid.  Smile Corresponds nicely with the pointy-nose procedures, e g you either AD-brake or stomp on the brakes - not a little of both!


I thought I was doing good trying to avoid those airport hotels... and look at me now.
Posts: 1299
Joined: Wed Apr 24, 2002 8:04 pm

RE: High-Bypass, Clamshell Reversers

Sat Aug 17, 2002 2:09 am

All the early wide bodies (747, DC-10, L-1011) came out with a thrust reverser system that worked on both the hot stream and the cold stream. With terrible reliability and regularly leaving bits and pieces on the runway, by the time the A-300 came out, the hot stream portion of the thrust reverser system was gone.
Even though the thrust reverser system is not required for certification and is not used in braking tests, some airlines place their own restrictions on where a wide body could go with a thrust reverser inop. For instance, Eastern would not permit a wide body (especially a L-1011) into LGA without fully operative thrust reversers.

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