Re: cascade reversers

From:         rdd@cactus.org (Robert Dorsett)
Date:         03 Feb 93 01:07:12 PST
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> In <airliners.1993.127@ohare.Chicago.COM> luca@xenon.stanford.edu (Luca De Alfaro)
> writes:
> rdd@cactus.org (Robert Dorsett) writes:
> 
> >>Thrust reversers are0 gravy: they deflect engine exhaust at some forward angle,
> >>thus applying "reverse thrust."  There are two types of thrust reversers:
> >>cascade and clamshell.  The type used depends on the geometry of the engine
> >>and its nacelle: smaller engines use clamshells; large fans tend to prefer
> >>cascade reversers.  There are exceptions in both directions..
> >
> >How do cascade thrust reversers work?
> 
High-bypass jet engines develop their thrust by directing air around the
turbine core.  This is "cold air."  "Hot air," from the turbine exhaust, con-
tributes a small proportion of thrust.  Maintaining the bypass ratio and 
thrust puts a lot of burden on nacelle design: sometimes (as with the PW4000,
for instance), the turbine core pokes out the end, and there's simply no way 
to use clamshell reversers.

So, cascade reversers are mounted further forward on the engine.  They redivert
the *cold* air up, forward and out.  First, panelling on the engine cowling
slides open.  Next, thrust is blocked.  Third, shutters angle upward, to 
deflect incoming air.  It's an impressive effect.

There are several rows of these "shutters," hence the name "cascade."  





---
Robert Dorsett
rdd@cactus.org
...cs.utexas.edu!cactus.org!rdd