Thrust Reversers (was: Re: Wing "flaps" that raise on landing)

From: (HICKEY  S)
Organization: University of New Brunswick, Fredericton, NB, Canada
Date:         03 Feb 93 01:07:11 PST
References:   1 2 3
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In article <airliners.1993.127@ohare.Chicago.COM> (Luca De Alfaro) writes:
> (Robert Dorsett) writes:
>>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?

Clamshells are formed by two tapered half-cylinders that normally lie
flush with the engine, but are rotated back into the exhaust to butt
end-to-end, catching and reversing the thrust from BEHIND the engine:

	-----------=========	--------------------	 \
(front)		stowed			deployed	  \
	-----------=========	--------------------     /

Cascade reversers, on the other hand, are activated by sliding the
rear portion of the bypass casing of the engine rear-ward, and using
a number of deflector panels placed directly into the thrust stream
INSIDE the engine bypass to divert the thrust stream forward:

	-------------		---------  /----
	------------------	----------/-------
(front)		closed			open
	------------------	----------\-------
	-------------		---------  \----

The reversers don't interrupt the core flow, but since the fan provides
(typically, at sea level) 75% of the thrust of a fanjet engine, enough
thrust is reversed using this method to be effective.