Re: DC-8 thrust reversers

From: (Bruce W. Watson)
Date:         12 Feb 93 11:12:10 PST
References:   1
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In article <airliners.1993.138@ohare.Chicago.COM> (Mike Howells) writes:
>I've heard the DC-8 is approved to deploy its inboard reversers inflight to
>slow itself down or whatever.  Can anyone confirm this?
>Also, how much drag does it provide?  I would bet a crapload.
>| Mike Howells                                                                |
>| Commercial Pilot                                                            |
>| Airplane Single and Multi-engine Land                                 ave   |
>| Instrument Airplane                                                         |

   Yes, I can confirm this. I've had many conversations with (mostly KLM)
ex-DC8 captains who all claim that reverse thrust is approved in flight.
There are several prop and turbo-prop aircraft approved for this type of
thing. As for the DC-8, it was usually used to increase rate of descent,
maintaining constant airspeed. The amount of thrust permitted (as I'm told)
is up to the spinup position (however that's measured on the DC-8 -- perhaps
N2?), and not to be used inside the FAF. I suppose that there 
probably wouldn't be a problem using reverse on all 4, if you could get
the turbines to spinup at the same rate. Unfortunately, not having the two
outboards go to reverse simultaneously can be trouble - asymmetric thrust. 
This is something of a general problem; for example, in an older 747 you
may have noticed (on takeoff) that you sat in position for a moment with
the brakes set while all 4 engines were spun up (to 55% or 70% N1 depending
on how the particular airline measures spinup) before releasing the brakes
and applying (possibly derated) takeoff thrust. The same reasoning is why
after applying reverse on the 747 commits to a full stop -- it's not 
possible to go back to forward thrust for a go-around without a major
risk of severe yaw (I admit I only *know* this for the -200).