Re: Flaps & spool up

Date:         05 Jun 99 02:09:27 
From:         engrc@cae.ca (Robert Courteau)
Organization: CAE Electronics Ltd.
References:   1
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Stephan Stephany LAC-CC wrote:
> Concerning a jet airliner in final approach,
> is there such a thing as an automatic partial
> spool-up when flaps are deployed (I mean, if
> you deploy the flaps beyond some degree there's
> something like an autothrottle that spools up
> the engines to a given minimum rpm)?

Well, yes and no. Most tranports have a low/high idle system , which
increases the minimum engine power setting when in approach
configuration, to ensure the engine acceleration time from idle to max
go-around is within reasonable limits (i.e. below 10 seconds), giving
better response in case of a late go-around decision. This only spools
up the engine if it was sitting at idle to start with - which would not
normally be the case during approach. Turbofans have very sluggish
spoolup response at low rpms, so increasing the idle setting by 5% can
reduce the idle-to-max spoolup time by some 30%. This system is part of
the engine control system - not the autothrottle.

Robert Courteau