Re: Surge on GE90

From:         b17864@vaxb.phx1.aro.allied.com
Organization: AlliedSignal Engines
Date:         10 Jul 95 16:36:53 
References:   1 2 3
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In article <airliners.1995.977@ohare.Chicago.COM>, whurwitz@world.nad.northrop.com (Wayne M. Hurwitz) writes:
>
> Is this correct for the GE90?  My experience is that engines are started
> with air turbine starters, which actually inject air into the turbine
> to rotate the shaft.  The compressed air source comes from either an
> APU or cross bleed from an engine that is already running.  But then
> I deal mostly with military applications, which may be different.  On
> the other hand, it seems like it would take an awful lot of electrical
> power to spin up a GE90, which would be prohibitive when sizing a
> starter/generator.

Large turbofan engines are started by an air turbine starter which is mounted
to the accessory gearbox.  Bleed air (from a ground source, APU, or other
engine) spins the turbine up to speed.  Power is transmitted from the starter
through the gearbox and to the main engine shaft.

Small engines (biz jet size or APUs) can use electric starters and they do
take a lot of electrical power.

Old engines and very small missile engines use impingement starting.  This is
where air or hot gas is injected into the engine's turbine to initiate
rotation.  The J-85 used this system (or at least the early ones did) as do
most cruise missile engines.


Mark Johnston
AlliedSignal Engines
Phoenix AZ