Re: Jet engine rpm

Organization: AlliedSignal Engines, Phoenix, Az
Date:         08 Oct 96 13:00:10 
References:   1
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In article <airliners.1996.1960@ohare.Chicago.COM>, writes:
> A recent Flight International magazine has an article and cutaway
> on the RR Trent engine. Maximum Shaft rotation speeds were given
> as 3,500 rpm for the Fan (LP Turbine), 7,700 rpm for the IP stage
> and 10,000 rpm for the HP stage. For the Fan the rpm results in the
> blade tips being supersonic - or near it.
> I was under the (miss)impression that jet engine shaft rpm were
> very much higher than this - like 70,000 rpm plus. Maybe I'm thinking
> of smaller older engines. I know that some of the model aircraft jet
> engines (based on turbochargers) have shaft speeds of around 90,000rpm.
> These engines are only a few inches across though.
> Can anyone comment on this with say rpm of the Conway, Viper, Olympus
> etc engines. Thanks for answers.

To really oversimplify things, the tip speeds of the turbomachinery
is usually kept constant. For a smaller engine, a higher RPM is necessary
to achieve these speeds.  I don't have any exact numbers handy but for large
engines, core speeds on the order of 9,000 to 10,000 rpm are typical.  For
smaller biz-jet and turboprop engines core speeds run in the 25,000 to 30,000
rpm range.  Commercial APU's may run in the 50,000 rpm range.  An extreme case
is an engine being developed by former employee under a govt contract that
is 1" to 2" in diameter and will spin at 200K rpm using dental drill

Hope this helps.

Mark Johnston
Sr Developement Specialist
AlliedSignal Engine
Phx AZ