[AR] Re: P&W GTF
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: Arocket List <arocket@xxxxxxxxxxxxx>
- Date: Sat, 4 Apr 2020 18:15:33 -0400 (EDT)
On Sat, 4 Apr 2020, Kevin Ho wrote:
There is some similarity, to be sure. Note, though, that the fan
shroud is not just ornamental :-), it modifies and controls the airflow
so that the "propeller" can operate efficiently at higher speeds...
That’s actually the great thing about geared fans - tip speeds are below
M1.
Really? I don't have numbers for the P&W engine handy, but I'd be
surprised if they were, especially at Mach 0.8 cruise where the input
airspeed adds quite a bit. As I understand it, modern fans generally do
run their blade tips transonic, M=1.5 or so -- done right, this gives you
a considerably smaller fan, for a given thrust, than an all-subsonic
design. But my information may be out of date.
(Kevin's main point, that the gearing lets you reconcile the different
preferred RPMs of a small turbine and a big fan, remains valid -- that's
the point of the exercise.)
Henry
Other related posts:
