Roger

Merlin (in P-51) turned 3000 rpm on take off. Prop speed was 1500 rpm
(2 to 1 reduction gearing).

Engine life was about 250+/- hrs (not in combat).

Probably happened but never heard of the reduction gearing 'going
west'. Was not a 'common' failure mode to be worrried about.

Big John


On Wed, 03 Dec 2003 02:05:35 GMT, Roger Halstead
wrote:

On Tue, 02 Dec 2003 12:57:49 GMT,
(Corky Scott) wrote:

On Mon, 01 Dec 2003 17:20:55 GMT,
(Corky Scott) wrote:

The PSRU was the one thing he felt should be done
by people who knew how to do them, and contracted NIS to develop one.

To make a long story short, the PSRU did not work well and things have
been in litigation for a while. Making a PSRU to handle 120 to 180
horsepower is one thing, making one to handle over 400 horsepower is
something entirely different.

Corky Scott


Thanks Corky,

I appreciate the info.
As I see it (and I don't know squat about PSRUs except their goal) a
high ratio PSRU as used in a turbo prop which has a very high ratio
(planetary) is easier to build than say the 2:1 or 3:1, BUT the
planetary also has the advantage in being used on an engine without
pulses being inherent in their operation.

The life of a PSRU on a piston engine has to be complicated. It not
only has to handle linear torque and thrust, but virtually any other
imaginable angle as well. Then it has to be designed to avoid any
resonances with those power train pulses AND take the positive and
negative torque without beating the snot out of the gears which means
next to nothing for slack (which brings its own set of problems).
Helical, double helical, spur, planatery...each with it's own set of
pluses and minuses.

BUT, didn't the big 12 and 16 cylinder Vs in WWII have PSRUs? Course
those engines had very short TBOs too. Then again they weren't
exactly babied either.

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