Message-ID: <409998EC.8FA9B723@frontiernet.net>
Date: Wed, 05 May 2004 20:46:20 -0500
From: Jim Sower <canarder@frontiernet.net>
MIME-Version: 1.0
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Pulley Sizing (was Coolant Pressure Gauge)
References: <list-3207771@logan.com>
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If I mean to run my 13B at 7500-8000 I'll need a sure 'nuff oversize alternator
pulley and probably EWP.  By that time EWP should be well proven :o)  My Lyc
alternator is overdriven way too much IMO and I aim to go with a bigger pulley.

But I'll have to build it myself :o((  ... But it will transfer to my 13B alt
:o)) ... Jim S.


Mark Steitle wrote:

> Mike,
> I will measure my e-shaft pulley when I get home tonight, but I'm sure it
> is larger than 4.5".  I wouldn't be too concerned with a 10,800 rpm's max
> for the alternators, but with a 5.5" (17.28" circumference) e-shaft pulley
> and a 2.5" (7.85" circumference) alternator pulley, the ratio is
> 2.2:1.  So, the alternators would be turing 15,840 rpm at 7200 engine
> rpm.  That is 58% over the 10,000 rpm figure.  That what makes me nervous.
>
> Since multi-V belts have become so commonplace, I feel certain that I can
> find something around 4.5" that I can adapt.  Guess I'll have to make a
> trip to Pic-A-Part and see what I can find.
>
> Mark
>
> At 02:03 PM 5/5/2004 -0700, you wrote:
> >The alternator speed isn't a problem, it doesn't care how fast you spin it
> >(unless you have an alternator that is way out of balance).  On my RV-4
> >with Lycoming engine the alternator is over-driven about 4:1, I have the
> >2-1/2 inch stock alternator pulley, the crank/ring gear pulley is about
> >10" diameter so the alternator will see 10,000 at cruise.  This is typical
> >of most Lycoming installations on experimentals and is not a problem on
> >thousands of planes.
> >
> >My e-shaft pulley is 4-1/2 inches dia.  I think it is a stock pulley as
> >the timing pointer is at the edge of the pulley.  That makes the
> >alternator over-driven at 1.8:1.  Using a 6000 rpm cruise with my RD-1C
> >that makes the alternator spin at 10,800.  Close enough.
> >
> >There are enough Lyc drivers that were uncomfortable with this that
> >someone makes a 4" pulley for the alternator.  Aircraft Spruce 02-03
> >catalog page 245, p/n 07-06828 $48.95.  (A waste o' money except for the
> >feel good factor.  If you'll accept MY explanation I'll accept your 48.95
> >and SAVE YOU shipping costs!
> >P-)
> >
> >Regarding water pump speed, I've been working on this for a few weeks with
> >my 13B dynafocal adaptor.  I've mostly come to the conclusion (yet open to
> >more data or ideas) that the factory pump and pulley are sized to provide
> >the needed flow capacity at any given engine speed at the horsepower
> >levels we are running at.  So, to make it easy I'm sticking with the stock
> >pump at the stock pulley ratio.
> >
> >Mike
> >Mike McGee, RV-4 N996RV, O320-E2G, Hillsboro, OR
> >13B in gestation mode, RD-1C, EC-2
> >
> >At 12:06 2004-05-05, you wrote:
> >>Well, that's interesting.  This reminds me of a nagging question I have
> >>had, but haven't asked.
> >>
> >>I was curious about the need to go to a smaller crank pulley to slow down
> >>the water pump and alternators.
> >> From memory, the crank pulley is about 5-1/2", the alternator pulleys
> >> are about 2-1/2", and the water pump
> >>pulley is about 4" diameter.
> >>
> >>So, running an RD-2C (2.85 ratio), the alternators will be turning about
> >>20k during climb-out and the wp will be turning
> >>about 10K rpm.  That seems too fast to me.  I could probably find larger
> >>pulleys for the alternators, but
> >>then there's the water pump pulley.  Your unplanned experiment would
> >>suggest that we can run the wp slower
> >>and still cool adequately.
> >>
> >>This brings me to a second option.  I think a simpler approach would be
> >>to reduce the size of the crank pulley.
> >>The problem is that I haven't found a multi-V reducing pulley at any of
> >>the after-market suppliers.  I really don't
> >>want to change over all the multi-V pulleys to single V pulleys, but that
> >>is one option.
> >>
> >>Another solution might be to find a smaller pulley from another vehicle
> >>and adapt it to fit the rotary.  If that doesn't
> >>work, I could have one made.
> >>
> >>So, am I worrying about nothing, or is this a real problem?
> >>
> >>Mark
> >
> >
> >
> >>>  Homepage:  http://www.flyrotary.com/
> >>>  Archive:   http://lancaironline.net/lists/flyrotary/List.html
>
> >>  Homepage:  http://www.flyrotary.com/
> >>  Archive:   http://lancaironline.net/lists/flyrotary/List.html

--
Jim Sower ... Destiny's Plaything
Crossville, TN; Chapter 5
Long-EZ N83RT, Velocity N4095T