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Good point, Dale. Also, it might be possible to have a little pump
"pressurize" the reservoir when above X altitude.
Ed
Ed Anderson
RV-6A N494BW Rotary Powered
Matthews, NC
----- Original Message -----
From: "Dale Rogers" <rogersda@cox.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Wednesday, August 04, 2004 10:04 AM
Subject: [FlyRotary] Re: May not work above 8000 MSL was [FlyRotary]
> Ed,
>
> Might this be one of the advantages of having a separate
> reservoir (with 2-cyle oil)? Except when pulling negative
> G's, a reservoir mounted well above the pump would give it
> a little head pressure that would be independant of the
> atmospheric pressure.
>
> Just a thought,
> Dale R.
> COZY MkIV #1254
>
> > From: "Ed Anderson" <eanderson@carolina.rr.com>
> > Date: 2004/08/04 Wed AM 07:16:02 EDT
> > To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
> > Subject: [FlyRotary] Re: May not work above 8000 MSL was [FlyRotary]
> > Re: Oil injection, and more
> >
> > You may be correct, Al. Without testing it would be hard to say.
> >
> > No question my theory could be wrong - but as you say something must
have made Atkins come to the conclusion that the metering pump does not work
above 8000. If his claim is valid - then there must be some cause related
to altitude. The only part of the fuel metering system that would be
affected by altitude that I can see is the oil feed from the shaft boss to
the pump.
> >
> > We know that as pressure changes across an aperture will cause the flow
rate to change - whether (as you point out) the difference due to altitude
is significant enough to account for any lessening of oil flow is the
question. Whether or not a few pi would ensure adequately flow sufficient
CCs of oil will depend on the size of the orifice through which the oil
flows. I agree if the aperture is sufficiently large then a few PSI change
in pressure will make little (if any) difference in flow. However, if the
orifice is small and the flow barely adequate to meet the needs say at 14.7
psi then 11 psi could lessen the flow. Not claiming that flow would cease,
but it may well be diminished.
> >
> > My 0.02
> >
> > Ed
> >
> >
> > Ed Anderson
> > RV-6A N494BW Rotary Powered
> > Matthews, NC
> > ----- Original Message -----
> > From: Al Gietzen
> > To: Rotary motors in aircraft
> > Sent: Wednesday, August 04, 2004 1:07 AM
> > Subject: [FlyRotary] Re: May not work above 8000 MSL was [FlyRotary]
Re: Oil injection, and more
> >
> >
> > Subject: [FlyRotary] May not work above 8000 MSL was [FlyRotary] Re:
Oil injection, and more
> >
> >
> >
> > Dave may be correct, Perry.
> >
> >
> >
> > Here is what I think could occur. First, The oil meter pump itself
is a positive displacement pump.
> >
> >
> >
> > Therefore, from the standpoint of the pump it will always disperse any
oil fed to it into the injectors and combustion chamber under some amount of
pressure. However, the shaft opening that drives the pump also provides for
the oil flow from inside the Engine Front mount into the metering pump.
There is a hole in the boss of the metering pump shaft (on the inside of the
front housing) that is open to the atmosphere.
> >
> >
> >
> > At sea level of course this hole in the boss results in 14.7 psi of
pressure on the oil in the meter shaft. So as the positive displacement
pump opens a chamber - the oil flows into the chamber with the help of this
14.7 (or what ever the differential between the pressure in the pump chamber
and the atmosphere- it will something less than 14.7 but probably greater
than 12?) and gets "squirted" toward the injectors underpressure.
> >
> >
> >
> > Ed;
> >
> >
> >
> > I hear what you're sayin', but I really don't think so. How much
pressure does it take to make hot oil flow through a short length of tube
(or a port in the pump) at a VERY low flow rate? Very little. We're
talking a few cc/min; and I'd guess even a couple of psi, would do the job
nicely. And at 8000 ft we still have; what, about 11 psi.
> >
> >
> >
> > As we go to higher altitudes it is probably more likely that we'd get
vapor lock upstream from the fuel pump before we stop getting oil from the
metering pump.
> >
> >
> >
> > This is just off the top of my head, so, you know, maybe there is
something I overlooked. The question is: what phenomenon was Atkins
observing? He obviously had some reason for his statement.
> >
> >
> >
> > Al
> >
> >
>
>
> >> Homepage: http://www.flyrotary.com/
> >> Archive: http://lancaironline.net/lists/flyrotary/List.html
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