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Subject: RE: [FlyRotary] Re: EWP - Success at last?
Date: Sat, 11 Oct 2003 14:03:35 -0400
Message-ID: <0B27ED95697C4D4CBC82D79E790FE567086F87@exchange.rfgonline.com>
Thread-Topic: [FlyRotary] Re: EWP - Success at last?
Thread-Index: AcOQDxaTWY/bnoASRRe0qGt+BnG5awAAHn8g
From: "Robinson, Chad" <crobinson@rfgonline.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>

>> ... The way MTBF figures work, if you have two devices both operating
>> at the same time you're roughly TWICE as likely to have a failure ...
>
> Which is not exactly the point.  The point is the likelihood of a =
[complete]
> cooling failure.  That would go up roughly infinitely if you had two =
units.
> Further, there would be no need to "change at TBO" - you could run =
until
> failure.  As for check valves, I can envision a couple of ways to =
build a
> "dirt simple, dirt cheap" valve that would be more than sufficient for =
our
> purposes.  Ed or whoever just bought a toy mill could start a cottage =
industry.
> With check valves, one could switch water pumps periodically in =
flight, thus
> keeping them both "exercised" and promptly detecting any failure.  As =
for high
> demand moments, if the pumps were plumbed parallel, you could use them =
both for
> takeoff, climb, etc.=20

Yes, for all the reasons you listed, especially the last, my preference =
is two pumps in parallel. Unfortunately, _I_ do not have a mill, toy or =
otherwise, and do not plan to buy one, so if anybody has a way to manage =
this I'm most interested in hearing it.

> ... Viola' a dirt simple, dirt cheap check valve.=20

I can think of a few problems with this arrangement. For instance, at =
full flow, the two pieces would be forced together, essentially forming =
a single "vane" cutting the flows in half. No problem, but if you =
reverse the flow, what forces the vanes apart allowing the flow to force =
them completely flat/open and thus blocking the flow? OK, slight =
engineering change - if you hammer the very tips into a small angled lip =
this would allow reverse flow to "catch" on them and force the halves =
apart. They wouldn't seal as well, of course, but better than nothing.

You also have to deal with the heat of the coolant - again, careful =
epoxy selection would be a must.

The commercial versions seem to use either a flap or ball, with a spring =
to assist the return. I'd almost rather spend my $200 per valve for =
something so critical. God forbid those suckers detach, flow down to the =
radiator, and completely block the flow from BOTH pipes.

If we're talking about elegance here, I'd almost rather see something in =
"Y" form where the valve is a butterfly between two inlets and combines =
the flows into a single outlet. Then only one valve is needed. If only =
one pump is pushing, the butterfly valve would block reverse flow into =
the other pump. If both pumps are pushing the butterfly valve would open =
relatively evenly (assuming equal flow from both pumps) and allow both =
to flow.

Regards,
Chad