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----- Original Message -----
From: "Finn Lassen" <finnlassen@netzero.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Thursday, March 04, 2004 11:25 PM
Subject: [FlyRotary] Re: Ideal Cooling System Plumbing (was Re: [FlyRotary]
Re: overflow connections
> However, there is one failure mode (with which I'm intimately familiar)
> where sensing the coolant level in the overflow bottle (and possibly in
> pressurized expansion/header tank) will not help: Blowby from
> compression and/or combustion gasses forcing air into the coolant system
> (and the coolant out). Actually a nice big header tank might be able to
> handle or hide it and then a increasing pressure trend would be the clue
> that it's getting worse and worse.
>
> Finn
This is a case where "what actually happens" after the "blowby gas leak
starts", is dependent on the size coolant hose running out of the bottom of
"pressurized coolant expansion/header" tank: If the hose is "large", like
in the Ford (1" or almost full "radiator hose dia"), then the blowby gas
would come UP that "coolant normally DOWN" hose - and over-pressurize the
expansion tank's pressure cap and release pressure.
- Now, with no leak, just infusion of hot, high pressure gas, the first
indication would probably be a forcing of coolant up the pipe and out past
the pressure cap, and thence out the vent line routed to come out in pilots
view at aft side of engine cowl, and he'd see the brief spurt of coolant and
be warned. That should be a nearly instantaneous indication.
- Next/nearly simultaneously, whatever qty of coolant was expelled out
of engine block & thence out past pressure cap and windscreen, would be
replenished out of the expansion/header tank (reason I keep calling it a
header tank - it replenished and keeps head of pressure on pump).
. . . . . . . . .-- There might, or might NOT, be enough coolant expelled
to cause the low level light to come on. If only a slug of coolant was
ejected and pilot missed that, then the leaking gas might mix with water and
simply circulate and be, by design, trapped off by the 1 or 2 "vent lines"
previous proposed, and wind up in the pressurized expansion tank and simply
blow out as "gas", not "coolant". Thus, there would be no more lose of
coolant, only a continued infusion of leaking combustion gas mixed with
water - maybe like the "froth" mentioned by Tracy & others. So, if "not
enough" coolant was ejected to empty the expansion tank, & no more coolant
is lost, then "high coolant pressure gage reading" is all the pilot will
have - so the suggestion of a "high pressure warning" (set just a bit above
cap release pressure) would be good to have.
So, for "hot gas leak", qty gage may have no reliable value. However, for
"true leaks", the "low coolant sensor in the exp tank" should be the best,
earliest indication of a simple leak.
Funny but serious suggestion for "hot gas blowby the pressure cap" - put a
"party favor whistle in the overflow line by the canopy" - non-electric "gas
leak aural warning tone". With a good muffler, maybe the whistle could be
heard? Probably not. What else could we do?
David
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