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Mark, thanks a lot for the photo and explanation. Fills out my
understanding a lot more.
I think we've resolved the ambiguities of my original input. I agree with
all you said in this response.
- Air trap in the thermostat bypass area seems to be a real "gotcha" if
not carefully handled. Frying an engine on initial startup has to be a real
bummer.
I'm glad you are going to monitor coolant level in the expansion tank. I
may not have been paying attention so I'll ask: Are you using a "custom"
expansion tank or one from an auto? If homemade, will you scrounge a
"level" sensor from a car's expansion tank? Any particular one? Already
done it?
Will your expansion tank be "highest possible"? Or "anywhere" relative to
top of engine?
David
----- Original Message -----
From: "Mark Steitle" <msteitle@mail.utexas.edu>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Thursday, March 04, 2004 1:19 PM
Subject: [FlyRotary] Re: Ideal Cooling System Plumbing -- PLUS 'best coolant
leak indicator'
> David,
> Somewhere I got the impression that your radiator returns were on the top
> of the radiators. Bottom
> should be fine.
>
> I'll embed a couple of comments (and a wp flow diagram) to your comments.
;-)
>
> Mark
>
> >The system I propose draws COOLANT off of the BOTTOM. The AIR goes out
the
> >top, at least when you are filling the system on the ground with no flow.
> >The main purpose is to be able to FILL the system and PURGE ALL AIR -
right
> >out the top of the engine - the highest spot you can find.
>
> Be alert to the possibility of air being trapped in the bypass circuit of
> the wp housing.
> Since I had removed the dual thermostats and welded up the bypass holes, I
> had to remove
> the hex plug (unique to the 20B) on the side of the wp housing to get the
> pump to
> prime. Not sure how you would accomplish this on the 13B. Maybe
drill/tap
> a 1/8npt
> in the bypass area of the wp housing? If you kept the thermostat, just
> remove it while
> filling the system.
>
> HOWEVER, if plain old EXPERIENCE were to ever
> >indicate that air was being trapped in the top of rad, then an AIR VENT
LINE
> >could be installed at high point in rad or a hose there that would feed
back
> >into the bottom (below liquid level) in pressurized expansion tank
>
> This is what I have been recommending. But I plumbed mine to the side
> fitting of the exp.
> tank, still below liquid level.
>
> >- would
> >be a "2ND AIR VENT LINE", with same function as the air vent line from
> >highest point in engine block back to the expansion tank, below liq
level.
> >Both lines would be flowing a small amt of coolant that would be
bypassing
> >the rad, not being cooled, so, again, the caution to use SMALL AIR BLEED
> >LINES or RESTRICTOR in the lines.
>
> A line from the top of the engine shouldn't hurt anything, except that the
> coolant won't
> be cooled. As you mention, this is not an issue if the line is kept
> small. However,
> if you have a method to bleed the air at time of filling, then I don't see
> where this line is
> needed. Any air will be caught in the flow and eventually be separated
> through the
> radiator air-bleeder. But, I don't see where it would hurt anything,
> unless it were to
> break in flight.
>
> >Air in the system: We have hoses at the water pump inlet and outlet, and
> >the pump is high up on the engine in a "plugs normal installation".
> > - Where does the hose from the pump outlet feed back into the
engine
> >block - high or low on engine? (Basic question that I can't visualize
> >because I don't have an engine yet)?
>
> The wp outlet connects to the top of the front side housing. There are
two
> holes on
> that housing where the coolant enters and exits the engine. From the
exit,
> it goes
> through the wp housing passages and up through the thermostat and out to
> the radiator(s).
> (Ref. attachment)
>
> > - Likewise, where is the "hot coolant outlet" from the engine block
> >where the hose connects to the radiator? Should be high up near the top
> >like on all cars?
>
> Yes.
>
>
> >Anyway, the assumed short hose from pump outlet to somewhere on engine
could
> >have a leak;
>
> There is no hose here, only a gasket. (see attachment)
>
> > likewise, the hot coolant hose that runs DOWN from near the top
> >of block to the rads could have a leak anywhere below that outlet from
block
> >all the way down to connections to the radiators.
> > - As long as there is a head of coolant in the engine, there is
going to
> >be a head of coolant down at the rads, and so the pump is going to have
> >coolant at the bottom of rads to suck UP to the pump.
>
> Yes, provided we're drawing off the bottom of the radiator and not the
top.
>
> > - I don't envision any significant pump-stopping air at the bottom
where
> >pump is sucking from as long as there is any coolant in the block.
> > The
> >pump is going to suck from bottom of rads and pump out of its outlet into
> >the engine block and/or out the "leak" until there is ZERO coolant left
in
> >the rads, at which time the pump stops ciruclating - but not because of
> >"system configuration", rather for lack of liquid.
>
>
> This is where the rotary is different than other engines. It can get an
> air-lock in
> the coolant bypass circuit. Normally happens when first filling, or
> re-filling the
> cooling system. By the time the thermostat opens, you've damaged the
engine.
> Once you've "primed" the system, this is probably not going to
> happen. Although
> a coolant shortage could cause the pump to loose its prime.
>
>
> > - Again, I simply assume any AIR THAT IS BEING SUCKED IN AT THE
LEAK
> >will be up ON TOP of the coolant, not down at the bottom of the liquid
> >column where the pump sucks from.
>
> I think that the air could accumulate anywhere there is insufficient flow
> to move it
> along to somewhere else.
>
>
>
> >Now, to address the discussion of "What is the best indication of a
leak?"
> >
> > - THIS IS THE BEST SYSTEM: It tells you coolant level in EXPANSION
> >TANK has decreased too much, BEFORE the level in the BLOCK has even begun
to
> >suck air. This is the ideal warning - warned BEFORE the engine is
damaged,
> >gives "more" time (depending on speed of leak) to take action to land and
> >save the engine, if that is possible, given where you are and where the
> >closest landing spot is.
>
> I plan on monitoring Coolant Level (sensor in exp. tank), Coolant
Pressure,
> and
> Coolant Temp using Tracy's EM-2.
>
> Mark S.
>
>
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