Del Johnson wrote:

I have some questions about the cooling system and would like to

float

my

design by the group before proceeding.

Attached is a drawing that depicts the proposed system.  The red

lines

indicate the pressure side of the cooling system (outflow from the

pump)

and

the green lines reflect the low pressure side ( return flow).

I would like to use the Mazda thermostat, to control the

re-circulation

of

coolant in the water pump during cold operating conditions.  The

high

pressure output line to the radiator will be through a welded on tap

that is

located below the thermostat so there should not be any restriction

in

the

flow to the radiator.  The primary reason for using the thermostat

is

that I

would like to use an exhaust augmentation system which precludes

using a

cowl flap to regulating the exiting cooling air.

I'm tight on vertical space in the cowling.  Placing the radiator

cap

immediately above the thermostat might require a small bump in the

cowling.

I therefore included a separate small reservoir that has the

pressure

cap so

that it can be located elsewhere under the cowling.  This unit also

contains

one or more bleed line taps that will purge the system of steam

vapors

should the system overheat.   I included in the design a low

pressure

check

valve that will prevent the high pressure coolant from backflowing

to

the

low pressure side.  Any buildup in steam pressure will open the

valve.

What is the minimum size (volume) of the overflow bottle?
How many lbs of pressure should the overflow bottle hold?
If you are using standard car overflow bottles which make / model

car

overflow bottle are you using?

Any comments or suggestions on the design that I presented?

That looks like it will work Del but you will be giving away some
MPG and speed by using a thermostat instead of a cowl flap to control
engine temperature. A cowl flap will reduce the cooling drag
when max cooling is not required during cruise.

The pressure in the system is about 25 psi when a 25 psi pressure cap
is used. I recommend a 25 psi pressure cap as it increase the all

important

boiling temp. If the coolant boils that is a catastrophic engine

failure

IMHO.

Something around a gallon seems right for a pressure bottle.

Here is the system I recommend. Note the pressure cap controls the

pressure

on the pump inlet side. There will be pressure drops throughout
the rest of the cooling system.

The Corvette has a nice metal pressure bottle. I had Ed Klepies weld
one up for me so I could use highly reliable AN hose. More rotary
powered airplanes have crashed by using low automotive quality

plumbing

than for any other reason.

Paul Lamar

My question concerning pressure was in regard to the overflow bottle.  I
assume anything less than 25 lbs (if your running 25 lbs on the other

cap)

would be ok.

I was thinking about welding up my own  metal bottle rather than using

the

plastic automotive ones but thought I would poll the group if plastic

car

overflow bottles were being used.

I'm not sure that your point about loosing MPG and speed is correct if

I'm

using exhaust augmentation to pull the cooling air through the cowling.

If

exhaust augmentation doesn't work out, I can remove the thermostat, plug

the

recirculation hole in the pump and install cowl flaps.

The over flow bottle is at atmospheric pressure so just about anything

will

work that will take the heat.

I think the correct NACA term for that is cooling air ejector rather than

augmentor.

The required length of an ejector makes them rather impractical for use
with a single engine tractor. A twin or pusher is another matter.

As I recall your ejector design is different and located under the rad.
It looks like it will work but perhaps it  would be too deep
to fit into a stock cowl. Have you made any scale drawings yet? Also
I think you should run both exhaust pipes into one side. I was thinking of

doing

a 3D for you on this but I did not think it would fit in a stock cowl.
What kind of airplane are you building again?

The thing about air ejectors is they primarily work at low speed
when dynamic pressure is too low to force enough air through the rad.
As the speed and air flow through the rad builds up they become
less effective. That is when  you need the cowl flap.

Paul Lamar

Paul, Has anyone done a flow schematic with the inclusion
of the pressure bottle? Am I correct in saying that the
"pressure bottle" is actually a header tank? Do you intend
am overflow tank as well, or a coolant recovery tank if you
will? I am working on my radiator locations and tank placements.
I haven't to this point had enough hands on
time to get a good feel for routing. Do you, or has an ACRE
subscriber done a flow layout? Anything you have will be helpful
 as I start getting into the plumbing layout.
Thanks,
Bill Jepson

Yes it is a header tank. You still need a coolant recovery tank. Not
shown in the 3D. I guess I need to add that to the 3D.

We discussed a real coolant recovery system a few years ago. I think we
concluded you need a 50 psi pump to get the coolant back into the engine
while the engine is still hot and running.

Paul Lamar

First, to answer Paul's question:   I am building a Glastar.  There is quite
a bit of room to work with both on the sides of the and underneath the
engine.  The cooling air ejector/muffler, that I proposed, places the two
functions in parallel.  The traditional serial connections (muffler followed
by ejector) would be too long to fit under the cowling.

I'm not sure that I agree with your statement (Paul's) that cooling ejectors
work primarily at slow air speeds.  Are there any studies that support your
assertion that you will loose speed and MPG at high air speeds.  I'm  not an
engineer but I design plumbing systems for large multistory buildings
(apartment complexes, etc).  An engine operating at,  cruise (75% power) is
like flushing a toilet or dumping a bucket of water into a mop sink.  If the
building isn't vented the water in the traps near the toilet (or sink) would
be suck out.   Regardless of air speed the cooling ejectors will create a
vacuum and that vacuum should increase as the quantity of exhaust gases
increase (which parallel engine cooling requirements).  Only if the engine
output is significantly reduced would the cooling ejectors affect become
marginal.  However, studies have shown that even at idle engine speeds there
is still a cooling affect from the ejectors.

There aren't that many airplanes flying with cooling ejectors but all the
ones that I have heard about, report good cooling.  Charles Airesman VariEze
is an example of a fast airplane that incorporated cooling ejectors into the
design.

Responding to Bill Jepson's comments.  I wasn't considering the coolant
recovery bottle as a header tank.  Why would you need a header tank?  Cars
don't use them anymore.  All of the air should be purged from the system
(except for the recovery bottle).  Years ago, header tanks contained some
air that buffered the expansion of the coolant.  Didn't recovery bottles
replace the expansion tank?   Is there any advantage to maintain some
pressure in the recovery tank (5 to 15 lbs)?

On the question of the size of the recovery bottle:  Does anyone know the
volume of coolant taken up in the 13b engine? It would seem that if you know
how much coolant it takes to fill the system that you could calculate the
size needed for the recovery bottle if you calculate the expansion of the
fluid over the operating temperature range.

Del Johnson

 
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