Paul, My old heat exchangers are, oil, 316 cub inches and water
750 cub inches if I have converted from metric correctly. These provide
too much cooling for the P port renesis.
New Exchangers Oil, 297 cu inches and water 650 cub inches
total over 900 cub inches and fit surprisingly well inside the new
sleek cowl. Comparison to others that I know of, Combined total of 623
cub inches ,, just cools.
Combined total total of 770 cub inches for a 20B and reportedly cools
I was aiming for around 800 cub inches, but with the thermostat
fitted went with the biggest I could fit without going silly , as in
making other things difficult to fit in the cowl. The biggest
restriction I found was to be able to route the exhaust around the Water
exchanger keeping about 3 inches clearance. Dave Léonard's idea of
having the air enter the exchangers from underneath is brilliant as it
keeps the front oil exchanger tucked up under the front of the engine
and away from the cowl meaning no unnecessary bulges to the cowl. That
also gives a reasonable flow of air directed at the exhaust pipes to
cool them as quickly as possible.
Still agonising as to if I bother fitting EGT probes to this
engine. I have them in my current engine and they do not last long at
all giving terrible readings that just keep me awake at night with
worry. I know of an engine with over 400 hours on it that has run
terribly hot all its life without ever having EGT probes fitted.
Recently stripped and inspected for no damage whatever. The next
question is “What can I really do about excessive EGTs ?” I can control
A/F ratio which has a bearing on EGT’s but that is all. I thought the
timing may alter the EGT, but not really. The only thing that may, is
your spark system that will give a cleaner burn. So still wondering?.
Neil.
Just adhere to a few water cooling principles. Don't let the cores
"see" the exhaust pipes.
Exhaust heat radiation is a severe problem. The exhaust pipes run
bright red. Keep
the core as cool as possible.
A diffuser on top of the core protects the core from under cowl and
engine heat.
A one degree F increase in air temperature the core is subjected
too, is a one percent
reduction in cooling. Try to find large area thin cores.
Too much volume in the core adds weight. Water is 8 pounds per
gallon and much
heavier than fuel. Dave Leonard used a sledge hammer approach with
a 3 inch thick
water core. 1000 to 1500 cubic inches :)
Use a Kay's and London wedge shaped diffuser.
Start with a 20% of the core frontal area as a scoop area
Violate these principles at your own peril :)
Your lucky as there are no hills or tall trees near your air strip.
You can climb
out at high speed. Better for cooling. Could save your butt :-)
Here is the 650 HP, 2 rotor, time to climb engine cooling system.
Each core is only about 450 cubic inches and about 3/4 inch
thick. There are 2 cores
back to back in a cross counter flow configuration. Note the
diffuser is protecting
the cores from the bright red turbo housing.
Paul Lamar
In regards to EGT's; I recommend reading Wikipedia article on thermocouples.
It mentions thermocouple "aging" as a source of problems. Which type are you
using? Type K are the most common and have a temperature range to 1370*C.
You could look to using a Type R thermocouple manufactured with
Platinum/Rhodium
wires and capable of 1600*C. Then there are the Tungsten/Rhenium
thermocouples of
Types C/D/R which are good to 2315*C. Your temperature instrument needs to
match the type of thermocouple required or you will induce a cold
junction error
into the device reading. The problem is that Type K and J are the most
commonly
used thermocouples. Also, regular wire can not be used to extend the
thermocouples
for a remote sensing point.
You MAY be able to change your thermocouples and
then calibrate the display to read correctly at 1500*. The higher
temperature range
thermocouples should last longer in service as they will not approach their
operating limit. Do your probes go right in to the exhaust stream? You
may get some
extra life out of your current probes by welding a sealed tube in the
pipe that is
an almost snug fit for the probe.
These are called thermowells. A pipe thread weld-o-let
is welded to the pipe and the thermowell is threaded in. Then the
thermocouple is installed.
The reading will not be as quick to respond but your probes may last
longer.
Dale Davies
.
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