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Message
Rusty,
With the use of the special Howe radiator with the
oil coolers built into the tanks, the following MAY need to be checked
out. The transfer of heat from the water to the oil is a function of both
the temperature difference between the water and the oil (delta-T) and the flow
rates of the respective fluids. I.E. if the water is too hot, you
obviously cannot get the oil any cooler than the water, so that becomes
limiting. From your description of behavior, it sounds like your water is
cooling okay.
The second factor, the flow rate of the oil and
water, could be negatively affected by the use of the water thermostat. The
thermostat works by restricting the flow of water from the engine through the
radiator, therefore when you reach 180 degrees, it slows down the water flow.
This means that the water flowing by the oil cooler tubes (in the headers) is
going slower. This reduces the *rate* of heat transfer across the tube (the heat
transfer coefficient), so that it may reduce the cooling effectiveness of the
oil cooler. If we take your 240 degree oil, expose it to the radiator
inlet tank (180 degree) you only have 60 degrees delta T to work with. On the
other end of the radiator, you have much cooler water (any measurement?) which
would improve the delta T, but if the heat transfer coefficient is small, that
won't help much.
1. Do you have a drawing and/or
specs from the manufacturer that you could scan and email to me to look at? I
would be interested in trying some heat transfer calculations on the system, but
need the physical layout details to make much sense of it.
2. Try removing the thermostat
and running a duplicate flight to see if the oil temps come down. This would be
an indication of velocity (flow rate) limited heat transfer.
Bill Schertz
----- Original Message -----
Sent: Tuesday, September 02, 2003 5:53
AM
Subject: [FlyRotary] Re: flight #2 and
#3
Rusty, my experience is that (at least the more
recent rotary engines) can withstand oil temps into the engine of up to 240F
for at least a short period of time without causing damage (been there, done
that). Oil Pan temp is going to be quite a bit higher than oil coming
out of the cooler, so I would guestimate that your oil into the engine is at
least 15-20F less (probably more like 20-30F) than oil pan temps.
After all, the oil in your pan (a lot of it) has just come from cooling the
rotors, so is bound to be carrying a lot of heat.
I drilled and tapped a 1/8" NPT hole in the
fitting where my oil returns to the engine after going through the cooler for
oil temp sensor.
Ed Anderson
----- Original Message -----
Sent: Tuesday, September 02, 2003 12:20
AM
Subject: [FlyRotary] Re: flight #2 and
#3
But 210 into the engine is gospel from Racing Beat.
That's
depressing. I may have to call Bruce tomorrow and get his view on
this. I just took another look at the log that Finn posted a
while back, and he did have a period of time where the oil pan temp was 242,
while the oil return from the cooler was 201. If (huge, unproven "if")
this is the case with my engine, then I'll be OK, but I need to measure the
temp into the engine to be sure. I believe the archives would show
that Finn suggested this to me a while back. Guess I should have
listened.
If I'm close to staying under 210, I could consider using
a 160 degree thermostat. I know I've seen one of those before, but I
can't find it listed anywhere at the moment.
Bill-
I'm using a custom made Howe radiator with an oil/water heat
exchanger built into each tank. I have the oil plumbed in series
with the exchangers, such that it goes through the hot tank
first, then the cooler tank. After the second exchanger, it goes
through a filter, then back to the engine. In thinking about this, I
might be able to drill and tap a hole in the top of the spin on
filter bracket for a temp sensor. I'll have to take a closer look
at that. My goal was to not have to have a separate air/oil
cooler, but rest assured, the big ugly cowl has room for one if
needed.
Rusty
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