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Mark, here is a more credible source about slow coolant
flow than me.
A common misconception is that if coolant flows too quickly through the
system, that it will not have time to cool properly. However the cooling system
is a closed loop, so if you are keeping the coolant in the radiator longer to
allow it to cool, you are also allowing it to stay in the engine longer, which
increases coolant temperatures. Coolant in the engine will actually boil away
from critical heat areas within the cooling system if not forced through the
cooling system at a sufficiently high velocity. This situation is a common cause
of so-called "hot spots", which can lead to failures.
Here is the URL if you want to read
more
Ed
----- Original Message -----
Sent: Sunday, September 30, 2007 10:09
AM
Subject: [FlyRotary] Re: Oil Delta -
T
Ed,
Yes, I'm happy with the coolant temps. I wish the oil would allow a
little more margin, but 190* @ 5200 is ok for 90* OAT. I'll be gong out
to the airport in a while and I'll check the calibration on the coolant
sensors.
Mark
Overcast with 40% chance of rain today. :-(
On 9/30/07, Ed
Anderson <eanderson@carolina.rr.com>
wrote:
I suspect that you temp sensor location may be the
problem rather than calibration. If its outside the main flow channel,
then its hard to tell just how close or far off of the main flow temps it
may be registering.
On the other hand if your coolant engine outlet temp
is measuring only 161F (and assuming that is somewhere near the actual temp)
then you radiator is clearly doing its job by cooling down the coolant
before it enters the engine. When I am cruising at 5400 rpm my coolant
temps range from 155F-175F depending on OAT. This is temp out of the
engine. Since your temp is in the same ball park, it appears your
radiator is doing a good job especially given the 90F OAT.
Ed
----- Original Message -----
Sent: Saturday, September 29, 2007
10:13 PM
Subject: [FlyRotary] Re: Oil Delta -
T
Ed,
OK, I'll recallibrate the sensors ONE MORE TIME! They were
reading within a degree of each other before I relocated one of
them. I did take the time to verify the EC-2 sensor was reading
correctly at 212* during the switch. But I didn't check it lower
than that. I'll use ambient temp for a low reference.
I suspect the problem may be where one of the sensors is
located. The first sensor is located on the WP housing at the outlet
from the engine. Since that is one of the factory locations, I don't
see any problem there. The second sensor is on the WP housing inlet,
but not on the main line, it is on the one returing from the swirl tank,
but is very close to where the main WP inlet is located. It is
fed by a line that runs through the swirl tank from the outlet side
of the radiator, but at the top instead of the bottom (to draw any air out
of the radiator). Directly across from this fitting is the "hot"
inlet to the radiator. I'm sure that some of the coolant goes
straight across the core to the swirl tank fitting. (Yes, this is
confusing me too) I questioned the wisdom of putting the sensor
where I did, but did it anyway due to the ease of installation (No
draining the cooling system, no drilling, no tapping). Anyway, this
was supposed to be a "temporary" test setup.
So, it looks like I probably need to find a better place to locate
the second sensor. I'll check the accuracy of this sensor at
around 150* and see what it shows. If there is a significant error,
I'll dive into the EC-2 calibration system one more time (heaven help
me).
Mark
On 9/29/07, Ed
Anderson <eanderson@carolina.rr.com > wrote:
Mark, if you really had excess air
flowing through your radiators the coolant would drop more than 4 Deg
F. In fact, the more air flow the more coolant Delta T you would
drop through the radiator. So if you had something like 180F in
and 120F out then I might suspect too much air flow through the cores,
but not with a drop of only 4 deg F. In fact if that delta T
is correct (which I suspect it is not), then you would need tremendous
coolant flow rates for it to carry away the engine heat it needs to at
5200 rpm.
I did some back of envelope
calculations.
IF your coolant flow was 30 GPM at 8.25
lb/gal coolant with a 0.65 (50/50 mix) Cp, then a 4 degreeF drop in
coolant temp would only be getting rid of 644
BTU/Min.
At 5200 rpm and a 19:1 A/F ratio you would
need to get rid of approx 3100 BTU/Min through your radiator. I
suspect that the 4 degree drop you are measuring may be in
error. I assume you are measuring temp at radiator inlet (engine
outlet) and radiator outlet (or engine inlet) It would
take something like a 20 deg coolant temp drop at 30 GPM flow or a
flow rate of 150 GPM at 4 deg drop to get rid of that much
heat.
On the other hand if you were flowing 60 gpm of
pure water and had a 6.5F drop that would get rid of the required
BTUs. I have no clue as to the flow rate of a 20B water pump, but
suspect my guess of 60 gpm might be on the high side.
Since you are apparently cooling just fine with
the radiators, then :
1. My calculations are
incorrect
2. Your coolant temp drop is more than 4
Fdeg
3. your flow rate is >50 gpm
4. You oil system is dumping the excess heat
that your radiators are not getting rid of.
FWIW
Ed
----- Original Message -----
Sent: Saturday, September 29,
2007 7:51 PM
Subject: [FlyRotary] Re: Oil
Delta - T
Tracy,
I flew again today. I'm still staying very close to the
airport and was forced to limit my altitude to 2500' due to
clouds. OAT was about 90* and oil got to 215, but came right
down after leveling off and settled in at 190*. The strange
thing is the water temps in economy cruise (5200 engine rpm, 1800 prop
rpm) were in the 157* range. I'm measuring water temp in and
out. Water out was about 161*, so I'm getting very little temp
drop through the radiator. We're figuring that this is probably
due to too much air to the water radiator or too rapid
coolant flow through the radiator (I'm running the 20B
pump). My main pulley has been downsized, but I may also
need to enlarge the wp pulley a little to slow the flow.
I'm considering doing a quick mod to check this theory. If
that's true, then my oil temps should drop because I suspect airflow
through the two radiators are fighting for the exit space and the
water radiator is winning.
Mark
On 9/29/07, Tracy Crook <tracy@rotaryaviation.com > wrote:
Haven't had any 100+ days since installing the Renesis but
cooling is similar to the 2nd gen I had a few years ago when we
had 10 consecutive days of 100+ temps. Didn't have to wait it
out but simply limited power after initial climbout. Still had
more ROC than most certified planes at the reduced power
setting. I start with around 2500 FPM on a standard day and
never had to settle for less than ~1000 fpm due to heat issues.
Hope my 20B RV-8 does as well or better but I will install
spray bar for initial tests.
Tracy (delayed 20B test schedule due to motorcycle
distraction)
On 9/27/07, Mark Steitle <msteitle@gmail.com > wrote:
Tracy,
So, what do you call a "hot" day? In Austin, it is
normal during the summer for temps to be in the upper 90's and
even above 100 on occasion. I don't want to be grounded
waiting for the Texas heat to subside. I guess I could
install a spray bar for summer flying. Right now I can keep
temps in the green up into the low 90's. Living in
Texas, I would like a little more margin than that. Not
everyone can swing a summer home in
Colorado. ;-)
Mark S.
(Just happy to be flying again.)
On 9/26/07, Tracy Crook <tracy@rotaryaviation.com > wrote:
Engine will cool at any throttle setting that enables the
plane to fly. The coolant & oil temp curve looks about
like the power required curve of the airframe, minumum at around
95 mph and rises on either side of that speed. Only
exception is WOT at Vx on hot day. Engine will exceed
redline temps if this is maintained more than a minute or
so. Fortunately there is never any real need to
do that.
Tracy
On 9/26/07, Mark Steitle <msteitle@gmail.com > wrote:
Tracy,
Is there a particular speed that you must reach before
your system cools?
Mark
On 9/26/07, Tracy Crook <tracy@rotaryaviation.com > wrote:
For another data point, the delta T on oil cooler
depends on power setting on my installation (no big
surprise). It is around 40 degrees F at higher power
settings.
Tracy
On 9/18/07, Mark Steitle <msteitle@gmail.com > wrote:
For those that are flying (rotaries), I'm curious as
to what delta-T you're seeing across the oil cooler.
And at what speed you attain adequate cooling.
Mark
S.
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