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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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