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Dennis, I would like to see your temps at 6500 msl and 20"
Hg manifold pressure quite a bit lower. The coolant is a bit high
but acceptable for those conditions (but may not be for other conditions) ,
but the oil temps is a bit on the high side to me. When my
RV-6A is operated under similar conditions, my coolant ranges between 170-180F
and oil temps the same.
However, when you say inlet temps - do you mean inlet to
your ducts or is that the inlet to your throttle body. The reason I
ask is 90F seems very high for OAT at 6500 MSL and since you are using that
figure to determine your Delta T across your cores, you need to insure that it
is correct.
Another reason I question the 90F temp is that
with a 45F temp increase across your cooler core. If we assume the air
velocity through your duct is an ideal 0.1 * Cruise speed then your mass flow
through your core with a deltaT of 45F would only remove approx 700
BTU/Min. IF duct air velocity were 0.2*Cruise Speed then at 45F
it would remove approx 1319 BTU/Min. You don't say what your fuel
burn is so I'm assuming at 164 MPH TAS you are making at least 100 HP (probably
a good deal more) which would mean you need to get rid of a minimum of 1500
BTU/Min through your oil cooler. So since you oil temps are a bit on the
high I think it safe to say you are marginal in getting rid of the oil
BTU. But, if the OAT was 50F vice 90F then your delta T would be
85F.
With a 0.1*cruise speed duct speed and 85F delta T you
would be getting rid of approx 1250 BTU/Min. While still a bit on the low
side probably good enough so that the excess oil BTU not discharged by the oil
cooler is being picked up by the coolant. If your duct speed is a bit
faster than my assumption then you would get rid of more.
I found when I solved my oil temp problem that my coolant
temps came down considerably. So one system can "leak" heat over to the
other system to discharge.
So it is important that the correct inlet temp for your
ducts be used to derive your deltaT, I strongly suspect that 90F is your
throttle body inlet temp rather than your OAT at 6500 MSL.
For one thing, 4" of H20 inside the cowl does seem a bit
high but I notice it drops off to 2" H20 which is more acceptable. But,
6.5" H20 across the core would appear to be a value which would indicate
that your duct is doing a fair job. The dynamic pressure at 165MPH
is around 10" H20. The best duct (Streamline = 0.84 Efficient) would give
you around 0.84 *10"h20 = 9.155" H20. Your 6.5/10.899 = 60 % would
indicate the duct is doing a fair job. However, the cowl pressure
may be lowering this value a bit.
In any case, need to know whether your inlet to your ducts
was actually 90F or was this your throttle body inlet temp which is almost
always higher than OAT.
Good work on gathering data.
Ed
----- Original Message -----
Sent: Saturday, September 22, 2007 11:40
PM
Subject: [FlyRotary] RV-7A Cooling
I still working to improve my oil cooling -
Renesis engine, PSRU 2.8:1, Catto 76X88 composite prop, water and oil
radiators under engine at about 30 degrees to inlet air flow, James cowl -
shark intake under spinner . See pictures below.
Today I
flew and recorded some temperature and static pressure numbers for anyone to
comment on.
Test conditions:
90 deg OAT = inlet air
temperature
About 6500 foot altitude
TAS - GPS and EM-2 : 165 mph
Manifold pressure 20in.
RPM 5700
Water Temp - 192 deg F
Oil
temp leaving oil cooler - 207 deg. F
Oil temp in oil pan - 235 deg. F
Temp of heated air leaving oil cooler -135 deg F (135-90 = 45 deg temp
rise of cooling air through the oil cooler)
Temp of heated air in cowl low
and near firewall 133 deg. F
I measured static air pressures at
5 points inside the cowl as follows:
1). Inlet side of oil cooler:
10.5 in water
2). Back side of oil cooler: 4 in water ( 10.5 -
4 = 6.5 in water pressure drop across oil cooler.)
3). Midway between oil
cooler and firewall: 2.75 in water
4). Right side within 4 inches of
firewall and 3 inches above bottom of firewall: 2 in water
5). Left side
within 4 inches of firewall and 3 inches above bottom of firewall: 2 in water
Before these tests Bobby H. and I were thinking I needed more
outlet area to improve my cooling. I am seriously considering
a big
cowl flap to lower the pressure in the cowl. Does this data support this
position?
Hopefully better minds than mine will know!!
Dennis H.
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