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.
