Hi
Bobby,
The theory I have
read indicates that once your open area has passed 25-30% of your core area,
that from that point on - exit area dominates. In other words, it does not
make much difference how much more you enlarge your inlet area if the air can
not get out. Air pressure simply builds under the cowl in back of the
core and restricts further enhancement of thorough flow. That is if I
understood what I read correctly.
Ed
From:
Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Bobby J. Hughes
Sent: Saturday, July 11, 2009 3:52
PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Water Spray Pump
Bill,
I don't think I
have a problem getting air out of the cowl. The exit area is
greater than 3X the size of my inlets with no restrictions. The inlet ducts
and wedge diffusers tested very good on a bench wind tunnel setup. But I need
to review that data to make sure it's close to my actual
flight data. I really don't have any other options for my
radiator inlets other than a small enlargement. My radiators are
2.75" thick and have a denser fin count than the Griffin type Dennis
and Tracy are flying. I expect Air Delta T to be better than 81F.
Any difference
in controlling the inlet air verses traditional cowl flaps on the
exit?
Bobby
From:
Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Bill Schertz
Sent: Saturday, July 11, 2009 12:07
PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Water Spray Pump
Time I chimed in. I have been
testing with short flights trying to get my temps in line. I cannot stay at
full throttle beyond climbing to ~2500, at which point I throttle back to 5600
- 6000 rpm, and bring the speed up to 110 knots. Temps then stabilize below
200 - 205.
As part of my diagnostics, I have
always had a air pressure differential measurement from my Blue Mountain
(sigh) unit, and it would indicate ~3 to max 4 inches of water pressure
difference between the front of the rad and behind it under the
cowl.
For further information, I have
installed a temporary set of pressure probes that run to a manometer in the
cabin. This has told me the following:
1. The entrance to the rad is
getting good pressure 6-7 inches water pressure,
but
2. The exit is not functioning
well enough, because I get 3-4 inches pressure under the
cowl.
My theory as to why this is
difficult to fully cool includes.
1. The cowl was designed for an
air cooled engine, rejecting heat at 350 cylinder head temperature, which is a
bigger driving force than we have.
2. I used the two cowl inlets in
the original cowl to supply the two rads.
3. I have a third entrance for the
oil cooler, so I have ~ 50% more airflow to get out of the
cowl.
Bobby, I would install some
manometers to see if it is a problem getting the air in -- or out before you
modify your cowling.
Bill Schertz
KIS Cruiser #4045
N343BS
Phase I
testing
----- Original Message -----
Sent:
Saturday, July 11, 2009 10:44 AM
Subject:
[FlyRotary] Water Spray Pump
Like Dennis I am having to
throttle back and reduce boost after reaching pattern altitude. Flight
testing this week showed I can stabilize my oil temp at 220F at 130 mph,
6400 rpm and 30" MP. Air Delta T after my radiators averaged
81F. This power setting gives a 600 fpm climb and about 185-190 HP. Not
very impressive for a RV10. My initial climb out was around 1000-1250
fpm with OAT at 95F. Water temp stabilized at 200F. My oil
to water exchanger was transferring 43F to the water.
My total inlet area is 58 sqin
and 21% of core face. The numbers indicate that opening my inlet area to 68
sqin or 25% should allow me to cool my full net 238 HP. Before
starting major fiberglass work at 102 F I am thinking of testing a super
fine mist on the radiators. I would like to see what my oil temps would
be if I can drop the water temp by 10-20 degrees. The pump information
attached is a 15 bar pump and meets the specification for continuous use and
is safe to run dry. It's an espresso machine type pump but does not
have on\off time limitations. Other pumps like his have a 1/1 or 2/1
On/Off in minutes for cooling. If lowering my water temps to 180-185F
has a positive effect on oil temps then I will open my radiator duct this
fall when it's cooler. Besides, I have another test for this pump. I don't
have an intercooler and having a 1 pound 15 bar pump will tempt me to test
manifold water injections after my super charger.
--
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