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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