Bobby, I did some rough
calculations for your engine at 6400 rpm and 31 “ Hg to get the BTU you needed
to get rid of through the radiator (only).
Assuming all the water
turns to vapor (which it won’t, but we use lots of assumptions), and that you
only need to get rid of say 10% of your additional heat (not trying to cool the
entire engine output – just some delta that helps keep the cooling around
180F). I assume your basically cooling system would get rid of 90% of the
heat and you just need the water for that extra
10%.
Assuming all of that,
My calculations indicates one pint of water 100% vaporized would provide that
additional cooling for approx 1.8 minutes. So if you had a gallon (8
pints) then it should provide that additional margin for around 1.8 * 8 = 14.4
minutes. So assuming it takes you 2 minutes to get to where your airspeed
starts overcoming your cooling deficit. Then a gallon might give you sufficient
water for around 6 -7 take offs before you need to refill. Just a SWAG and
of course it is likely to be less than that because all the water won’t turn to
vapor and therefore like everything else will be something less than 100%
efficient. But, a starting point.
Perhaps Dave Leonard
can provide some real world consumption on amount of spray water to
cool.
Ed
From:
Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Bobby J. Hughes
Sent: Saturday, July 11, 2009 6:36
PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Exit Area
[FlyRotary] Re: Water Spray Pump
Ed,
I agree. My inlet area
is 21% or 58 sqin and my exit area is at least 200 sqin. I may open my
inlets up to 26% depending on the water spray test.
Is there any
disadvantage to limiting inlet flow in cruse as opposed to exit cowl
flaps?
Bobby
From:
Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Ed Anderson
Sent: Saturday, July 11, 2009 1:32
PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Exit Area [FlyRotary]
Re: Water Spray Pump
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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