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Thanks, Al. Another Data point.
Most of us using the two GM cores for radiators have approx 650 cubic inch of core volume and 200 sq inch of core frontal area. I normally fly cruise at 7.5 GPH and my coolant and oil temps are between 165F and 185F depending on OAT. Right after take off both may hit 200F until airspeed builds up but I am burning between 16-18 GPH during take off and initial climb out.
I agree that trapped air is a very significant (and often undiagnosed) problem area. Tracy Crook showed me a very simply way to tell. Run your engine until you reach an operating temperature (>120F) then place your hand on the side tank of the radiator (assuming its mounted more or less vertically), if you have air trapped, there will be a definite and sharp change in temperature of the metal of the side tank to the touch between the air and coolant level - cooler where the air is trapped at the top. It normally takes me 3 runs to 5000 rpm (while watching the coolant temps) before I have most of the air out. Now, if I had been smart enough to have put in a air bleed in the top of my cores as you suggest it would have been easy to get rid of the trapped air.
Early on when I was dealing with cooling problems, I made fiberglass exit ducts for the two radiators and found that they hindered cooling - but, I had to compromise the ducts passages significantly to simply fit them under the cowl - so probably not a valid test.
Cooling is certainly an area where small details can make a big difference and symptoms are often difficult to trace to the underlying cause. So much interaction and one thing affecting several parameters so which one fixed the problem, etc.
Fortunately, my cooling problems are in the past. The most significant thing I did for the rotary was to move the oil cooler up under the prop spinner where it got plenty of air flow. That dropped my oil temps by 30-40F which in turn brought down my coolant temps and all was well.
One last thing, is sometimes a cooling problem could indicate a good thing. I noticed that each time my engine power production went up as a result of intake/exhaust experimenting, that my temps also went up a bit. Fortunately, applying the StreamLine ducting to my intakes improved airflow/pressure recovery sufficiently to deal with the increased heat rejection required.
Ed
Ed Anderson
Rv-6A N494BW Rotary Powered
Matthews, NC
eanderson@carolina.rr.com
----- Original Message ----- From: "al p wick" <alwick@juno.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Sunday, February 05, 2006 10:14 AM
Subject: [FlyRotary] Re: NPG Coolant Temperature vs 50/50
<Cavitation theory:
Don't forget, I operate same engine as EGG, totally stock. With none of
the cooling issues. I think that eliminates cavitation as explanation.
Here's what I think it's all about....
Problem: You'd like better cooling, but are unsure about what's causing
marginal cooling.
Test: Compare to my performance to prove that it's air flow thru
radiator.
Method:
a) Measure your radiator fin area in Cubic Inches. If more than 408 C.I.
proceed.
b) Operate engine, place hand all over radiator to verify no trapped air
pockets.
c) Determine 7.4 gph throttle setting. This makes your power output same
as mine.
d) Warm up engine (heat soak it, don't just get it warm).
e) perform climb test with throttle at 7.4 gph setting. Take off at sea
level, climb to 12k ft.
If coolant temp raises during the climb, you clearly have air flow
problem thru radiator. Test different air flow concepts.
Notes:
-My testing found trapped air in cooling system is 10 times more
significant than any other factor. Install dynamic air bleed to make sure
you are free of air.
-I have no oil cooler, so if your temp rises during climb, you have very
significant air flow problem.
-I have no rad air exit ducting. I found it aggravated my cooling. Even
though all the articles you read say the opposite. So don't make
assumptions.
I suspect this test can really help.
-al wick
Artificial intelligence in cockpit, Cozy IV powered by stock Subaru 2.5
N9032U 200+ hours on engine/airframe from Portland, Oregon
Prop construct, Subaru install, Risk assessment, Glass panel design info:
http://www.maddyhome.com/canardpages/pages/alwick/index.html
On Sat, 04 Feb 2006 21:05:11 -0500 Chad Robinson <crj@lucubration.com>
writes:
Ed Anderson wrote:
> Delta T = Q/cM, now if the combined effects of c and m provide
13% less
> heat transfer capability than the 50/50 mixture that would
indicated
> that to carry away the same Q at the same flow rate, the delta T
of NPG+
> would need to increase by 13%. So if I were getting 180F with the
50/50
> for the same Q load (and flow rate) then with NPG+, I would
expect 180
> *1.13 = 203F. Yet, if I understood correct we have reports that
lesser
> temperatures results noted by users of NPG - this leaves me a bit
puzzled.
I don't have the answer, but how about a hypothesis? Suppose they
have a
cavitation problem. A more viscous fluid tends to reduce the onset
of
cavitation, no? And is there any data on what pressure their system
is being
run at?
Regards,
Chad
--
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