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Al, I have 7/8" ID lines (AN-16 hose) plumbed to
both with similar fittings which are about the largest that I could put on
the cores. I fully agree that there are a number of variables that
can determine whether a system is successful or not. It only takes a bit of
a difference between two installations to make one successful and the other not
so successful.
Having gone through my flight test phase with
marginal cooling, I agree with your approach, a little too much cooling
(if there is such a thing) won't hurt you and is easy to retify, too little
cooling can hurt and is harder to fix. You are also exploring a bit
different regime with your three rotors, certainly more heat to dump and perhaps
other variables are different as well. So in your case, I would not
consider GM cores to be the best approach. At a miminum, I would think you
would need three of them, which would prepresent a physical configuration
challenge at the least. So I think your route of the custome radiator was
a prudent one.
Also, it is sometimes the case that the real cause
of overheating it not what you think. While I initially though I had
coolant system and oil system over heating problems, it turned out it was really
the lack of adqequate oil cooling that was the core problem. Bleed over of
heat that the oil cooler was not dumping was picked up by the coolant system and
was causing elevated coolant temps.
Once I solved my oil temp problems, the coolant
overheating problem went away. So they do seem to interact a bit
more on the rotary, probably because over 1/3 of the waste heat is dumped
by the oil cooler, so if its only 70% effective, then the other 30% has to be
taken care of by the coolants system - which might not be able to handle
it.
I found a source for Kuchemann and Weber's book
Aerodynamics of Propulsion, which I hope I get before Christmas. I have an
excerprt of Chapter 12, and it can get a bit confusing as they are not as
careful about some the designation of some of their various coefficients as I
would have liked. But , all in all about the best theortical text I've
found (that I could almost understand). So far I've identified 7-8
different coefficients that characterize the phenomona that causes each
pressure-drop or losses in just the air side of a heat exchanger
system. These factos include losses associated with:.
Inlet area, Duct/Diffuser Walls, Duct Angle,
inlet/core size ratio,Cooler Core pressure drop, Cooler core heating
effect, cooler core passage exit loss, and rear exit duct size.
What I have found most useful from the chapter is
the relationship between pressure drop across the core and maximum heat
transfer. Sometimes folks think that maximum pressure drop equates to
maximum cooling and of course, that is not necessarily the case. The
maximum pressure drop would be caused if the core was a solid block - but,
clearly that would be the worst case for cooling because the air mass flow would
be zero.
As best as I can tell at this point, there is an
equation in the chapter that reveals the optimum pressure drop/Mass flow balance
between pressure across the core and air mass through the core. I am
working on trying to see if I can understand it well enough to program it into a
spreadsheet to see what it would indicate about GM cores and other types of
radiators.
By, the way, Al how is your project
coming? Any forecast completion dates?
Ed
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----- Original Message -----
Sent: Monday, December 15, 2003 11:09
AM
Subject: [FlyRotary] Re: evap core versus
radiator
I fly with two in series and
have more than adquate cooling for most regimes of flight. A steep full
power climbout on a hot day will push the system to its limits, but otherwise
they work just fine for the power an NA 13B is likely to produce.
Ed;
I certainly
wouldn’t argue with what works. What size lines and connectors are you
using?
I tend to try to
err on the side of too much cooling; and may have in my setup. There are
a number of variables we don’t really have a good handle on until we go fly,
and it’s not a limitation I want to have to deal with.
Al
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