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I think I'll pass on the boil -over, getting to the
age where too much fun can be dangerous {:>).
Yes, many of us do use a coolant pressure
gauge. It told me when I recently compromised the coolant "O" ring due to
a trapped piece of apex seal on the side of the rotor (hasty rebuild)which
created sufficient friction to locally fry the Teflon Coated "O" ring. I
think I have the honor of being the only known case of frying one of
those. My coolant pressure started to climb on long trip from NC to
Mississippi, it increased approx 1/2" psi every 45 minutes. My the time I
got to Charlies, the pressure was reading 18-19 Psi. So second time had to
rebuild engine down in Louisiana in June.
I suspect that you are correct, Al. The
operating temperatures recommended my Mazda long ago are undoubtedly
conservative especially with regard to the capability of various "O" rings to
withstand the heat.
However, I am not certain what
else might occur as a result of over heating. I have read that
overheating can cause the apex seal to chatter and create wear on the rotor
housing. I have seen speculation that uneven heating of the block might
cause it to "banana" and bearings to wear/seize. One story is that
the aluminum rotor housing will "shrink" if over heated (actually it appears
that the aluminum housing might indeed tend to "crush" under pressure of
tension bolts and overheated metal) and was one of the things to
check/measure during an rebuild.
I would think that folks in the racing crowd would
know first hand of damage overhead engines might incur.
Lynn????
As I indicated, I and several others have
exceeded those limits by healthy margins for limited time without indications of
damage.
However, I for one have had too many engine
rebuilds for other reasons to intentionally cook one to destruction - I'll
defer to someone else to do that {:>)
All this talk about boil-over has me thinking about
a cool drink and going to neighbors to watch super bowl game (actually, we turn
on the set and then never get around to watching it ).
Check in later.
Ed
----- Original Message -----
Sent: Sunday, February 05, 2006 2:50
PM
Subject: [FlyRotary] Re: NPG Coolant
Temperature vs 50/50
Boil over. Man is that fun!
I deliberately caused boil over with multiple high speed taxi tests. I
think I did it three times. When it happens, there's no stopping it. You loose
substantial quantity fluid and all of the engine components are heat soaked. I
don't know if there would be any value to shutting off engine, then
restarting. Likely not. Lack of fluid movement would likely cause even greater
coolant loss.
Certainly lots of things you can do to prevent it. Some simple ones
like throw away overflow bottle and operate cooling system with 2 cups of air
under cap. Big asset, as it allows you to use coolant pressure as advance
indicator of system integrity. Yeah, I know you guys think your sys behaves
different. I am skeptical.
I sure would review those oil and coolant temp limits. I find that so
hard to believe. Maybe long ago. I'd dig into "what component fails, how does
it fail (like how long does it take)". Stuff like that. If failure mode
is gradual coolant loss past o-ring, I'd instrument that then test it.
Force it to happen. With the modern advances in material properties, I just
can't believe 230F coolant can affect an o-ring anymore. You know?
Ok, Al
That as you said, explains it. My
recollection of reported coolant temps were clearly in error and what you
cited about coolant temps using NPG does correlate. My mind is
happy!
I have fortunately never experienced cascade
boil-over and hope never to do so, clearly a terrifying and hopeless feeling
to encounter why flying. Shutting off the engine in such a situation
might bring things back under control - if you have plenty of
altitude. But, I would assume most boil overs happen after a high
powered takeoff on a hot day, so altitude may be lacking.
I can certainly understand why that would
induce someone to go to the NPG coolant.
Long, Long ago and in a place far, far away -
Japan to be exact. Mazda provided that 180F coolant temps (out of the
block) and 210F Oil temps (into the block) were the limits. These can
also be found in Racing Beat's technical catalog. I have on
occasion - and for very limited amounts of time - had oil temps as high as
230F and coolant as high as 250F. These were cases where coolant was
still flowing and pressurized. After the first incident with an 86 N/A
block, I found I had coolant "O" ring compromised (coolant leaking into
combustion chamber), I then switched to the Teflon Enscapulate Silicon "O"
rings and on the one or two occasions when the temps reached 220F oil and
230F coolant - there appeared to be no damage.
I believe that those limits were established
for the mid 1980 era 13Bs and that block coolant galley improvements and
casting changes (as well as use of higher temps rubber seals) have probably
raised the permissible operating temperature. But, I do not know of
anyone who has tested an engine to destruction to find out
{:>)
Ed
----- Original Message -----
Sent: Saturday, February 04, 2006
9:32 PM
Subject: [FlyRotary] Re: NPG Coolant
Temperature vs 50/50
The Egg guys no longer operate at the normal 200F when they install
NPG. I don't recall the exact number, but they operate around 215F
(cruise). Which explains most of your theoretical differences.
They gain a significant safety bonus in the boil over temp. That
safety margin is what it's all about. At least from the risk perspective.
So by operating at a higher Delta T, they compensate for the reduced
efficiency of the fluid.
I've heard you guys describe the importance of operating coolant
around 185F or so? Are you sure of that limit? Is that just a recommended
thing, or hard and fast limit. I'm always skeptical of stuff like
that.
-al wick
Hi Al,
Appreciate your (anybody else welcome also)
views on one other thing that is still bothering me about the use
of NPG.
Given that NPG+ has a specific heat of 0.66
at 212F or 20% less than the 0.82 for the 50/50 mixture
and given that NPG+ is approx 7% more dense than the 50/50
- then that for the same flowrate for both it would seem that
NPG still has a 13% lesser overall capacity for heat transfer (at
the same temps 212F and flow rates).
Also assume that the engine is produce the
same heat load (Q),lets take alook at what temperature we might see with
NPG+ compared to the 50/50 solution. We have from the oldie but
goody Q = c*M*DeltaT the ability to solve for the temperature increase,
DeltaT.
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.
If my assumption is correct thus far, then
I am at a loss to understand the reports of lesser cooling temps when
using NPG+, it would seem just the opposite would happen, that
is - the coolant temperature would
increase.
Now, If the coolant temp with NPG+
actually does remain the same (or decreased) for the same Q
and flow rate, then it could indicate the engine heat load is not
being carried away as well as with the 50/50. IF the reports of
lesser cooling temps occurs when switching to NPG+ are
correct, then it would appear to me that the engine must then be
operating under a higher heat load (i.e heat not being transfer to the
radiators as effectively) . This doesn't even take into
consideration the possibly lesser flow rate of NPG+ for the same pump
speed as the 50/50 due to its higher 3 times higher viscosity (at
212F).
Yes, I have no problem understanding
that boil-over has been eliminated - but, is NPG actually cooling as
well as coolant temps may lead one to believe? I mean with NPG, I
could have a excessive block temperature and still not have boil-over -
but my rotary engine would likely have suffered damage.
What am I missing? Inquiring minds
(even old ones) want to know {:>)
Ed A
-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
-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
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