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Date: Thu, 2 Feb 2006 11:34:57 -0800
From: David Leonard <wdleonard@gmail.com>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Suitability of NPG for Rotary Engine use
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Ed,

You and everyone else make some good points, but calling NPG unsuitable is
going a little bit too far.  It has benefits and draw backs, but is entirel=
y
suitable.  The benefits may or may not out weigh the draw backs.  Each
builder has to make that decision, but you have not exactly been making a
fair comparison.  Sometimes you compare NPG to water, and sometimes to
50/50.  Having flown a wide variety of cooling mixtures I think I can clear
up some issues.

There is no doubt that pure water with some soap or water wetter does by
far the best job of carrying away the heat.  That was my preferred mixture
in the summer.  But given that I want to go places where the temp will
occasionally go below freezing - without changing out the coolant every tim=
e
- lets make all our comparisons of NPG+ (hereafter referred to as NPG) to a
50/50 PG or EG mixture (for environmental reasons I now use only PG).

First, I want to stress there that the use of NPG had NOTHING to do with my
engine failure.  If anything, it was my rushed conversion to its use - more
on that later.

*So here are the benefits of using NPG*:

1) Can be run with zero or reduced pressure.  This is a particularly nice
feature in an aircraft, especially turbo, where the ambient pressure is
constantly changing.  At very high altitudes, the absolute pressure in the
system may not be much higher than 1 atmosphere.  If you are running near
the boiling point (which you shouldn't be - but I often did) going higher
could be enough to push you over the top and cause a boil over.  Also, a
leak in the system could cause boil over with 50/50 but will not affect
NPG's performance.

2) Much higher boiling temp - provides a greater protection from boil over.
A very nice feature as I have boiled over twice in flight.  Once it gets
started, there seems to be no quenching it until you land and let everythin=
g
cool down.  Turning off the engine for a minute would probably work as well
but I never tried that.  I think that once the true boiling starts the
thermal conduction goes way down and the metal parts get very hot and stay
that way because of the continued boiling.

3) Excellent corrosion protection and stability, especially for Magnesium.
This stuff could truly be unchanged for several years and provide much
better corrosion and electrolysis protection than mixtures with water.

4) Lower surface tension than 50/50.  Supposedly this helps conduct heat
away from hot areas.  It may also help off-set the effects of viscosity.
But I'm not sure if this really matters.

5) Non-toxic.  I am always spilling my coolant somewhere (not to mention
getting it in my mouth and all over myself and my airplane).  So I feel tha=
t
PG, either Sierra or NPG, is the responsible thing to do.

*Here are the draw-backs*:

1) Lower specific heat.  20% lower than 50/50, offset by 2% for its
increased density gives 17-18% less heat carrying capacity.  This is the
biggest draw back for our application.  To offset this factor, you have to
have an 18% increase in the temperature change.   While possible to do this
with increased peak temperatures it is better to just increase the capacity
of the radiator, as we want our coolant temps around 180.  So this is not a=
n
insurmountable problem, just a simple math problem - we need about an 18%
larger radiator in order to keep the same peak temperature.  This adds
weight and could cause a space problem, so it may not be worth the benefits
of NPG.

So IMHO, of course NPG is not a solution for high cooling temps.  But
because of its other benefits it is the preferred coolant IF your cooling
system is of adequate capacity.  Using water or 50/50 are the alternatives
to use if you need to get by with a system that is a little smaller than
optimal.

2) Increased Viscosity.  Actually, it is only 3 times more viscous than
50/50 at operating temp.  Not a factor in my experience.  Especially since
50/50 is twice as viscous as water - but no one seems to be bothered by
that.  If fact, the same can be said about specific heat.  There is more of
a change in specific heat in going from pure water to 50/50 than there is i=
n
going from 50/50 to NPG.

3) Flammable.  I'm not sure what significance this carrys.  I have spilled
it on a hot turbo and it just bubbles away like water.

4) Field repairs become very difficult.  On 2 occasions (not counting the
mammoth trip) I have fixed small coolant leaks while on a cross country.  O=
n
another occasion I had to replace coolant that boiled over, and I fixed a
third leak discovered on a local flight.  In each case I was able to simply
add tap water (usually carried in pitchers from the local cafe).  But NPG
can't even be found at most auto parts stores.  Adding water would work, bu=
t
be sure you have that high pressure cap with you!

*My real life experience:*

I flew with NPG+ for about 20 hrs in the middle of summer.  My coolant temp=
s
seemed to run about 20 deg higher than with 50/50, and 50/50 is about
20 deg hotter than pure watter (with water wetter).  (Ken Welter reports no
significant increase in temps with NPG used in his rotary powered coot).

I saw coolant temps as high as 250 without any apparent detrimental effects
except for an increase in SAG (and/or possibly detonation).  The engine was
almost self protecting at this point, as when it got hot I couldn't run as
much power because I would get SAG.

Even when the OAT was -3 F it flowed like water (maybe slightly thickened).
And the coolant was that cold too - believe me, you have not felt cold unti=
l
you have run coolant at -3 deg over your hands!  Kind of dangerous actually=
.

*My Engine failure:*

It is evident that my coolant escaped passed my radiator cap. I have more o=
r
less decided that one of three things happened.  The most likely being that
when I switched to a 7 psi cap I forgot to take into account that I still
had quite a bit of water in the system that did not drain out.  That water
boiled in the zero-pressure-at-altitude environment and forced out the
coolant.  And/Or, the differential pressure in the cooling system was more
than 7 psi and the water pump forced out the coolant.  Neither was the faul=
t
of the NPG.  I feel confident that if I had only left my pressure caps alon=
e
I would have flown home without a problem.

The other possibility is that combustion gassed pressurized the cooling
system and forced out the coolant.

Whatever the cause, it only occurred with the much higher power levels used
in flight than during my ground run which was at about 3000 rpm.  I did run
at over 4000 rpm, but for less than a minute.

Still hope to get the engine apart before I leave (in 3 weeks)

--
Dave Leonard
Turbo Rotary RV-6 N4VY
http://members.aol.com/_ht_a/rotaryroster/index.html
http://members.aol.com/_ht_a/vp4skydoc/index.html

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<div>Ed, </div>
<div>&nbsp;</div>
<div>You and everyone else&nbsp;make some good points, but calling NPG unsu=
itable is going a little bit too far.&nbsp;&nbsp;It&nbsp;has benefits and d=
raw backs, but is&nbsp;entirely suitable.&nbsp; The benefits may or may not=
 out weigh the draw backs.&nbsp; Each builder has to make that decision, bu=
t you have not exactly&nbsp;been making a fair comparison.&nbsp; Sometimes =
you compare NPG to water, and sometimes to 50/50.&nbsp; Having flown a wide=
 variety of cooling mixtures I think&nbsp;I can clear up some issues.&nbsp;=
=20
</div>
<div>&nbsp;</div>
<div>There is no doubt that pure water with some soap or water wetter does =
by far&nbsp;the best job of carrying away the heat.&nbsp; That was my prefe=
rred mixture in the summer.&nbsp; But given that I want to go places where =
the temp will occasionally go&nbsp;below freezing - without changing out th=
e coolant every time - lets make all our comparisons of NPG+ (hereafter ref=
erred to as NPG)&nbsp;to a 50/50 PG or EG mixture (for environmental reason=
s I now use only PG).
</div>
<div>&nbsp;</div>
<div>First,&nbsp;I want to stress there that the use of NPG had NOTHING to =
do with my engine failure.&nbsp; If anything, it was my rushed conversion t=
o its use&nbsp;- more on that later.</div>
<div>&nbsp;</div>
<div><strong>So here are the benefits of using NPG</strong>:</div>
<div>&nbsp;</div>
<div>1) Can be run with zero or reduced&nbsp;pressure.&nbsp; This is a part=
icularly nice feature in an aircraft, especially turbo, where the ambient p=
ressure is constantly changing.&nbsp; At very high altitudes, the absolute =
pressure in the system may not be much higher than 1 atmosphere.&nbsp; If y=
ou are running near the boiling point (which you shouldn't be - but I often=
 did) going higher could be enough to push you over the top and cause a boi=
l over.&nbsp; Also, a leak in the system could cause boil over with 50/50 b=
ut will not affect NPG's performance.
</div>
<div>&nbsp;</div>
<div>2) Much higher boiling temp - provides a greater protection from boil =
over.&nbsp; A very nice feature as I have boiled over twice in flight.&nbsp=
; Once it gets started, there seems to be no quenching it until you land an=
d let everything cool down.&nbsp; Turning off the engine for a minute would=
 probably work as well but I never tried that.&nbsp; I think that once the =
true boiling starts the thermal conduction goes way down and the metal part=
s get very hot and stay that way because of the continued boiling.
</div>
<div>&nbsp;</div>
<div>3) Excellent corrosion protection and stability, especially for Magnes=
ium.&nbsp; This stuff could truly be unchanged for several years and provid=
e much better corrosion and electrolysis protection than mixtures with wate=
r.
</div>
<div>&nbsp;</div>
<div>4) Lower surface tension than 50/50.&nbsp; Supposedly this helps condu=
ct heat away from hot areas.&nbsp; It may also help off-set the effects of =
viscosity.&nbsp; But I'm not sure if this really matters.</div>
<div>&nbsp;</div>
<div>5) Non-toxic.&nbsp;&nbsp;I am always spilling my coolant somewhere (no=
t to mention getting it in my mouth and all over myself and my airplane).&n=
bsp; So I feel that PG, either Sierra or NPG, is the responsible thing to d=
o.</div>
<div>&nbsp;</div>
<div><strong>Here are the draw-backs</strong>:</div>
<div>&nbsp;</div>
<div>1) Lower specific heat.&nbsp; 20% lower than 50/50, offset by 2% for i=
ts increased density gives 17-18% less heat&nbsp;carrying capacity.&nbsp; T=
his is the biggest draw back for our application.&nbsp; To offset this fact=
or, you have to have an 18% increase in the temperature change.&nbsp;&nbsp;=
 While possible to do this with increased peak temperatures it is better to=
 just increase the capacity of the radiator, as we want our coolant temps a=
round 180.&nbsp; So this is not an insurmountable problem, just a simple ma=
th problem - we need about an 18% larger radiator in order to keep the same=
 peak temperature.&nbsp; This adds weight and could cause a space problem, =
so it may not be worth the benefits of NPG.&nbsp;&nbsp;
</div>
<div>&nbsp;</div>
<div>So IMHO,&nbsp;of&nbsp;course NPG is not a solution&nbsp;for high&nbsp;=
cooling temps.&nbsp; But because of its other benefits it is the&nbsp;prefe=
rred&nbsp;coolant IF your cooling system is of adequate capacity.&nbsp; Usi=
ng water or 50/50 are the alternatives to use if you need to get by with a =
system that is a little smaller than optimal.
</div>
<div>&nbsp;</div>
<div>2) Increased Viscosity.&nbsp; Actually, it is only 3 times more viscou=
s than 50/50 at operating temp.&nbsp; Not a factor in my experience.&nbsp; =
Especially since 50/50 is twice as viscous as water - but no one seems to b=
e bothered by that.&nbsp; If fact, the same can be said about specific heat=
.&nbsp; There is more of a change in specific heat in going from pure water=
 to 50/50 than there is in going from 50/50 to NPG.
</div>
<div>&nbsp;</div>
<div>3) Flammable.&nbsp; I'm not sure what significance this carrys.&nbsp; =
I have spilled it on a hot turbo and it just bubbles away like water.</div>
<div>&nbsp;</div>
<div>4) Field repairs become very difficult.&nbsp; On&nbsp;2 occasions (not=
 counting the mammoth trip)&nbsp;I have fixed small coolant leaks while on =
a cross country.&nbsp; On another occasion I had to replace coolant that bo=
iled over, and I fixed a third leak discovered on a local flight.&nbsp; In =
each case I was able to simply add tap water (usually carried in pitchers f=
rom the local cafe).&nbsp; But NPG can't even be found at most auto parts s=
tores.&nbsp; Adding water would work, but be sure you have that high pressu=
re cap with you!
</div>
<div>&nbsp;</div>
<div><strong>My real life experience:</strong></div>
<div>&nbsp;</div>
<div>I flew with NPG+ for about 20 hrs in the middle of summer.&nbsp; My co=
olant temps seemed to run about 20 deg higher than with 50/50,&nbsp;and 50/=
50&nbsp;is&nbsp;about 20&nbsp;deg&nbsp;hotter than pure watter (with water =
wetter).&nbsp; (Ken Welter reports no significant increase in temps with NP=
G used in his rotary powered coot).
</div>
<div>&nbsp;</div>
<div>I saw coolant temps as high as 250 without any apparent detrimental ef=
fects except for an increase in SAG (and/or possibly detonation).&nbsp; The=
 engine was almost self protecting at this point, as when it got hot I coul=
dn't run as much power because I would get SAG.
</div>
<div>&nbsp;</div>
<div>Even when the OAT was -3 F it flowed like water (maybe slightly thicke=
ned).&nbsp; And the coolant was that cold too - believe me, you have not fe=
lt cold until you have run coolant at -3 deg over your hands!&nbsp; Kind of=
 dangerous actually.
</div>
<div>&nbsp;</div>
<div><strong>My Engine failure:</strong></div>
<div>&nbsp;</div>
<div>It is evident that my coolant escaped passed my radiator cap. I have m=
ore or less decided that one of three things happened.&nbsp; The most likel=
y being that when I switched to a 7 psi cap I forgot to take into account t=
hat I still had quite a bit of water in the system that did not drain out.&=
nbsp; That water boiled in the zero-pressure-at-altitude environment and fo=
rced out the coolant.&nbsp; And/Or, the differential pressure in the coolin=
g system was more than 7 psi and the water pump forced out the coolant.&nbs=
p; Neither was the fault of the NPG.&nbsp; I feel confident that if I had o=
nly left my pressure caps alone I would have flown home without a problem.
</div>
<div>&nbsp;</div>
<div>The other possibility is that combustion gassed pressurized the coolin=
g system and forced out the coolant.&nbsp;</div>
<div>&nbsp;</div>
<div>Whatever the cause, it only occurred with the much higher power levels=
 used in flight than during my ground run which was at about 3000 rpm.&nbsp=
; I did run at over 4000 rpm, but for less than a minute.</div>
<div>&nbsp;</div>
<div>Still hope to get the engine apart before I leave (in 3 weeks)<br><br>=
-- <br>Dave Leonard<br>Turbo Rotary RV-6 N4VY<br><a href=3D"http://members.=
aol.com/_ht_a/rotaryroster/index.html">http://members.aol.com/_ht_a/rotaryr=
oster/index.html
</a><br><a href=3D"http://members.aol.com/_ht_a/vp4skydoc/index.html">http:=
//members.aol.com/_ht_a/vp4skydoc/index.html</a> </div>

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