One thing to keep in mind about the pressure rating of the
radiator cap you are using. All are rated relative to a standard sea
level ambinent pressure. This means that he air pressure itself is
contributing 14.7 psi at sea level.
So at sea level when your differential pressure coolant
gauge is reading 10 psi - the absolute pressure in your coolant system is then
14.7 + 10 = 24.7 psi. Now if you are flying at 8000 MSL your
ambient pressure is approx 1/2 at sea level. So your 14.7 psi CAP now has
the lesser capacity of 7.3 + 10 = 17.3 psi absolute pressure capacity -
somewhat less than the 24.7 psi absolute it had at sea level.
When you increase in altitude this component naturally
decreases. So while a 14.7 psi CAP may work fine at sea level, more than
one person found that at altitude that rating was insufficient
and some coolant was lost.
I personally would not fly with less than a 21 psi cap and
currently fly with a 24 psi radiator cap.
There is another factor that occurred to me. Once
a hot coolant system blows the relief valve on the cap, that lowers the
pressure inside the system, superheated (>212F) coolant can quickly flash to
steam and further cause lost of coolant. So a Higher PSI cap can lessen
the chance of that happening.
Sent: Thursday,
March 24, 2011 5:30 PM
Subject:
[FlyRotary] Re: On the subject of installations...Coolant Pressure
Lynn,
You have hit my quandary squarely on the
head. Assuming that the pressure was zero at room temp and rose to say
6-7 pounds at 200 degrees, and assume that the flow restriction in the system
caused a pressure rise of about 2 pounds at 2000 rpm and a pressure rise of,
say, 6-7 pounds at 6000 rpm. Under that scenario, you would have a
pressure that ran at between 7-9 pounds at 2000 and rose to 12-14 pounds at
6000. Those pressures would be easily contained with the stock cap of 14
pounds. And the pressure would be constantly changing with rpm and
possibly temp of the system as you were under power or not.
I have a 21 pound cap. My system
climbs smartly to the top and stays there. No fluctuation with rpm, no
real fluctuation at temp because it has already hit the 21 pounds before the
engine is actually hot. (around 190)
Something is wrong and I don’t
understand what it is.
Bobby
I am going to insert answers to your
questions in your msg below.
Bill B
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Bobby J. Hughes
Sent: Thursday, March 24, 2011
1:57 PM
To: Rotary
motors in aircraft
Subject: [FlyRotary] Re: On the
subject of installations...Coolant Pressure
Bill,
This is all I can think of at the moment.
Are you running a thermostat or did you
plug the hole between the inlets and outlets of the water pump?
No thermostat. The Renesis has a thermostat
tower which is too tall to fit under my cowl, so I removed it and fabricated a
flat plate with two 1.25 aluminum tubes for the inlet and outlet of the water
pump. That hole you are referencing exists in the tower, but not in my
plate.
If plugged did you drill a small hole in
the plug to allow air a place to escape? I used a #30 drill.
Any air in my system would have to be
carried to the highest point, (radiator cap) then be forced by pressure to the
bottom of the swirl tank where it would be trapped. This seems to be
working because I have found that after I open the system for some reason, the
level in the swirl tank will go down and there is never any air at the top of
the radiator.
After an engine run is the radiator the
same temperature at the inlet / outlet / bottom and top? If I have trapped air
only part of my radiator gets hot to the touch. Dual pass barrier leaking?
Seems to be. I have mistakenly laid
my arm on the top of the radiator after a run…usually I manage to get off
pretty fast! :>) I can not see into the radiator tank on the
barrier side. It is possible it could be leaking. I suppose if
there was a rag in the thing it could be trapped here also. I have no way
to see in there even if the hose was removed. I would need some kind of
flexible camera or something like that.
Use an extra CHT channel and clamp it to
the inlet of your radiator to measure Delta T.
Good idea. I will have to rig one
up. I don’t have an extra now.
My water pressure does not vary that much
in operation. But it does hold a little pressure for a few days after shutdown.
1-2 psi.
What is your pressure during
operation? What is the pressure cap rating? Does it vary at all
with temp and/or rpm? Mine is maxed out..always!
What size hoses? I’m running 1in.
The RX-8 uses 1.25 hoses. I stuck
with that size as well.
Where are you measuring water pressure?
The hose that comes off the top of the rear
iron goes to the top of the radiator, just below the cap. A tee in this line
has the water pressure sender in it. The radiator cap is just a cap, not
a pressure cap. The outlet in the radiator neck goes to the bottom of the
swirl tank.
Is your pressure cap on the bleed / swirl
tank?
Yes.
Any pictures of the plumbing?
Not of the current setup.
Bobby
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Bill Bradburry
Sent: Thursday, March 24, 2011
10:23 AM
To: Rotary
motors in aircraft
Subject: [FlyRotary] On the
subject of installations...Coolant Pressure
I need some help with figuring out my
cooling problems.
Just so it doesn’t get lost in the
following BS, I need to state that I think the problem is related to the
coolant pressure. It seems to me to be way too high. I am beginning
to think that the coolant is somehow partially blocked.
Now the rest of the story….
After I did the flight described in the
attached email, I installed an opening in the bottom of the cowl that would
work something like a cowl flap that is permanently open. The new opening
is 9 inches by 5 inches or 54 sq in.. There is a flare in front of the
opening that is at an angle of 45 degrees and extends down into the airstream
about 4 inches. (it is 6 inches long.) This opening is in addition
to two 6 X 6 openings, one of which has a 3 inch diameter exhaust pipe in it.
This helped a little, but nothing like I
expected it would. The pressure inside the radiator inlet dropped from 10
inches of water to 8 inches of water. (by the way, Steve was right about
it being inches of water and not inches of Hg.)
The pressure after the radiator and inside
the cowl dropped to 8 inches as well. The temperature of the water
dropped to 208 and the oil a couple of degrees. Neither of these had the
result that I expected.
My water pressure cap is rated at 21
lbs. I have not calibrated the sender that came with my EM-2 and it shows
3 lbs when the engine is cold. I assume that this is zero. When in
flight the pressure climbs to 24 lbs and stays there. I assume that at
this point, the cap is at 21 lbs and is bleeding off air. There is about
a pint to a quart of air above the coolant in the bleed tank.
This morning I ran the engine on the
ground for about 10-15 minutes at an rpm of 3000 to 3200. The OAT was 75
degrees.
I read the temps and pressures every
minute or two during the run. I hope this doesn’t get jumbled
during transmission.
Oil temp –
80
103
130
139
144
155 162
165
Air temp after cooler -
97
109
122
129
133 134
Water temp
-
86 126
161
173
178
190
198 199
Air temp after rad -
109
133
157
169
179 183
Water pressure
-
2
11
17 20
21
24
I noticed that the water pressure could be
brought from 2 lbs to 9 lbs by changing the rpm while the engine was still
relatively cool
What should I expect for water pressure at
lower temps and how could I go about making a determination that the water
passages are clear?
I am beginning to think that a rag has
been left either in the engine or the radiator. I have never torn the
engine down and I sent the radiator out to have a leak repair a couple of years
ago. It is a double pass radiator. I can look into the end that has
both sides connected thru the radiator cap neck, but not into the inlet and
outlet end.
Suggestions???
Thanks,
Bill B
From: Bill Bradburry
[mailto:bbradburry@bellsouth.net]
Sent: Sunday, March 20, 2011 5:29
PM
To: 'Rotary motors in aircraft'
Subject: On the subject of
installations...
My water temp has been running between 199
and 217, depending on the OAT. The oil is pretty steady at around
175. Today I finally got to fly with pressure probes inside the
cowling. I was all set to try and enlarge the inlet to the radiator to
solve the problem. It turns out that “in” is not the problem,
it is “out” that is the problem!
I have 10 inches of Hg pressure in the
radiator inlet and 10 inches of Hg on the outlet side as well as the same
pressure everywhere I measured inside the cowl. I need to open up the
cowl some so more air can get out. I had considered a cowl flap but that
would not work in this instance because the problem is at cruise. I need
a permanent opening. I am considering louvers and I am looking for a
source. I know some of you are using them. Where did you get them
and how are they installed so that they look ok?
I am also considering some kind of flare
around the exit area to create a low pressure area to help suck air out. Do
any of you have those and do they seem to work?
While I look into this, I also need to do
something about my muffler…Thank you, Bobby!
I wonder about that spiral muffler some of
you are trying??
Bill B 9 hours and counting…
By the way, I was considering putting a 1
or 2 inch wide piece of cardboard across the bottom of the oil cooler to
partially block it in the hopes that more air would then flow through the
radiator. Sort of like truckers do with the radiator in cold
weather. What opinions do you have about that idea? I realize it
would make more sense if the oil was really cool, but I think the oil might not
get much hotter if an inch or so was blocked. What do you think???