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Sorry, thanks Bill. I recall now. Also you are
correct, got distracted and did not finish.
But back to your situation. First, to get a bit more
specific.
At 2200 rpm and a modest 14.7:1 Air Fuel Ratio and
14" Hg manifold pressure and with 2/3 of the waste heat going to the radiators
for rejection, you engine would be producing approx 26 HP.
Previously, I neglected to account for your reduced
throttle setting (near idle) and was using WOT parameters. But, now with
manifold pressure around 14" Hg the power out put would be close to 26 HP,
it could be a bit less. But, in any case, that would mean you need
to reject only around 750 BTU/Min through your radiator to keep your temps
within limits.
You indicate you have an
approx. 80F delta T across your radiator core with the coolant temp at
210F. A large delta T is one indication of slow air flow as each unit of
air is carrying more heat. You have a fan which apparently has the
spec to draw 970 CFI across the 11" dia of the Fan. Lets assume that was
the flow through the entire core. Then that would give you 970*.0765 = 74
lbm/min of air mass with the Fan alone.
Q = 75 * .25 * 80 = 1500 BTU/Min
just due to the flow resulting from your fan -- the prop blast
would likely help that figure.
So if I am not completely off in
left field, it would appear that with 760 CI core, you should easily be cooling
at 2200 rpm. However, unless your temp readings are way-off,
its pretty clear that you are not. Possible things that come to
mind.
1. Coolant flow being
impeded. Possible causes:
(a), Hole in bottom of thermostat
housing not plugged and no thermostat you DID plug the 1/2"
hole in bottle of the thermostat housing, did you not? (I presume the
Renesis has it as the older 13Bs all did) - if you do not plug this hole and are
NOT using a Mazda (must be Mazda RX-7) thermostat then you could be losing 20%
of your cooling effectiveness (particularly at lower rpm).
(b). Pump belt slipping- but I
think the Renesis uses a serpentine belt so that is not likely - besides,
if it were you would probably hear and smell it.
(c). Double pass radiator
causing a 33% drop in flow rate - could be, but still hard to believe it
would not cool at 2200 rpm with 720 CI even it this postulation were
true. But, if the hole in the bottom of the thermostat is not plugged AND
the pump is facing more back pressure due to the double pass, the
combination could result in a larger than 30% decrease in coolant
flow.
(d). Air trapped in block -
already discussed this one
2. Air flow being
impeded. Possible causes:
(a) Insufficient air
inlet/outlet
(b) Flow Separation in the ducts
3. Sensor readings in
error.
Do you have
any other indications of overheating, pinging of the block after shut down,
smoking block, etc.
If I were to make a WAG, I would
still say it is trapped air. The reason is you have enough core, you have
a Fan (which I don't and many do not) which should make ground cooling at 2200
rpm a breeze (no pun intended). So unless the coolant is not
flowing as we expect, that is the only other thing I can think of is trapped
air.
Regarding your question about
running without a cap. In fact, I do just that when I am trying to get air
out, however, my cap is on the suction side of the pump and is on a header
tank. So not as likely to get any thing pushed out. You cap is
apparently on the pressure side of the pump?
So the pump could push some coolant
out - particularly if there is any obstruction/restriction, in fact given
that you have a double pass radiator with its resistance, I think it likely that
even low rpm operation would result in coolant being pushed out the radiator cap
hole - unless it is on the suction side of the pump.
Do you have any photos of your
installation you could post??
Ed
----- Original Message -----
Sent: Thursday, October 04, 2007 10:03
AM
Subject: [FlyRotary] Re: Problem?
[FlyRotary] Re: Coolant Water Pressure
Yep,
Ed.
I have your original
prop…a Performance Prop 76 X 88. Tractor configuration…It is a Lancair
Legacy.
The air going through
the radiator after the fan is picking up 80*, which seems like a lot to
me….This is measured after the fan and may not be representative of the rest
of the core. But prop blast should be supplying the balance of the core with
at least some air….
I was running at
2100-2200 rpm during this test which I failed to mention. If you look at
your calculations you were doing before you were distracted by the prop
question, I think you were about to arrive at the conclusion that it should be
cooling…??
My coolant is a 50/50
antifreeze mix. I mention this because of the next
question.
Back in my car repair
days, you could tell if the thermostat was sticking by removing the radiator
cap and watching to see if the water started to flow as the engine heated
up. I don’t have a thermostat, so can I remove the radiator cap and
start the engine to determine flow, or will the high flow pump shoot
antifreeze all over my plane?
I am interested in
your completed calculations to see what you determine my cooling results
should be.
Without the folks on
this list, only really gifted people like you and Tracy could ever hope to
“get er done”.
Thanks,
Bill
B
From:
Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Ed Anderson
Sent: Wednesday, October 03, 2007 7:19
PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Problem?
[FlyRotary] Re: Coolant Water Pressure
Yes, it sounds like the air should
rise to the top of your slanted radiator. However, My experience has
been that unless I run the engine up to around 5000 rpm for about
15-30 seconds (does not have to be long) that I do not have much success
getting air out of the block. It seems to take that velocity of coolant
flow to drag the water out of the block.
You have over 700 cubic inches of
core, so that should be plenty for cooling a two rotor.
A multi pass radiator (two pass in
your case) can require more coolant pump flow as indicated by this extract
from a pretty respected name in racing/cooling
circles:
Double pass
Double pass
radiators require 16x more pressure to flow the same volume of coolant through
them, as compared to a single pass radiator. Triple pass radiators require 64x
more pressure to maintain the same volume. Automotive water pumps are a
centrifugal design, not positive displacement,
so with a double pass
radiator, the pressure is doubled and flow is reduced by approximately 33%.
Modern radiator designs, using wide/thin cross sections tubes, seldom benefit
from multiple pass configurations. The decrease in
flow caused by multiple passes offsets any benefits of a high-flow water
pump.
Again, these are just back of the
envelope calculations based on a great deal of assumption about your
parameters. My gut feel is that 700 cubic inches should have no problem
cooling your installation at those power settings even being a double pass
radiator. So I would look else where.
You indicate you have an
approx. 80F delta T across your radiator core with the coolant temp a
210F. You have a fan which apparently has the spec to draw 970 CFI
across the 11" dia of the Fan. Lets assume that was the flow through the
entire core. Then that would give you 970*.0765 = 74 lbm/min of air
mass.
Q = 75 * .25 * 80 = 1500 BTU/Min
just due to the flow resulting from your fan - it would seem that plus
whatever flow you are getting from your prop - Prop??.
Hey, this dumb question just
occurred to me - I assume you are running with a prop?? in a
tractor configuration. I lose track of who has
what.
----- Original Message -----
Sent:
Wednesday, October 03, 2007 5:12 PM
Subject:
[FlyRotary] Re: Problem? [FlyRotary] Re: Coolant Water
Pressure
I have an aluminum
double pass radiator with the finned core size of about 18.25 X 18.25 X
2.25. It is behind the engine and leaning rearward at the top at about
a 30-35* angle. The water from the engine enters on the left lower and
crosses the bottom half of the radiator to the right side then rises and
goes back across the top of the radiator and exits the top left side and
returns to the engine.
My radiator cap is
at the top right corner of the radiator at the point where the water starts
its second pass through the top half. My pressure port is just below
the radiator cap. The pressure sending unit is in a “T” with the hose
which goes to the ¼” port at the top of the rear iron connected to the other
side of the “T”. I thought that this hose could have some effect on
the pressure, but I am not certain why it
would.
Any air in the
system should either rise to the top of the radiator, or if it was trapped
in the block, it could come through the hose to the radiator. All air
should be found therefore? Under the radiator cap. I have never found
any air there.
I think I found out
a little something about the fuel system today. I only put a few
gallons in the right tank and have been checking for leaks and running the
engine on this fuel. I wanted to run it down to the “non-usable” level
and then do the same thing with the left tank. So I have been really
low on fuel. My pressure has been holding, but I thought that I could
hear bubbles from time to time going through the
lines.
Anyway, before, I
could get a good start by setting the mixture at about 4 PM oclock and it
would fire up in a couple of blades. Today, I tried hitting the primer
button a couple of times and it would start and immediately die. I
finally had to set the cold start on and leave it on just to get the engine
to run! Finally after it warmed up, it ran with the mixture set at 12
oclock, but it was not steady. As my fuel ran out, the pressure
dropped finally to about 28 lbs and the engine started its death
rattle. I shut it off at that time.
The temperature had
risen to 210* the ambient temp was 87-88* and the air after the radiator was
168* This is with my radiator fan running. (11” and 970 CFM)
probably about 10-12 minutes of running the
engine
.
My oil temp was
only 160* and the air temp after the oil cooler was 145* , I think that this
would gone higher if I ran longer, because the oil in the pan was up to
170-180* or so. The pan holds 5 qts, 8 qts in the
system.
Water pressure was
up to 22-23 lbs and oil pressure was 70 lbs.
All my temp probes
are within a degree or so of one another and with a mercury thermometer in
the hangar when reading ambient temp and the engine is cold. I think
they are all correct.
I have the air/fuel
ratio setup that comes with the EM-2, but it doesn’t work till the O2 sensor
gets to about 800* or so, no help on trying to figure out starting
ratio.
The timing brings
up a good point. I got the Renesis out of a wrecked car with 1800
miles on it, so the timing is set to the factory setting for the
Renesis. I have never checked it. Does anyone know what the
factory setting would be for the Renesis??
Staging is a good
point, but I think that you are correct about having enough fuel to run a
low speeds and not enough to run faster. I was running out of fuel and
probably didn’t have enough to rip it.
You really have
good insights when you are helping folks.. You are pretty right on with your
advice.
Thanks,
Bill B (Must
mow yard…Must mow yard..)
From:
Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Ed Anderson
Sent: Wednesday, October 03, 2007 12:53
PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Problem?
[FlyRotary] Re: Coolant Water Pressure
Yes, too hot for that rpm, I
agree.
Assuming you followed the
good suggestions offered by Al, Lynn and others regarding getting all the
air out of the block - really important! I almost cooked engines two
times because of excess air in the coolant system. Here is something
that may quickly tell you something about the air you may have in the
system.
I can't recall what type
of radiator set up you have, but with the Two GM cores I use which are
mounted vertically, you can touch the side tank of the radiator and
determine if there is air in the system. In my case, if I do
a complete drain and refill of the system, on the first run up the core's
tanks will be hot approx 2/3 of the way up and then they are much
cooler - indicating that the remaining 1/3 of my core is filled with
air. It generally takes me 3 runups reaching 5000 rpm before I
can touch the core tanks and find them hot all the way from top
to bottom. So depending on your radiator set up that might be
something you can quickly check.
If the mixture is too lean, you
can get a backfire out the intake, too rich and its generally the exhaust -
where unburned fuel cooks off. So that and black smoke would indicate
to me too rich a mixture. I presume you do not have an Air/Fuel
ratio indicator - strongly recommend you get one, that tells you right away
whether you are running rich or lean. Even a cheap one can be a
tremendous help in finding out whether too rich or too
lean.
One thing you may want to check
is your ignition timing. If using Tracy's EC2 you need to set the static
timing around 35 Deg BTDC. The EC2 backs off 10 deg from that (25Deb
BTDC) as its default starting point for ignition timing. So if you set
the static timing to say 25 Deg then the EC2 would be having the engine
operate at a 25 - 10 deg = 15 Deg BTDC which is pretty retarded timing for
the rotary. OR if you set it too far advanced then the timing
might be too advanced.
So just recheck it when you get
the chance.
Another possibility is your
injection system might not be staging properly. IF that were the case,
the engine might work fine below the staging point but not above it.
Could possibly be a sticking secondary injector (if too rich or
lean). But, that is a bit down the likely list. Something
impeding the fuel flow might provide sufficient fuel and low rpm but not
sufficient to run at high rpm.
----- Original Message -----
Sent:
Wednesday, October 03, 2007 11:23 AM
Subject:
[FlyRotary] Re: Problem? [FlyRotary] Re: Coolant Water
Pressure
Ed, this is at
about 2000 rpm. Like a fast idle. I am getting all kinds of
fuel cut like stoppages if I try to run the engine faster. I haven’t
seen more than about 3700 rpm, but I just started it and have not tried to
tune anything. I figure I will have to run longer to get it tuned
and the cooling is holding that back.
Speaking of that,
you guys were talking a while back about the effects you see when the
engine is too lean, or too rich. Talking about backfires, etc and
what each effect represents. I have forgotten what means what…senior
days, not moments!
Do any of you
remember how that went? I am having some problems getting started
and am not certain if I am too rich or too lean. I am getting
backfires out the exhaust at times and smoke from the exhaust at that
time. (black)
I ran the
batteries down yesterday trying to get started due to this. When I
originally started the engine, I flooded it. I am trying to prevent
this now and am concerned that I may not be using enough
mixture.
Bill
B
From:
Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Ed Anderson
Sent: Wednesday, October 03, 2007
10:05 AM
To:
Rotary motors in
aircraft
Subject: [FlyRotary] Problem?
[FlyRotary] Re: Coolant Water Pressure
You indicate you get
overheating after 10-15 minutes run time. I may have missed it, but
is this at idle, max throttle or what. Also what is your OAT.
If at idle or low power then, yes what you are seeing is not what it
should be. On the other hand, if at WOT or high power settings, then
10-15 minutes run time would be indication of a great cooling
capacity. I can not run my engine more than a minute or two at WOT
on a 80F day without temps getting into the 200F range. But, that is
at 5800-6000 rpm. At idle, the temps stabilize and I can idle all
day with safe temps.
My coolant system runs with no
air cushion and yes, I get a hydraulic "lock" pressure reading of as high
as 25 psi immediately upon engine start up. After a 30 - 60 seconds
of running the pressure drops down to zero and then after a few
minutes running builds back up as the coolant warms up to operating
temperatures.
Plenty of suggestion have been
made about what to check - all good.
----- Original Message -----
Sent:
Wednesday, October 03, 2007 9:30 AM
Subject:
[FlyRotary] Re: Coolant Water
Pressure
Bill, the definitive test is
the one I described below. Really encourage you to do it as described.
Resist assumptions. Convert your ideas to
measurements.
----- Original Message
-----
Sent:
Wednesday, October 03, 2007 6:08 AM
Subject:
[FlyRotary] Re: Coolant Water
Pressure
I think that
I would see air under the radiator cap if I had a compression gas
leak? I never see any air.
To check a
piston engine for head gasket leaks, you would put the cylinder at TDC
and pressurize the cylinder to about 150 lbs with compressed air and
check the radiator for air bubbles…How do you check a
rotary?
I will check
the pressure sender against a mechanical gage.
There is
obviously a heating problem, but I think the pressure is higher than
it should be until just ready to boil. I shut the engine off at
210*, and at 22+ lbs, the boiling point should be well above
250*??
Thanks for
the suggestions of where to look, guys…
Bill
B
From:
Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On Behalf Of Al p
Wick
Sent: Tuesday,
October 02, 2007 7:49 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Coolant
Water Pressure
Your coolant reservoir should be above engine.
1) If it is, remove two cups of air from the
reservoir. Then repeat your test.
2) If you now see pressure rise above 22
psi within 5 minutes of cold start, you clearly have compression gases
leaking into cooling system or bad
gage.
3) Air in the block is 10 times more
significant than any other cooling factor. Make darn sure you don't
have any. It causes local boiling, high temps, strange
behavior.
Operating with two cups of air under cap is an
important safety and diagnosis advantage. Everyone should do it. With
that two cups, you only see 22 psi if you have a genuine problem. You
only see 0 psi if you have genuine problem. The pressure is then a
very fast and reliable indicator of system integrity. So two cups of
air has no negative effect on system efficiency, just a substantial
improvement in safety. Only time it could be a negative would be if
your reservoir was way too small, way too low, or flowed way too much
coolant.
Since you describe high temps AND pressure, I
suspect you have temperature
problem.
I deliberately overheated my engine many times
so that I was intimate with pressure and temperature patterns.
Then tested various concepts. Don't recommend you do the
same.
I just recently got my
Renesis started again after finishing my cowl. I seem to be
getting very high coolant pressures. I can only run the engine
about 10-15 minutes before hitting the redline at 210*. My
water pressure is at 27 Lbs at that time. I only have a 22 Lb
radiator cap, so I assume that I am blowing into the recovery tank,
but I have not confirmed that. My oil temp has never exceeded
about 165*. It might have gone higher if I could have run
longer???
This whole water
pressure thing has me a little baffled. Since this is a closed
system and the only way pressure can build is due to the expansion
of the coolant after heating???, I am confused by some comments that
have been made from time to time. I remember something that
Tracy said about his pressure would
build for a time, then go to zero. It seems to me that the
pressure should correlate to the temp pretty closely since it is a
closed system??
Can someone enlighten me
a little on the science of this pressure? It seems to me that
there could be some pressure build up on the positive side of the
pump, but it would go negative on the suction side, so the net
effect of the pump should be close to
zero??
Also, my Renesis had
only 1800 miles on it when I bought it, so I did not have to tear it
down. As a result, I am somewhat in the dark as to how the
water flows through the system. Could someone help me with
that? I had to remove the thermostat tower for height
clearance , so I made an adapter plate that takes water from the top
outlet of the pump and sends it to the radiator (double pass), then
from the radiator, it returns to the lower inlet of the
pump.
Thanks,
Bill
B
-al wick
Cozy IV powered by Turbo
Subaru 3.0R with variable valve lift and cam timing.
Artificial
intelligence in cockpit, N9032U 240+ hours from Portland, Oregon
Glass panel design, Subaru
install, Prop construct, Risk assessment
info:
http://www.maddyhome.com/canardpages/pages/alwick/index.html
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