What is the area at the opening
of the scoop? What is the area at the face of the cooler? Does the
area of the duct increase at all points after the
entrance?
The opening of
the scoop is 14.5" by 4.25" or 61.625 SQ. IN. The duct does open up
to the cores, although it is only about 12" from the opening to the
junction of the 2 cores, which are in a shallow
"V".
Some things to consider about
the air flow: The typical optimum thickness from an airside pressure drop and
drag standpoint, for a typical radiator core is about 2.3 to 3”; and that is
with a scoop area increase of about 4:1 entrance to core. You can go
thicker on the core with about that ratio, but you are starting to press your
luck especially if the air has to make a significant turn. The two cores
in series makes for an equivalent thickness greater than the actual combined
thickness because exit and entrance losses. So for cores in series, you
have to slow the air significantly to get it all to go through both cores
rather than spill at the scoop entrance, plus you need sufficient flow so can
take the heat load from both with a temp increase of maybe about 50F or
less.
I
may have misled you about the series statement. What I meant was the the
coolant flow is in series rather than in parallel. The cores are not
stacked one behind the other, but both face the scoop. I have diffusers
built into the plenum, and the air flow seems quite good through the
radiators. The oil cooler, on the other hand, needs some diffusers to
push the air more toward the outside. Another idea is to remove the oil
cooler altogether from the main scoop, and add an additional scoop for the oil
cooler. This would leave more air for the radiators, but be higher
drag. At this point, I guess I could settle for cool and
slower.
It does seem very likely that
you are going to have some trapped air if you don’t have a bleed at the
highest point. You may need to add a threaded bung and a petcock valve;
or as I refer, a small o-ring plug that is drilled with a small port into the
bottom and then out the side at the top of threads and just below the o-ring.
Just loosen the plug about a turn while you are filling until all the
air is out.
I
agree. I've ordered an AN-16 elbow to redo the turn out of the
thermostat housing. I'm going to drill a hole and tap it, in the side of
the fitting for a plug.
Are you able to get a timing
light on the mark? Set up the timing according to Tracy’s
specs.
I
did set it with a timing light, but it was pretty close to the static
setting. I couldn't really adjust it with
the RPM's above 3000, so I subtracted the 4 degree from it, and set the timing
for 1500 RPM's at 21 degrees BTDC. I hope that this is
right.
Steve
Subject:
[FlyRotary] Re: Still high temperature
and I
agree that it appears to be insufficient cooling. Since others are
running the evaporator cores with no trouble. I assume that the issue is
air flow. John Slade seems to have no trouble with his temperatures, and
has the identical plane and scoop. Actually I've added a front end to my
scoop to get outside the boundary layer, but still have high
temperatures.
I have a
P-51 style scoop that I had put on earlier with the old cooling system.
I removed it when it didn't improve the cooling, but the old set up I think
was beyond help. Maybe I should try it with the new set
up.
I was
also wondering about any other factors causing excessive heat from the engine,
like timing. I haven't tried to retard the timing any, but I know that
in piston engines, if you get the timing too advanced, it can result in allot
of heat.
-----Original
Message-----
From: Rotary
motors in aircraft [mailto:flyrotary@lancaironline.net]On Behalf Of Al Gietzen
Sent: Sunday, September
19, 2004 3:28
PM
To: Rotary motors in
aircraft
Subject:
[FlyRotary] Re: Still high temperature
The high temps
are indicating insufficient cooling capacity ( I guess that’s obvious);
which means insufficient air flow or too little heat exchange area. If
others are getting adequate cooling at the same power with the same cores,
then it is air flow. As I recall, you are no longer running the
coolers in series, but there still may be a pressure recovery issue with
your scoop, or just too small an opening; more like the
first.
After a few runs
it seems that the air should be purged. Do you have a means of
checking (confirming your temps to be sure there isn’t some boiling going
on?
Al
Subject: [FlyRotary] Still high
temperature
I would appreciate input to a problem
that I have. I just overhauled the
engine, and reworked the cooling
system. I'm now using the A/C evaporator
cores for radiators. The problem
I'm having is, that when I take it up, I'm
seeing coolant and oil temperature of
about 210 degrees. That is climbing
to pattern, leveling off, and
throttling back to low power. The oil stays
pretty much where it is, and the
coolant come down just a couple of degrees.
When throttle back to land, the coolant
and oil both come down to about 180
at touchdown. I taxi back to the
hanger and shut down with oil and coolant
about 190-195, but after shut down, I
get all sorts of gurgling noises from
the header tank, which is fed by the
tap on the side of the thermostat
housing. The gurgling noises go
on for 5-6 minutes, which would seem like
the engine is overheated, but while
hot, it doesn't seem overly hot. The
other end of the header tank feeds
coolant to the turbo, so maybe the hot
water is coming from it ? Maybe my
header tank should be fed differently ?
Also at this time, after a short
flight, there is only a couple of cups of
additional coolant in the overflow
tank.
I assume that the higher than desired
coolant temperature, and the gurgling
noise are related. I pulled the
water pump off today to double check it,
and all seems OK. The pump only
has about 10 hours on it. When I run it on
the ground, and feel the radiators
after shutdown, they are uniformly hot.
I put a furnace blower pointed at the
scoop, and I'm getting very even
airflow through the radiators.
The oil cooler, on the other hand, has about
75% of the air going through the middle
of the cooler, so I'm going to have
to add some deflectors in the plenum to
push more air to the outside. That
seems to be a less significant issue at
the present.
Any thoughts ?
Steve Brooks
Cozy MKIV
Turbo rotary
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