To all.
I'm trying to catch up with the list and am a bit distraught.
Cooling of the Woodcomp/Airmaster/Whirlwind/Sensenich/ or a carved baseball
bat propellers, is an interesting argument. In my opinion backed up by
testing of now some 6 different propellers and ten blades, I have found the
following based on the assumptions below:
Assumptions:
The exterior cowl is standard. The round inlet holes are clean and at least
open to the 3 inches. The exit duct is unmodified.
The engine cold air duct installs are stock for both the 912S and 914.
No plenum over the cylinders.
The installation of the coolers is stock to include the 1.5 to 2 inch drop
of the oil cooler.
The duct and radiator and oil cooler sides are sealed to the extent no light
can be seen around the radiators, and only through the fins of the radiator.
(I use a lot of red RTV silicone.)
To the best of ones ability, on visual inspection, air can only go through
the cooling fins.
The sides are sealed very well with cowl seal to the lower cowl.
The gap between the oil cooler and glycol cooler is no more than 1/8 inch.
The forward end of the duct is sealed to prevent airflow blowing up into the
spinner/front of the engine area bleeding off duct pressure.
The cowl inlet has been smoothed to allow a smooth flow inlet.
The metal duct has not been significantly modified in shape or form.
The engine has a 1.2 bar radiator cap is installed, and glycol ratio is a
minimum of 50/50 with Dexcool or similar orange coolant. (Not Evans as the
BTU transfer rate is lower and requires a larger radiator and or higher
volume water pump in the hot Florida climate.)
The #3 exhaust pipe is wrapped with exhaust wrap fiber or a heat shield is
fabricated to reduce radiated heat on the temp probe giving erroneous
results.
The propeller has a twist ratio of about 16 degrees (i.e. root at 16
degrees and tip at zero) which is pretty much common for props suitable for
the Rotax 9 series.
Idle speed on a Rotax is at least 1800 RPM.
Note: Full Synthetic oil (Mobile 1 MX4T) runs a bit cooler than the
Aeroshell Sport +4. It also warms up slower. CHT's are a bit lower with
full synthetic in certain conditions. Could most likely be because the oil
is cooler and running here in The States on Ethanol laced fuel and lower
octane makes less heat. I have insufficient data to confirm.
With the above assumptions satisfied the Europa XS will be able to idle
(1800 RPM) on the ground on a standard day into a light breeze for a
minimum of 20 minutes before glycol temps hit 245F .
With the engine run up to 2500 RPM the time is extended to 25 minutes.
Note: At 245F, at idle, if a shut down is initiated, one rarely hears
boiling on the ground, however, after high power run ups where cylinders and
heads are hot, it is not common if a quick shutdown is made, some boiling
may be heard. This is normal as the boiling point is about 266 F. Read the
ROAN website for more detail.
Technique: With a constant speed propeller, increase the RPM to 2500 and
manually position the prop to a courser setting to drop the RPM back to
about 2000. This really increases the draw.
Note: The propeller pushing air down the inlet does not cool the engine, it
is the prop blast creating a draw around/behind the cowl exit. This is an
undeniable fact. It was proved in the 30's.
Climb out cylinder temperatures will hold at 245F to at least 10,000 feet at
90 knot climb. 245F is my personal max to prevent boiling.
Climb out at 75 knots will eventually creep to above 245 by about 5000 feet
and will continue to climb. I do not recommend climbing below 90 knots
indicated especially at OATs above standard.
Typical problems of the Europa XS:
The glycol cooler is designed for cruise conditions at high power settings.
Not ground operations.
The mono on the ground prevents the XS cowl exit to operate with efficiency.
It negates the draw from the rear of the cowl. See Cooling 101 for cowl
modifications.
The XS cowl overcools at cruise due to its fixed exit.
On the ground, the oil heats so slowly, the CHT is nearly at your max for
takeoff. A flap is a simple fix to block the oil cooler for a faster warm
up and the oil flow stays high.
Note: I'm not a fan of oil thermostats, but they have been used effectively
by some. I have not had good luck with the Aeroshell Sport+4 with
thermostat, but it was OK for the Mobile 1 MX4T.
The 914 turbo and oil tank exacerbates the hot corner formed near the #3
probe. Reflected heat in this corner is relieved by the scoop on the duct,
but that scoop also decreases the delta P on the radiators.
So a quick and dirty to cool better.
Follow Cooling 101 techniques and seal the duct.
Pitch the prop more on the ground to increase airflow.
Mono's can use a wider exit or a mechanically actuated lip on the exit (cowl
flap) to improve ground draw.
Use both the CHT supplied and the pain in the A__ , notoriously inaccurate,
liquid coolant temp probe, to monitor the cooling health of your engine. (I
do not practice this, I just keep head temp below 245.)
Feel free to use tape and formed blocks of foam to make a draggy ramp to
increase the draw out of the rear of the cowl for you mono owners to
experiment.
If you can't help spending money:
A larger radiator is nice, but then you need a thermostat for cruise, or:
Rebuild the cowl and spend many hours to install new ducting, a slightly
larger radiator (about 50% larger is about right), install a movable cowl
flap, on the mono widen the cowl exit to compensate for the blockage with
the gear down...
Thinner radiators are slightly better, but don't confuse thinner with
passage size. Many thinner radiators have smaller cooling tubes requiring
much more surface area. A two inch deep radiator with 1/8 inch by 3 inch
wide tubes and 1/4 inch finned area between with a surface area of about 60
square inches works very well in vehicles as our South African partner found
out. I believe the BTU transfer rates at MoCal. Our motorcycle engine
could use a radiator that is 3+" deep, 5" high and 10" inches wide rather
than our 3" x 3.5" x 10" 8 bar block. Rotax's new radiator is 1.3"x 13" x
5.5" 13 tube which has the same cooling area as our poor old block.
Lockwood Rotax Service prefers the larger version on their aircraft which is
about 2 x 6 x 16 inch 10 tube which cools about any plane, but it runs a
bit cool if ducted in a tight cowl. So the current Rotax Guru's are looking
for a radiator with about 50% more coolant tube volume. So I'm thinking we
need a radiator closer to 6 inches tall with 12 bars and a cowl flap or
thermostat to make an all season no compromises aircraft.
Remember, an airplane is 20,000+ compromises flying in close formation. The
choices on these compromises is yours.
Just my thoughts.
Regards,
Bud Yerly
Custom Flight Creations.
Absolutely Stock 914 install with various propellers tested.
-----Original Message-----
From: Roland
Sent: Wednesday, August 03, 2016 9:32 AM
Subject: Europa-List: Fwd: Re: Cooling issues XS 914 on the ground
Heather and Jim,
good point to seal all gaps thoroughly - I'll first focus on this. I've
already installed an aluminum sheet to press more air through the radiator.
Only a very low amount of air goes through a gap below the radiator to the
7-row (!) oil cooler, which won't cause a lot of additional resistance. I've
also noticed, that I have a gap between the upper edge of the cooling duct
and the lower cowling just below the spinner, which I also have to close....
I have some hope, that the Whirlwinds would also contribute to additional
cooling. I think I'll let the Airmaster-dealer make a Quote for me.
I'll see if I can ad some photos later.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=459153#459153
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