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mikenjulie.parkin(at)btin
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 Posted: Fri Dec 18, 2009 12:04 am Post subject: Europa Cooling - Rotax 914. |
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For the Cowling experts among us......
I have been flight testing my cowl flap modification over the last week or so. The modification introduces a rotating door in the cooling duct aft of the water and oil radiators. The door can close the duct completely, operated by a MAC servo with a manual backup for emergency opening. On the ground after start with the door closed, the engine warms up quickly, solving the protracted wait for the minimum oil temperature for take-off which was previously the norm. However, when airborne, the effect of the door is surprisingly minimal. In the cruise at 130kts, with the flap open the temperatures are as usual sub 100 degs – 60 to 70 degs maybe. With the duct closed, the temperatures (water, oil, CHT) are only raised by about 10 degs. One advantage is it makes my cabin heater a little more effective.
Now, on the ground, with the door closed, the engine would overheat but, in the air (winter temperatures remember) in the cruise over-heating is unlikely.
Plainly, with ram air entering the upper cylinder cooling inlets, this is where the major cooling takes place.
I must confess, the efficiency of the upper cooling surprised me!!!
Comments?
Regards,
Mike
[quote][b]
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frans(at)paardnatuurlijk.
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| Posted: Fri Dec 18, 2009 12:34 am Post subject: Europa Cooling - Rotax 914. |
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Mike Parkin wrote:
| Quote: | However, when airborne, the effect of the
door is surprisingly minimal. In the cruise at 130kts, with the flap open
the temperatures are as usual sub 100 degs - 60 to 70 degs maybe. With the
duct closed, the temperatures (water, oil, CHT) are only raised by about 10
degs. One advantage is it makes my cabin heater a little more effective.
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Keep in mind that the maximum opening for optimal airflow is about 1/3rd
of the radiator surface. Air won't be able to rush with 100kts through
the radiators, so you need to compress the air after the radiators to
let it exit with the same speed as the surrounding air. Any opening more
than 1/3rd of the radiator surface is not going to have much effect at all.
When the flap is "closed", how much exit area do you still have? Mind
you that even small openings can have quite a large effect.
Although you have ram air cooling for the cylinders, I don't believe you
can cool the oil substantially without using the radiator. If your oil
temp doesn't increase when you have the flap closed, I suspect that
there is still plenty of air going through the radiator.
Frans
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ami(at)mcfadyean.freeserv
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| Posted: Fri Dec 18, 2009 12:54 am Post subject: Europa Cooling - Rotax 914. |
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<<If your oil
temp doesn't increase when you have the flap closed, I suspect that
there is still plenty of air going through the radiator.
| Quote: | >
Except on a winter's day, when (on many more open installations) an oil
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cooler is not needed at all.
Duncan Mcf.
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mikenjulie.parkin(at)btin
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| Posted: Fri Dec 18, 2009 1:09 am Post subject: Europa Cooling - Rotax 914. |
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'Although you have ram air cooling for the cylinders, I don't
believe you
'can cool the oil substantially without using the radiator. If your
oil
'temp doesn't increase when you have the flap closed, I suspect that
'there is still plenty of air going through the radiator.
'Frans
Frans,
As I said in my original post "The door can close the duct completely"-
plainly there will be some leakage around the door, but not much. Although
the position indicator shows the door closed, I would need a camera to
observe the door in flight to be absolutely sure. Your point about oil
temperature is not my experience over the years I have been flying the
aircraft. Almost always, the oil temperature lags the CHT/water
temperature. I have never seen the oil temperature above the water/CHT.
With the original configuration, that is with both radiators mounted
adjacent, the temperatures of cht/water/oil were usually identical. Some
years ago, during a particularly hot summer in Switzerland, after take-off
during a slow climb following Dave Buzz, I had a lot of trouble keeping the
temperatures within limits. The only way to rectify the situation, was to
leave the formation and fly back down the valley at a higher airspeed.
After that trip, I lowered the oil cooler to improve the overall cooling.
However, with my aircraft, flying at the higher IAS is the answer.
Regards,
Mike
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frans(at)paardnatuurlijk.
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| Posted: Fri Dec 18, 2009 1:46 am Post subject: Europa Cooling - Rotax 914. |
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Mike Parkin wrote:
| Quote: |
'Although you have ram air cooling for the cylinders, I don't
believe you
'can cool the oil substantially without using the radiator. If your
oil
'temp doesn't increase when you have the flap closed, I suspect that
'there is still plenty of air going through the radiator.
'Frans
Frans,
As I said in my original post "The door can close the duct completely"-
plainly there will be some leakage around the door, but not much. Although
the position indicator shows the door closed, I would need a camera to
observe the door in flight to be absolutely sure. Your point about oil
temperature is not my experience over the years I have been flying the
aircraft.
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Ok, I take your word for granted! I have not been flying yet, so I can't
speak from experience.
I have intentionally made it impossible to close off the cowl flap
completely, as I believed that I need at least SOME air going through
the radiators. Maybe I was wrong with that.
Frans
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