In a message dated 10/1/2007 2:58:40 AM Eastern Daylight Time,
europa-list@matronics.com writes:
Concerning the Jabiru, there is little room between the prop and the
front cylinders to provide a correct diffuser, so the inlet must be of
larger size, and the efficiency will be lower.
But the engine can be adequately cooled all the same, at the price of a
little more drag, of course.
Hi Gilles and all,
I've had a chance to test my turbulators installed at the mouth of my left
cooling intake and they worked exceedingly well. I've seen, on average, a 25F
drop in CHT's on the left side now that I have turbulated the airflow
entering the left side intake. One cylinder dropped 45F and went from being the
second hottest of the six to the coolest. Interestingly, the engine is now
running in the 240F-260F range on all CHT's, but the delta pressure did not
change!
This has left me with the impression that all this talk about 6" of water
column being needed for adequate cooling is a bunch of bullshit put forth by
the engine manufacturers to make you go away and be quiet.
I still have 3" WC on the right at cruise and the hottest CHT is about 250F.
The coolest CHT on the right is 219F in cruise. I still have 5" of WC at
cruise on the left side and the highest CHT is now about 260F, down from 295F
on
the hottest cylinder in cruise. The coolest on the left is now 235F, down
---From 275F prior to the turbulators. All of my testing results indicate
that
pressure is the absence of flow, not a sign of flow. Internal cooling duct
pressure, measured against static pressure inside the cowl, seems to be have an
inverse relationship to flow, if indeed it has any relationship at all. My
test results show pressure is meaningless and FLOW is what we're after.
I think ultimately what I'm going to do here is dimple the area around my
intake ducts like a golf ball. The zigzag tape is ugly and I can't think of a
way to make it pretty, so I think dimples are the answer. Should make for
quite a conversation piece, don't you think?
Clearly, Andy Silvester used the Lancair cowls as a model for his Europa
cowl set. I've studied close up pictures of the Lancair cowl to try and find
out
what the difference between the two really is. The only thing I notice is
the Lancair inlets protrude about 1" farther in front of the cowl than mine
do., I think this has something to do with the pressure wave I've observed in
front of my left intake with my crude string tests. So Gilles, you are likley
correct in your analysis.
FWIW, every Sonex cooling suggestion I've tried has lead to hotter, not
cooler temps. So, Jabiropaphiles, my suggestion is don't bother with anything
Sonex has to say.
The moral of this story is: for better FLOW, excite the area just outside
the hole. Almost pornographic, isn't it? (notice how I didn't say for better
PRESSURE?)
Now, I'm back to analysis of boundary flow on the wings.......
Regards,
John Lawton
Whitwell, TN (TN89)
N245E - Flying
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