In a message dated 9/25/2007 2:58:31 AM Eastern Daylight Time,
europa-list@matronics.com writes:
thanks a lot for that. There are three or four Jabiropas here. One I
know of is very happy but the others less so. My main question is do you
have any baffles to force the cooling air throught the fins, or do you
rely on the pressure in the plenums? My friends are using deflectors
rather than baffles which I feel is a bit imprecise. I am more familiar
with the sort of baffles EZ guys use on Lyconental engines where careful
baffling works well.
The Jabiru agents here in UK do not seem to have much in the way of good
ideas.
Hello Graham,
My 3300 is one of the newer ones with the larger head cooling fins, but just
before they switched to hydraulic lifters.(S/N 33A756 or #756) The engine
came with fiberglass ducts of unknown origin, IOW, not Jabiru factory ducts,
that fit over the top of the cylinders. I'm pretty sure Andy had the same guy
who made the cowls make the ducts, but I've not verified that to be fact. Two,
round 4" aluminum intake rings are captured by the cowl (similar to a
Lancair) and serve to direct air into the ducts. I used 3mm rubber sheet to
make
a
transition from the ring to the duct. This rubber helps damp vibration
between the cowl and the engine and allows the two to move independently of
each
other. The two 4" rings together give me 25 square inches of intake and that
should be more than enough for adequate cooling and it is has shown to be
adequate on all but the hottest days. I only really see one cylinder that gets
a
bit hot in climb above 95F ambient temperature and it's still 30F below
redline. I do have internal baffling to direct air over the center cylinders,
but
it is very subtle, maybe 3 mm tall on the inside top of the duct, parallel to
the cylinder. Small changes in the height of these baffles make huge
differences in CHT's. The height of the baffle is determined by trial and
error.
I'd
start at about 5-7mm and whittle it down from there until a balance is
achieved. You could make an internal baffle with successive layers of duct tape
to
determine the height, then replace it with either flox or a flat fiberglass
piece cut to the shape of the inside of the baffle, then flox that into
place. Initially, I was told to start with 1 cm high baffles, but it only took
one
short flight to realize that was way too much for my installation.
I've been doing some manometer testing on the pressure differential between
the inside of the cowl and the inside of the duct and it has left me thinking
that my left duct just isn't the right shape. Using Jabiru's manometer
testing method, my results have been completely contradictory to what Jabiru
says
it takes for adequate cooling. So, I'm testing a new left side Sonex styled
sheet metal duct today. I'll let everybody know if it works. If it does work,
I'm going to do some manometer testing on it and get some hard numbers to
play with in terms of what it really takes to make the left side run cool. Film
at 11:00PM......
Regards,
John Lawton
Whitwell, TN (TN89)
N245E - Flying
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