Just a note on Jabiru 3300 (solid lifter) cooling issues on the ground
and in the air that we've experienced here at Custom Flight Creations.
We just finished about 100 hours of research and development trying to
get Dr. John Kershner's Jabiru with the nice looking Andy Silvester Cowl
to cool. Propeller is a 64 inch Sensenich Wood Prop.
We drew heavily upon Sonnex, Jabiru techs and our own John Lawton's
success.
We have built a similar looking but two part lunch box over cylinder
duct for ease of accessibility and maintenance. The duct is part metal
and fiberglass. The between cylinder barrel and head gaps were
extensively worked to optimize airflow, cooling pressures and heat
extraction.
Extensive work was done to try to direct and augment airflow through the
square heads. (You know, air doesn't like to go around square corners
or over and around those wires.)
Our results are very promising. Taxi for 25 minutes before the hottest
cylinder gets to 275F at 80 F outside no wind. I can live with that.
Climb is possible to 3000 AGL at 75 KIAS and Max Continuous before we
hit 304F (80F outside temp) then we must retard the throttle and
accelerate to 90 IAS to keep the cylinders cool. At max continuous, it
will stay right at max temp, however when we reapply full power, we are
greeted again by temps going above redline, which is not acceptable.
The cowl exit has been extensively modified as the supplied duct on the
bottom has proven to be a ram air intake so we added a cowl flap to get
a better draw. The cowl inlets are a bit small for the fin spacing as
air rapidly goes through the fins without picking up the heat. The
spacing of the cylinders fins and their thickness are partially to blame
on the old engines, but we can't fix that. The new engines were
refined, but alas are not interchangeable with the older engine.
Oil Temps in the climb and 110 Knot cruise are within limits, thanks to
a well sealed oil cooler, however, the oil temperature went up as speed
increased above 120 KIAS at max continuous due to the poor design of the
NACA and oil cooler placement. Yes it is true, as the speed goes up the
air stalls at the oil cooler and decreases its efficiency to nil. More
work needed, but trying to do it without messing up his paint is a pain.
The engine at cruise will die if the carb heat is pulled and then the
throttle retarded so we have a carburation issue still. It is just too
lean it seems. Many things may be at play. We'll investigate one at a
time.
Shock cooling is a pain so the inlet has a dam on the front cylinders to
help out, but it bears watching. We lazy Rotax people normally don't
have to go to the cooling page of the EIS as part of our descent check,
so make it part of your crosscheck.
To our friend in Argentina:
Thanks to Johns Lawton's and the Jabiru crowd's research, the mixture
per cylinder has been identified as a problem in some of the stock
engines. The induction system we found is prone to small leaks which
leans the cylinders and causes high EGT and CHT. We are pulling the
carb (again) to take out the owner installed lean kit. The smooth bore
inlet to the carb is a good idea, but please ensure the hose clamps and
rubber and gasket parts in the induction are sealing well. Also, the
induction hose must be able to hold its shape and still be flexible
enough to take engine movement. If that tube collapses your engine
dies. My experience has been if your cylinders are running hot and the
EGT is high, fix the induction, by either fixing air leaks, jetting the
carb differently or moving the mixture clip or both. I have not tried
rotating the carb off axis.
John Kershner's plane was a 95 knot trigear and now goes 127 knots at
max continuous with a speed kit properly installed and some cooling drag
massaging. I was surprised that the 100HP 912S goes faster, but then
again, prop speed and size and a gearbox multiplies the torque so they
are about even as far as engines go with fixed pitch props.
The Jabiru USA Rep, Pete K, was emphatic that tuning and cooling issues
were best answered by using a Sensenich 62 inch wood prop. As the
engine rpm passes 2750 or so, torque drops off and engine horsepower
increases with engine speed but not a lot of extra power is felt.
Propeller airplanes fly on torque so his assumptions make sense when
comparing engine charts side by side. Most guys don't consider the
torque multiplier of the 2.43 gearbox on a Rotax. The Rotax prop turns
slower at 2250 RPM which looses out in potential thrust on a short 64
inch prop where as the short bladed Jabiru turns near 2750 RPM at max
continuous. But it burns more gas turning that fast.
The Jabiru is a nice looking engine that came on line before all the
bugs were worked out, in my opinion, and it is a bit of time and
patience to get it right. I have watched many folks on the net and
after about 2 years of tinkering it works OK.
I just had to look at it myself, as I have avoided the Jabiru in the
past as heavier, thirstier, and harder to cool. I can make a Rotax cool
with my eyes closed assembling the FWF. But what is life without
challenges... I have put a couple thou of my own money into working out
the deficiencies for my owners at the shop and we may do a cooling 102
on the Jab for those suffering in silence who are still willing to
experiment... If it works, parts will be made available.
Here's hoping that we get all the bugs out.
Best Regards,
Bud Yerly
Still recovering from Sun 'n Fun.
----- Original Message -----
From: AirEupora<mailto:AirEupora@sbcglobal.net>
To: europa-list@matronics.com<mailto:europa-list@matronics.com>
Sent: Tuesday, April 12, 2011 10:05 AM
Subject: Europa-List: Re: JABIRU 3300 BRAND NEW OVER TEMPERATURE
DURING TAXI
<AirEupora@sbcglobal.net<mailto:AirEupora@sbcglobal.net>>
I can not address this problem as I have not run my engine, but I was
told by Jim McCormick to build a square box in front of the carburetor.
I'll include a couple of pictures.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=336709#336709<http://forums
.matronics.com/viewtopic.php?p=336709#336709>
Attachments:
http://forums.matronics.com//files/carb_box_021_853.jpg<http://forums.mat
ronics.com//files/carb_box_021_853.jpg>
http://www.matronics.com/Navigator?Europa-List<http://www.matronics.com/N
avigator?Europa-List>
http://www.matronics.com/contribution<http://www.matronics.com/contributi
on>
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