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This home
page upgrade is long due but the focus has been riveted on getting ready for
the taxi trials. Also, this phase of the progress mainly consists of small
achievements that somehow have to be gathered to get something to write
about. We have also had an inspection by the Technical Counselor Sakari Havbrandt, whom of
course made some remarks. Those were very much in line with our own ideas and
therefore mainly felt like confirmations rather than setbacks. Sakka however, joined the line of skeptical people about
the engine cooling. We are not surprised since quite a few people including
ourselves have been in that line for a while. Pusher
engine cooling is a well known problem area, especially on sea planes.
Extended slow downwind taxiing in the water is a common reason for cooling
problems. At least
we can say we have been aware of it and taken some firm approaches to not
facing a dead end if our first attempts shouldn’t turn out successful.
Looking in the books and listening to experienced people, gives at hands that
the cooling air intake should be located in a good air flow and measure some
20 square inch per 100 hp. Furthermore the air outlet should have area about
three times that. The inlet air flow speed should be reduced so that the
cooling air has a relatively high pressure and moderate speed. We receive
comments that our intake is too small but it is in fact 26 sq. in. and
thereby actually should be larger than necessary. When
focusing on these matters you may realize that many intakes are more generous
they need be and as usual, you will not likely know if something is too good.
There is a penalty though, increased drag even if this is not absolutely
certain. It depends on whether the frontal area is driven or if the intake
has a detrimental effect on the airflow and of course the way the outlet is
arranged. Anyway, we
have tried to do it by the book and forthcoming taxi trials outside the
factory will certainly tell us something about where we stand. Finally,
on July 5:th the most major milestone so far was
passed, we started the engine for the first time. After a removal of an
internal carburetor cap, the engine started promptly and ran with a
surprisingly soft and low sound. The exhaust stack muzzles are located inside
the cowling at the cooling air outlet. A strange
coincidence was that this first day of the engine running
happen to be the so far hottest in As planned
since long and also encouraged by Sakka, two
cooling fans are installed. These are located a bit down stream the intake
where the air speed is reduced and ducted directly over the cylinder heads. A Dynon DEK-180 is installed and gives a
superb information of a number of engine parameters such as RPM, oil
pressure and temp, fuel pressure, CHT and EGT on all four cylinders. Invaluable data when looking
for engine problems. This data was also downloaded to a laptop and every
parameter is thereby plotted by the second for afterward scrutinizing. We found
that the number one cylinder was running 15 to 18 deg hotter than the coolest
but is also the farthest away from the cooling fan. By sealing the Jabiru provided cooling duct at the No. one cylinder, the
temp difference was brought down to a mere 10 deg. related to the least warmest. So, what
is then our general experience of the two first days of engine running and
taxiing? The first
day was quite hot and calm with an estimated wind of 5 knots while the second
day was cooler with a wind of at least 10 knots. We ran the engine approximately one
hour each day without ever reaching the red limits on any of the engine
parameters. During propeller vibration tests on day two, the airplane was
parked in a 10 knot tailwind and run for 11 and a half minutes at various
rpm’s without reaching red values on CHT or
oil temp. We could also see that when parked into wind or taxiing, the CHT increase was slowed down, halted or even reversed. At
RPM’s above idle an obvious suction was
detected at the intake scoop also in tailwind. Can we be
anything but satisfied? Certainly when flying the power output is higher but so
should the ram air cooling be. There will
of course be more testing before we go out to the airport but we do think
that these first two days of running the engine has moved us a giant step
forward to the forthcoming first flight. Thanks for your interest Lage |