We have a Europa XS monowheel with a Rotax 912S engine, fitted with a
Airmaster prop. The engine and plane have been flying for four years
with about 400 hours. We have had problems with starting for several
years, and have not been able to reliably start the engine since last
October. The engine would either not start at all, or start up in a
very rough mode others have called the 'sub-idle harmonic', which shakes
the engine so bad it risks serious damage to engine and plane. Getting
out of this sub-idle harmonic mode would require too much throttle, in
that when the engine did take off, it would most often shed some part or
another, usually just the exhaust.
We have tried nearly everything we could think of, including many
carb syncs, carb cleaning, new 25 Ahr battery, new heavy duty starter,
installation of ignition kill switch for starting, new plugs, fresh gas,
checking high and low voltage ignition wires various ways, etc.
In a conversation with one of the guys at Lockwood Aviation, he
mentioned that the slipper clutch was now mandatory on all 912S engine
sales (as well as the HD starter), and that he thought it helped greatly
with starting (I'm still not sure why). As our engine was one of the
first 912S to be sold, we were unable to get a slipper clutch with our
engine, although we asked for it. On hearing the slipper clutch might
help, we immediately removed the gearbox from the plane and sent it to
Lockwood for a slipper clutch, getting it back last Wednesday.
On first try, the engine rotated the prop about one revolution and
then came to very sudden stop. We both thought we must have left a
wrench or something in the gearbox, but the prop could be easily rotated
by hand, so the engine was not seized. It turns out this was the
infamous kickback which we had heard about but never experienced before.
On the next attempt, the engine kicked back again, but then continued on
for an otherwise good cold start (with choke). After a warm-up, a warm
start was tried, which was good, the best since building the plane, it
just started right into a very smooth idle.
The next day we called Lockwood again, and was given advice on
starting without kickback. This weekend we flew the plane four times
with both cold and hot starts using the recommended technique, and all
were good starts (no kickback). We FINALLY have a usable plane again.
THANKS Lockwood Aviation.
So, for anyone with a 912S that has no slipper clutch, get one if you
have starting problems. Hell, even if you don't have starting problems
(yet), get it anyway, you also get a smoother idle out of the deal.
regards,
Terry Seaver
A135 / N135TD
BTW: The recommended technique that got rid of the dreaded kickback;
cold start-
1) crack the throttle about 3/16"
2) start cranking the engine with ignition enabled and choke off (in)
3) after starter gets up to speed, pull the choke out.
warm start-
1) crack the throttle about 3/16"
2) disable ignition
3) start cranking the engine
4) when starter is up to speed, enable ignition.
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