Rotax 912
Is Rotax 912 engine's ignition timing variable or fixed?
Is Rotax 912 engine's ignition timing variable or fixed?
by Sean Griffin » 7 months ago
Fixed.
With the exception of a wee bit of retard if you have an engine with (connected) "Soft Start".
(From Bill Martin "The engine starts with the timing at TDC and after a few seconds changes to the standard BTDC setting.")
Optimum engine RPM is around 5200 (range 4800-5600 ??).
Few, if any standard aircraft engines have variable timing (past starting aids). Car/motorcycle engines do and this may be kept or not, when converted for aircraft use.
Just like your lawn mower, aircraft engines are designed to operate within a small RPM band. Operating outside the recommended engine speeds is likely to lead to a shorter engine life.
Having a narrow engine speed range allows the designer to strive for minimum weight/best power : weight, optimum volumetric efficiency, cooling and long in-service life.
by Roger Lee » 7 months ago
Without getting into too much,
If you have the green striped labeled ignition modules they start with 4 degrees BTDC and after the engine starts goes immediately to 26 degrees BTDC.
If you have the yellow striped "soft start" system then the engine starts with 3 degrees ATDC and then after start it stays there for 4-5 seconds and switches to 26 degrees BTDC.
Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell
by Rotax-Owner » 7 months ago
Check out these two free video courtesy of Lockwood Aviation that helps explain things!
https://www.rotax-owner.com/en/videos-topmenu/free-videos/708-rotax-lockwood-easy-start
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