Indeed... Any more discussion about mags?

An experienced aero-engine engineer, who flies his own Rotax 912-powered aircraft, just made this comment to me:

In the "Shut down" checks, I personally would add throttle to idle immediately before the switching off......I find the engine shut off is much softer if the throttle is brought to absolute idle, then 1 mag switch turned off, followed 1 second later by the second switch. Note, I am not advocating letting the engine actually idle below 2200 for any real period of time.

I think that was mentioned previously on this thread.

Many thanks to all previous - much appreciated.

Cutting the ignition circuits separately, with a bit of time in between, was indeed already suggested in #52. I didn't think to mention reducing to idle, thinking that self-evident, but I now realise it isn't: from the few times I was a passenger behind a Lyco/Conti, I remember they are stopped by cutting the mixture, at fairly high rev (1200 rpm comes to mind?)
But yes, surely, slow the Rotax to idle before stopping it, that will bring less stress on the gearbox - even with a slipper clutch installed, as it should be.

Edit: idle on my 912UL is much lower than 2000, perhaps 1300 or 1400 rpm depending on temperature. The one thing I do take care about is to run it fast enough when very cold i.e. after the first start of the day. Sometimes as high as 3000 rpm, for the first few seconds, then gradually reducing.

which was post #13 with some typos.

But the critical point is to read the manual and do what your particular engine needs. Lycoming, deHavilland, Rotax are very different engines and should be treated that way - according to their manuals.

Indeed. I know nothing of operating Rotax engines but having observed them in use I can see they might require very different handling to the old iron. The shutdown procedure for the Gipsy Major, for instance, calls for idle throttle, both mags 'off', then throttle fully opened.

The reason for the fully opened throttle is that if there are glowing carbon deposits in the cylinder to provide an ignition source, the engine might 'run on', albeit lumpily. Opening the throttle wide at such very low RPM (it's after the mags have been cut) reduces the vacuum in the throttle venturi to the extent that what is drawn into the engine is mostly if not entirely fresh air, so not combustible, and the engine stops with no tendency to run on.

I would never turn both mags off and then back. Got over 18 years on my Lycoming 150hp and have never done it.:)