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THE question I could never find a good answer for (labelling of the ignition switch)

Noe wrote:

I know every POH says it, I just never found a convincing reason as to why

The measured RPM diffs L/R/Both don’t change irrespective of how you play with your mags (they do change when I move mixture tough ), I guess rpm diffs is what matters not how you get them….

Last Edited by Ibra at 09 Sep 14:06
ESSEX, United Kingdom

“When switching from L to R, there has to be some middle point where both are ON, or the engine would stumble.”
The switch earth’s the relevant mag to make it off. So in between neither is earthed – both are on. But it will be difficult to hold in exactly that position. Off earth’s both. Both earth’s none.
PS For 7 years our O200 had the L and R key switch positions reversed, and nobody noticed. The Jodel was under the CAA, and it was only noticed when I had a bad mag drop when about to depart after her second Star Annual, and returned to the engineer for checking.

Maoraigh
EGPE, United Kingdom

Maoraigh wrote:

PS For 7 years our O200 had the L and R key switch positions reversed, and nobody noticed. The Jodel was under the CAA, and it was only noticed when I had a bad mag drop when about to depart after her second Star Annual, and returned to the engineer for checking.

That’s interesting. My understanding is that one of the mags is an impulse magneto and only that one should be active when you start the engine. So when you turn the key to “start”, the non-impulse mag is grounded. If the L/R connections were reversed then the wrong mag would be grounded and you would have starting problems.

ESKC (Uppsala/Sundbro), Sweden

Hand propping the Super Cub (Continental C90) is done in “both”.

Same on the C90 in the Vagabond. I am not 100% clear whether there are impulse couplings on both or not.

EGLM & EGTN

Small Continentals typically have impulse coupling on both mags.

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