(Robert M. Gary) wrote
I had to cancel a flight today because one of the plugs in my Mooney
doesn't seem to be firing (tried to burn it clean but no luck).

Usually such problems are resolved by cleaning/regapping. Takes about
15 minutes if you know which plug it is, requires only simple hand
tools, and it's quite legal for an owner to do. It's pretty easy to
figure out which plug is the problem - let the engine cool somewhat,
start it, immediately switch it to the bad mag only, and let warm a
bit. The cold jug is your culprit, and of course you know which plug
based on which mag you have selected. Of course if you have an engine
monitor it's even easier. It's worth learning how - keeps you from
cancelling trips.

Anyway, it got me wondering what would happen if you lost both plugs
in a cylinder during cruise (certainly take off would suck).

I actually had that happen. Both plugs fouled. It was in the TwinCo,
so I only lost one jug out of 8 - takeoff was a bit anemic, but it was
a long runway and by the time I noticed anything wrong, I was airborne
and climbing 1000 fpm. In your Mooney, I would expect the takeoff to
approximate what you would get if the density altitude was maybe
5000-7000 ft higher than it actually is.

I often
cruise around in my Mooney at 45% power (as indicated on the EDM). I
would like that I would have at least 45%, right?

Depends on altitude. My estimate is that you would have more than 70%
but less than 75% of whatever is available at that altitude with the
engine working properly. That is certainly consistent with my
experience.

Michael