Dual Spark Plugs

[Tommy Cookers]

Duel plugs, other than avoiding failure through redundancy, are at best a band aid. A proper head/piston design greatly enhances flame travel through squish, swirl and tumble. These convection mechanisms augment flame travel by double digit factors.
Alfa is a poor source for supporting duel ignition. They were wedded to the hemi combustion chamber which has poor squish and intake charge characteristics. Similarly, hemi combustion chambers were common in aircraft engines, though they needed redundant ignition by regulation.

those of us who have done our own aviating know the mandatory ignition checks before flight
(these require that the engine runs significantly slower on either magneto individually, than it does on both magnetos together)

does this mean that these engines have no squish, swirl, or tumble ?
if S,S&T were present then there would be no 'rev drop' on single magneto running, and no light aircraft could legally fly ??

[autogyro]

Duel plugs, other than avoiding failure through redundancy, are at best a band aid. A proper head/piston design greatly enhances flame travel through squish, swirl and tumble. These convection mechanisms augment flame travel by double digit factors.
Alfa is a poor source for supporting duel ignition. They were wedded to the hemi combustion chamber which has poor squish and intake charge characteristics. Similarly, hemi combustion chambers were common in aircraft engines, though they needed redundant ignition by regulation.

those of us who have done our own aviating know the mandatory ignition checks before flight
(these require that the engine runs significantly slower on either magneto individually, than it does on both magnetos together)

does this mean that these engines have no squish, swirl, or tumble ?
if S,S&T were present then there would be no 'rev drop' on single magneto running, and no light aircraft could legally fly ??

I think the primary reason for the 'mag' check pre-flight is to make sure the engine still runs with one mag turned off or failing.
I think the check states the rpm on one mag should not fall 'below' a certain level, not that there should be a rev drop.

The designs of most light aero engines are still pre WW2 thanks to the huge expense passing regulations for new designs.
I know this from bitter experience with Cof A applications from the CAA.
These engines have very basic chamber design and low compression for use with 100 plus octane fuel.
Ancient power units closer to early tractor engines than modern technology.

Of course any modern light aero piston engine would use a much better ignition design than dual mags.

[olefud]

Duel plugs, other than avoiding failure through redundancy, are at best a band aid. A proper head/piston design greatly enhances flame travel through squish, swirl and tumble. These convection mechanisms augment flame travel by double digit factors.
Alfa is a poor source for supporting duel ignition. They were wedded to the hemi combustion chamber which has poor squish and intake charge characteristics. Similarly, hemi combustion chambers were common in aircraft engines, though they needed redundant ignition by regulation.

those of us who have done our own aviating know the mandatory ignition checks before flight
(these require that the engine runs significantly slower on either magneto individually, than it does on both magnetos together)

does this mean that these engines have no squish, swirl, or tumble ?
if S,S&T were present then there would be no 'rev drop' on single magneto running, and no light aircraft could legally fly ??

As mentioned, I think the requirement is that RPMs do not drop beyond a given limit in order to establish that both mags are in proper operation. No drop in RPM is quite acceptable

While I have limited knowledge of all light aircraft engines, the generic Continental O-170 type indeed has poor squish, swirl and/or tumble. It is a 1940s design with, as a result of the above and with the individual plugs being poorly positioned, typically shows some RPM drop at low RPM static runup