Hi Ed,
thank you for your response;  I had not thought of the pooling of fuel
in the plugs; they are little cups, after all.
However, my main question was not in regard to flooding but to fouling,
ie SAG in the cruise: why should 'plugs down' be more susceptible to
fouling in cruise?

 

 

I recall disconnecting the front and rear plug wires on visiting radial aircraft engines to let the water run out of the harness, prior to start up. Usually in the spring and fall when big swings in temp would condense water in the (never truly sealed) harness. If they had set out in the rain while parked, good luck starting them at all. Changing all of the lower half plugs was sometimes called for. Also turning the engine backwards by hand, to assure there would be no hydraulic  lock up from scavenged oil and , or, fuel was required.

 

If you think a rotary is a pain in the patuti, move to Alaska for a winter of starting radials.

 

A properly performed starting procedure would usually get things going in the AM, so in every one of our own planes, the crew chief of that plane (me) ran it to temp first thing, and checked the radios, and cycled the props, including feather and unfeather, control freedom and flaps and so on. You might have to drag a dead cylinder for a while before it came to life from heat of compression warming it up, but seldom did we have to change plugs on our own aircraft. Visiting planes, and visiting pilots yes, many plugs down the drain.

 

Needless to say there are a number of cylinders on the bottom of a radial, and those  cylinders get the oil and fuel fouled plugs. But start they do, and with the most lame ignition systems ever assembled. The cloud of oil smoke is not from the top cylinders is it?

 

Our base commander was an Admiral and he could not start an engine on a warm summer day. The ADs (aircraft engine mechanics) would hate to see him coming to fly my plane D-18 tail number 128. They would end up on their knees between the seats trying to unflood a R-985. Eventually they made me do it.

 

Note that the stock rotary plugs look very similar to big airplane plugs, with a half acre of ground electrode and a very small (can't miss) air gap.

 

So, if you crank it a few blades with the ignition on, and then turn on the pumps, perhaps flooding could be less of a problem.

 

I still think it would work.

 

Lynn E. Hanover