Lynn,

 

as always, your inputs are real world. I think I am at the point where I have to confirm or refute the float level issue. I am running at this time at up to 6gph and the goal is closer to 10gph. Even if I do not have that problem now, it may still come and bite me later.

Thanks a lot for your inputs! 

 

Richard Sohn
N2071U

In the olden days right after rotaries were invented (by NSU) you could still do a clean cut at full throttle and "Read" the plug porcelain color to help determine engine mixture at full throttle. Champion and others sold battery powered magnifying loupes so people could look closely at the hot end and make a tuning or heat range change.

 

The tree huggers took away leaded motor fuels, and the replacement anti knock compounds burn black for lean and rich, so no more plug reading is possible. You can still do it with low lead avgas, and I ran that in my Fiat until the State people figured out that I was buying 3 dollar avgas just to avoid the road taxes on the $1.25 street gas. Genius............

 

So I gave up on the Fiat and started using unleaded street gas in a rotary. If no turbo is involved, just use 87 octane.

 

So, you cannot tell anything about plug heat range or mixture tuning by looking at the plugs anymore. Use the coldest heat range plugs you can find and if you want different heat ranges for leading and trailing?????????????

 

Then put the coldest plugs in the trailing holes. There is one indicator still left as a last chance before the engine dies, and that is cement boil around the center electrode. It takes a strong light, and the black color may be burned away right at the end of the porcelain, but if you see little silver looking bubbles around the electrode, the plug tip is running too hot. That could be too much advance, (over 27 degrees BTDC)  and/or too high a heat range, and/or too lean a mixture.  

 

Tune with EGT and F/A to get into the best power (best power for any engine is just a hair rich of peak EGT).

In piston engine tuning you always hear that Bubba leaned her too far and she melted a piston. More likely Bubba had too high a heat range plugs in it, and detonated the hell out of it for quite some time when a  piston came out through the breather.

 

Best power (just rich of peak EGT) is also best heat, real hot for exhaust valves, piston domes and plug tips.

 

So the piston airplane engines need huge over rich (not best power) for take off and climb to help fuel cool the engine and help prevent detonation and keep the 1920s ignition system lighting the fire. Rich mixtures being very easy to light.

As you climb away from sea level total engine output goes down for lack of Oxygen and fuel flow is reduced

to account for that. But still well rich of peak EGT. Once the pig is going as fast as it will go, then quickly lean it to your cruise setting, spending as little time as is possible at peak EGT. Or with two controllers switch to the (cruise controller). Rotaries are fairly insensitive to poor tuning at full throttle, as lots of important stuff will melt before the cast iron pistons leave on you. Also the rotary (with a killer ignition system) will run well lean of peak EGT, as well as way rich of ideal mixture. Well rich is more fuel than can be burned with the Oxygen available, and lean of peak EGT means that excess Oxygen is passing through the engine for lack of enough fuel. The EGT will start going lower than peak.

 

Of course the lower fuel flow also means less power and lower top speed, with the advantage of lower engine temps and wear, and longer range.  Remember to go rich again closer to the airport lest you find a very soft engine for a go around.

 

So, on avgas the white plug nose means way too lean. On unleaded street gas the white nose means too lean and way too high a nose temperature. On unleaded street gas the plugs will always look a filthy black.

 

Test with ice cold plugs even if you foul one from time to time.

I would gap them at not more than .015" so you are testing the engine and not the ignition system.

 

Lynn E. Hanover