lean for taxi ?

[A Squared]

That is a really good way to explain it...wow...you dont mind if I add that to my notes do you?

-mini

No, go right ahead ... but if you make any money off it, you gotta cut me in for a share. <g>

 

[ROB-x38]

Some good aircraft/engine systems discussions here.

From http://www.lycoming.textron.com/main.jsp?bodyPage=/support/publications/keyReprints/operation/sparkPlugFouling.html

At engine speeds from 1000 to 1200 RPM, the spark plug core temperatures are hot enough to activate the lead scavenging agents contained in the fuel which retards the formation of the lead salt deposits on the spark plugs and exhaust valve stems.

The above reference suggests spark plug fouling is unlikely at enigne speeds > 1000 RPM.

So taking the case where we are taxiing an aircraft with a throttle setting producing slightly less than 1000 RPM, presumably fuel will be being metered through the main jet. In this case wouldn't a leaner mixture prove beneficial when trying to reduce the likelihood of spark plug fouling?

On the other hand, playing devil's adovate, it's interesting to note that in the above article Lycoming doesn't once mention to lean the aircraft on the ground to avoid fouled plugs. Hmmm...

Thoughts?

 

[avbug]

I've removed and cleaned a lot of fouled plugs that fouled at RPM settings much higher than 1,000, and a at power settings much higher than idle. The reference you quoted doesn't suggest in the least that fouling is unlikely, only that scavenging properties are better at higher power settings.

Temperature has nothing to do with engine RPM, but everything to do with engine power being produced, and mixture setting for any given power setting.

Weather fuel is being metered through the main jet or not depends on the idle setting of the engine. As stated earlier, don't confuse the RPM of the engine with the mixture, liklihood for fouling, temperature, or idle.

 

[midlifeflyer]

Midlife, this statement suggests a misunderstanding of idle mixture.

No doubt.

Thank you. Your explanation was very helpful.

Let's take my hypothetical flight one step more. I'm flying my piston airplane from my home in Leadville to Florida. If I am understanding what you are saying properly, there is really no issue with respect to the mixture at higher than idle power settings.

But might I want to have that idle jet adjusted somewhere along my route? Or, using your slow faucet analogy, is the difference still pretty insignificant?

 

[avbug]

A Squared fauced anology is an excellent one, and works for the cockpit mixture control with respect to idle. The mixture control will have an effect right at the cutoff point, but you aren't adjusting mixture, you're shutting off fuel. You could try the same thing by shutting it off at the selector valve, too.

If you set your idle mixture in leadville, then you'll want to reset it for lower elevations. If were me, and I knew I'd be moving my base, I'd make an enrichening adjustment prior to leaving. Then fine tune it on arrival.

Or, you could always stop on the way. The decision, as always, would be governed by where has the best food selection.

 

[SLagonia]

My Cardinal POH calls for "aggresive Leaning during taxi" -

 

[JeffSKDTW]

Gentlemen -

This discussion has been very enlightening. Thanks.

 

[A Squared]

The decision, as always, would be governed by where has the best food selection.

See, it always comes down to BBQ.

 

[tathepilot]

Gentlemen -

This discussion has been very enlightening. Thanks.

yes, very much so !