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squawkvfr

Engine Start: Mags first vs Mixture first?

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HiI just had a quick question regarding piston engine startup procedures. From what I can tell, modern inline-engined aircraft (e.g. Cessnas, Pipers) have you push the mixture to Full Rich BEFORE you turn on the ignition. However, for radial-engined warbirds (e.g. Gooney Birds) you turn on the ignition (or starter) and get the prop turning FIRST, then you add the mixture. Why is that? Is there an underlying difference between the way the two engien types work?

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Radials is ignition first then magnetos. Your run of the mill Cessna is mixture rich and mags on and then ignition. The reason for turning radials over first is the possibility of hydrolock that can happen.

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Also.. full-rich before cranking (Cessna / Piper, etc) is for carbureted engines.. fuel-injection calls for a different startup..Cold.. 1/4 throttle, mixture full rich. fuel pump on until positive fuel-flow is indicated..then mixture to cut-off.. crank immediately, richen mixture after ignition.Hot.. Hot starts are tricky.. normaly, no pump is needed. Start with throttle at idle; mixture to cut-off... crank while opening the throttle, and be quick to richen as it fires..

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Start the airplane how the operating handbook has you start it. Even with the same engine installed in different airframes they can have differing operating procedures. In Pipers Warriors that I flew the POH said that in order to lean to the proper mixture during cruise was to leave the throttle full open and pull the mixture back to the desired RPM. In most other aircraft it is set the throttle to the RPM you want and then pull mixture back to the proper exhaust gas temperature or before the engine runs rough then again adjust the throttle to the proper RPM once the mixture was set. I don't know what the difference was between airframes.

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In Pipers Warriors that I flew the POH said that in order to lean to the proper mixture during cruise was to leave the throttle full open and pull the mixture back to the desired RPM.
You sure about that Chris? That sounds more like Lycoming's recommendation for take-offs above 5000' (full throttle... lean to max rpm). You flying out of some High Density Altitude airports?At Purdue we used 65% power (which btw performance chart indicates you can get that well over 12,000' on a std day). On our PA-28-161s you would have to look up the RPM setting for the %power you were going to use at planned altitude. Once at cruise altitude, you'd pull throttle back slightly below the intended rpm setting (book says 35rpm) lean to peak rpm, then make a final adjustment with the throttle.c401_cvs mentions the hydrolock problem... this comes as a result of oil collecting in the lower cylinders (of a radial engine) which of course, you do not have in a Piper or Cessna (ok ok... most Pipers or Cessnas :()

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Radial engines are just too cool... Fire one up an an airport - all heads turn...Regards,Scott

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You sure about that Chris? That sounds more like Lycoming's recommendation for take-offs above 5000' (full throttle... lean to max rpm). You flying out of some High Density Altitude airports?At Purdue we used 65% power (which btw performance chart indicates you can get that well over 12,000' on a std day). On our PA-28-161s you would have to look up the RPM setting for the %power you were going to use at planned altitude. Once at cruise altitude, you'd pull throttle back slightly below the intended rpm setting (book says 35rpm) lean to peak rpm, then make a final adjustment with the throttle.c401_cvs mentions the hydrolock problem... this comes as a result of oil collecting in the lower cylinders (of a radial engine) which of course, you do not have in a Piper or Cessna (ok ok... most Pipers or Cessnas :()
Yeah they are 161's as well 2007 models if that makes much of a difference.

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That's a very interesting question and I don't think there's been a direct answer yet.I have just a guess. Because radial engines are arranged vertically it would be best practice to run the cylinders through a few cycles before you begin any combustion…this would help remove any oil (condensation too?) that’s pooled in the lower cylinders and perhaps lubricate the parched top cylinders. At the very least it would help even the oil distribution in a system that’s sort of naturally challenged by gravity at rest ;)Horizontally opposed cylinders would all tend to drain back into the case and sump; and, lubricate more evenly and faster on start. They all have roughly an equal and optimal relationship with the oil sump.

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That's a very interesting question and I don't think the you have an answer yet. But I have a guess. Because radial engines are arranged vertically it might be best practice to run the cylinders through a few cycles before you begin any combustion…this would help remove any oil (condensation too?) that’s pooled in the lower cylinders and perhaps lubricate the top cylinders. At the very least it would help even the oil distribution in a system that’s sort of naturally challenged by gravity at rest. ;)
That would also apply to inverted engines?

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Yeah they are 161's as well 2007 models if that makes much of a difference.
Yes I suppose it very well could... models I am referring to were from the mid-80s. Thanks for the reply.
I don't think the you have an answer yet.
c401_cvs mentions the hydrolock problem... this comes as a result of oil collecting in the lower cylinders (of a radial engine)

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That would also apply to inverted engines?
I do not see why not... tho some engines might be more susceptible than others...I took an aerobatics course in a Chipmunk some years ago (ok many years ago)... Seems to me "we" would pull the prop thru for a couple turns to prime the engine... and maybe to check for hydrolock too.

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From research I've done online, apparently this "mags-first" starting technique also applies to the Allison-engined P-38. So it might have been used in all WWII aircraft in general, regardless of engine type? Just throwing that out there as a possibility.

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