Never close-throttle idle?

Jay Honeck

Jay Honeck

Touchdown! Greaser!
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Jay Honeck
We are replacing a cylinder on our RV, and I've been reading my maintenance bible "Airplane Maintenance and Repair" (Carmody, 1998) just to brush up on stuff I rarely do.

On p. 62 he writes "Don't close throttle idle on any engine." He explains that you need a minimum of 1200 RPM to keep the spark plug nose core temperature at 9000 degrees Fahrenheit or above, which is the minimum temp needed to prevent plug fouling.

I must admit that I do not follow this rule, because anything over 1000 RPMs results in damage to my prop and wheel pants due to stone chips.

I also know that the inside of my engine is a mess, thanks to all the lead deposits from running 100LL. (We can't get unpolluted car gas here anymore.) If you've ever shot lead bullets and then examined the barrel of your gun, that's pretty much what any engine running 100LL looks like inside.

What say the group? Do you guys never let your RPM drop below 1200?
 
Shell:
After start up, the engine should be operated at 1000 - 1200 rpm for the initial warm up period and not at the 600 -650 rpm idle speed.
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Lycoming:
The engine should be operated at engine speeds between 1000 and 1200 RPM after starting and during the initial warm-up period. Avoid
prolonged closed throttle idle engine speed operation (when possible).
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Continental:
During a long approach maintain 1000 to 1200 R.P.M. and "gun" the engine at intervals to prevent fouling.
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I'll idle 800 rpm, but I lean it almost to the point of starvation. Can't say I notice the plugs, valves or heads being excessively loaded with lead, quite the opposite. I do run fine wire plugs though, don't know how much of a factor that is.
 
I ground idle at 1000 and lean VERY aggressively until it's time to go.
 
If I idled the 310 around at 1200, I'd wear out brakes in no time flat.
 
You won't find any seaplane pilots who follow this. Where does lycoming or conti say the same?
 
Same here, idling at pre-set idle (600, IIRC) and leaning the heck out of the engine. No issues with fouling in my O-320.
I cannot imagine taxiing at 1200 either, that would make me twitch.
 
Continental says they like to see 900 RPM for "extended idle" in the O-470. Something about splashing oil where it needs to be, or whatever... take with appropriate grain of salt, or whole salt shaker.
 
SkyDog58 said:
Meh, what do they know? Our resident expert on all things under the sun says otherwise.
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There's two ways to deal with the problem of fuel loading at idle, either run the **** out of the engine, spray rocks all over the place and wear out brakes, or you can reduce the fuel supply. Which sounds like the wiser option? For the record, Lycoming has the worst operating advice for their engines imaginable which surprisingly leads to increased parts sales in the form of mid time cylinder sales.
 
denverpilot said:
Continental says they like to see 900 RPM for "extended idle" in the O-470. Something about splashing oil where it needs to be, or whatever... take with appropriate grain of salt, or whole salt shaker.
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That, and even with alternators, many planes barely charge (or even discharge) at 600-650 rpm.
 
The low voltage light comes on below about 700 in mine. I usually idle at 800 to 1000 leaned to the max.
 
Prolonged idle at 600-700rpm will foul the plugs. Normal use is fine, if you are going to be sitting still for awhile, its a good idea to bring the idle up a bit.
 
Bill Jennings said:
That, and even with alternators, many planes barely charge (or even discharge) at 600-650 rpm.
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This time of year if you have any significant vampire loads like old clocks and what not, a battery may not be fully charged even many minutes into a flight. But anyway, sounds like the consensus is a couple hundred extra RPM isn't a bad idea, as long as you're paying attention to what's behind you.
 
Jay Honeck said:
We are replacing a cylinder on our RV, and I've been reading my maintenance bible "Airplane Maintenance and Repair" (Carmody, 1998) just to brush up on stuff I rarely do.

On p. 62 he writes "Don't close throttle idle on any engine." He explains that you need a minimum of 1200 RPM to keep the spark plug nose core temperature at 9000 degrees Fahrenheit or above, which is the minimum temp needed to prevent plug fouling.
Click to expand...

9000°F??!! How does a plug get anywhere near that? That's arc welding temperatures. 9000 degrees in a plug in an aluminum head that melts around 650°F. Right.
 
Unless the magnetos output drops to the point the plug can't fire, I wouldn't worry about it. He probably meant 900, not 9000, unless he meant the actual spark temperature.
 
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Dan Thomas said:
9000°F??!! How does a plug get anywhere near that? That's arc welding temperatures. 9000 degrees in a plug in an aluminum head that melts around 650°F. Right.
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I'm not sure the exact temps, but basically a spark plug is an arc welder, and the ceramic depth is what is used to control the heat range of the plug.
 
Usually idle at 900 to 1000, haven't had any problems.
 
800-900 always seems to make a nice 'caught up' idle that doesn't seem to be lugging around the prop. Most big 6 cylinders seem fine at 700.
 
Henning said:
800-900 always seems to make a nice 'caught up' idle that doesn't seem to be lugging around the prop. Most big 6 cylinders seem fine at 700.
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Yeah, but if aggressively leaned, I *want* it missing a little bit... I just don't want to sit there farting around with something for an hour listening to it doing that. :)

Just go flying... and you don't have to worry about idling problems too much. Especially if you're not buying "shock cooling"...

(Ooh, stir that pot!) :)
 
Jay Honeck said:
We are replacing a cylinder on our RV, and I've been reading my maintenance bible "Airplane Maintenance and Repair" (Carmody, 1998) just to brush up on stuff I rarely do.

On p. 62 he writes "Don't close throttle idle on any engine." He explains that you need a minimum of 1200 RPM to keep the spark plug nose core temperature at 9000 degrees Fahrenheit or above, which is the minimum temp needed to prevent plug fouling.

I must admit that I do not follow this rule, because anything over 1000 RPMs results in damage to my prop and wheel pants due to stone chips.

I also know that the inside of my engine is a mess, thanks to all the lead deposits from running 100LL. (We can't get unpolluted car gas here anymore.) If you've ever shot lead bullets and then examined the barrel of your gun, that's pretty much what any engine running 100LL looks like inside.

What say the group? Do you guys never let your RPM drop below 1200?
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can't you lean at idle?
 
I bet these folks will tell you that shock cooling exists.

PolarBearPlunge2010.jpg
 
Any truth to this statement? "For Lycoming engines, idle at 1100 to 1200 RPM to ensure adequate cam lubrication."

Also just found this, from Lycoming Service Letter L192B (never mind, the info below was already posted earlier, and I've been reading this thread backwards):

"The engine should be operated at engine speeds between 1000 and 1200 RPM after starting and during the initial warm-up period. Avoid prolonged closed throttle idle engine speed operation (when possible). 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. Avoid rapid engine speed changes after start-up and use only the power settings required to taxi."
 
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I had the idle decreased to 300 rpm when I had my Amphib (lycoming 0360), even when not a Amphib. That engine did just fine. Was cool taxiing around ka thuka, ka thuka, ka thuka. All the other taildraggers wished theirs was. Admission for that was putting it on Amphibs, mechanic say. See you dont to be taxiing much on the water, sometimes, like when are being blown backwards "sailing".
 
denverpilot said:
Yeah, but if aggressively leaned, I *want* it missing a little bit... I just don't want to sit there farting around with something for an hour listening to it doing that. :)

Just go flying... and you don't have to worry about idling problems too much. Especially if you're not buying "shock cooling"...

(Ooh, stir that pot!) :)
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I lean regardless, but I don't like the engine catching on the props inertia shaking the crank weights around. A little noise is ok, but if it causes a shake I don't sit there.
 
This is all my continental IO520 FAA operators manual has on prolonged low idle, worse case you just burn your plugs off, I've done some long idles up to docks or for sailing on my amphib, with a good amount of mixture pulled out I've never had a issue.


image.jpg


image.jpg
 
Lean aggressively on the ground. If you're stopped, don't go below 1000 rpm. If you're taxiing, it should be ok to go to idle to keep from having to drag the brakes. This is what I've been taught in every airplane I've ever checked out in.
 
wilkersk said:
Lean aggressively on the ground. If you're stopped, don't go below 1000 rpm. If you're taxiing, it should be ok to go to idle to keep from having to drag the brakes. This is what I've been taught in every airplane I've ever checked out in.
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Why not go below 1000RPM?
 
James331 said:
Why not go below 1000RPM?
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Keep up the air pressure in the cowling with the prop. The 260 Commanche has a special prop available that carries an extra 'flap' of chord length at the blade section that goes over the cowl inlets.
 
So a design flaw in the PA24?


Clark1961 said:
One reason is to keep alternator output up.
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According to my FAA approved engine operators manual it's just a matter of plug fowling, which can be avoided or cleared if needed.


In the POH

image.jpg



Just depends on the aircraft, but to say no aircraft should taxi at idle is silly.
 
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James331 said:
So a design flaw in the PA24?




According to my FAA approved manual it's just a matter for fowling, which can be avoided or cleared if needed.
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Lots of HP planes have trouble keeping cool sitting in line on a hot day, especially if you have a long hold for release. Personally I shut down, but that is the basis behind the 1000rpm recommendation when it is recommended from what I have seen.
 
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