Throttle Idle on Ground?

Pilot121

Pilot121

Well-Known Member
Hello,

During my flight lesson the other day, I was holding short of the runway, waiting for takeoff clearance and performing the run up. I set the power to idle, but my instructor told me not to do that because it could foul the spark plugs. The mixture was full rich, and it was hot outside - about 26 C. Is this a common practice? I always thought you should have the power back at idle instead of holding the brakes, but is that not the case?

Thanks,
Pilot121
 
The simple answer is you should maintain approximately 1000 RPM. You might also lean the engine about an inch or so until cleared for take off then enrichen it again, or you might set the mixture for the density altitude where you are located. You haven't really provided enough information to make a definitive answer possible but I hope my comments help a bit.
 
flyslow_va said:
The simple answer is you should maintain approximately 1000 RPM. You might also lean the engine about an inch or so until cleared for take off then enrichen it again, or you might set the mixture for the density altitude where you are located. You haven't really provided enough information to make a definitive answer possible but I hope my comments help a bit.
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Thanks! That definitely helps a lot!
 
Another good reason to keep the idle up at around 1,000 RPM is to keep the oil pressure higher allowing for better lubrication of all the parts.

While taxiing, and coming to a stop you can bring the engine to idle, but once you're stopped bringing up the power to 1,000 RPM will be just fine, and the brakes won't suffer at all while you're sitting still.
 
ATN_Pilot said:
Running the power at idle isn't a problem. I do it all the time. But running the mixture full rich will definitely fowl the plugs, especially if you've got a lengthy taxi. I always lean right after engine start and don't go rich until it's time for the run-up.
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This is not entirely true. However, it is most of the time. 90% of carburetors are set up this way where they require ground leaning and some leaning in flight as well in order to keep plugs clean. However some carburetors are set up (mixture adjustment screws) to not require ground leaning or any leaning in flight below 3000 ft. Neither of these are bad, just different. However you can't hurt an engine leaning on the ground so if you don't know, just go ahead and lean and you're be safe. You can figure out proper leaning airborne with EGT going to peak then back 25-50 degrees rich of that or the "lean until it starts running rough and them come back in until it's smooth" method.
 
JustinS said:
Another good reason to keep the idle up at around 1,000 RPM is to keep the oil pressure higher allowing for better lubrication of all the parts.

While taxiing, and coming to a stop you can bring the engine to idle, but once you're stopped bringing up the power to 1,000 RPM will be just fine, and the brakes won't suffer at all while you're sitting still.
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This is important for keeping oil pressure up. Once your engine starts and is running smoothly at 700-800 rpm I would start getting it up towards 1000 for both oil pressure and proper generator/alternator function for charging. All of this aside, I would not taxi at 1000rpm if you're having to ride the brakes, do what JustinS says and taxi at whatever power setting you need to until you are stopped and then 1000 is appropriate. Nothing wrong with 1200 while you're running through the pre-runup part of your checklist or briefing in order to help warm things up before you do a full runup.
 
Dan208B said:
However you can't hurt an engine leaning on the ground so if you don't know, just go ahead and lean and you're be safe.
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Would I lean on the ground the same way as in the air, i.e. look for peak egt, or does it not matter how much it's leaned?
 
Pilot121 said:
Would I lean on the ground the same way as in the air, i.e. look for peak egt, or does it not matter how much it's leaned?
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On the ground while at 800-1,000 RPM if you lean until you get a slight rise in RPM (30-50 RPM) then you've leaned it enough. If it starts to cough and sputter, you went too far, put the mixture back in a little bit. Be careful if you have it too leaned out, and you want to goose the power to make a tight turn on the ramp or run up area, she might quit on you or stumble...

I was a CSEL addon student, and my instructor taught me that you can lean the IO-360s on the Cessna 172 really far out. So while I was solo, WAYYYY leaned out while taxiing in after arriving at another airport for flight team competition practice, I had to make a tight turn to put it in a corner parking spot on the ramp. I put in a lot of throttle as I started to round the corner, and she coughed and sputtered and then "Boom!" loud bang out the exhaust of unburnt fuel. I threw the mixture in real fast to save it from dying, and at that point everyone from the team on the ramp was just starring and laughing... Good times....:oops:

Leaning on the ground can be a bit of an art for a new student as there are so many new sights and sounds that it is sensory overload, and even just leaning for a slight RPM rise for the taxi can be difficult to perceive. I had many a student unable to perceive it when they were new to the airplane. Ask your instructor about it, and ask him to show you. That may help you out quite a bit.
 
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Pilot121 said:
Would I lean on the ground the same way as in the air, i.e. look for peak egt, or does it not matter how much it's leaned?
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What he said ^^^ with the exception that again, if the carburetor is not correctly set up (more common than it should be) you may not get the rise, in which case it will just start to die. So either just rich of a rise or just rich of starting to die is good for taxi. You won't get any notable EGT reading at those low power settings, things are just too cold.
 
While this procedure is for the IO-360 it works for most engines.
Only thing I would add is to lean aggressively on the ground. You can't hurt the engine. This will act as an "idiot" check on takeoff if you forget to reset the mixture as the engine will cough and sputter. If, however, you only lean a little on the ground, then forget to reset the mixture prior to takeoff, you could cause some damage to the engine.
 

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Pilot121 said:
Would I lean on the ground the same way as in the air, i.e. look for peak egt, or does it not matter how much it's leaned?
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What are you flying? For most trainers all you have to do is bring it back until it stumbles and put it back in just enough to keep the engine running smoothly. Just remember to push it in just a little bit before doing a run up, so you don't choke out the engine.
 
A150K said:
What are you flying? For most trainers all you have to do is bring it back until it stumbles and put it back in just enough to keep the engine running smoothly. Just remember to push it in just a little bit before doing a run up, so you don't choke out the engine.
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A Piper Archer II. That's good to know about not choking the engine.
 
Pilot121 said:
A Piper Archer II. That's good to know about not choking the engine.
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Chocking the engine won't damage it or anything. Basically, if you don't enrichen it slightly, it will stumble when you add power if you had leaned it out properly after start up.
 
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