Idling below 1000 RPM

flyingcheesehead

flyingcheesehead

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I was just reading through the Cold Weather Operations section of Lycoming's Key Operations manual, and came across this on Page 50:

After start, do not idle engine below 1000 RPM. It’s not good practice to idle engines below 1000 RPM at any time.
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Wait, what?

Okay, so in a big truck, you avoid idling below about 750 RPM due to low oil pressure. Is this why you shouldn't idle aircraft engines below 1000 RPM? Or is there a different reason?

I also have seen notations in a couple of different POH's that say not to idle at 1000 RPM or greater until a certain oil temperature is reached.

So, which is it? And why?
 
Just a guess..........

Lyc probably wants a 1000+ rpm setting so the thick oil can be slung out and up into the cam lobe faces to lubricate the lifters..... Just a guess.... Altho too much oil pressure will kill oil coolers too.. Apparently the oil pressure relief valve cannot dump excess pressure fast enough...
 
N801BH said:
Just a guess..........

Lyc probably wants a 1000+ rpm setting so the thick oil can be slung out and up into the cam lobe faces to lubricate the lifters..... Just a guess.... Altho too much oil pressure will kill oil coolers too.. Apparently the oil pressure relief valve cannot dump excess pressure fast enough...
Click to expand...

There's probably also something regarding torsional vibrations at the low RPMs. On Lycomings I think they're relatively high at <1,000 RPM operating conditions, so someone probably came up with that recommendation. The engines also just seem to be happier at 1,000 RPMs, whereas Continentals seems to happily lope along at lower idles.

On the oil pressure relief valve, the oil has to get pretty cold for it to be a real concern, and if you've preheated, it isn't one. That said, I remember hearing that on the TIGO-541s they had measured something like 400 PSI at the oil pump outlet on a cold start, so I believe those engines had a separate bypass for cold starts.
 
Ted DuPuis said:
.....something like 400 PSI at the oil pump .
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..



:hairraise::hairraise::hairraise::yikes:.. The oil pump is a positive displacement device so high pressures are not unusual.. But 400 PSI ?? Without a secondary relief valve you can bet more then one oil filter would be launched into outer space..:yes::eek:
 
Is this "guideline" meant just for ground ops like taxiing and stuff or is it also intended for in flight? One of the before take off checklist items on the 172 checklist (Lycoming engine) that I still follow from my training days includes an item specifically to "check idle" before takeoff to verify the engine idles properly. The checklist does not specify any difference in cold weather ops and I gurantee the flight school that developed this checklist is very thorough and would not overlook this not would they want damage done to their planes engines.
 
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I pull it back to check idle then return to 1000 RPM after the run up which happens after the oil is warmed up. Maybe it wouldn't be a problem then.
And what's really considered cold? I'm in Texas and I think 40 is cold.

Btw, it's snowing here....
 
Would not 1000 rpm idle be the rpm at which the propeller generates enough airflow to help the engine not overheat (compared to the "work" the engine has to do at other higher or lower rpm while the plane is stationary)?

I really dont know and am asking - no sure why i thought that was the reason.

Edit: oh nevermind; i see it colder weather ops u quoted (but would not 1000 rpm idle be the value regardless of ambient temp?)
 
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Jeanie said:
I pull it back to check idle then return to 1000 RPM after the run up which happens after the oil is warmed up. Maybe it wouldn't be a problem then.
And what's really considered cold? I'm in Texas and I think 40 is cold.

Btw, it's snowing here....
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Cold = Below freezing.
Really cold= Below zero
Stupid cold= Below -25f
 
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Jeanie said:
I pull it back to check idle then return to 1000 RPM after the run up which happens after the oil is warmed up. Maybe it wouldn't be a problem then.
And what's really considered cold? I'm in Texas and I think 40 is cold.

Btw, it's snowing here....
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Lucky gal..... it was 60 degrees colder here last night.....:)
 
I wonder if it has anything to do with mixture and not fouling the bottom plugs. My O-360 will load the bottom plugs up something fierce, even with very aggressive leaning practices if the engine is idled continually much below 1000rpm.

Is there any logical explanation for this phenomenon Ted?
 
pilot117 said:
I wonder if it has anything to do with mixture and not fouling the bottom plugs. My O-360 will load the bottom plugs up something fierce, even with very aggressive leaning practices if the engine is idled continually much below 1000rpm.

Is there any logical explanation for this phenomenon Ted?
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Yep. :D

Leaded fuel. ;)
 
The Lyc I fly behind doesn't spin the alternators enough to produce enough outputs to relieve the battery until just about 1000 RPM's...
 
Kelvin said:
The Lyc I fly behind doesn't spin the alternators enough to produce enough outputs to relieve the battery until just about 1000 RPM's...
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Thats another - related - reason - you can get the battery to discharge pretty fast with lights on at night and low rpm-
 
Kelvin said:
The Lyc I fly behind doesn't spin the alternators enough to produce enough outputs to relieve the battery until just about 1000 RPM's...
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Certainly a consideration... I like to have taxi lights and rotating beacon on at a minimum when taxiing, and that plus avionics certainly draws more than the alternator is putting out at idle. However, I generally don't have to taxi for very long and the batteries go right onto battery minders as soon as I put the plane in the hangar, so I'm not worried about a slight discharge for a few minutes.

However, the Mooney doesn't like to begin taxiing, and it also doesn't like to stop. I'll set it to 1000-1200 RPM to get it going, and it takes a dozen seconds or so to get to a normal taxiing speed, but then if I don't reduce it to idle, that IO-550 is still pushing enough air to just keep accelerating. Landing, I go to idle prior to the flare and I stay at idle all the way to my hangar. However, as expensive as brakes are, they're cheaper than engines!

Does anyone know if Continental has any sort of similar instructions available online? Would there be a difference between the Lyc vs. Conti when at idle?
 
I don't let my E series idle below 1000 because of the idle-misfire. It sounds cool, but it loads up the plugs. I always idle around 1000 as lean as I possibly can. Richen only for take off and climb.
 
N801BH said:
:hairraise::hairraise::hairraise::yikes:.. The oil pump is a positive displacement device so high pressures are not unusual.. But 400 PSI ?? Without a secondary relief valve you can bet more then one oil filter would be launched into outer space..:yes::eek:
Click to expand...

I think that was only for the TIGO-541, which probably has a bigger pump than the normal engines. But yeah, it's a lot!
 
flyingcheesehead said:
Certainly a consideration... I like to have taxi lights and rotating beacon on at a minimum when taxiing, and that plus avionics certainly draws more than the alternator is putting out at idle.
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You need to get that alternator checked.
 
In my experience the big Continentals idle great.

Big Lycomings do not like to idle below 1000 RPM. I never looked at it as right or wrong, it's just what they want. If conditions are just right you can get them to run slower maybe 800, but not when they're cold or hot.

I've never understood some of the checklist items. Full rich, check idle, is bound to generate some four letter words from those that actually follow this routine.
 
flyingron said:
You need to get that alternator checked.
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Meh... I don't think so. Multiple big taxi lights plus a full stack, and it's not like it's drastically discharging... And it keeps up fine, charging by 800-900 RPM. It doesn't behave differently from any other airplane I've flown.
 
flyingcheesehead said:
Meh... I don't think so. Multiple big taxi lights plus a full stack, and it's not like it's drastically discharging... And it keeps up fine, charging by 800-900 RPM. It doesn't behave differently from any other airplane I've flown.
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Pretty normal.
 
LED landing/taxi lights help the ground electrical load.
 
Ted DuPuis said:
LED landing/taxi lights help the ground electrical load.
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Yep - And were the plane mine, I'd add 'em as soon as the bulbs went out. We put LED taxi and landing lights on the 182 and Archer a few months ago. BIG improvement in brightness, less power draw, and they last a helluva lot longer than 15-20 hours apiece. Good riddance, GE 4509's!

The Mooney has four lights, haven't had one burn out yet.
 
On the 310, the biggest improvement was on the taxi light. The incandescent version was so dim it provided no illumination whatsoever. The Whelen version is the same as the landing light, just a 40 degree diffuser instead of 10 degree.

I'm very happy with the night landing package now!
 
From the POH of a 1980 C152:

Code: 
NOTE  
Illumination of the low-voltage light and ammeter discharge indications may 
occur during low RPM conditions with an electrical load on the system, such  
as during a low RPM taxi.  Under these conditions, the light will go out at 
higher RPM.  The master switch need not be recycled since an over-voltage   
condition has not occurred to de-activate the alternator system.
 
Lycoming could care less about your electrical load, They care about engine things like vibrations created at Idle.
 
Lycomings idle just fine at the specs from their manuals, which call for 650 to 750 RPM. Idling at 1000 when cold is to make sure that thick oil gets onto the cam lobes and cylinder walls.

Idling at 1000 all the time is just a recipe for burning out brakes. You'd have to ride them the whole time while taxiing.

Dan
 
I read an article recently that explained that at idle less than 1000, the plugs don't get hot enough to burn off the sediments and you wind up with fouled plugs
 
Higher RPM is required on the ground to maintain the aircraft battery and prevent discharge. This rpm is called the critical rpm. My light for the alternator will come on below 1300rpm which for most aircraft I would assume to be about 1,000 rpm minimum. It is not all about engine as the above comments suggest.
 
Richard Stefanick said:
Higher RPM is required on the ground to maintain the aircraft battery and prevent discharge. This rpm is called the critical rpm. My light for the alternator will come on below 1300rpm which for most aircraft I would assume to be about 1,000 rpm minimum. It is not all about engine as the above comments suggest.
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You joined 2 years ago and your only post is on a thread from 5 years ago?
 
Come to think of it, in carbed 172s (and the 150 I just got checked out in) the runup checks carb heat by a slight decrease in rpm, then check engine idle with no carb heat. Seems to be more prudent to leave the carb heat on then check idle. Ideas on that?
 
woodchucker said:
Come to think of it, in carbed 172s (and the 150 I just got checked out in) the runup checks carb heat by a slight decrease in rpm, then check engine idle with no carb heat. Seems to be more prudent to leave the carb heat on then check idle. Ideas on that?
Click to expand...
That’s how I was taught to do it
 
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