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What's your idle RPM?

V

Vlad

Well Known Member
Interested in ###. After 314 hours on factory new O-320 the idle became 350 rpm. It seemed kind of low to me and I turned the screw in about half turn. Now it's high. What are yours on idle? Explain why if you will.
 
My engine will quit at 350 rpm. I believe mine came at 600 rpm (my memory is not that good, so don't quote me). I set mine at 500 rpm so at idle the engine will continue to run. Higher rpm makes fixed pitch RV 9 floats down the runway.
 
Walt said:
I like to see around 600-650 when hot.
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Is it better for the engine to have it at a particular RPM? Just curious, b/c Mike Seager suggested to me that, for the RV-9, I get the rpm down as low as possible to reduce float. 500s or lower is what I seem to remember him recommending.
 
Anything less than around 600 and most engines start to run rough, you also risk the engine quiting at an inopportune time if the RPM gets to low, most folks don't like that.
 
Walt said:
Anything less than around 600 and most engines start to run rough, you also risk the engine quiting at an inopportune time if the RPM gets to low, most folks don't like that.
Click to expand...
So it's primarily determined by engine smoothness? And when should the rpm be set? When the engine is cold or warm?

Also, is it true that engines with heavier props will generally idle smoothly at a lower rpm than engines with light props? Again, just curious. Just wondering what to expect with my Catto prop.
 
So it's primarily determined by engine smoothness? YES

And when should the rpm be set? When the engine is cold or warm? WARM

Also, is it true that engines with heavier props will generally idle smoothly at a lower rpm than engines with light props? YES

Again, just curious. Just wondering what to expect with my Catto prop.
 
My idle stop is set to 525. 650 makes it float on landing too much. I never idle at 525 but that is where the stop is set..

I generally idle around 850 to 1000. That heavy metal fixed pitch will idle low.
 
Before the single pmag install, I idled at 700rpm. It would go lower but run rough.
After the pmag install I reset the idle to 450rpm. It can go lower, but again it will run rough.
I will install the second pmag soon and see what happens.
I have a metal prop.
 
I did the two Slicks, one and one, and two P-Mag routine. I went from 650 and close to smooth to 390 and smooth as can be. That is with a three blade Catto. Having variable timing is amazing! I have no idea what the exact firing angle is at low idle, but it is no where near the 25* fixed with a Slick. Maybe 10 or 15*? IMHO it is the closest thing to a CS-style landing you will get with a Catto.

Bob
 
850 RPM

Mine is idling at about 850 RPM, anyting lower will make it run rough. There is probably two causes for this: Low weight Whirlwind propeller and the fuel devider that will have troubles in supplying fuel evenly to all four cyilinders at such a low fuel flow (fuel injected). But, due to the CS-prop, "floating" was never a problem. Maybe others can land shorter/stop quicker. I gues I need about 250-300 m (750-900 ft) to touch down and stop comfortably without having to "step on the brakes".

Regards, Tonny.
 
Vlad, did it "become" 350 suddenly??

If so, you might need to look around and see if something is loose or fouled. Getting too much air,.. not getting spark,... etc.

Unless you know the idle setting moved,...
 
During the first 8 flights, my hot idle (after landing and while taxiing in) is consistently about 700-750 with my Catto prop. Given many admonitions to get the idle speed as low as possible to mitigate the RV-9 float, I should probably begin adjusting it down a bit. Approximately how many turns should I expect to have to turn the idle adjustment spring/screw to get the idle speed down? I was thinking that I'd try to reduce it about 50 rpm at a time but would like to make a good guess at how much of a turn would be required on the screw to get that. Thanks.
 
OTOH

Well, here I go sticking my neck out again! :eek: I sure do hate disagreeing with Walt, who provides a vast amount of great accurate information on this forum.

BUT....... If you have a fixed pitch prop, I think you should set your idle as low as you possibly can, down into the 450 range.

Here's my rationale: On the ground, taxiing around, you don't have to close the throttle unless you want to. You can idle at 700, or 800 if you wish. But in flight, just because you close the throttle, it doesn't mean you will idle at 450. The forward airspeed will speed the prop up. You will float a lot less with a low idle speed set. Then, at the end of your rollout, you just open the throttle a bit, and idle at your desired RPM.

Perhaps a carbureted engine will idle happily at a lower RPM than an injected one.

YMMV, and I'm sure it will! :)

Walt said:
Anything less than around 600 and most engines start to run rough, you also risk the engine quiting at an inopportune time if the RPM gets to low, most folks don't like that.
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PCHunt said:
Here's my rationale: On the ground, taxiing around, you don't have to close the throttle unless you want to. You can idle at 700, or 800 if you wish. But in flight, just because you close the throttle, it doesn't mean you will idle at 450. The forward airspeed will speed the prop up. You will float a lot less with a low idle speed set. Then, at the end of your rollout, you just open the throttle a bit, and idle at your desired RPM.

:)
Click to expand...

That has been exactly my experience.
 
Last edited:
Lycoming Key Flyer Operations

http://www.lycoming.com/support/tips-advice/key-reprints/pdfs/Key%20Operations.pdf

By the recommendations of Lycoming, see link above, you should not let the engine idle below 1,000 RPM after start. I have heard that this also helps in avoiding premature lifter wear and since I'm running an H2AD engine I have tried to follow this recommendation. I have a wood prop and my actual low idle setting is approx 700 RPM, but I try not to let it idle there very often.

I know that this idle speed may be controversial, it is just what I try to follow based on Lycoming recommendations.

I know a another concern with this practice will be excessive brake wear, but I have close to 200 hours on my plane with the original brake pads, which still have plenty of wear left in them based on my inspection 2 months ago.
 
Having variable timing is amazing! I have no idea what the exact firing angle is at low idle, but it is no where near the 25* fixed with a Slick. Maybe 10 or 15*? IMHO it is the closest thing to a CS-style landing you will get with a Catto.

Bob[/QUOTE]

Bob actually at idle you have very low manifold pressure, ergo you get max ign timing (advance). Seems counter intuitive but that's how it works. At high MP it will retard back to base timing, probably 25, then as you climb and or reduce throttle it will beging to advance.
This is one of the (false) reasons why people are so impressed with EI. They are great, but the smooth idle comes primarily from the ign timing, not the more powerful spark. If you were able to set a pair of slicks at 35-40 you probably would not be able to tell the difference at idle.
Tim
 
tim2542 said:
Bob actually at idle you have very low manifold pressure, ergo you get max ign timing (advance). Seems counter intuitive but that's how it works. At high MP it will retard back to base timing, probably 25, then as you climb and or reduce throttle it will beging to advance.
This is one of the (false) reasons why people are so impressed with EI. They are great, but the smooth idle comes primarily from the ign timing, not the more powerful spark. If you were able to set a pair of slicks at 35-40 you probably would not be able to tell the difference at idle.
Tim
Click to expand...

It depends on the system. Most aircraft systems use an RPM based curve and then just use manifold pressure to supplement that. So at low idle the advance may not be above 25. It's 18 on my aircraft at low idle.
 
My RV6 with a O-360/Hartzell/Electroair/Bendix Mag would idle at 550 RPM and sounded and felt like clockwork. Really smooth. The RV6 I fly now with a O-360/Blended Airfoil Hartzell/Slicks doesn't idle smoothly below 700 RPM and is a bit more difficult to slow down in the pattern.
 
Vlad said:
Interested in ###. After 314 hours on factory new O-320 the idle became 350 rpm. It seemed kind of low to me and I turned the screw in about half turn. Now it's high. What are yours on idle? Explain why if you will.
Click to expand...
Vlad:

The O-320 should have the idle set at 550 to 650 RPM as per Lycoming. I doubt it the engine will run at 350 RPM. If it is running there check your Tach. There is a slight difference in idle between planes due to airflow. BUT! not as much as what you are seeing.
Barry
 
:)
thinkn9a said:
If so, you might need to look around and see if something is loose or fouled. Getting too much air,.. not getting spark,... etc.

Unless you know the idle setting moved,...
Click to expand...


Yes, Wallace the spark plugs probably contributed I had heavy lead deposits on bottom ones.

Barry_Barry said:
Vlad:

The O-320 should have the idle set at 550 to 650 RPM as per Lycoming. I doubt it the engine will run at 350 RPM. If it is running there check your Tach. There is a slight difference in idle between planes due to airflow. BUT! not as much as what you are seeing.
Barry
Click to expand...


Barry my tach is a cable driven certified product and doesn't show that small ## I borrowed a portable tach from FBO to check.


Now I am idling at about 500 and I am happy.

Below is not idle :)


rpm.jpg
 
curtis said:
http://www.lycoming.com/support/tips-advice/key-reprints/pdfs/Key%20Operations.pdf

By the recommendations of Lycoming, see link above, you should not let the engine idle below 1,000 RPM after start. I have heard that this also helps in avoiding premature lifter wear and since I'm running an H2AD engine I have tried to follow this recommendation. I have a wood prop and my actual low idle setting is approx 700 RPM, but I try not to let it idle there very often.

I know that this idle speed may be controversial, it is just what I try to follow based on Lycoming recommendations.

I know a another concern with this practice will be excessive brake wear, but I have close to 200 hours on my plane with the original brake pads, which still have plenty of wear left in them based on my inspection 2 months ago.
Click to expand...

The link actually says to keep the idle speed correctly adjusted at 600 to 650 rpm.

It says don't operate under 1000 rpm, not set the idle speed to the high number....
 
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