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What's your idle speed?

bjdecker

Well Known Member
Ambassador
Folks,

I believe my idle speed is set to high for ground operations at my local airport. Closing the throttle completely, when warm, yields 780 RPM & oil pressure in the 55 PSI range.

At this setting, I find that I'm touching the brakes a bit more than I would like.

op manuals for reference:

https://www.lycoming.com/sites/default/files/O-HO-IO-HIO-AIO & TIO-360 Oper Manual 60297-12.pdf

https://www.lycoming.com/sites/default/files/(L)IO-360-M1A Oper & Install Manual 60297-36.pdf

I've reviewed/searched every page of the Lycoming Operators Manual for the O-360, HO-360, IO-360, AIO-360, HIO-360 & TIO-360 Series engine, and can find no mention of a recommended Idle RPM --- only behaviors and how to set.

So, for the hive mind, what's your Idle RPM?

Cheers!

Brian
 
Just looked at my last flight - during rollout my idle speed is about 600-650 RPM, and idling just before shutting down, about 720-740 RPM. I can taxi with the engine just idling, depending on wind direction and slope. I don't need to ride the brakes to keep from going too fast, but I keep my toes on them just in case.
 
O-360 I have it set at 650 when warmed up. I lean for ground ops and get it to rise to 710. That’s almost perfect for me.
 
My opinion is that you should set it low. Like 550 or 600. You can always bump it up with the throttle for normal operations, but a low idle speed will help your landing distances and will give you options for managing brake wear.
 
One really needs to consider the prop first. Is it constant speed or not?

I have a constant prop and low rpm is about 790. No issues in any way shape or form with float/slowing down etc. Have heard many others with a fixed prop needing to get it quite a bit lower though.
 
One really needs to consider the prop first. Is it constant speed or not?

I have a constant prop and low rpm is about 790. No issues in any way shape or form with float/slowing down etc. Have heard many others with a fixed prop needing to get it quite a bit lower though.

Fair point -- I have Constant Speed, Hartzell F7497-2 (72, Blended Airfoil).

Also worth mentioning, the aircraft is an RV-7 taildragger.
 
IO-360-M1B + Harzell CS prop. I'm in the very beginning of Phase 1 and have mine set at 750. I found that setting it less than that causes the engine (on the ground) to run very rough and stumble. 750 was about the lowest I could keep it running smoothly.
 
I have my idle set to a point where the engine won't quit on the ground - somewhere around 6-700 RPM. I try and hold rpm about 1000 RPM during normal ground op as I have read this provide better engine lubrication. Lycoming Manual states 1000-1200 for warmup. I use a bit more brakes but can always back down a bit momentarily when approaching an intersection. I taxi slow.
 
Mags or EI

It also matters whether you have Mags or electronic ignition. It seems with dual mags the typical Lycoming doesn't seem very happy under 650 rpm. With my Lightspeed + Mag combo, I can idle slower than that easily.

And for short field ops on fixed pitch, you want set slower. Just went through this discussion with a newbie who wasn't comfortable because idle was under 750. That's fine if you don't want to land on short fields...
 
It also matters whether you have Mags or electronic ignition. It seems with dual mags the typical Lycoming doesn't seem very happy under 650 rpm. With my Lightspeed + Mag combo, I can idle slower than that easily.

And for short field ops on fixed pitch, you want set slower. Just went through this discussion with a newbie who wasn't comfortable because idle was under 750. That's fine if you don't want to land on short fields...

Another good catch...

I am running dual Lightspeed Plasma III's -- minimum advance is 20°. Typically at idle the advance will be @ 35°BTDC
 
My Setup

RV-6, O-320, Lightspeed and Slick, Catto monster light balsa fixed pitch. Unless I have reason to do otherwise, I’ve always set idle speeds to the slowest the engine will run smoothly on any piston engine whether it’s an airplane, model airplane, lawn mower, car or whatever, when warmed up. I look for about a 25 RPM rise when smoothly pulling the mixture to idle cutoff. As my second A&P mentor said while waggling a finger, “Never adjust a carburetor on a cold engine.” Same for fuel injection, of course. Anyway, that works out to about 650 RPM on our airplane. It might even idle a bit slower if it had a heavy metal prop or a constant speed. With two magnetos it would likely need to be about 750 or so. In fact, if our engine is on the idle throttle stop, it won’t quite run on just the magneto. Even at that, we need a stab of brake now and then when taxiing downwind at idle.
 
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Prop/EI definitely makes a difference. For fixed pitch I’ld rather have my idle speed slightly too low………..static idle will be rough but with the air pushing the prop on final it picks up 100+ RPM.
I’ve got dual EI and a Catto, static idle is 480-500. About the time I’m slowing to taxi speed on the landing rollout the RPM’s are slowing down and I add just a kiss of throttle to keep it about 600 RPM. Really helps with short field and taxiing.
 
Old RV-6 with O-320 160HP and Sterba wood prop, 80 pitch, with Landoll balance ring. When I bought the airplane, first landing demonstrated the prop was still producing thrust at idle in the flare...
First thing I did when I got home with it was to turn the idle down from 800 RPM, to 550.
 
I have my idle set to a point where the engine won't quit on the ground - somewhere around 6-700 RPM. I try and hold rpm about 1000 RPM during normal ground op as I have read this provide better engine lubrication. Lycoming Manual states 1000-1200 for warmup. I use a bit more brakes but can always back down a bit momentarily when approaching an intersection. I taxi slow.

Agreed, I leave mine at 1000 rpm’s min. Replace brakes every two years. No problem in and out of a 1,500’ strip
 
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My 7A with a 390A, dual P-Mags, and a composite Hartzell is around 500-550 when warmed up. As others have said, I wanted it as low as possible and just high enough to keep running. I always lean for ground op's and can always add just a bit of throttle if necessary.
 
Another good catch...

I am running dual Lightspeed Plasma III's -- minimum advance is 20°. Typically at idle the advance will be @ 35°BTDC

35º BTDC at idle? I'm hoping that's a typo.

I would suggest it should be set more like 5-10º for easier starting, and then the much higher advances for higher RPM at altitude, such as 35º to 38º BTDC at 2500RPM at 10,000'.

My opinion is that you should set it low. Like 550 or 600. You can always bump it up with the throttle for normal operations, but a low idle speed will help your landing distances and will give you options for managing brake wear.

Well said Kyle. I agree with this.

For the majority of our engines which use a "pressure to increase pitch" governor setup, constant speed propellers are at the low speed stop (fine pitch) setting generally below 800-1000 rpm, which is why you need to run a governed engine up to around 1500 RPM to achieve sufficient governor pressure to test cycle the propeller. Whether constant or fixed pitch, the lower the RPM, the less thrust the engine provides.

600-650 rpm is a good low idle stop speed for a Lycoming or Continental engine and is a common setpoint for certified aircraft, which provides minimum oil pressure at idle, while also providing minimal thrust during descents and on landing (minimal thrust is discussed in the Safety Information section of most aircraft AFM's, e.g. my 1975 Beech AFM has this). Whether EI or magnetos, a properly set ignition having clean spark plugs will provide normal engine idle at 600 RPM.

For ground operations, the idle rpm you use should be driven more by your electrical charging system. Most alternators provide good voltage by 1000 rpm, whereas generators might need 1200rpm, but that should set by a throttle setting - not idle stop adjustment.
 
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35º BTDC at idle? I'm hoping that's a typo.

I would suggest it should be set more like 5-10º for easier starting, and then the much higher advances for higher RPM at altitude, such as 35º to 38º BTDC at 2500RPM at 10,000'.

The EI systems are smart enough to retard ignition at cranking speeds.
 
Not an RV, but I fly a bunch of fuel injected 172s, and they all have the idle set around 650ish. That's holding the throttle aft with a little bit of tension. If you let go, cable slop causes them to creep up a little bit. Say approximately 700. or so. It's low enough that the alternator goes off line if you pull it all the way back and hold it there.

These are new 172s. 1 slick mag and one electronic mag.
 
35º BTDC at idle? I'm hoping that's a typo.

I would suggest it should be set more like 5-10º for easier starting, and then the much higher advances for higher RPM at altitude, such as 35º to 38º BTDC at 2500RPM at 10,000'.


.

I run my 320 with 35* at idle. At cranking RPMs it is 0 and above 1000 drops back to 23 then ramps with RPM. I have fuel heating issues due to injecting via the primer ports and this extra advance helps. Absolutely nothing wrong with using this much advance at idle as high vacuum conditions like a lot of advance. Many of the early auto EFI systems used extra advance at idle to increase RPM to deal with heavy draw accessories like AC and high elec loads.
 
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