Low idling?

[Strega]

So I just got back from the airport, and noticed something that I need to mention....

Why must instructors/students idle their 172s soooo low that you can hear the impulse coupler snapping away? of all the ways to wear this device out, running the engine with it snapping away has got to be number one!

[Handski]

Among other things... to test the engine at its lowest power setting and make sure it won't quit. Realistically in flight, you'll never reach a power setting as low as you can on the ground (with airflow), but I think its for peace of mind for the pilot as much as anything.

Also, when the newer 172's first came out, there was a rubber stop on the throttle at the lowest power setting. It was flexible though. If a pilot were to pull the power all the way back, and continue to pull (as students tend to do when they're scared), they COULD actually choke off the fuel and shut 'er down. It has since been replaced with a hard plastic stop.

I'd need an AME to back me up on that one, but I've heard that from a mechanic myself a few years ago so I hope I've got my facts straight.

[yzfer]

I always try to idle at 1000rpm. check engine idle just prior to take off on the run up, but then back to 1000. even just before shutdown, the short period of time between when i've stopped and pulled the mixture to ico, bring er up to 1000 when checking the few things you need to.

[cgzro]

If you are going to do stalls or spins I'd strongly suggest u do a minimum idle speed test. I have had engine stoppages in spins. Other aerobatics are even worse such as tail slides which have actually stopped an engine and started it backwards.

So it's not black and white!

[Ballsssssss]

Among other things... to test the engine at its lowest power setting and make sure it won't quit. Realistically in flight, you'll never reach a power setting as low as you can on the ground (with airflow), but I think its for peace of mind for the pilot as much as anything.

Also, when the newer 172's first came out, there was a rubber stop on the throttle at the lowest power setting. It was flexible though. If a pilot were to pull the power all the way back, and continue to pull (as students tend to do when they're scared), they COULD actually choke off the fuel and shut 'er down. It has since been replaced with a hard plastic stop.

I'd need an AME to back me up on that one, but I've heard that from a mechanic myself a few years ago so I hope I've got my facts straight.

The idle speed is set at an adjustable hard stop on the carb/throttle body. You can pull the throttle back as hard as you want and will break the lever before you move that idle adjusting screw.

Running at low idle is a good way to foul your plugs.

[GoinNowhereFast]

500-600rpm a good "limit"? If it goes too low, oil pressure drops off too far as well. If I don't own the airplane, I will operate it they way the owner/operator wants me to fly it.

[CP]

I used to bring in the otter ( on floats) to the dock on 1 mag to parallel park against the current in YTH. Could letterally go sideways to the dock. If I recall correctly the rpm was tickling 200. A cooler sound I have never heard.

[mcrit]

Was this on the taxi or not moving? If it was on the taxi I'd say they kept the idle low so as to keep a decent taxi speed without riding the breaks. If it was while they were sitting still, then yeah, bring it up to 1000.

[torquey401]

If the impulse couplings are snapping while idling, there is a problem. Maybe the idle is set too low and/or maybe the mags have issues. Most small Lycoming and Continentals should idle around 600 RPM with the idle mixture set correctly. Start-up and warm-up should be done at 1000 RPM or so. Some engines have bigger issues with plug fouling, so the RPM used by the operator will be at his discretion. Just my .02.

[scm]

The navajo engine manual recommends between 1000-1200 idle RPM to keep the plugs clean and prevent buildup in the oil due to low combustion temps. That, and it saves the battery.