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Quick Question For Cessna 172 Pilots/Students  
User currently offlineFSPilot747 From United States of America, joined Oct 1999, 3599 posts, RR: 12
Posted (11 years 6 months 3 weeks 6 days ago) and read 12751 times:

I should know this, but I haven't been in this situation in a couple years.

What exactly do you do when your RPM drop exceeds 50 RPM during the run-up magneto check (in regards with cleaning up the spark plugs)? I would ask one of the instructors at the airport, but I'm not gonna be there for a while. I have an idea of what to do, but I want to be certain before I end up in that situation.

Thanks,
FSP

7 replies: All unread, jump to last
 
User currently offlineFlyingbronco05 From United States of America, joined May 2002, 3840 posts, RR: 2
Reply 1, posted (11 years 6 months 3 weeks 6 days ago) and read 12731 times:

I was taught to have the engine at 1700 RPM and check the magnetos. They shouldnt go below 1500, i think. It's been a while since I have actually flown in a 172.

FB05



Never Trust Your Fuel Gauge
User currently offlineFlyingbronco05 From United States of America, joined May 2002, 3840 posts, RR: 2
Reply 2, posted (11 years 6 months 3 weeks 6 days ago) and read 12727 times:

b. Magnetos -- CHECK (RPM drop should not exceed 125 RPM on either
magneto or 50 RPM differential between magnetos)

If you get below 50RPM i would NOT take the plane off.

FB05

http://pages.prodigy.net/jedinein/c172sop.html



Never Trust Your Fuel Gauge
User currently offlineFlyf15 From , joined Dec 1969, posts, RR:
Reply 3, posted (11 years 6 months 3 weeks 5 days 22 hours ago) and read 12685 times:

What you're refering to is fouled plugs. I've had it happen to me a few times. The engine will be running fine, upon mag check, when going to left or right the engine will drop oh say, 300rpms, and get pretty rough. To take care of it (burn it off), run the engine up to full power and lean out the mixture and maintain that for a minute or two. Go back and do another mag check. If everything goes as it should, you'll be good to go. If its still running rough (I'm just guessing here, it hasn't ever continued to be rough for me), I suppose you could try to burn it off again, but its most likely something else.

User currently offlineSllevin From United States of America, joined Jan 2002, 3376 posts, RR: 6
Reply 4, posted (11 years 6 months 3 weeks 5 days 21 hours ago) and read 12667 times:

I agree with with Flyf15, with the exception of running the engine at full power. You'll generate extra propeller wear, and at high power settings running lean can lead to detonation (unless you are SURE you are significantly lean of peak).

At 1700rpm, detonation from running close to peak is very limited, and you aren't spinning the tips nearly as fast near the ground. Expect to run the engine for about 2 minutes to clear the fouling. Beyond that, if it hasn't cleared up, you may have some additional issue.

Steve


User currently offlineRadarbeam From Canada, joined Mar 2002, 1310 posts, RR: 4
Reply 5, posted (11 years 6 months 3 weeks 5 days 20 hours ago) and read 12644 times:

The way I do it is

Step on the brakes
Set mags on both
Set power to 2,300 rpm
Lean mixture to lean until rpm drops
leave it about one minute or two
If it's still rough taxi back, shut down and get in another plane

Radarbeam


User currently offlineFSPilot747 From United States of America, joined Oct 1999, 3599 posts, RR: 12
Reply 6, posted (11 years 6 months 3 weeks 5 days 20 hours ago) and read 12631 times:

So basically, instead of having your mixture full rich, just lean it out as far as you would over 3000 ft? ..or more than that? Then full power? I remember now the full power and mixture lean, just didn't remember how much.

Thanks,
FSP


User currently offlineLymanm From Canada, joined Jan 2001, 1138 posts, RR: 1
Reply 7, posted (11 years 6 months 3 weeks 5 days 19 hours ago) and read 12610 times:

Not full power, 2000RPMs. Then lean. It's all in your handy POH!


buhh bye
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