Staying lean during runup?

Challenged

Challenged

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Challenged
What do most of you do here, in regards to leaning during your run-up? I believe I'm only making about 45% power during during a normal run-up procedure (sea level airport).
 
i stay just rich enough to reach run up RPM
 
Challenged said:
What do most of you do here, in regards to leaning during your run-up? I believe I'm only making about 45% power during during a normal run-up procedure (sea level airport).
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I dont think you'll harm the engine, but the numbers for the mag-drops may be off.
How long is your run-up, no need have it howling for minutes off the end of the runway.
 
I never thought about this and assumed that if you leaned during taxi, you would go full rich for the run up.

What % power is made at run up rpm at sea level? Any risk of damaging detonation?
 
Cessna seems to think you go rich again for the run-up... from the 172SP POH:

After engine start and for all ground operations, set the
throttle to 1200 RPM and lean the mixture for maximum
RPM. After leaning, set the throttle to the appropriate RPM
for ground operations. Leave the mixture at this setting until
beginning the BEFORE TAKEOFF [run-up...my add] checklist. After the
BEFORE TAKEOFF checklist is complete re-lean the
mixture as described above until ready for the TAKEOFF
checklist.
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I enrich the engine, then lean during the run-up to achieve the maximum power setting I'll be using for the takeoff.
 
I stay as lean as I can and keep the engine running. i don't run speed up too much for the "run up" there is no need to have the engine screaming and kicking up rocks. Ground mag checks tell you little, and you don't have to run too fast to get the alternator and vacuum pump into their working range. I also don't haul the props into feather each time. IMO many airplanes suffer more unnecessary abuse during pre-flight than at any time in the air.
 
Are you making your static RPM? Does the engine feel different than normal? At sea level you should be able to go full rich with no adverse affects on power.
 
At sea level, I go full rich on the runup per the POH although I'm otherwise aggressively leaned on the ground. At altitude, I'll lean accordingly.
 
Originally Posted by Mike I
Cessna seems to think you go rich again for the run-up... from the 172SP POH:


N801BH said:
That would NEVER work at airports @ 7000 msl..:no::nonod:
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Which is why we create our own personalized checklists :yes:
 
JHW said:
I stay as lean as I can and keep the engine running. i don't run speed up too much for the "run up" there is no need to have the engine screaming and kicking up rocks. Ground mag checks tell you little, and you don't have to run too fast to get the alternator and vacuum pump into their working range. I also don't haul the props into feather each time. IMO many airplanes suffer more unnecessary abuse during pre-flight than at any time in the air.
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I've discussed this with some engine gurus, and they tell me that if you don't run up to book RPM, you risk not getting a proper check of the drop due to the way the carburetor functions -- you need to get it open to a certain point before the numbers are valid. At lower values, you can certainly find out if all the plugs are firing if you have an engine analyzer, but not how well they are firing, and without that, you may not accurately perceive how the engine is running, especially with a partially fouled plug rather than a dead plug.

Also, if you have a c/s prop, you need to get the RPM high enough to get a good exercise of the prop. At low RPM, the prop may not even be coming off the low pitch stops, and pulling the prop back will have no effect.
 
Ron Levy said:
...but not how well they are firing...
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you don't get that either way. A mag check at at altitude at high power and lean is the only meaningful running check of plugs. On the ground, it's just working or not working.

Ron Levy said:
At low RPM, the prop may not even be coming off the low pitch stops, and pulling the prop back will have no effect.
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Since I'm not pulling back prop controls for every pre-flight I expect to see no effect. Exercising props on the ground is something we as a group do far too much of.
 
Uh huh. At my airport there is a fella who believes that cycling the prop at least ten times is an FAR and then let the engine scream until he has finished his coffee and rearranged his flight bag.. He also seems to have a lot of engine problems with burned valves and cracked cylinders over the years. He says the engine manufacturer requires the oil to be in the green before take off or it voids the warranty. He certainly has needed a lot of warranty repairs.

Anyway, I taxi so lean that the engine will quit when you try to do a run up.
Obviously I have to go rich to do the run up - over with in seconds. And then it is on the runway and full throttle to the blue yonder. So the going back to lean or doing a partially lean runup is not an issue at 600 msl.

On landing it is lean until she stumbles as I taxi.
Been doing it this way for decades and I do not get fouled plugs or burned exhaust valves on my engines.

If the ramp/runway is icy I will do the mag check during the full throttle take off run - I don't watch the tach, just listen/feel for the rpm drop as I cycle the mags. After you have done that a number of times so that you know how it feels when everything is right, the day you find a fouled plug it will grab your attention right now.
At high altitude airports you are unlikely to get detonation doing a run up with the mixture at best power - especially if you keep it quick, 6 or 7 seconds is all it takes.
 
I try to do my runup in the same configuration as I will be taking off, so that is full rich or leaned for power at high altitude airports.
 
Max lean at all times on the ground including run up checks. All knobs in for take off.

I have a low compression 80 octane engine and no carb. I don't like fouled plugs.

YMMV
 
I perform my run-up at 1800 RPM. I do this with the mixture enrichened slightly from the taxi position (otherwise it will run rough at 1800 RPM). A lean mixture is fine at this power setting. From what I understand a leaner mixture will result in a more strict mag check and I'm looking for a drop of around 75 RPM either way. I cycle the prop once unless it seems sluggish on a cold day in which case I will do it twice.

I do my entire run-up as a flow, then pick up the checklist and confirm that I hit all teh items. Once I have done all my pre-takeoff checks and confirmed with the checklist I execute the final item "mixture rich". This is for sea level. Obviously at higher density altitudes I will use the PoH takeoff fuel flow chart.
 
JHW said:
Since I'm not pulling back prop controls for every pre-flight I expect to see no effect. Exercising props on the ground is something we as a group do far too much of.
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Good thing you weren't flying my Cougar the day the prop control disconnected sometime during approach/landing/re-start. Had you been flying it and lost that engine on departure, you'd have been unable to feather it. Fortunately, I follow book procedures, so I found the problem and had it fixed before departing.

There are many good reasons for cycling the prop before departure, starting with getting warm oil up in the hub so the prop will operate properly on departure, to the aforementioned discovery that control of the prop has been lost. You also get a good check of the oil system response so you know whether or not the engine is sufficiently warmed up for flight. Generally speaking, the folks who wrote the POH know what they're talking about, so unless you know a good, demonstrable engineering or aerodynamic reason to deviate from the book, deviation is almost always unwise.
 
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Maybe I missed it but I haven't seen anyone mention how a lean mixture would affect a carb heat check...
 
Ron Levy said:
There are many good reasons for cycling the prop before departure, starting with getting warm oil up in the hub so the prop will operate properly on departure
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yes there are some reasons but that's not one of them
 
timwinters said:
Maybe I missed it but I haven't seen anyone mention how a lean mixture would affect a carb heat check...
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Depends on how lean you are. sometimes i note the rise in RPM with carb heat applied and determine the carb heat is working excellently
 
JHW said:
yes there are some reasons but that's not one of them
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My cold-weather experience says otherwise. You do what you want, but remember that it's contrary to the recommendations of the FAA and the aircraft and engine manufacturers.
 
Anyway, I taxi so lean that the engine will quit when you try to do a run up.
Obviously I have to go rich to do the run up - over with in seconds.
Click to expand...

Generally speaking, the folks who wrote the POH know what they're talking about, so unless you know a good, demonstrable engineering or aerodynamic reason to deviate from the book, deviation is almost always unwise.
Click to expand...

What they said.
 
Hey, find me some 80 octane fuel, and some straight 40wt mineral oil, and I'll follow the POH(Maybe).

Things have changed in 40 years. We've learned things about av engines in that time too.
 
timwinters said:
Maybe I missed it but I haven't seen anyone mention how a lean mixture would affect a carb heat check...
Click to expand...

At my sea-level home airport, I have found that running up with the mixture leaned can make it difficult to see any drop in RPM when carb heat is applied. I suspect it's less of an issue at high altitude airports.
 
Dr. O said:
Uh huh. At my airport there is a fella who believes that cycling the prop at least ten times is an FAR and then let the engine scream until he has finished his coffee and rearranged his flight bag.. He also seems to have a lot of engine problems with burned valves and cracked cylinders over the years. He says the engine manufacturer requires the oil to be in the green before take off or it voids the warranty. He certainly has needed a lot of warranty repairs.

Anyway, I taxi so lean that the engine will quit when you try to do a run up.
Obviously I have to go rich to do the run up - over with in seconds. And then it is on the runway and full throttle to the blue yonder. So the going back to lean or doing a partially lean runup is not an issue at 600 msl.

On landing it is lean until she stumbles as I taxi.
Been doing it this way for decades and I do not get fouled plugs or burned exhaust valves on my engines.

If the ramp/runway is icy I will do the mag check during the full throttle take off run - I don't watch the tach, just listen/feel for the rpm drop as I cycle the mags. After you have done that a number of times so that you know how it feels when everything is right, the day you find a fouled plug it will grab your attention right now.
At high altitude airports you are unlikely to get detonation doing a run up with the mixture at best power - especially if you keep it quick, 6 or 7 seconds is all it takes.
Click to expand...

This is the way it should be done^^^^^^^^^^ Always lean aggressively on taxi so if you forget to enrichen the mixture on T/O your engine will quit or stumble.
I've also talked to some shops that say it's less stress on the engine/prop/hub/etc to cycle your prop at a lower rpm than your mag check. ie; Mag check 1700RPM. Prop 1200 rpm. As long as you have good oil pressure your prop will cycle off the stops and go into high pitch, just not as fast. Of course this is just what I've heard some shops preach. Always follow your flight manual :wink2:
 
Challenged said:
What do most of you do here, in regards to leaning during your run-up? I believe I'm only making about 45% power during during a normal run-up procedure (sea level airport).
Click to expand...

Suggest you look into Mike Busch webinars on the subject. If you like detail and accurate advice these should answer your question:

http://www.eaavideo.org/video.aspx?v=2274677932001

https://www2.gotomeeting.com/register/170496514

I hate to say it BUT you guys are seriously missing the boat not getting into the Experimental world of aviation. We are essentially leading the world in product development, performance improvements and many other areas of general aviation. The jerks in charge will do their best to make things more difficult and frankly I don't see the Experimental world lasting much longer in this over-control atmosphere from DC. But, hey, you never know. Maybe common sense will come back some day - just not holding my breath......:yikes:
 
Goofy said:
Suggest you look into Mike Busch webinars on the subject. If you like detail and accurate advice these should answer your question:

http://www.eaavideo.org/video.aspx?v=2274677932001

https://www2.gotomeeting.com/register/170496514

I hate to say it BUT you guys are seriously missing the boat not getting into the Experimental world of aviation. We are essentially leading the world in product development, performance improvements and many other areas of general aviation. The jerks in charge will do their best to make things more difficult and frankly I don't see the Experimental world lasting much longer in this over-control atmosphere from DC. But, hey, you never know. Maybe common sense will come back some day - just not holding my breath......:yikes:
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Checking them out now, Thanks.

I'm one that was never taught to lean during taxi and runup.
The only instructor to do this was my Tailwheel instructor (he owned the Super Decathlon, so maybe that's why).
 
hkyplr18 said:
I've also talked to some shops that say it's less stress on the engine/prop/hub/etc to cycle your prop at a lower rpm than your mag check. ie; Mag check 1700RPM. Prop 1200 rpm. As long as you have good oil pressure your prop will cycle off the stops and go into high pitch, just not as fast. Of course this is just what I've heard some shops preach. Always follow your flight manual :wink2:
Click to expand...

Another way I was taught to cycle the prop is to briefly run up to 2400, pull back to 2200 and then pull back the throttle for the rpm to drop advance back past where you had it for a couple of seconds. The rpm should go up to 2200, stay there and you should feel how the plane tugs against the brakes. That way you know that not only does the prop cycle, you also know that your governor works. I tried to take off with a governor that didn't govern before, no fun for the engine, and the pilot.
 
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Challenged said:
That's what the EDM830 indicates

Sent from my mobile
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That may not be very accurate. What engine is this and what RPM and MP do you see during runnup? If it's a fixed pitch prop, HP is pretty much proportional to the square of RPM for the same air density. For example if max rated power occurs at 2700 and you runnup at 1700 you'd be at roughly 40% (17/27)^2.

In any case there's no worry about detonation at such a low power and going as lean as it will run smoothly at runnup RPM provides a better indication of any weakness in the ignition and fuel delivery systems. You will see a greater RPM drop than you would with a rich mixture but either way the drop should be similar on either mag.

But since you have an engine monitor, that's what you should use during runnup to validate the engine. The best technique is to set the throttle for the runnup RPM in your POH, lean till it's slightly rough and enrichen enough to smooth it out. Let things settle for 10 seconds or so and then normalize the JPI's EGT display (this isn't necessary but makes it easier to see changes in EGT). Switch to one mag while watching the EGTs and verify that they all go up (typically 20-50°F).

Then switch to the other mag (no need to go back to both if the EGTs all went up) and confirm that the EGTs remain about as high as on the first mag then switch back to both. If a plug is fouled the EGT for that cylinder will drop dramatically when you select it's magneto and it won't rise from what you see on Both when you select the other mag.

It may be necessary to add a tiny bit of throttle after tweaking the mixture to restore your target RPM but IMO you can also skip that step if the change in RPM due to leaning is 100 or less and if you typically see a drop there you can just start with a bit more RPM in the future to simplify things.
 
I hate to say it BUT you guys are seriously missing the boat not getting into the Experimental world of aviation. We are essentially leading the world in product development, performance improvements and many other areas of general aviation.
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I hate to say it, but you experimental guys are also leading the world in accidents. By your own description you guys are test pilots. But unlike professional test pilots you fly your friends and family in your experimental craft.

I'm not brave enough to be a test pilot.
 
JimNtexas said:
...But unlike professional test pilots you fly your friends and family in your experimental craft...
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because a legend cub and a 70-year-old PA11 are oh so radically different:rolleyes: Is it the lack of metal fatigue and multiple accident repairs that makes the e/ab version so much more dangerous in your mind ?
 
JHW said:
because a legend cub and a 70-year-old PA11 are oh so radically different:rolleyes: Is it the lack of metal fatigue and multiple accident repairs that makes the e/ab version so much more dangerous in your mind ?
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In my mind it's primarily the pilots, especially the ones who put much more effort into building airplanes than they do learning to fly them. For the most part I don't believe that structural inadequacies are a significant issue with most E-AB airplanes although I've seen a few I wouldn't dare leave the ground in with things like control surfaces attached with screen door hinges and sheet metal screws. But I have flown some with flying characteristics that clearly demanded a fairly high level of flying skills and it wouldn't surprise me if that was a factor in many E-AB crashes, especially when combined with rusty and/or limited aviation skill sets.
 
Lance, there is also an argument to be made that there are quite a few people incapable of designing a fuel system
 
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