Taxi leaning in a C172

[ACARS]

Hello

Studying for my ground school - My instructors (I had about 4 different FI) have never taught me to lean during a taxi (airfield is below 3000').

I bought a new checklist - it suggests leaning for taxi.

What do you teach and why?

[nick14]

Flying out of EMA in a PA28,

I will always lean the mixture prior to taxi. Only a slight amount mind but enough to stop the plugs fowling as the wait can often be 5 mins and at low power the plugs often 'soot up' so to speak. The last thing you want is to be at the hold having to burn off the carbon or worse get caught out by it.

My advise would be to ask your instructors, they will all give you a roundabout setting for taxi leaning, most important thing is not to forget before your power checks and before you enter the runway, then again it is in the checklist.

Nick

[julian_storey]

I bought a new checklist - it suggests leaning for taxi.

Check what the POH says :ok:

[Oktas8]

enough to stop the plugs fowling

Would that be after a birdstrike?

(Sorry, couldn't resist. :E)

More seriously: yes, read the flight manual. Specifically read the second half of Section 4 dealing with expanded normal procedures.

I've found the "below 3000' " idea has little relevance to modern aeroplanes. I don't think it's mentioned in flight manuals - perhaps it is worth leaning as per the flight manual instead.

Cheers,
O8

[modelman]

Taxi leaning in a C172


You will find it much more comfortable taxying whilst sitting upright.:p

I'll get me coat....

[OneIn60rule]

Keep it lean.

Sometimes though if it's TOO hot you'll want it slightly rich.

If you want to lean it just do the same process you'd normally do in the air. Wind back until the r'vs drop and then go up slightly.


Can't the instructors tell you?

1/60

[Islander2]

I will always lean the mixture prior to taxi. Only a slight amount mind but enough to stop the plugs fowling as the wait can often be 5 mins and at low power the plugs often 'soot up' so to speak.Sorry, nick14, but the part of your quote I've emboldened is incredibly bad practice.

We're all human, and it is therefore only a matter of time before you take off without the mixture full rich (this is not a discussion about high density altitude take-offs, so let's assume we're talking typical UK airfield). There lay detonation dragons. It might not do too much damage to a 150HP Lycoming or Continental (although you definitely don't want to try it), but it could be a very expensive mistake to make when you transition to larger-engined aeroplanes, especially turbocharged ones.

Most agree these days that engines should be leaned for taxi, but the accepted wisdom is to lean them very heavily such that they will falter and be unable to achieve high power as you advance the throttle fully when (and it is when, not if!) you try to take off having forgotten to readjust the mixture setting.

[Lurking123]

Do what the book says. I also agree with the last post - aggressive leaning on the ground. OK, you may one day embarrass yourself when trying to select full power but at least you fail safe.

[nick14]

I take your point and I will bear it in mind for the future.

It is a noticable position for the mixture knob to be in and I always richen before applying power for the power checks. If I forget then it is caught by the pre takeoffs, that is after all the reason we have checklists.

I under stand it is easy to miss checks or forget things and I will be more vigillent in future.

Thanks
Nick

[Islander2]

I always richen before applying power for the power checksNick14, you'll think I'm getting at you, I know, but that's another practice you'll come to change in time. A power check with weak mixture is much more likely to show up ignition system defects than one undertaken fully rich. And at typical power check power setting, the mixture control can be in any position without fear of damaging the engine.

[bookworm]

And at typical power check power setting, the mixture control can be in any position without fear of damaging the engine.

I'm not sure my engine got that memo. ;)

So how do you set mixture for (i.e. in advance of) the power check? If I try to go to reference power with the mixture as I have it for taxying, the noise is less than sweet!

[Islander2]

Ah, that'll be that crummy induction system on the Lycoming, not a problem on my Continental. ;)

Seriously, though, if you mean it runs rough I imagine it is down to the fuel/air ratio spread between the cylinders. I'd just richen it up for the power check to the point where it no longer runs rough. Odd if you have GAMIjectors, however, which I thought you did.

[bookworm]

Odd if you have GAMIjectors, however, which I thought you did.

No, factory Lycoming IO-320s, which in our case are fairly well balanced, but not as well balanced as you'd get with GAMIs I guess.

[nick14]

No not at all,

It nice to recieve impartial advice on this forum. Its more than I get from the school anyway.

I will certainly try it next time I fly.

With such a weak mixture is there any risk of detonation at 2000 RPM on a O-320? Its a fairly old aircraft (most PA's are). I guess its the fear of damagin an engine that keeps most students/low hours guys from messing around, something to learn with experience I guess.


Cheers

Nick

[Oktas8]

I guess its the fear of damagin an engine that keeps most students/low hours guys from messing around

Like me! Contrary to the advice offered above, I recommend leaning in accordance with the flight manual. If the flight manual says to lean for run-ups, great! I suspect it doesn't... (Note - this is advice for inexperienced pilots flying other people's aeroplanes. If you're flying your own aircraft, I wouldn't presume to tell you how to operate it!)

But I'm certainly in favour of leaning for taxi in accordance with the flight manual. For reasons stated above, if you're going to do it, do it aggressively.

[Islander2]

Like me! Contrary to the advice offered above, I recommend leaning in accordance with the flight manualI would have thought that leaning in accordance with the engine manufacturer's recommendations is an acceptable alternative ... and Lycoming publish documents where they say their normally-aspirated engines can be leaned to any mixture you like as long as the power is below 75%. Note of warning however, the same people that advise power checking with lean mixture will also advise you that 75% is nothing like a sufficiently conservative power setting to make that statement!

With such a weak mixture is there any risk of detonation at 2000 RPM on a O-320?Well, check the POH to see what power that gives. Is it less than 60% (I expect it will be around 50%)? If so, it is well within Lycoming's 75% criterion and there is not the slightest prospect of inducing even light detonation.

[ACARS]

Check what the POH says

I checked the POH that my flight school gave me and there is no mention of it.

The "well known brand" checklist I bought suggests it. As I am low hour student, I don't like the idea of forgetting to put it back to RICH before take off roll. Even with checklists we can still miss items.

I will listen to my instructors - they have never mentioned it - next time I am up I will ask them.

[markkal]

Hi guys,
Check this one out, and if you can, read other articles on site as well, well worth it !!!!

Pelican's Perch #77: Startups & Runups (http://www.avweb.com/news/pelican/186619-1.html)

[Big Pistons Forever]

Related to this discussion is a personal pet peeve, the mixture check during run up.

Many pilots simply yank the mixture knob out untill the engine dies. This doesn't prove anything except that the mixture idle cut off works and is inviting a lean cut backfire which will destroy the engine baffles.

A far better way (assuming no EGT guage) is to set POH recommended runup RPM apply carb heat watch for the RPM drop and then slowly lean. The RPM should rise as the overly rich mixture caused by the carb heat is corrected and then further leaning should start to produce an RPM drop. At this point you have proved the mixture control works so return to full rich, cancel the carb heat and you should be back to the original RPM.

And yes I aggessively lean on the ground for 2 reasons

1) The mixture has to be leaned a lot to have any affect at low RPM. and

2) If I were to forget to go to full rich prior to takeoff , the engine will stumble before I got to max power

[Oktas8]

ACARS - you mentioned your copy of the POH has no mention of leaning for run-up. Well, you're probably right. However to be fair to Islander2, he was referring to something slightly different.

Look in Section 5, Performance. There should be a table entitled something like "cruise power settings" with altitude, RPM, power, fuel flow. Look at the sea level altitude information, and probably the lowest power setting will be something like 55% power, 2150rpm, 7.5 US gallons per hour. (The numbers in your POH will of course be different.) On either the same page or perhaps in Section 4, Normal Procedures, there will be a statement on how to lean the mixture. It will include the advice not to lean at power settings above 75%. Put those two concepts together and you will see that it likely will not hurt the engine to lean the mixture for runups.

Actually the above is only an approximation, because (with a fixed pitch propeller) an engine developing 75% power when the aircraft is stationary will generate a lower rpm than 75% power at cruising speed. So context is important to avoid damaging an engine. Hence my recommendation to follow the AFM / POH, unless you know more than the manufacturer! (I'm not being sarcastic - on some things, with experience, some pilots do know enough to go outside the AFM.)

Islander2 - yes, I would accept advice in an engine manual even if it wasn't in the flight manual.

Regards to all,
O8