Piston engine ops

[Skaz]

question for all...and chaps like avbug, bobysamd, wrightavia etc i.e. all you guys and gals with loads of experience (with aeroplanes )

recently had a discussion with a fellow aviator in my company re piston engine handling procedures....this was on a C402C.

We've been taught that you bring the mixture back a bit (1/3 to maybe 1/2 of full rich) after start, for the taxi so the plugs dont foul up.

Then during the before T/O checks , right to left, rpm 1700, bring the mixtures back till you get a rise in rpm and then drop, to make sure they work, then prop check, and mags.

Now the Issue:
my colleague disagrees with the above and does the mixture check after start, by bringing the mixtures back till he sees a temp rise EGT.

This because he reckons there are not very close tolerances between the piston, rings and sleeve and the pistons needs to heat up fast to avoid 'slapping around in the sleeves', and reducing the mixture with 1700rpm will burn the rings ......?

Another point was :
Descent, after FREDA checks, Ive been taught by two previous CP's to bring the power back from cruise (29'MP, 2350RPM,90FF, with Cowls closed) to 26'MP, leaving the rest the same. next power reduction will be in circuit with 24-26'MP, 2500RPM, and 100FF. Reasoning was that you reduce the power changes since after take-off by half each time
i.e. Max power for T/O was 39'MP, 2700RPM and FF for T/O, the MP is reduced 9-10' to 30 or Top of green for climb and then 29' for cruise. Thus for descent reduce change by half again and set 26' (first redcution was about 10' , second was about 5, and third about 2)....

Colleague (and I am aware of this method, as I use it on the C210 and similar a/c) is to reduce the MP 1' per minute or 1000' of altitude lost. This of course being to reduce chances of shock cooling.

The discussion then turned to the virtues of certain manufacturer's piston engines as Continental is viewed by some as a 'wimpy' engine, in having TBO of 1600hrs and Lycoming as 'stronger' or 'tougher' engine with TBO of, methinks 2000hrs.....

I have never had any major problems with Continental engines, apart from a llittle bit of vapourlock in a C310, and stubbourn starting when hot........but then again, the Lycomings in the BN2 Islander can be b!itches to start when theyre hot as well!

We also discussed the problems with aviation training , as it seems a lot of instructors teaching new pupes to fly, are still 'wet behind the ears' themselves ' and lack the real-world experience you gain out on the line. certainly this can compound 'bad' engine handling habits....

This is a bit of a long post, but youre views and opinions would be welcomed.

One last thing: Is anybody aware of a book or DVD or course or something that covers these above topics? Experince gained from real worls operations etc?

Cheers

 

[avbug]

Skaz,

That's a lot of question(s). Book, first. Anything by Cas Thomas. Fly the Engine comes to mind, but there are a couple others for which I can't think of the title presently. Read that book before you operate your engine again.

Mixture check? Are you checking to see that it's still attached to the airplane? That it's free? What are you attempting to check with the mixture? (Sort of like a wing check. Yep, it's still there).

The only reason to pull your mixtures back during taxi is to prevent ground idle fouling. On a carbureted engine this is only applicable if your idle mixture setting isn't correct for your field elevation and temperature (density altitude). Unfortunately, it's rare I see a properly set idle mixture. Therefore ground leaning during taxi is generally necessary.

On a fuel injected engine, it may or may not be necessary, depending on several factors.

You can't hurt the engine at idle by leaning it, so feel free to lean agressively. If you are going to lean on the ground, do so agressively (again, if the airplane is properly maintained, this isn't necessary...but,). The reason for this is that the engine will bark at you if you forget to set the mixture for takeoff. If you have it leaned as far as you can for taxi, not only won't you load up the cylinders or foul anything, but you'll get instant feedback that the mixtures aren't set. Conversely, if you lean just slightly off full rich, then you can take off in that condition and do possible damage to the engine (melted pistons, burned valves, detonation, etc).

You're not accomplishing anything noting an EGT rise during the runup by "checking" mixture. Bringing the mixtures back after start and looking for an EGT rise doesn't do anything either, other than lean for taxi.

This because he reckons there are not very close tolerances between the piston, rings and sleeve and the pistons needs to heat up fast to avoid 'slapping around in the sleeves', and reducing the mixture with 1700rpm will burn the rings ......?

Your friend needs to learn more about the engine. He has no idea what he's talking about. In fact, his thinking is convoluted; he's trying to re-engineer the engineering of the engine. (Say that five times, fast). Burn rings? How does one burn rings? The rings are below the piston head. Burn valves, perhaps, but not at seventeen hundred RPM. That's too low a power setting.

The piston is smaller than the cylinder walls; that's what the rings are for. The rings seal the cylinder, and ride along the wall. The cylinder is larger at the top than the bottom, and the rings expand and contract in a spring fashion to seal the cylinder throughout the travel of the piston. The pistons are not going to heat up fast and seal the cylinder. That's the job of the rings. Further, leaning during taxi isn't going to heat the engine up appreciably faster; that leaning isn't making much difference at idle power, at all.

What is a FREDA check?

Shock cooling is a hotly debated topic; no hard evidence exists either way despite plenty of research. I can tell you from personal experience that it does indeed occur; that rapid thermal changes can cause cracking in cylinders, especially between the spark plug holes in the cylinder head.

Discussions of Lycoming v. Continental are entertaining, but pointless. Lycoming has had certain problems such as catastrauphic crankshaft failures, etc. Continental went through a bout of cylinder failures a few years back due to some metalurgy changes.

TBO doesn't mean anything; it says nothing about function or durability. It's a time set in which overhaul is recomended, and applies to first-run engines only (except under Part 135, and then as approved for the operator).

As for instructors, you're right. There exists today a heritage of inexperience, but it's been that way for twenty years. Inexperienced instructors teaching pilots who then go on to become instructors with no experience, ad nauseum. It's no wonder that so many myths, errors, and foolishness abounds.

 

[Timebuilder]

We've been taught that you bring the mixture back a bit (1/3 to maybe 1/2 of full rich) after start, for the taxi so the plugs dont foul up.

I almost always reduce the mixture for the taxi in the fuel infected engines and the carbureted 172RG, which likes to foul plugs.

I'm not so sure that you want to heat up the components "fast". I'd be more inclined to seek an even warmup. Since I never flew a 402, I'd start by checking the manual. What does it say?

In any event, the manual and the checklist should agree, and they should dictate the procedure you should follow.

I like to see a rise in EGT during leaning before I take off because I want to burn off any excess fuel and loose carbon that is left over from starting or taxi. I figure that the mixture is "working" if I see a reduction in fuel flow when I lean after starting, and then see an increase in the fuel flow when I go rich for the mag check.

I'm sure Avbug will have some thoughts on the eternal Continental vs Lycoming debate!!

 

[Timebuilder]

Looks like we were typing at the same time.

Thanks for the insights, Avbug.

 

[MarineGrunt]

Great post!

 

[wingnutt]

ah yes, Cessna 400 series, the flying wonder bread truck...

our company ops dictated a 1" reduction in MP per minute but our check airman claimed 2" per 2 minutes was fine...go figure.

and as far as leaning on the ground, we never did. wed just do the mag check, and if a larger difference was noted than allowed, lean it out and run it hard for a minute or two to clean off any buildup.

...sounds like avbug nailed all the rest for ya

 

[Skaz]

avbug will try to get books from that chap online, decent bookstores are kinda scarce in the desert here

Mixture check - to see that the mixture levers actually do control amount of fuel metered to engine, and not stuck on one setting.

Wingcheck - yup, always do one of those

FREDA - fuel, radios, engine(s), DI, altimeter

got to 1 1/2 times, 5 still a bit off.

If I remeber correctly, we used to lean the mixtures on the PA28's at the airschool too, for the same reason to avoid plug fouling. Methinks it might be a good habit to get into, seeing that the engineers dont fly!
Saying that you cant hurt the engine at idle by overleaning...Ive been called a bit slow so let me just make sure I understand you : this would be 'cause the engine isnt under a lot of stress and high temperatures etc, so will just basically 'choke' on too much air and not get hurt...right?
The matter of the donkey barking at you with incorrectly set mixture for take-off: could you elaborate or rephrase please, not quite with you. Methinks that the engine would just 'choke' again 'cause of too much air and too little fuel when throttle is opened...right?(barking?)
We always have the mixtures set full rich for take-off and monitor the fuel flow in the little white triangle or correct position on FF dial.
The reduction in mixture for runup: I check the rpm first increase slightly and then drops off.
Please elaborate on the bit :

Conversely, if you lean just slightly off full rich, then you can take off in that condition and do possible damage to the engine (melted pistons, burned valves, detonation, etc).

OK, so if I understand you correctly , leaning during taxi does not heat the engine faster, just reduces spark plug fouling....thought so.

Interesting what you say about the TBO. This is sure to result in heated debate in the pilot's orifice
If it applies to first run engines only, how does it apply to owners and/or operators (other than Part 135 which methinks is on-demand-charter?) surely there must be a maximun number of hours between overhaul and this must be supervised by the authorities?

Timebuilder you made me laugh mate ! see if you can spot why

I almost always reduce the mixture for the taxi in the fuel infected engines and the carbureted 172RG, which likes to foul plugs.

thanks for the input though, much appreciated.
I think an even warmup would be good too, make sure the whole engine and all the whirring , turning, and going-up-and-down bits all heat up the same.
You mention 'carbon' ? Ive been more aware of lead deposits? even using 100LL (the blue stuff)

cheers guys, thanks

 

[Timebuilder]

I see you've never had a fuel infection.

There was this one girl I knew in 1974....

 

[wingnutt]

I see you've never had a fuel infection.

There was this one girl I knew in 1974....

...that or perhaps hes never flown a Sierra on a hot day in south florida after stopping in some obscure field to releive oneself, then spend the next 20 minutes trying to get that pig to start back up

 

[greyhound]

What about these scenarios.....

Airports with high elevation?
While climbing?

Would you do a run-up or takeoff with mixtures FULL RICH at a field that is over 5K ft. MSL? Or would you lean for best power before takeoff? (I'm referring to a piper or light twin type aircraft)

Also, what about while climbing?
Keep it rich ALL the way to cruise altitude? (Does not sound right to me.)
I was once ascending with a new instructor, and he did not like it when I began to lean the mixture as we would gain altitude?
His reasons were to aid in cooling, and produce more power!

So what's the right answer?

 

[WrightAvia]

I was once ascending with a new instructor, and he did not like it when I began to lean the mixture as we would gain altitude?
His reasons were to aid in cooling, and produce more power!

We lean for climb in the jump planes all the time. They are 182's with the big conversion engines in them. We don't lean, till the EGT drops below a certain temp (placarded next to a digital egt guage) and then we keep it at that temp by leaning, all through out the climb.

As far as "not" leaning being an aid in cooling, as long as you are within the green arcs on the cylinder head temp and oil temp, who cares? If you have to, lower the nose for a while, that's how you cool off a hot "air cooled" engine during a climb.

You are going to make more power, by being properly leaned for climb. All you are doing by being over rich during climb, is sooting up the bottom of the plane and fouling your plugs.

 

[Timebuilder]

I've always leaned for the higher altitude, and often for climb and cruise. No sense wasting valuable fuel.

 

[metrodriver]

I always leaned above 3000' density altitude. Do not lean on a turbocharged engine though during climb! Reason for that is that the turbocharger keeps the intake air at the same pressure (which drops on a normally aspirated engine) on the way up. Since this pressure stays constant, so does the amount of fuel required.

If you are at 3000' on a 100 degree day with high humidity you might find your density altitude already way above 5000'. If you take off full rich with a normally aspirated engine under that condition you will miss out on 200 rpm or more. My technique without an EGT gauge was to start reducing the mixture till you read max rpm. Note the position of the mixture control because this will be max rpm at richest mixture, what you want for take-off. Now pull the mixture back some more to see where you start losing rpm. This will be max rpm/ leanest mixture (and you're on the lean side of peak EGT). Now bring the mixture back to the first position of max rpm/ richest mixture.
The reason I reduce to rpm drop is to see how wide the range is between the richest and leanest mixture settings, that way I'll be pretty sure where peak EGT should be and that I'm operating on the rich side of peak
Of course if you have fuelflow, EGT and CHT gauges you can make the leaning a lot more accurate.

 

[Skaz]

thanks guys, lotsa good gen...

wingnutt Sierra? dont believe I have.....might be same scenario as BN2 in the Okavango in mid summer.... 'cmon start you b#@tch!!

Greyhound In carbureted a/c, yeah, in fuel injected...um, no, turbocharged no as well, full rich for take-off, but lean for the climbout. 120lbs aside for the 402, or little white triangles.

WrightAvia fuel helps cool the engine as well, as you no doubt know, but if the FF is set in the climb and the donkey get a bit hot, I lower the nose as well for more airflow, C402 cruise climb at 120KIAS works well.
Afirm on the plug fouling

metrodriver cheers, makes sense to me. Although it has been a very long time since I flew anything that hasnt had either fuel injection or turbocharging, good thing you refreshed my memory!

 

[bobbysamd]

Leaning mixtures

We've been taught that you bring the mixture back a bit (1/3 to maybe 1/2 of full rich) after start, for the taxi so the plugs dont foul up . . . .Then during the before T/O checks , right to left, rpm 1700, bring the mixtures back till you get a rise in rpm and then drop, to make sure they work, then prop check, and mags.

This sounds like SOP for operating at high altitudes, e.g, Denver or Prescott; the idea indeed being that you don't want to foul the plugs. However, you are not leaning mixture to see if it works; you are leaning for maximum RPM (and power) for takeoff.

I cannot add anything else, nor can I improve at all on Avbug's and the other posts above.

We also discussed the problems with aviation training , as it seems a lot of instructors teaching new pupes to fly, are still 'wet behind the ears' themselves ' and lack the real-world experience you gain out on the line. certainly this can compound 'bad' engine handling habits....

I agree in large part with that. Flight schools, for all their advantages in terms of standardization, are major offenders.

There is a great deal of incest in flight schools (Sorry, that's the best word I can come up with, but read on and you'll see what I mean.) Schools generally hire their own grads who teach the next generation of students, ad infinitum. The only aviation these instructors know is that school, and the message becomes diluted and increasingly dogmatic as it is passed on from generation to generation.

The problem can be solved by providing good, in-depth, proper training and reinforcing it during instructor standardization. Yes, you can hire instructors from the outside, but they still must go through standardization so that they deliver the same message. So, bringing in fresh blood from the outside is not necessarily a cure to the problem.

 

[Timebuilder]

So, bringing in fresh blood from the outside is not necessarily a cure to the problem.

In fact, it could start some arguments!

It's always a good idea that the student understand the "why" of a training process.

 

[Skaz]

does anybody know where I can get those books by Cas Thomas?

Amazon.com and Kalahari.net doesnt have them.

 

[A Squared]

Skaz,

try searching for Kas Thomas, that might help. Some of his stuff is published by TBO Advisor Books, PO bBox 477, Wilton, CT 06897.

He is (or was) the editor of TBO advisor magazine.

 

[Crizz]

As always avbug and others... your threads are very informative. Keep the good info comming for those of us newly minted CFIs who are still wet behind the ears with a thurst for knowledge.

 

[greyhound]

Good info.....

I'm always adjusting the mixture.
After starting.
Before taxiing.
While climbing.
On descent.

I was just confused by my new instructor.
It went against what I was taught at another place.

Here's another scenario.
You're in a seminole, and you experience an engine failure.
We're taught Mixtures RICH, props, throttle etc.....etc....
Would you still advance the mixture "rich" on the good engine at high density altitudes or at cruise altitudes?

Wouldn't that prevent the good engine from producing the most power? (Kepping it rich at high DA.)
You might be fouling up the plugs on the good engine now wouldn't you?
Is it wise to go back and lean the mixture on the good engine after you secure the dead engine?
Sounds right to me, but schools don't always teach this.