Pilot induced engine failure due to overleaning?

[PTK]

In the Sept 2012 issue of Plane & Pilot magazine, Bill Cox has written about engine reliability. He alludes to overleaning as potential example of pilot induced engine failure. 

What is he referring to when he says overleaning, can someone please explain?

[PilotDerek]

Overleaning? Isn't that just not enough fuel hence the engine stops? 

[jetdriven]

Define overleaning

[DaV8or]

He could be right if he means over leaning in the climb. This is one area that conservative leaning is prudent IMO. Staying well ROP is a really good idea in my mind. All other phases of flight, I'm not so sure. The only question mark is, I occasionally see EGTs exceeding 1450 during cruise. I make adjustments to lower this number. If one lets EGT go 1500 and above for prolonged periods, I can see how it might damage the exhaust system.

[carusoam]

Ovations have a blue box on the EGT meant to target EGT for climb.  It is ROP, but leaner than full in on the knob.

Any more lean on the red knob is in the area of the "red box"...

Is that what they mean by over leaning?

 

Best regards,

-a-

[Lood]

Maybe it's simply flying at too lean a mixture for a certain power setting? An engine will be damaged if it is not properly leaned - be it ROP or LOP. There are many pilots still flying around with a single analogue CHT gauge as the only temperature indicating instrument except for the oil temp gauge. Most of us started out like that and a single analogue EGT gauge was seen as quite advanced. However, in those days, almost every pilot flew ROP and the leaning technique was just about fool proof.

[jetdriven]

Quote: DaV8or

He could be right if he means over leaning in the climb. This is one area that conservative leaning is prudent IMO. Staying well ROP is a really good idea in my mind. All other phases of flight, I'm not so sure. The only question mark is, I occasionally see EGTs exceeding 1450 during cruise. I make adjustments to lower this number. If one lets EGT go 1500 and above for prolonged periods, I can see how it might damage the exhaust system.

[Hank]

My Owner's Manual says to leave it Full Rich whenever operating above 75% power. So if I set 80% power because I want to go fast, or the headwinds are strong, don't lean. Some people do anyway. NOTE:  in 1970, LOP operations were not considered for carbureted engines.

[danb35]

Quote: allsmiles

What is he referring to when he says overleaning, can someone please explain?

[WardHolbrook]

Our air cooled engines aren't always. During certain phases of flight (high power, low IAS) like takeoff and climb they need fuel to keep cool as well. Unless you've got the proper equipment installed and the proper training, you really have no choice but to operate the engine according to the POH. That's OK, it's way GA engines were operated for decades, but we've learned that there are better ways to do it . Operating LOP isn't blackmagic voodoo, but it does have to be done correctly. Google GAMI and you'll find links to a couple of training options that you have. It's worth the investment, at today's fuel prices the ROI is pretty attractive.

[jetdriven]

I am a diehard LOP operator but ROP target EGT climb is the only safe way to do it. LOP climb can be done, but the fuel savings are less than a half gallon a flight.  Not nearly worth the trouble

 

[DaV8or]

Quote: jetdriven

Turbo airplanes have a TIT limit of 1650 IIRC because the exhaust and turbo start to melt above that. I have read that a naturally asiprated engine wont develop a hot enough EGT to damage exhaust.  FWIW peak EGT on our machine is ~1530.

[Hank]

Aluminum melts closer to 1200ºF; Lycoming wants you to keep it below 500º because it begins to soften not much above that, which would spoil the tight seal under the heads to say nothing of what would happen to the bolt holding everything together. The bolts would sink into the softening aluminum, and then what happens to the torque originally used to hold everything tight?

There is very different stress on the exhaust system, it's not bolted together with stress applied lengthwise along the bolt.

[WardHolbrook]

Quote: DaV8or

Not saying that it does or doesn't damage the exhaust, only that some have had exhaust failures with LOP ops. Consider this- aluminum melts at what, nearly 1000F and Lycoming says you can safely operate up to 500F, but everyone seems to agree that keeping temps 380F and below really helps cylinders. Could not the same thinking apply to exhaust systems? Less heat = longer life?

[Cruiser]

Quote: jetdriven

I am a diehard LOP operator but ROP target EGT climb is the only safe way to do it. LOP climb can be done, but the fuel savings are less than a half gallon a flight.  Not nearly worth the trouble

 

[Parker_Woodruff]

Quote: jetdriven

I am a diehard LOP operator but ROP target EGT climb is the only safe way to do it. LOP climb can be done, but the fuel savings are less than a half gallon a flight.  Not nearly worth the trouble

 

[John Pleisse]

Funny...the more things change, the more they stay the same.

[DaV8or]

Quote: WardHolbrook

...and many have had exhaust system failures running conventionally ROP as well. It's sort of like saying that everyone I've know who is now dead ate strawberries at least once in their life therefore, strawberries are deadly. Unless it can be positively attributed to LOP operation, all you've shown is that exhaust systems occassionally fail.  

[Hank]

Quote: Parker_Woodruff

19-22 minute climb to FL200 at 100% power, 115-120 KIAS, approx 25 GPH = 8.33 Gallons

24-27 minute climb to FL200 at 85% power, 110-115 KIAS, IIRC approx 13.5 GPH = 5.4 Gallons (plus the initial 1000-2000 feet were at 25 GPH) so let's call it = 6.0 gallons

I've also now sacrificed 4-6 minutes of not going 190 KTAS, and am more like 145 KTAS in the top of the climb.

[KSMooniac]

Quote: DaV8or

All true. However, can we say for a fact that running a cylinder at 400+ degrees is the cause of the failure? There certainly have been failures of cylinders running LOP. It seems that when somebody's engine fails catastrophically, they just want to believe what they want to believe as to why it failed.

Anyhow, I'm still not clear as to why the concept of cooler operating temperatures = longer service life doesn't seem to apply to exhaust systems. If I read the forums right here, they seem to be saying, "Run your exhaust as hot as you want, it doesn't matter." Maybe we just need some study on the subject. Seems like all we have is, stuff happens to exhaust systems.

It also should be noted that my argument isn't an anti LOP argument. It's just an observation.

[M20F]

Quote: KSMooniac

[DaV8or]

Quote: KSMooniac

Why do you say "There certainly have been failures of cylinders running LOP?"  That is an assertion I sure wouldn't make.

Cooler temps should be better for exhaust systems too, but they aren't stressed anywhere close to the levels that the cylinders are.  Higher load + higher temp = shorter service life.  Exhaust systems are primarily stressed by vibrations.  Also, exhaust systems are much cheaper than 4 cylinders.

[KSMooniac]

Quote: M20F

[KSMooniac]

Quote: DaV8or

Have you not heard of any LOP operators having cylinder problems? I believe Byron here on this forum had cylinder problems and he's a staunch LOP advocate. I never said I believe that cylinders fail due to LOP per say, but it does happen to those that operate LOP and when it does, they usually like to chauk it up to manufacturer defect, or how the previous owner operated the plane. The point being, that just as nobody has hard proof that LOP harms exhaust systems, likewise nobody has hard proof that ROP harms cylinders.

It's true that an exhaust system costs about the same as just one cylinder, but a failure of either can kill you. Again, I am not trying to talk anybody out of operating LOP, or advocating ROP. I'm saying, that if there were to be a downside of LOP ops, it could potentially be in the exhaust system. Therefore, keeping EGTs lower might actually help extend the life of your exaust system just like keeping CHT lower extends the life of your cylinders. Just a thought. No proof. No science one way or another.

Carry on as you wish.

[Parker_Woodruff]

Quote: Hank

Let's run some numbers using an average of 5 minutes longer in the climb. Five minutes = 1/12 hours [easy number!].

At 190 KTAS, you'll go 15.8 nm; at 145 KTAS, you'll only go 12.1 nm, so you'll be 3.75 nm "behind" by climbing LOP. At your slow top of climb speed, it will take you 1:33 longer to make up that distance, or only 1:11 longer at cruise speed.

Rounding the fuel difference down from 2.33 gal to 2.0 gallons, at $5.50/gal, is $11.00 fuel savings, or $425.81 per hour at 145 KTAS [which becomes $557.75/hr at 190 KTAS]. No, $11 per flight won't break the bank, but do it thirty times per year and you'll earn yourself a free fill up. Almost two tanks for my little plane.

Or does the extra minute-and-a-half really make a difference in arrival time?

Sorry, sometimes my engineering background shows up. To an optimist, the glass is half full; to a pessimist, the glass is half empty. To an engineer, the glass is too big.