High Power N/A ops LOP vs Full Rich

[aaronk25]

Well when I cruise into a strong head wind I crank out ever bit of speed I can get as allowed by CHTs. With 1600 hours on the cylinders and no stress cracks and all reading mid seventies I haven't seen any issues. I will run 2600-2700rpm at 11-11.3gph at 4000ft and have cht in winter of 330-340f. In summer I run same power settings but limit Fuel to 10.6gph to keep temps at or below 360f.

In winter at 4k feet I'll indicate 161kts at peak egt. 2700rpms.

I could care less about ICP, with the exception I wouldn't run 30rop at those power levels. I don't think at peak egt there is enough ICP to tear a 360ci 200hp apart. I don't buy it, some of you do, but I don't . Sure there is probably a bit more wear, but my oil analysis doesn't show it (Byron you have mine) but I don't believe running at high power at peak egt is even a fractionally as harmful to a engine as flying less than 50 hours a year which is what most of the fleet does.

I got a feeling some won't make 2000 hours because the engine will be corroded out and here I'll be abusing mine and sail right up to 3000 hours.

The rest of the time (when I get a tail wind). I like getting up high and running 8.2gph and take it easy.

It is nice to get up high and cruise along when things aren't rung out to the last drop. Lot more relaxing .

[Shadrach]

All comes down to altitude and % HP. At sea level this is no bueno. At 5000 feet there's nothing wrong with it.

When I did the full rich vs LOP CHT comparison the DA at my comparison altitude was approximately 900 ft MSL. 27LOP was the number that generated full rich CHTs.

[Shadrach]

Could be that equal CHT does not mean equal ICP. The combustion event is shifted so the ambient temp in the cylinder is lower. I'm not sure that this guarantees the ICP is lower too. I admit I understand fairly little of this. But something about running full power 27LOP just doesn't seem right to me.

I'm not recommending anyone do this, nor do i think one flight is adequate to come to a hard conclusion. Just sharing my experience. I don't know what you mean by "combustion event has shifted so the ambient temp in the cyl is lower"

[Cruiser]

If you look at the ICP chart posted earlier on this thread you will see the curves for take-off full power and peak EGT are measured at about the same HP. The curves are almost identical, the peak EGT curve not having as high an ICP.

In fact, all the LOP curves are lower ICP than the one run at peak so I think it is safe to say that any LOP setting is going to produce lower ICPs than any ROP setting. 

[DS1980]

 I don't think at peak egt there is enough ICP to tear a 360ci 200hp apart. I don't buy it, some of you do, but I don't . Sure there is probably a bit more wear

It is possible to generate ICPs  that are harmful to an engine at peak EGT. These would be present anytime CHTs  are in the range to affect the aluminum alloy that our cylinders are made of. If you believe there is more wear occurring in your engine, what is causing the above average wear?

 

With that said, I think you're OK due to the fact that aircraft engines are a low stress application. If you tuned your IO-360 to put out 400 HP (or some HP to make it high stress), you could not get away with running at peak EGT at 4000 feet.

 

There are enough ICPs to tear the IO-360 apart. I may be a slow tear, but to be fair, it is there. Show a lot of care, I hope in mind this you'll bear. But tell you how to run your airplane? I wouldn't dare.

[Shadrach]

It is possible to generate ICPs  that are harmful to an engine at peak EGT. These would be present anytime CHTs  are in the range to affect the aluminum alloy that our cylinders are made of. If you believe there is more wear occurring in your engine, what is causing the above average wear?

 

With that said, I think you're OK due to the fact that aircraft engines are a low stress application. If you tuned your IO-360 to put out 400 HP (or some HP to make it high stress), you could not get away with running at peak EGT at 4000 feet.

 

There are enough ICPs to tear the IO-360 apart. I may be a slow tear, but to be fair, it is there. Show a lot of care, I hope in mind this you'll bear. But tell you how to run your airplane? I wouldn't dare.

They are low stress to a degree, but consider that a C6 corvette with a 364 C.I. engine is not making 200HP at 2500RPM. 

[DS1980]

They are low stress to a degree, but consider that a C6 corvette with a 364 C.I. engine is not making 200HP at 2500RPM. 

I have always thought the comparison between auto and aircraft engines to be lacking. I get what you are saying, but the Chevy also doesn't benefit from lower pressures from altitude flying, running at a constant RPM, or being constantly monitored by a trained (hopefully!) pilot.  I guess I could say it clearer: In cruise, at altitude, an aircraft engine is a low stress application. Plus, the internal parts are over-engineered to compensate for ham fisted Vette drivers. You're not one of those are ya??

[Shadrach]

I have always thought the comparison between auto and aircraft engines to be lacking. I get what you are saying, but the Chevy also doesn't benefit from lower pressures from altitude flying, running at a constant RPM, or being constantly monitored by a trained (hopefully!) pilot. I guess I could say it clearer: In cruise, at altitude, an aircraft engine is a low stress application. Plus, the internal parts are over-engineered to compensate for ham fisted Vette drivers. You're not one of those are ya??

No, I'm a P-car guy. However, I do admire that Chevy has made the corvette a real competitor, there is really nothing out there that will match it for the money.

Back to low stress applications, maybe you're correct. I just think that any engine that has RPM controlled with load rather than throttle is not necessarily low stress. An airplane engine is always governed by load (other than while taxiing); it's like opening the throttle of your car and looking for a hill steep enough to hold it to the speed limit!

[DS1980]

Agreed, and well said. But it's relative. We are asking a big engine to put out modest HP at modest compression ratios at modest air densities.

 

I learned to fly in Vernal UT and Craig CO, so both high altitude airports. My instructor was very seasoned and was retired from flying money from bank to bank, in a twin, at high altitude. I asked him how many hours he had and he said very casually "Well, I stopped counting at 35,000." I also asked him how many times he had to set his airplane in the dirt. He had one precautionary landing in a sage brush field that turned out to be nothing. One! In 35,000 hours! 70,000 engine hours! Guess where he taught me to run the engine? 50 ROP, just as he did for 35,000 hours. How did I, and most importantly, he, get away with running engines so harshly for so long with hardly any consequences? The engines we fly are low stress and overbuilt. A contributing factor-flying out of high density airports.Thank goodness they are forgiving for a ham fisted classic Austin Mini driver as myself.

[jetdriven]

At high altitude, his engines can only put out something like 55-65% power anyways, there is no mixture setting that can harm them, except from high CHTs due to baffling or poor design.  I wonder how many jugs didnt make it to TBO running at 50 ROP?

 

The cylinder pressures in a 200 HP IO-360-A with the 8.7:1 compression ratio are real, and can melt down in a hurry if ran at peak EGT at takeoff power. Normal is 800 PSI and detonation sends that to over 1000 PSI.  Busch and Deakin have written about airplanes with an injector plugged,can  hole a piston in 90 seconds.

https://www.savvyanalysis.com/articles/detonation-and-pre-ignition

http://www.mydigitalpublication.com/display_article.php?id=244514

[DS1980]

So Aaron, your thoughts?

[Shadrach]

Agreed, and well said. But it's relative. We are asking a big engine to put out modest HP at modest compression ratios at modest air densities.

 

I learned to fly in Vernal UT and Craig CO, so both high altitude airports. My instructor was very seasoned and was retired from flying money from bank to bank, in a twin, at high altitude. I asked him how many hours he had and he said very casually "Well, I stopped counting at 35,000." I also asked him how many times he had to set his airplane in the dirt. He had one precautionary landing in a sage brush field that turned out to be nothing. One! In 35,000 hours! 70,000 engine hours! Guess where he taught me to run the engine? 50 ROP, just as he did for 35,000 hours. How did I, and most importantly, he, get away with running engines so harshly for so long with hardly any consequences? The engines we fly are low stress and overbuilt. A contributing factor-flying out of high density airports.Thank goodness they are forgiving for a ham fisted classic Austin Mini driver as myself.

My wife just moved from a not so classic Cooper S into a 2013 Fiat Abarth... 1.4L that puts out 114.29 Hp per litre.  Pegs the fun meter with only 2500lbs to move, but likely not what I'd call low stress...but I digress...

 

The genesis of this thread was born out of high power LOP ops not 65% high DA operations.  I did another flight on Sunday taking off from my home field (Ele 706ft) with a DA of minus 1700ft, OAT was 28F baro 30.4.  Without being too particular about the calculations, that means I was running ~ 300ft DA at 2000ft MSL. Full rich was 223 ROP at that altitude and CHTs at that setting were 288. To match those CHTs on the lean side I needed to go to 56LOP. With the Ram Air open I was showing nearly 32" of MP (not claiming that number is accurate, but the gauge does read the ambient Baro on the ground... 

 

The moral of the story for me is that the number you need to match full rich CHTs (and in my mind full rich ICPs) on a given day, all other things being equal, varies on conditions and taking a cookbook approach is not optimal. 

[aaronk25]

So Aaron, your thoughts?

 

 

There are only 2 situations where we can damage the engine.

1.  High CHTs and High ICP like peak egt at take off because the heads aren't as strong.  Your comment about high ICP and High CHT is right on.

2. Heavy Detonation and detonation won't take place until the CHTs are hot.  

 

 

If we ran liquid cooled jugs and remained at 8.7 compression ratios I believe we could take off at 30ROP wide open throttle and not have any issues with detonation, even on auto gas. 

 

I know someone wink wink who has done some testing with a IO360 8.7 compression 200HP that has ran auto gas and tried to get the engine to detonate.  Its possible but there isn't any configuration that could make it detonate until the CHTs got to 380, then it was barley audible and the somewhat rapid rise in chts backed up the fact that the engine was in light to medium detonation.  Under the same conditions the engine could cruise on 100LL at 4000ft WOT at peak all day long, but when running 91 octane no lead it had to be ran 25 lean of peak or detonation was audible, but just barley with a slight but constant rise in CHT.  At 25 LOP on auto gas or peak on 100LL resulted in the same CHTs. 

 

The point is I can't even get my IO360 to show any signs of detonation even when ran in the worse possible configuration on 100LL and the only way I can get a IO360 to even start to show signs of detonation on MOGAS is to run it dead center in the middle of the "RED BOX" and even then it won't even start to detonate until the chts get up to 380-400 degrees!  So if the temps are kept under 380 the cylinder heads strength is still high enough to hold up to any ICP and detonation is ZERO or so low its undetectable. 

 

 

Everything I have seen is HEAT is the problem.  I don't want to hijack the thread but this leaded crap we have to run is ridiculous.  If we had a 91 octane, no ethanol grade of fuel made that had the same type of quality control that avgas requires and everyone had a engine monitor life would be great and we would get the lead sludge out of our engines and related components.  By the way MOGAS from back in the day when peterson ruled out the mooney car gas had a RVP of 15!!!!! now most states limit the RVP to 7-9.  So its alot better fuel than it use to be.  100LL is about 6.5 RVP so its almost there!!!

[Shadrach]

Aaron,

 

I agree, when running 100LL detonation is nearly impossible to induce in a N/A aircraft engine. You'd need a super hot day with the gear and flaps hanging out while pitching to whatever attitude put you just behind the power curve and then lean for best power. Then you'd have to hold it there until CHTs reached ~420df.  It's just not a likely event unless it's something you're trying to achieve. 

[DS1980]

Good points, but I would concentrate more on pre-ignition than detonation, as an engine is more tolerant of detonation than pre-ignition.

 

For your 2 points about harming an engine, here's my additional thoughts.

1.) On takeoff, our engines usually aren't' heat soaked like they become in climb or cruise, so they are actually stronger at takeoff because they simply aren't as hot. This is why it's important to stay out of the red box, as the engine could be generating damaging ICPs, but these would not show up until the CHTs began to rise, which is a lagging indicator.

 

2.) Agreed, but would be more concerned with pre ignition. Again, not going to show up until the engine has been operating in a damaging way for a while.

 

It does all come down to heat. Excessive heat is the byproduct of something not being right. That's why I think that in the original post, when Ross was seeing 306 CHT, even if the ICPs were higher than normal, they weren't damaging, as his F doesn't have THAT much cooling capacity to suggest artificial cooling to that degree, even if he has the cowling closure and spot on baffling.

[jetdriven]

Aaron,

 

I agree, when running 100LL detonation is nearly impossible to induce in a N/A aircraft engine. You'd need a super hot day with the gear and flaps hanging out while pitching to whatever attitude put you just behind the power curve and then lean for best power. Then you'd have to hold it there until CHTs reached ~420df.  It's just not a likely event unless it's something you're trying to achieve.

It'd agree with you except above ~85% power in a high compression IO-360 engine. There is not much data to prove that above 85% power. I feel pretty strongly that in the ~90% and higher range, detonation (or detonation-induced preignition) could occur and the damage would be so sudden as to ruin an engine in a couple minutes. Bonanzas have melted pistons in less than two minutes at takeoff power with dirty injectors which lean the cylinder out to peak EGT.

[scottfromiowa]

Good stuff. Very interesting thread guys. First car I owned was a 1980 Fiat X1/9. I would love to have had that Abarth engine in that car. Handling was "on rails", but the1.5 Litre engine was pretty anemic. I think it had 115 TOTAL HP. Still a lot of great memories on backroads with that car...

[Cruiser]

Shadrach, on 27 Nov 2013 - 4:39 PM, said:Aaron,

 

I agree, when running 100LL detonation is nearly impossible to induce in a N/A aircraft engine. You'd need a super hot day with the gear and flaps hanging out while pitching to whatever attitude put you just behind the power curve and then lean for best power. Then you'd have to hold it there until CHTs reached ~420df.  It's just not a likely event unless it's something you're trying to achieve.

 

It'd agree with you except above ~85% power in a high compression IO-360 engine. There is not much data to prove that above 85% power. I feel pretty strongly that in the ~90% and higher range, detonation (or detonation-induced preignition) could occur and the damage would be so sudden as to ruin an engine in a couple minutes. Bonanzas have melted pistons in less than two minutes at takeoff power with dirty injectors which lean the cylinder out to peak EGT.

What exactly are we agreeing with?

 

Aaron's description is of an extreme situation, not normal operating settings.

Byron's comments are on takeoff power/plugged injectors.

 

If we are agreeing that detonation can occur in a Lycoming IO360 engine, I will agree with that also.