Turbo Ops -- UGH!

[AirBaker]

Well, since his plane is turbocharged, it's no worse on the speed either, so why not take the savings (owner won't have to raise rates as much) and added endurance?

Are you sure about that?

 

[AirBaker]

With a carb?

Missed that detail.

From your last post, just seems like you've got an uphill battle to get to LOP.

 

[flyingcheesehead]

Look, I'm not going to rehash the leaning argument here. Every time I talk about it, someone tells me I'm wrong.....

That's not what I said. Just passing along a tip...

FWIW, the plane has a wastegate with a mechanical linkage to the throttle.

...which won't work with your setup. Oh well.

 

[flyersfan31]

Now I'm really confused. I read through Deakin's articles on the Pelican Perch. Don't know what to think, really. Looks like, if I read his graphs correctly, LOP is the only way to go. Next step is the APS course so I at least do LOP the right way.

One thing that did strike me is that maybe the Cessna POH recommendation to lean to 50dgF ROP on Peak TIT isn't too bad, and probably better than my 100degF ROP. However, that's still 1635F on my turbo - I'm no metallurgist but all I've read is that it's on the high side, even for Inconel.

Not to get into a big LOP discussion, but earlier someone said I can claw back the power lost by going LOP by increasing MP. Doesn't that then change the mixture you set? Increased throttle = increased airflow = changed mixture or am I missing something? This is why I don't want to screw around until I know exactly what I'm doing.

 

[flyersfan31]

turns out I was missing something. Engine driven fuel pump increases fuel flow with MP increase.

I've spent the last 2 nites reading everything I can on this.

 

[sba55]

As long as you watch the temps & the manifold pressure to avoid overboost. I can guarantee you, because I've watched it, that I can't lean much above 75% power without causing a temperature and rough-running problem.

I don't doubt it. There isn't much leaning to be done ROP above 75% anyways if you don't want to abuse your engine. Between 75 and 80% power, one needs to be 180-200d rich anyways. Although I'd never run that power ROP. ICPs are going to be excessive, which won't help engine longevity. LOP is a different story.

LOP at 60-75% results in a rough engine (at least at non-oxygen altitudes). I can run AT peak at 60% (meaning some cylinders are over lean, some not) without it running too rough.

Makes perfect sense. Without balanced fuel flows, you just can't lean too much since the power output of the cylinders will start to diverge a lot as you get rid of more excess fuel. And vibration isn't good for an engine, either.

Now I'm really confused. I read through
One thing that did strike me is that maybe the Cessna POH recommendation to lean to 50dgF ROP on Peak TIT isn't too bad, and probably better than my 100degF ROP.

NO. 50dfROP is the _worst_ possible mixture setting to run pretty much any engine at. That's right about where you find the hottest CHTs and the highest ICP (internal combustion pressures). Heat+pressure = cylinder killers. Your turbo can take higher EGTs, your engine can't take high CHTs. I'm sure Lyc has realized this by now, but why would they publish a more conservative figure? Their engines wouldn't produce quite as much power and they'd lose money on the remans. Take a look at this graph:

http://www.avweb.com/newspics/182536landmarks.jpg

turns out I was missing something. Engine driven fuel pump increases fuel flow with MP increase.

I've spent the last 2 nites reading everything I can on this.

You got it. So, since you have some extra MP if you have a turbo, you can always regain the speed. Another way to look at it is that leaning to the lean side of peak reduces power for a given MP. So you could also (don't do this, though, but just as an example) start from wide open throttle and just lean to 100dfLOP, which would probably give you about 85-90 power (NOT A GOOD IDEA, but just to make the point).

Are you sure about that?

Yes

-Felix

 

[flyersfan31]

NO. 50dfROP is the _worst_ possible mixture setting to run pretty much any engine at. That's right about where you find the hottest CHTs and the highest ICP (internal combustion pressures). Heat+pressure = cylinder killers. Your turbo can take higher EGTs, your engine can't take high CHTs. I'm sure Lyc has realized this by now, but why would they publish a more conservative figure? Their engines wouldn't produce quite as much power and they'd lose money on the remans. Take a look at this graph:

http://www.avweb.com/newspics/182536landmarks.jpg

Thanks.

If you assume TITs run about 100degF higher than EGT, then you're farther out on the EGT curve at 50R TIT, on the slight downslope of CHT. Not much, but probably better than when I was running 100R of TIT!!

Regardless - all the data looks pretty ugly for ROP. I just want to make sure I have it all down pat before I jump in the cockpit.

 

[AdamZ]

Any other recommended sources of info?

I can lend you the owner's manual for my Snow King Snow blower.

OTOH why not just build the ch801 with me no need for a turbo.

 

[sba55]

Thanks.

If you assume TITs run about 100degF higher than EGT, then you're farther out on the EGT curve at 50R TIT, on the slight downslope of CHT. Not much, but probably better than when I was running 100R of TIT!!

Regardless - all the data looks pretty ugly for ROP. I just want to make sure I have it all down pat before I jump in the cockpit.

If you want to experiment, you can always run 60% power or less and set pretty much any mixture you like to see what happens. Good luck!

-Felix

 

[Henning]

If you want to experiment, you can always run 60% power or less and set pretty much any mixture you like to see what happens. Good luck!

-Felix

This is exactly why people say they loose a bunch of performance running LOP, once you lean past peak, you are no longer at 60% power for a given manifold pressure/rpm combination. If you want to play, try this: Fly your book ROP 60% numbers leaning with the mixture control to peak (note your fuel flow) and then progress your leaning by openning the throttle further, and using the prop to maintain your fuel flow and see where you end up.

 

[gprellwitz]

There's nothing you really need to know that only the owner would know before you can run this engine safely LOP. In fact, you arguably need to know less about the engine to run LOP than to run ROP.

Since you have an engine monitor, things become even easier. Find peak EGT on the first cylinder to peak (if you're coming from the rich side). That number should remain constant no matter the power setting and it won't vary from flight to flight much, either. Then continue leaning and see what happens. If you can lean for another 20d on the _richest_ cylinder (so some of the other cylinders will be more like 40d LOP), you can run LOP at or below 70%. If you can lean even further to 70d without engine roughness, you can run LOP at 87%. If you stay at around 80% power and something like 60dfLOP, you're being MUCH nicer to your engine and the turbo than you would at 70% power and 100dfROP. And, since you're turbochanged, you won't loose any speed.

Easy way to tell %power LOP, too. Multiple fuel flow * 14.9 and you have a very accurate percent power figure. Only works LOP, though, since fuel flow and power output aren't really correlated ROP.

-Felix

Thanks Felix. I checked, and there are no operational prohibitions against operating LOP for this bird. The nice thing it that, even if we're not paying the fuel bill directly, it gives us longer range.

One question I have is how to do this without getting the engine too hot during the leaning process. We have it placarded to not exceed 400dfCHT,1500dfEGT , and I'd expect it to go above that during this process. In fact, that's a quandary I have in leaning to ROP, too!

 

[sba55]

Thanks Felix. I checked, and there are no operational prohibitions against operating LOP for this bird. The nice thing it that, even if we're not paying the fuel bill directly, it gives us longer range.

Definitely. I won't bother with LOP either if I'm not going that far. But for me, it's a difference of at least 250NM in range.

One question I have is how to do this without getting the engine too hot during the leaning process. We have it placarded to not exceed 400dfCHT,1500dfEGT , and I'd expect it to go above that during this process. In fact, that's a quandary I have in leaning to ROP, too!

That's a good point. A related point: If you're just experimenting, fly at or below 65%, and you can o whatever you want with the mixture without exceeding a limitation. That said, most people do what is sometimes called the 'big pull'. You can do this at any altitude, but I prefer to climb out ROP and then go to LOP in cruise. That's also easier, so I'd start with that.

Basically, you are trying to avoid exactly what you mentioned - spending too much time in the danger zone where CHTs, EGTs, etc. will rise to damaging levels. You just want to get to LOP as quickly as possible. Watch the fuel flow and lean to about 15gph in 3-5 seconds (assuming you have an IO550, a gph or so less for a 520). This will require you to lean a lot very quickly. Then you'll be well LOP. Slowly enrich until you're at peak. Note the EGT for the hottest cylinder. That EGT for that cylinder shouldn't change much from flight to flight, so you can use it as a reference point. Lean to 20dfLOP or whatever works for you, and note fuel flow. In the future, given the same RPM, you can skip all of this and lean for that fuel flow (or EGT for that cylinder where you wrote it down, but I find that leaning for a fuel flow at a given MP is a little easier).

This guy knows a lot more about it than I do:

http://www.avweb.com/news/pelican/182106-1.html

-Felix

 

[Joe B]

When you do the "Big Pull" you can feel the power drop in the proverbial seat-of-the-pants as the engine goes seriously LOP. You can then sneak up on Peak EGT from the backside by enrichening the mixture. If peak is "hidden" beyond your EGT or TIT limit you can stop before reaching the limit and still be operating nicely LOP.

Regards,
Joe

 

[gprellwitz]

Thanks guys! I've already got some of Deakin's articles printed out for study, and I've now added these two.

 

[flyersfan31]

I'm working through the APS online seminar and all I can say is WOW. There is a lot I didn't know. It all sounds good to me.

Question for the more informed masses:

I was warned by someone that running LOP would result in insufficient lead lubricating the valves. Comments?

 

[Henning]

I'm working through the APS online seminar and all I can say is WOW. There is a lot I didn't know. It all sounds good to me.

Question for the more informed masses:

I was warned by someone that running LOP would result in insufficient lead lubricating the valves. Comments?

Lead causes valves to stick.

 

[flyersfan31]

Lead causes valves to stick.

You're killing me. The person who told me this had a very serious expression when he told me. What's a non-gearhead to do??????!!!!!!!!

(I find the LOP arguments more compelling than the ROP, I just had to share that lead thing.)

 

[gismo]

Easy way to tell %power LOP, too. Multiple fuel flow * 14.9 and you have a very accurate percent power figure. Only works LOP, though, since fuel flow and power output aren't really correlated ROP.

-Felix

IIRC, 14.9 (actually I thought it was 14.7 but that's a nit) is for "high compression" engines only. Most if not all factory turbo setups use lower compression pistons which reduce the thermodynamic efficiency of the engine so the number is a bit higher for them.

 

[gprellwitz]

IIRC, 14.9 (actually I thought it was 14.7 but that's a nit) is for "high compression" engines only. Most if not all factory turbo setups use lower compression pistons which reduce the thermodynamic efficiency of the engine so the number is a bit higher for them.

From the Deakin article cited earlier:

If you really, really must know the HP you're pulling, there's an incredibly simple trick to find out. On the flat, horizontally opposed, air-cooled aircraft engines with 8.5:1 compression ratios (including TCM IO-520/550 and Lycoming IO-540), simply multiply fuel flow in GPH times 14.9. The result is HP. If you insist on percent, divide that by the rated power of the engine. For the same engines with 7.5:1 compression ratio (most factory-installed turbos), the numbers are worse, and the multiplier drops to about 13.7. IMPORTANT NOTE: This formula works only at LOP mixture settings! When operating ROP, the excess fuel is largely wasted, not burned, so the linear relationship between fuel flow and horsepower breaks down.

 

[Skip Miller]

You're killing me. The person who told me this had a very serious expression when he told me. What's a non-gearhead to do??????!!!!!!!!

(I find the LOP arguments more compelling than the ROP, I just had to share that lead thing.)

Tetraethyl lead is an anti-knock compound, not a lubricant. You have just run into one of the many old wives tales that get started who knows how and when , and then self-perpetuate for f'ing ever.

-Skip

 

[flyersfan31]

Tetraethyl lead is an anti-knock compound, not a lubricant. You have just run into one of the many old wives tales that get started who knows how and when , and then self-perpetuate for f'ing ever.

-Skip

That's what I thought.

 

[Anthony]

Tetraethyl lead is an anti-knock compound, not a lubricant. You have just run into one of the many old wives tales that get started who knows how and when , and then self-perpetuate for f'ing ever.

-Skip

It get perpetuated by some A&P's. I had one tell me this when my Tiger was in the shop for its Annual a few years ago. I don't go there anymore.

 

[Henning]

You're killing me. The person who told me this had a very serious expression when he told me. What's a non-gearhead to do??????!!!!!!!!

(I find the LOP arguments more compelling than the ROP, I just had to share that lead thing.)

Where the confusion comes in is with the design of the valve guide itself. On an engine designed to run on leaded gas, the bottom of the guide is machined with a square lipped notch that rolls and holds a little donut of lead. This started because when the began putting lead in gas, the guides had a taper in which the lead would wedge and cause valves to hang up.

 

[Richard]

IIRC, 14.9 (actually I thought it was 14.7 but that's a nit) is for "high compression" engines only. Most if not all factory turbo setups use lower compression pistons which reduce the thermodynamic efficiency of the engine so the number is a bit higher for them.

IIRC, APS uses 15.0 to 15.5.

 

[sba55]

IIRC, APS uses 15.0 to 15.5.

Doubt it. Walter uses 14.9 and 13.7 himself as far as I know. Note that the number goes down, not up, with lower compression engines.

-Felix

 

[gismo]

From the Deakin article cited earlier:

Yeah, I meant higher as in more gph per HP but the number is actually HP/gph so obviously I should have said lower (lo compression: 13.7 vs high compression: 14.9). I guess I was misremembering the .7 from the 13.7.

-lance

 

[flyersfan31]

So, what's too hot for turbo ops? Tried lop ops and all looked good but 40lop tit is1645 (1685 is peak) Reduce PWR so tit is under, say, 1500?

 

[Henning]

So, what's too hot for turbo ops? Tried lop ops and all looked good but 40lop tit is1645 (1685 is peak) Reduce PWR so tit is under, say, 1500?

1645 is fine, if you want to reduce power, do it by pulling the mixture back a bit further (remember, when you're in LOP operations, mixture regulates power primarily, prop secondarily).

 

[sba55]

1645 is fine, if you want to reduce power, do it by pulling the mixture back a bit further (remember, when you're in LOP operations, mixture regulates power primarily, prop secondarily).

And to emphasize this - there's not much need to reduce power with throttle LOP. Lean first, and then reduce RPM if you want to reduce power. Reducing RPM doesn't change the mixture much, so you don't need to re-lean after that. And since ICPs are low enough LOP, pretty much any RPM setting works, as long as it's within manuf. specs. I do my descents at full throttle, 90 dfLOP, and 2000 RPM (non-turbo'd).

-Felix

 

[flyersfan31]

TIT seems to be my limiting factor. The APS "go fast mode" of 20dLOP results in peak/near peak (1685IT). I was running today, 8500ft, +10degF, 50LOP (which, coincidently is Cessna's book setting ROP), 370max CHT (#3), 1635TIT, 1470 max EGT (#3 & #5), 138ktas, 11.5gph, vs a book performance of about 143ktas 14.3gph at 50ROP. So, LOP works pretty well, very very slight roughness so clearly the injectors aren't "perfectly" matched. Enriching for more power quickly bumps me up the TIT heat curve to peak, and obviously will push the CHT over 380, but in all a good compromise.

Descents are easier too, pulling RPM back and watching the temps drop nice and slow, no need for fiddling around. All in, I have to say this LOP thing is a pretty good solution.

That is, as long as low-mid 1600s aren't bad for the turbo. I now make sure TIT is 800 before engine shutdown, usually between idling during taxi and a 1-2min cooldown will do it.

 

[Henning]

TIT seems to be my limiting factor. The APS "go fast mode" of 20dLOP results in peak/near peak (1685IT). I was running today, 8500ft, +10degF, 50LOP (which, coincidently is Cessna's book setting ROP), 370max CHT (#3), 1635TIT, 1470 max EGT (#3 & #5), 138ktas, 11.5gph, vs a book performance of about 143ktas 14.3gph at 50ROP. So, LOP works pretty well, very very slight roughness so clearly the injectors aren't "perfectly" matched. Enriching for more power quickly bumps me up the TIT heat curve to peak, and obviously will push the CHT over 380, but in all a good compromise.

Descents are easier too, pulling RPM back and watching the temps drop nice and slow, no need for fiddling around. All in, I have to say this LOP thing is a pretty good solution.

That is, as long as low-mid 1600s aren't bad for the turbo. I now make sure TIT is 800 before engine shutdown, usually between idling during taxi and a 1-2min cooldown will do it.

Many of the smaller diesels I run have the same turbos as used with aircraft, and they run TITs of 1750 for sometimes weeks at a time on generator applications....YMMV

 

[sba55]

TIT seems to be my limiting factor. The APS "go fast mode" of 20dLOP results in peak/near peak (1685IT). I was running today, 8500ft, +10degF, 50LOP (which, coincidently is Cessna's book setting ROP), 370max CHT (#3), 1635TIT, 1470 max EGT (#3 & #5), 138ktas, 11.5gph, vs a book performance of about 143ktas 14.3gph at 50ROP.

Out of curiosity, why the difference in speed? Did you increase MP to counter the loss in power due to LOP? What %power was this at?

Glad to hear it worked out for you!

-Felix

 

[skidoo]

I know this thread is a couple years old, but desire more information. Like the OP, I purchased my T182T with 500 hours on it. I now have 565 hours. I have been operating it like the OP, by the book. My turbo seems to be operating perfectly at this time. I don't know if there are any symptoms prior to a turbo failure or something to inspect at annual. I would hate to have the turbo fail so early.

Anyway, I have read all 6 of the fire breathing turbos articles and Lycoming's article regarding so called "experts" promoting LOP operations. With all the different opinions, I'm still not sure where to operate. Until otherwise convinced, I will operate by the book. But, from what I have read here, this is scary too.

In this article " http://www.avweb.com/news/pelican/182104-1.html " he talks about it being a bad thing to reduce power to 25" after takeoff. But, I don't see an explanation as to why it is such a bad thing to do. In my POH, a normal climb setting is 25" MP, 2400 rpm, and 16 GPH fuel flow. These points are clearly marked on the instrumentation. So, can anyone give a rational reason not to pull back MP to 25" and then gradually lean to 16 GPH after takeoff for a "Normal" climb setting? Can anyone support this practice?

 

[Clark1961]

I'm a bit puzzled. Deakin states that reducing MP to 25 is also leaning the mixture which may be an undesired event. Is that not reason enough to be leery of reducing MP?

I believe Deakin is considering an engine set up for max power (~100 rich of peak) prior to pulling MP back. In a turbo where we set full rich for takeoff then pulling MP back shouldn't be a major concern. I say it shouldn't be a major concern since the engine should be set up such that full rich is always rich enough at any MP setting. Obviously, one should heed Deakin's advice and monitor TIT and CHT after any change in power.

Lot's of hidden assumptions in my statement about "full rich for takeoff" so be a bit on the careful side. Monitor TIT prior to pulling MP back.

 

[skidoo]

Yes, full Rich is standard procedure for takeoff power. So, I pull back MP before leaning to 16gph.

Also, this engine is rated for continuous 87% power. It seems that unless power is well under 75%, that Peak TIT would occur beyond red-line of 1685F. So, what would be harmful of leaning until 1585F TIT without seeing the true peak. For about 75% cruise power, 2200 rpm, 26.5MP, all the temps appear very reasonable.

 

[Ted]

In this article " http://www.avweb.com/news/pelican/182104-1.html " he talks about it being a bad thing to reduce power to 25" after takeoff. But, I don't see an explanation as to why it is such a bad thing to do. In my POH, a normal climb setting is 25" MP, 2400 rpm, and 16 GPH fuel flow. These points are clearly marked on the instrumentation. So, can anyone give a rational reason not to pull back MP to 25" and then gradually lean to 16 GPH after takeoff for a "Normal" climb setting? Can anyone support this practice?

It would depend on the specifics of the plane. Deakin says he is talking specifically about Continentals, which have differences in fuel systems from Lycomings. Specifically, Continentals place a pretty high significance of their fuel flow on throttle position vs. Lycomings. For example, on the 310 when I have the throttles pulled back for 25"/2500 RPM near sea level (climb power), fuel flow reduces to about 18 gph per side. Get up to 5000 ft where 25" is full throttle and it's more like 22-23 gph per side. This is on Continental IO-520-E engines, 300 hp @ 2850 RPM (5 minutes max above 2700 RPM). I could see something like that being potentailly bad on a high-powered turbocharged engine.

Compare to the Aztec, where I also use 25"/2500 RPM for climb (Lycoming IO-540-C4B5 engines, 250 HP @ 2575 RPM). Throttle position has a marginal impact on fuel flow, but not significant. I'm actually able to get more fuel flow near sea level on the low-powered Lycomings part throttle than on the Continentals, but once I get up to a higher altitude I can get more fuel flow out of the Continentals.

I've been flying the 310 doing the 25"/2500 RPM climb power because that's how the previous owner, who flew it for about 2500 hours that way, said worked. After 2500 hours of time with the engines making TBO, I'd say he's right. But I don't like seeing the CHTs get up as much as they do due to low fuel flow, so I may experiment with other options a bit to see what I can get.

When flying the Aztec, I lean in climb based on CHT, and try to keep it below 400F (below 380F is what I really aim for, but sometimes difficult to obtain in the summer due to the poor cooling in that airframe). That ends up being about 18-20 gph a side with cowl flaps fully open in the climb. It's pretty much the same engine as in your T182T, just naturally aspirated, and I have no idea what sort of cooling the T182T has.

 

[Clark1961]

Also, this engine is rated for continuous 87% power. It seems that unless power is well under 75%, that Peak TIT would occur beyond red-line of 1685F. So, what would be harmful of leaning until 1585F TIT without seeing the true peak. For about 75% cruise power, 2200 rpm, 26.5MP, all the temps appear very reasonable.

Other than pointlessly burning/using excess fuel I'm not sure there is a problem with the procedure you describe. The previous owner of my TurboDakota (TSIO-360FB) got more than 600 hours SFRM that way. As I understand the spec, it is permissible to exceed max temp when finding peak but don't routinely operate above max temp. That said, I'm not the manufacturer and I'm not about to buy your turbo or engine if either one quits on you. You're on your own.

 

[NC Pilot]

The other operational consideration is to allow the engine (and turbo) to cool down after landing. I know folks who idle for at least 5 minutes after parking to prevent oil cooking in the turbine bearings.

 

[Tom Gresham]

Remember that John wrote the Pelican's Perch series of articles several years ago. He now says that he (and the GA community) has learned some things that change a few of his recommendations since writing PP.

Those changes are incorporated into the APS online course, which is an incredible value, in my opinion.

Really, the APS course is an eye-opening experience for anyone running a large, piston aircraft engine, regardless of whether you have an engine monitor, injectors (balanced or not), or how you run your engine.

 

[Tom Gresham]

The other operational consideration is to allow the engine (and turbo) to cool down after landing. I know folks who idle for at least 5 minutes after parking to prevent oil cooking in the turbine bearings.

I believe that's been shown (by testing) to be the wrong approach in most situations. If you are at low power on approach, and you don't run at high power during taxi, the turbo should be as cool as it will get when you get to the ramp.

At best, it does nothing. At worst, running at idle for five minutes wastes fuel, delays your trip, and can increase temps.