why do some types endorse LOP ops?

[GeorgeC]

I was reading the wikipedia page on the Malibu and it mentioned LOP ops. My understanding is that LOP ops are standard on the Cirrus as well.

Do other types "officially" endorse LOP ops? Why do some types endorse it and others do not?

 

[murphey]

LOP is great for fuel injected with egt/cht monitor on each cylinder. Difficult with carb engines and the single egt that was standard decades ago, which is when many of our airplanes were built.

 

[Checkout_my_Six]

Cause if not done correctly one isn't really LOP....they could be at peak or slightly rich of peak. And that's the worst or hottest place to run.

 

[James331]

LOP is great for fuel injected with egt/cht monitor on each cylinder. Difficult with carb engines and the single egt that was standard decades ago, which is when many of our airplanes were built.

That.

Also mission profile, some low and slow planes just wouldn't gain as much as the newer high fast stuff.

 

[citizen5000]

LOP is optimum for both fuel burn and keeping the engine happy and cooler. Cirrus builds in a computer calculated LOP and makes graphical hint where to pull the mixture when the manifold pressure is 30.5 or below.

 

[GeorgeC]

LOP has what plants crave, it has electrolytes.

Perhaps a better question would be: if you bought a brand new Cirrus, Beechcraft, Mooney, or Piper with similar mission profiles and fuel injected engines and engine monitors, do all of the manufacturers endorse LOP ops? Why/why not?

 

[Checkout_my_Six]

Who cares? Are you worried bout the warranty?

 

[citizen5000]

Perhaps a better question would be: if you bought a brand new Cirrus, Beechcraft, Mooney, or Piper with similar mission profiles and fuel injected engines and engine monitors, do all of the manufacturers endorse LOP ops? Why/why not?

Cirrus head of service gives customers a half hour presentation on LOP and explains the full technical theory behind the capability. The Ops manual has a section on LOP. The factory recommends using it in cruise and descents and even in climbs if OATs allow.

 

[bradg33]

Cause if not done correctly one isn't really LOP....they could be at peak or slightly rich of peak. And that's the worst or hottest place to run.

This is really only true if you're above 60-65% power. At 60% or below, doesn't really matter where you put the mixture. So if you're above 7-8,000ft in a NA airplane, you're not going to hurt anything.

 

[Tantalum]

with egt/cht monitor on each cylinder

There was a debate at our club among some CFIs and safety officers between LOP and ROP in the older carburated planes.. many of the planes have the JPI monitors showing EGT and CHT for each engine and it was recommended to run LOP if you can safely do so, that it's ultimately what the engine craves. At a later meeting, when the original CFI wasn't there, someone came back and said "that's all fine and well but follow the POH and that says ROP" <- but the debate there was the POH was 50 years old and at the time the most you would have had is maybe one EGT gauge

**Personally I fly by the POH, if it says ROP then that's what I do. But yes, the Cirrus' lean assist does a fantastical job of helping you dial it in

P.S. - don't really understand why we don't have computers do this for our engines. You could always have a manual lean knob to override if you needed to for engine out, etc, but the JPI lean find and the Cirrus basically tell you where to put the mixture, the only thing missing is a little servo to do it for you

 

[Ted]

This is really only true if you're above 60-65% power. At 60% or below, doesn't really matter where you put the mixture. So if you're above 7-8,000ft in a NA airplane, you're not going to hurt anything.

That's a half truth. While you won't have to worry about detonation, you still can have high CHTs. My Aztec was a great example of that. Its lowest CHTs were at the lowest altitudes and CHTs went up as altitude went up, thanks to less cooling air. High CHTs reduce cylinder life, so it becomes one of those "Maybe not today, maybe not tomorrow, but soon and for the rest of your life" regrets.

 

[Jeff Cutler]

I haven't read 'new' plane specs in a while, but improved fuel delivery & balance (read spider and rails) and GAMI injectors are probably stock items on today's Cirrus and Cessna TTX and Mooney? to almost be foolproof temp management when operating LOP -- for the reason they put it in the POH.

 

[GeorgeC]

Who cares? Are you worried bout the warranty?

I am wondering why some manufacturers would say it's ok while others would not. Engineering differences? Legal/liability differences?

 

[bradg33]

That's a half truth. While you won't have to worry about detonation, you still can have high CHTs. My Aztec was a great example of that. Its lowest CHTs were at the lowest altitudes and CHTs went up as altitude went up, thanks to less cooling air. High CHTs reduce cylinder life, so it becomes one of those "Maybe not today, maybe not tomorrow, but soon and for the rest of your life" regrets.

Fair point, but CHT isn't really the reason for the "red box," right? Detonation risk, burned exhaust valves and high ICPs are. CHT isn't really a "direct" byproduct of mixture setting (like say EGT). You can affect CHT by adjusting the mixture, but it's primarily driven by air cooling. Doesn't matter where you're running the mixture, sometimes you're going to have to make adjustments for CHT based on atmospheric conditions.

 

[colojo]

My Acclaim has the TSIO-550G engine with tuned injectors. The cylinders run very balanced and LOP operation is a breeze. The POH doesn't talk about ROP or LOP.

 

[Checkout_my_Six]

I am wondering why some manufacturers would say it's ok while others would not. Engineering differences? Legal/liability differences?

If there isn't a way to monitor CHTs (i.e. no installed engine monitor) there's a risk of not being LOP and over heating cylinders. With the proper instrumentation the risk is low regardless of the brand engine.

Lycoming use to not recommend LOP for this reason....privately their engineers know otherwise. I personally know a few and flown with them LOP.

 

[Ted]

Fair point, but CHT isn't really the reason for the "red box," right? Detonation risk, burned exhaust valves and high ICPs are. CHT isn't really a "direct" byproduct of mixture setting (like say EGT). You can affect CHT by adjusting the mixture, but it's primarily driven by air cooling. Doesn't matter where you're running the mixture, sometimes you're going to have to make adjustments for CHT based on atmospheric conditions.

CHT is partially the reason for the red box. The factors that influence detonation are primarily:

- CHT
- Induction air temperature
- Horsepower being produced
- Oil temperature
- Mixture setting

As a rule, below 65% power you won't detonate the engine, but you can still have accelerated wear caused by high CHTs.

 

[GRG55]

That's a half truth. While you won't have to worry about detonation, you still can have high CHTs. My Aztec was a great example of that. Its lowest CHTs were at the lowest altitudes and CHTs went up as altitude went up, thanks to less cooling air. High CHTs reduce cylinder life, so it becomes one of those "Maybe not today, maybe not tomorrow, but soon and for the rest of your life" regrets.

As I am sure you experienced, I found baffling is critical in the Aztec. More than any of my prior Piper singles. Still the CHT and oil temps need to be monitored closely. I have had to crack the cowl flaps on occasion and I find that works better than richening the mixture at altitude.

I am debating installing GAMIs and wonder if you had them on your Aztec or any other airplane?

 

[Ted]

As I am sure you experienced, I found baffling is critical in the Aztec. More than any of my prior Piper singles. Still the CHT and oil temps need to be monitored closely. I have had to crack the cowl flaps on occasion and I find that works better than richening the mixture at altitude.

Correct. Generally I would do half cowl flaps above 10k, depended on the OAT.

 

[Tantalum]

Very small thread drift, sorry but:

CHTs went up as altitude went up

The Convair B36 Peacemaker had serious overheating issues, the backwards engines didn't help but I've read in many places that the high cruising altitudes meant that cooling the engines was a major issue

 

[Ted]

Very small thread drift, sorry but:

The Convair B36 Peacemaker had serious overheating issues, the backwards engines didn't help but I've read in many places that the high cruising altitudes meant that cooling the engines was a major issue

Yes, that is also true for most turbo engines. It makes sense because your induction air temps get hotter with altitude (higher pressure ratio required) and then your indicated airspeed ends up being slower as a result, so CHTs go up.

There are some exceptions to this situation, mostly if you have a really good intercooler system, which most turbocharged planes don't. A lot of it gets into issues of weight and drag that you always have to carry around to get that, which hurts you elsewhere.

 

[citizen5000]

AOPA just released a fun little video on fuel management. They also mention LOP ops in the video: https://generalaviationnews.com/201...=email&utm_term=0_62525a9780-f17df139c8-95105

 

[Tantalum]

As a serious question, why did liquid cooling never really become a thing in GA? I know it adds some weight and complexity, but I mean that's very mature technology by this point and I would imagine the added weight of the system would be more than offset by optimizing the cowl of the plane for airspeed etc. What would it weigh, an extra 20 lbs? You could probably get at least 5-10 knots out of a sleeker nose. The P-51 even utilized something called the Meredith Effect to get some additional thrust, after air passed through the radiator its expanding effect was exploited

The Extra 400 sported some impressive performance figures and had a liquid cool Continental 550. People worried about the low TBO which killed sales but the ones that are still flying I've read are killer planes with no issue. Someone on PPRUNE has one and loves it: http://www.pprune.org/private-flying/465368-extra-400-a.html#post6780367

 

[citizen5000]

The Rotax 912 is water cooled. You find them in most SLSA.

 

[Ted]

As a serious question, why did liquid cooling never really become a thing in GA? I know it adds some weight and complexity, but I mean that's very mature technology by this point and I would imagine the added weight of the system would be more than offset by optimizing the cowl of the plane for airspeed etc. What would it weigh, an extra 20 lbs? You could probably get at least 5-10 knots out of a sleeker nose. The P-51 even utilized something called the Meredith Effect to get some additional thrust, after air passed through the radiator its expanding effect was exploited

The Extra 400 sported some impressive performance figures and had a liquid cool Continental 550. People worried about the low TBO which killed sales but the ones that are still flying I've read are killer planes with no issue. Someone on PPRUNE has one and loves it: http://www.pprune.org/private-flying/465368-extra-400-a.html#post6780367

The RAM V Cessna 414A had a liquid cooled engine as well, they've had a few instances.

I think in general it came down to the fact that there weren't enough benefits to offset the cost and complexity. Plus keep in mind that certifying a new aircraft engine is really, really expensive, and it was a lot easier to just use what already existed.

 

[GRG55]

The RAM V Cessna 414A had a liquid cooled engine as well, they've had a few instances.

I think in general it came down to the fact that there weren't enough benefits to offset the cost and complexity. Plus keep in mind that certifying a new aircraft engine is really, really expensive, and it was a lot easier to just use what already existed.

And even with liquid cooled that heat ultimately has to be rejected to the thin air at altitude.

 

[Tantalum]

Plus keep in mind that certifying a new aircraft engine is really, really expensive

This I always forget. High costs and the thread of litigation are the core thing killing GA, or at least keeping it from growing. But to that point, rather than a clean sheet design, why not adapt an automotive engine? I am sure it would require some non-insignificant updating, etc. but you would have years, even decades of engine reliability data so it is not really "clean sheet" design. Oh well. just spit balling here. Pardon the thread drift

I'll follow the POH for the leaning technique. Primarily because running too rich has less adverse consequences than running too lean it seams (assuming you are attempting to do so in a Cherokee or soemthing without injectors and fancy gauges). And I'm not an engineer so don't trust myself enough to just dial it in right outside what the POH says. Ha!

 

[GeorgeC]

But to that point, rather than a clean sheet design, why not adapt an automotive engine?

Isn't that what Austro did?

 

[Tantalum]

Isn't that what Austro did?

Yes... but that's not necessarily apples to apples since they were making diesel engines..., other than the appeal of JetA I feel like the market is very finnicky with aircraft buyers and people aren't willing to experiment outside of the non Lyo/Conti world due to fear of reliability, support, maintenance, etc. To the original point though, I am sure Austro used an automotive engine as the basis for costs as well

 

[GRG55]

But to that point, rather than a clean sheet design, why not adapt an automotive engine? ...

You would not be the first to have that thought.

Short answer: if it was easy to do there would already be many hundreds of them flying. Even in the experimental/amateur built world, where certification costs are not a factor, the overwhelming majority are flying with Lycoming or Continental motors.

Slightly longer answer: there have been no shortage of attempts. From modified VW engines (Revmaster, etc) to Subarus, Mazda rotary conversions, Porsche's ill fated PFM (using the 911 engine) and all manner of American V-6 and V-8 derivatives.

The demands on aircraft engines, high output for long, continuous periods of time, are quite different from what automotive engines are subjected to.

 

[Ted]

This I always forget. High costs and the thread of litigation are the core thing killing GA, or at least keeping it from growing. But to that point, rather than a clean sheet design, why not adapt an automotive engine? I am sure it would require some non-insignificant updating, etc. but you would have years, even decades of engine reliability data so it is not really "clean sheet" design. Oh well. just spit balling here. Pardon the thread drift

Using automotive engines has its own issues as well. Austro did a better job, but the original Thielert engine had a lot of technical issues. In both cases it weighed more than the equivalent Lycoming, although without a doubt had a lot of benefits.

From a certification perspective, there are issues as well. The way auto makers build engines (and more importantly implement changes) doesn't sit well with the FAA, so you can't just pull engines off a production line. The way that Thielert got around this was by buying one day's worth of engines from Mercedes, and they certified around that one day, for which no changes were made. Problem was that when they ran out of engines, they ran out of engines. So there were longevity support issues built in from the factory. That would be avoided to some degree if you used something like a Ford 302 as your basis (which is what Ben Haas did) with aftermarket aluminum blocks/heads/etc. Then you could probably manage to minimize or eliminate the number of changes, and basically just take a proven automotive design to work with. But if you want to use a modern automotive engine that's going to get updated and changed, it's harder. This assumes you can even find an automotive OEM who will work with you.

Support wise, there are other challenges. A&Ps know how to work on Lycomings and Continentals, but that's about it. Airplanes are very mobile and tend to break down in inconvenient locations. So now you break down somewhere with your Uber Mach 5 engine, and the mechanic pops the cowls only to see a mess of hoses and wires and starts scratching his head. Oh, and he doesn't have the special whiz-bang-only-available-from-uber-code-reader (that'll be $10,000 for one of those), you get the idea.

Previous attempts have largely had issues because they either weren't developed well (this is typically the case in the experimentals that have them) or never matured. In some cases a bit of both (I think Thielert was a bit of both).

That's not to say I don't think the idea is great on the surface. I do, and 10 years ago I said I thought that would be the way of the future. I was right to some degree. Thielert was already around then and Austro came after them. What's left of Thielert is now owned by Continental. But in aviation "future" requires a lot of patience to get to. If I built an experimental, I would build it with an automotive derivative engine (well, plural, because I'd build a twin ). That said, you could also make some relatively minor changes to current aircraft engines and get some very significant improvements.

 

[Tantalum]

The demands on aircraft engines, high output for long, continuous periods of time,

Something else that I often forget. My Toyota has a scangauge on it and typical highway 70 mph cruise has me around 20 percent throttle open... going up hills that can hit 35 or so, and even there I noticed the temps climb and stay high until the power comes back down... merging on highways, even with fairly liberal use of pedal has it around 65 percent. Now I know throttle position isn't 1:1 percent power, but I can't imagine driving that engine at anywhere near 75 percent power for longer than a few seconds

 

[Tantalum]

Support wise, there are other challenges

That's a big one for sure I imagine

 

[Tantalum]

And that's the worst or hottest place to run.

There was an damning report of epic proportions where a Piper Chieftain had a dual engine failure that was blamed more or less on aggressive LOP operations: https://www.atsb.gov.au/media/1292159/aair200002157_001.pdf

Flying Mag did an article on it too but I can't find it now

 

[Ted]

There was an damning report of epic proportions where a Piper Chieftain had a dual engine failure that was blamed more or less on aggressive LOP operations: https://www.atsb.gov.au/media/1292159/aair200002157_001.pdf

Flying Mag did an article on it too but I can't find it now

That crash wasn't caused by LOP. The first crankshaft snapped because it was one of the Lycoming crankshafts that had issues. The 2nd engine melted because the pilot then went full power without going mixture rich and got into severe detonation and pre-ignition.

It's most basic mistake for any piston multi-engine pilot, and I had a student do it in a Navajo. Same thing. I failed an engine on him and he pushed the throttles forward. For a moment I could picture myself in that Chieftain as it went down after the 2nd engine melted.

I then shoved the mixtures and props forward and told the story of that crash and that if he ever forgot to go full rich when going to takeoff power on that plane for real he'd duplicate the report.

 

[Tantalum]

Yes I think that report got some flack afterwords about making too many LOP indictments

I do find that many CFIs still tend to err on the side of being too rich though and not properly educating students on the mechanics of how the internal combustion engine actually works and what your mixture settings are actually doing to the engine. I do get a little pain on the inside when I see people taxiing full rich at 700 RPMs. I've been told that at optimum lean taxi settings the engine should die if you open the throttle too much without enriching it.. I've gotten to know the mixture knob pretty well on the 172N to know where that optimum mixture setting is for taxi. Also love seeing the GPH numbers be almost perfectly textbook during cruise for the given altitude, etc.

 

[Clark1961]

Most of the POH/AFM that we have were written and approved 40 years ago. Engine monitors were largely unavailable. Sorta difficult for the manufacturers to suggest LOP operation.

That said Piper has two power setting categories for the 'kota. They have fuel flow settings for "Best Economy" and "Best Power" at 55%, 65%, and 75% power. What they really mean is ROP TIT, e.g. "Best Power" and Peak TIT, e.g. "Best Economy".

The factory engine (a stock reman.) would not run LOP. With GAMIs it runs LOP just fine and stays cool that way. Take the engine up high and run peak TIT then it will get just a little bit warm. CHTs are generally fine but the oil temp will be at the top of the green.

 

[Ted]

Most of the POH/AFM that we have were written and approved 40 years ago. Engine monitors were largely unavailable. Sorta difficult for the manufacturers to suggest LOP operation.

That said Piper has two power setting categories for the 'kota. They have fuel flow settings for "Best Economy" and "Best Power" at 55%, 65%, and 75% power. What they really mean is ROP TIT, e.g. "Best Power" and Peak TIT, e.g. "Best Economy".

The factory engine (a stock reman.) would not run LOP. With GAMIs it runs LOP just fine and stays cool that way. Take the engine up high and run peak TIT then it will get just a little bit warm. CHTs are generally fine but the oil temp will be at the top of the green.

The big thing about POHs is that they're written around limits, not goals.

I think these days pilots are much more keenly aware of goals than they used to be.

 

[citizen5000]

Auto engines are not designed to deal with extremes of temperature change or extreme changes in air density in short periods of time. Aircraft engines run at 100% power and redline in climbs then 75% cruise for long periods. An auto engine is only designed to accelerate for seconds then cruise at a fraction of total power. Aircraft engines produce a lot of torque at low RPM (2700) but car engines produce very low torque at that RPM level. Car engines are designed to be liquid cooled. Aircraft engines are air cooled. Auto engines produce peak power at 6000 RPM and if used in an aircraft would need extreme gear reduction that would add cost, complexity and maintenance issues.

 

[Ted]

Auto engines are not designed to deal with extremes of temperature change or extreme changes in air density in short periods of time. Aircraft engines run at 100% power and redline in climbs then 75% cruise for long periods. An auto engine is only designed to accelerate for seconds then cruise at a fraction of total power. Aircraft engines produce a lot of torque at low RPM (2700) but car engines produce very low torque at that RPM level. Car engines are designed to be liquid cooled. Aircraft engines are air cooled. Auto engines produce peak power at 6000 RPM and if used in an aircraft would need extreme gear reduction that would add cost, complexity and maintenance issues.

While auto engines would virtually all require a gearbox, you can design/tune them to make power at lower RPMs. They are designed the way they are to get the combination of power and economy that makes them desirable on the road.

None of the problems are insurmountable.