Low Power Cruise settings

[A64Pilot]

Honestly it appears that my IO-360 Lycoming will run smoothly LOP until the power is just so low that it’s just not logical to cruise that way, without Gami’s.

‘I’ve had Gami’s on two air-lane previously, a C-210 with IO-520 and my Maule with an IO-540.

‘I think Continentals combustion chamber design will allow LOP and still produce good power, and Lycoming’s is less tolerant as in power drops off more quickly LOP.

Neither engine is bad and neither is superior, they are very similar, but are different.

My IO-360 is a field overhaul, by someone who has a good reputation with the locals and advertises he balances within 1 gm, he may be CC’ing combustion chambers too, I don’t know, or just as likely my engine just got lucky and the fuel flows happen to match up with each cylinder by luck?

[A64Pilot]

Just now, carusoam said:

I may have over-simplified my statements...

My cylinders become useless, when any part of them wears too much...

To avoid that part from wearing...

I have one tool,

a single CHT sensor near the exhaust port...

It isn’t ideal...

But, it does work pretty well...

-a-

I have the same and when finances allow I’ll install a monitor, but a very valid argument is that my airplane has been flying around for 40 years without one, and it’s original engine made TBO.

‘So just how essential is a monitor?

I’m an engine guy, and I like having the info available, so I’ll install one, but readily concede that an engine can be operated well and safely without one.

[PT20J]

28 minutes ago, carusoam said:

Lycoming skips discussing LOP...

That's not entirely true. Lycoming just leaves it to the airframe manufacturers. Piper included a procedure for the Lycoming O-320 equipped Warrior for running LOP in a carbureted engine. The procedure from 45 or so years ago even included what some now refer to as the "big mixture pull."

Interesting fact I recently learned. We call some of our engines fuel injected, but from an engineering standpoint they are carbureted. The fuel flow through the injectors is continuous and the air and fuel are mixed outside the cylinder to create a homogeneous mixture before the intake valve opens.

Skip

[carusoam]

Life is good with a single numberless EGT and one CHT...

Lets face it... the IO360 with identical distances for all intake tubes is magical...

To get .1gph GAMI Spread probably takes effort...

As far as not having an engine monitor... 

That idea s*cks the first time something goes amiss...

My first 10hours of airplane ownership got a stuck valve... valve bent... making for a very scary long day...  no engine monitor to give a hint if I should land straight ahead or return to the airport...

Monitors pay for themselves the first time you have to hunt down simple things like a slightly blocked fuel injector... or a baffle folding over... or wanting to do a GAMI spread test...

not selling tools of the trade...  they are good to have on every flight...

-a-

[carusoam]

9 minutes ago, PT20J said:

That's not entirely true. Lycoming just leaves it to the airframe manufacturers. Piper included a procedure for the Lycoming O-320 equipped Warrior for running LOP in a carbureted engine. The procedure from 45 or so years ago even included what some now refer to as the "big mixture pull."

Interesting fact I recently learned. We call some of our engines fuel injected, but from an engineering standpoint they are carbureted. The fuel flow through the injectors is continuous and the air and fuel are mixed outside the cylinder to create a homogeneous mixture before the intake valve opens.

Skip

My bad...

My 65C POH skipped it altogether... and my memory that far back aren’t strong enough...

So... it didn’t make it into Mooney POHs... until the Ovation(?)

Do the most recent M20Js have an LOP power chart?

The M20R POH is about 300 pages long... to capture everything like this and performance on grass strips...

More data is more practical...

And if enjoyment of flying requires no bells and whistles... I’m good with that too...

GPS optional...

If flying in flaming dragon mode... use all the instruments you can get...

OH on an IO550, all in, is kind of expensive for most...

everyone will have a different cost/benefit tolerance...

 

It may have been... that the Mooney sales department was all focussed on speed, and their customers at the time were too...

Teaching a customer LOP without an engine monitor to match... would be a recipe for a warranty challenge...

PP thoughts only...

Best regards,

-a-

[PT20J]

Power is a byproduct of the amount and rate at which heat is released by combustion. LOP, the power decreases because the combustion rate and temps decrease. 

Skip

 

[PT20J]

2 hours ago, AH-1 Cobra Pilot said:

Quick and dirty, I would estimate the power loss as P=kmd²N³, (m is mass, d is distance traveled, N is frequency.)

Ergo, about 13% more loss between 2400 and 2500 rpm.

I haven't thought about this much, but since it is a reciprocating/rotating  mechanism, wouldn't there be momentum transfer back and forth between the pistons and the flywheel (prop)?

[AH-1 Cobra Pilot]

No, but it is not that much in total.  Probably about 10-15hp lost in the reciprocating motion.

Think of it in terms of all the exercise people get from The Shake Weight. 

[AH-1 Cobra Pilot]

26 minutes ago, PT20J said:

Power is a byproduct of the amount and rate at which heat is released by combustion. LOP, the power decreases because the combustion rate and temps decrease. 

Skip

 

Not exactly.  Try thinking about it in terms of pressure.

[A64Pilot]

53 minutes ago, PT20J said:

 

Interesting fact I recently learned. We call some of our engines fuel injected, but from an engineering standpoint they are carbureted. The fuel flow through the injectors is continuous and the air and fuel are mixed outside the cylinder to create a homogeneous mixture before the intake valve opens.

Skip

Not really, almost all spark ignition engines are indirectly injected, that is to say the fuel is usually injected onto the back of the intake valve and waits for the engine to inhale it. 

Until very recently ver few spark ignition engines were direct injection,which means the fuel is directly injected into the combustion chamber, Mazda is coming out with a direct injected gasoline motor which is very similar to a Diesel, just burns   gasoline. It’s sort of a hybrid spark / Diesel engine 

https://www.extremetech.com/extreme/253842-mazdas-2019-efficiency-breakthrough-diesel-engine-runs-gasoline

injecting to the back side of the intake valve does several things, it cools the valve for one, but more importantly it means you can continuously inject fuel and let the engine “inhale” it when it’s ready to do so.

‘A very major reason why Diesels are relatively low RPM motors is that you have to time fuel injection to when it’s time for combustion to occur, which is a very small amount of time, and until very recently with common rail the injection pressure to shorten the time interval required with higher RPM just wasn’t possible, Common rail runs such high pressures that its enabled all kinds of new possibilities with Diesels like multiple injection events and variable timing etc, well pressure and electronic injectors of course.

‘We aren’t carbureted because we have dry intakes, and carbureted motors don’t.

‘Now if we were Throttle body injection, then we’ll that’s pretty much a carburetor in a way, but we aren’t.

Edited March 2, 2021 by A64Pilot

[PT20J]

1 minute ago, AH-1 Cobra Pilot said:

Not exactly.  Try thinking about it in terms of pressure.

What causes the pressure?

[A64Pilot]

18 minutes ago, PT20J said:

I haven't thought about this much, but since it is a reciprocating/rotating  mechanism, wouldn't there be momentum transfer back and forth between the pistons and the flywheel (prop)?

The momentum transfer is huge and very efficient. An example of that is the engines that will shut down cylinders when the power isn’t needed, it’s very efficient, they shut down the valve train to eliminate pumping losses 

[PT20J]

2 minutes ago, A64Pilot said:

Not really, almost all spark ignition engines are indirectly injected, that is to say the fuel is usually injected onto the back of the intake valve and waits for the engine to inhale it. 

Until very recently ver few spark ignition engines were direct injection,which means the fuel is directly injected into the combustion chamber, Mazda is coming out with a direct injected gasoline motor which is very similar to a Diesel, just burns   gasoline. It’s sort of a hybrid spark / Diesel engine 

https://www.extremetech.com/extreme/253842-mazdas-2019-efficiency-breakthrough-diesel-engine-runs-gasoline

injecting to the back side of the intake valve does several things, it cools the valve for one, but more importantly it means you can continuously inject fuel and let the engine “inhale” it when it’s ready to do so.

‘A very major reason why Diesels are relatively low RPM motors is that you have to time fuel injection to when it’s time for combustion to occur, which is a very small amount of time, and until very recently with common rail the injection pressure to shorten the time interval required with higher RPM just wasn’t possible, Common rail runs such high pressures that its enabled all kinds of new possibilities with Diesels like multiple injection events and variable timing etc, well pressure and electronic injectors of course.

‘We aren’t carbureted because we have dry intakes, and carbureted motors don’t.

‘Now if we were Throttle body injection, then we’ll that’s pretty much a carburetor in a way, but we aren’t.

My point was simply that if the mixture is homogeneous, the cylinder doesn't "know" whether it came from a carburetor, a throttle body injector or continuous flow injectors near the intake valve and so, from a combustion standpoint, they are all the same. The carbureted Lycoming O-320 in a PA28-161 runs almost as well LOP as the injected Lycoming IO-360 in my M20J. 

[gsxrpilot]

19 minutes ago, PT20J said:

My point was simply that if the mixture is homogeneous, the cylinder doesn't "know" whether it came from a carburetor, a throttle body injector or continuous flow injectors near the intake valve and so, from a combustion standpoint, they are all the same. The carbureted Lycoming O-320 in a PA28-161 runs almost as well LOP as the injected Lycoming IO-360 in my M20J. 

My M20C with it's carbureted Lycoming O-360 would only run smoothly LOP about 20% of the time. And that was only with a few tricks and a little black magic. 

My 252 with it's fuel injected Continental TSIO-360 runs reliably smoothly LOP 100% of the time. With a spread between richest and leanest cylinders of only 0.3 gph, it will run smooth almost all the way to idle cut off. I've seen 100° LOP and the engine was still smooth. It's not a very useful number or setting as the power is very low. But it's indicative of well balanced fuel flow across all six cylinders.

[PT20J]

5 minutes ago, gsxrpilot said:

My M20C with it's carbureted Lycoming O-360 would only run smoothly LOP about 20% of the time. And that was only with a few tricks and a little black magic. 

My 252 with it's fuel injected Continental TSIO-360 runs reliably smoothly LOP 100% of the time. With a spread between richest and leanest cylinders of only 0.3 gph, it will run smooth almost all the way to idle cut off. I've seen 100° LOP and the engine was still smooth. It's not a very useful number or setting as the power is very low. But it's indicative of well balanced fuel flow across all six cylinders.

A big problem with induction systems is that the flow isn't constant. During the end of the exhaust stoke, the valve overlap allows pressure from the cylinder to enter the intake manifold. Then during the intake stroke, the cylinder takes a big gulp of air from the manifold. If the induction system isn't carefully tuned, all this pulsating airflow messes up the mixture distribution whether it has injectors or a carburetor. Some engines are just better than others in this regard. One thing Lycoming does is to run the intake air through the engine sump. This actually reduces the volumetric efficiency (by decreasing air density) but it helps better vaporize the fuel making the mixture more homogenous.

With my factory rebuilt Lycoming IO-360, at low altitudes, I can lean it so much that the EGT starts to rise again because the combustion is so slow (there is no practical value to this, but it was an interesting experiment). On a R-985 (float carburetor) the mixture is so even that I could lean it until it would backfire because there was still fire in the hole when an intake valve opened.

Skip

[A64Pilot]

985 is supercharged just like the 1340, due to this neither should have any reversion, as they are under boost.

Its the supercharger more than anything that gives very even fuel mixture, that and the fact the intake is under pressure.

Reversion is what that back flow is called, to see and feel it take the air filter off of just about any small motor and hold your hand behind the carburetor, you’ll feel the pulse and most likely your hand will be wet with fuel

You have valve overlap to take advantage of the inertia of the gasses flowing though the engine, a well designed normally aspirated engine will exceed 100% volumetric efficiency when operated at optimum load and RPM.

‘However as the exhaust in aircraft is the responsibility of the airframe manufacturer, it’s pretty common for them to be pretty poorly designed as far as tuning is concerned. 

[PT20J]

2 hours ago, A64Pilot said:

You have valve overlap to take advantage of the inertia of the gasses flowing though the engine, a well designed normally aspirated engine will exceed 100% volumetric efficiency when operated at optimum load and RPM.

Since the definition of volumetric efficiency is the ratio of the actual mixture mass drawn into the cylinder to the mass that would occupy the swept volume of the cylinder under ambient conditions, it is difficult to see how a normally aspirated engine could have a VE of >100%. The following graphs show the effect on VE of various valve timings and lifts. (From Heywood, Internal Combustion Engine Fundamentals, 1988)

[AH-1 Cobra Pilot]

11 hours ago, PT20J said:

ince the definition of volumetric efficiency is the ratio of the actual mixture mass drawn into the cylinder to the mass that would occupy the swept volume of the cylinder under ambient conditions, it is difficult to see how a normally aspirated engine could have a VE of >100%. The following graphs show the effect on VE of various valve timings and lifts. (From Heywood, Internal Combustion Engine Fundamentals, 1988)

And do not forget the Gulp Factor.  Anything over 0.5 rapidly deteriorates η_v.

The Mean Inlet Mach Index, or Gulp Factor, Z, is defined for a reciprocating piston engine as

                                        Z = (B/D_T)²NS/(nC_ma_o)                                               (1.)

where B = cylinder bore, S = stroke, D_T = valve throat diameter, C_m = mean valve discharge coefficient based on throat area, N = engine speed, a_o = sonic velocity in the intake duct, and n = number of valves.

[PT20J]

22 minutes ago, AH-1 Cobra Pilot said:

And do not forget the Gulp Factor.  Anything over 0.5 rapidly deteriorates η_v.

The Mean Inlet Mach Index, or Gulp Factor, Z, is defined for a reciprocating piston engine as

 

                                        Z = (B/D_T)²NS/(nC_ma_o)                                               (1.)

 

where B = cylinder bore, S = stroke, D_T = valve throat diameter, C_m = mean valve discharge coefficient based on throat area, N = engine speed, a_o = sonic velocity in the intake duct, and n = number of valves.

 

 

Hadn’t heard it called Gulp Factor before. Losses from forcing a compressible fluid through a constriction (intake valve opening) at high rates. One reason intake valves are as large as possible. There’s a good discussion in Taylor, The Internal Combustion Engine in Theory and Practice, Vol. 1, chapter 6. 

[A64Pilot]

Volumetric efficiency of greater than 100% is common in high performance engines, usually at full throttle and at the specific RPM that the exhaust and intake are tuned for, exhaust wise you have the restriction of the exhaust to occur just before the exhaust pulse goes though and as the exhaust valve opens, that makes the pressure in the exhaust be below atmospheric and the exhaust is sucked out of the cylinder.

‘On the intake side you design the intake so that the inertia of the gasses in the intake will have a higher than atmospheric pressure before the intake valve opens, so your pushing air into the intake and sucking it out of the exhaust and you have greater than 100% efficiency, but only at a narrow RPM range and usually only at full throttle, partial throttle’s purpose is to block incoming air.

Race motors have exceeded 100% for decades

https://forums.autosport.com/topic/94318-more-than-100-volumetric-efficiency-on-a-na-motor/

Edited March 3, 2021 by A64Pilot

[jlunseth]

22 hours ago, A64Pilot said:

A turbo is a pure heat driven turbine, and what makes a turbo “happy” is lower temps, and 25 LOP is hotter than 50 ROP, by 25 degrees of course. Replace those numbers with any others you want to, a turbo only know temps, it doesn’t care LOP or ROP.

‘Cylinder head temps follow power production, they are cooler at LOP because power is down, not because there is any “excess” air available to cool the heads. 

Well, I don't find the last statement to be true in my 231. First, yes, a turbo is an exhaust driven turbine, not quite accurate to say it is heat driven.  What is it about the heat that drives the turbine, as opposed to the exhaust flow through the turbine. The exhaust flow is hot, of course, but if you blew an equal mass of cold air through at an equal velocity, the turbine would generate the same work. More importantly though, the degrees LOP vs. ROP is a difference in EGT, it is not a difference in CHT. The CHT's generally run quite a bit cooler at 25 LOP than at 50 ROP. It is the CHTs we are concerned with, not the EGTs. EGTs have value only as a relative number (when did that cylinder peak, and how many degrees from peak EGT is that cylinder now), CHTs have value to us as an absolute number.

On the last statement, I am able to produce the same power in my engine whether ROP or LOP. When I cruise at LOP, I am at 71% or thereabouts. I have the ability, with a turbocharger, to vary my degrees LOP by increasing MP as well as by decreasing FF. So that is what I do to stay well LOP, I cruise at 34" MP and operate at 71% HP. I can operate at 71% HP on the ROP side also, if I want, but the CHT's will be quite a bit warmer, on the order of 80 degrees or more warmer.

The reduction in CHT is not due to extra air being pushed through the cylinders when LOP, just as the reduction in temp when going further ROP than normal is not due to fuel flushing through the cylinder. What is happening in each case, for different reasons, is that the rate of combustion is being changed so that the combustion event is more of a push than an explosion, and less temp is generated. In the LOP case the fire takes longer to find the lesser available fuel, in the ROP case, the fire takes longer to find the lesser available O2. It is the varying of the fuel/air ratio that determines LOP or ROP. The amount of power being produced is the area under a curve, you can have the same area with a short, high peak, and with a lower and more drawn out curve.  The lower drawn out curve will generate less heat because, among other things, the max ICP is lower.

LOP is easier on an engine because the same power is produced with a less harsh power curve, than ROP. You could, in theory, make the ROP power curve about the same as the LOP curve, but to do it you would have to operate much more ROP than most pilots are willing to do.

[gsxrpilot]

Very well said @jlunseth

[Fry]

I wonder why (apparently) everybody agrees that wear is proportional to "piston travel", i.e. higher RPM converts to proportionally higher wear per hour.

To me, this is absolutely not obvious, and I don't "buy" it.

Just think about this: at the same power, lower RPM means higher torque and thus higher forces. Why should that mean less wear?

I am running my engine at lower than the 2700 RPM (max. specified continuous RPM) for noise reasons. But by doing so, I get less air (at the same MP) into the engine, thus have to choose a lower FF, and I get less power. But flying is about speed (for me), so I don't want to go lower than 2600 RPM.

[Fry]

Because somebody asked how I do it: here is my self-made leaning calculator for the Lycoming IO-360.

The outer ring and center are fixed, the ring with the black numbers can be turned.

When flying ROP (right side of "RICH"), I use the indicated gph or MORE.

When flying LOP (left side of "RICH"), I use the indicated gph or LESS.

Keep in mind that 10.1 gph corresponds to 150 HP (in ideal conditions, in the IO-360 at 1:8.7 compression), thus 75% power of the IO-360. Because of that, 10.1 gph or less will NEVER put you inside the "red box", and that is the reason I don't use EGT for leaning anymore, since I am more concerned about getting optimal power than anything else. My CHTs in cruise are 300-320°F at this time of the year.

[ArtVandelay]

They use to have an app, but I think it was removed?