Lean of Peak (LOP) Engine Operation Explained

[Music] hello Bonanza fans today we're going to talk about lien of peak operations how we fly a lien of peak how it is different from Richard Piech from the engines perspective what advantages flying lien of peak has and also when rich if peak may be a better choice we'll look at some of the theory in a moment but first I want to show you in flight how we make clean of peak happen and what results we can observe you may be surprised how easy it is to switch the engine from rich of peak over to lean of peak it takes just one singer control the often neglected mixture knob too many lean of peak is a mysterious topic with some promise of fuel savings but it may cost of damaging the engine your burn up your valves afghans cheaper than an engine overhaul as some of the counter-arguments to be here at the airport let's find out what is fact and what is fiction and at the end we'll do a little math to see just how much the fuel savings can add up to you over time right now we're in cruise at 9,000 feet the outside the air is plus 4 degrees Celsius throttle is wide open give me 20 inches of manifold pressure and for the moment I'm flying Richard Piech with my a speed indicator showing 143 knots indicated and 165 knots to ESP we have a bit of a tailwind the over the ground we're showing 180 knots a couple of instruments I want you to pay attention to are the fuel flow that's the right half of this instrument here showing how many gallons of fuel are going into the engine per hour and we can control it of course directly with the mixture control push the mixture forward for more fuel now pull it back for less fuel and second this one here which is the digital engine monitor it has fire graphs where each bar represents one of the six cylinder my engine and each bar shows two different values the top of the bar shows the exhaust gas temperature eg teeth how hot is the gas that's pushed out of the cylinder after the combustion event the bottom portion of each bar represents the cylinder head temperature or CH showing us how hot the metal of the cylinder is and then we have these two numbers here at the bottom 13:49 and 305 those are precise digital readouts of egt and CH T for one of the six cylinders you see a little dot here under the number five meaning that the egt and CH T readouts are valid facility' five so my number five cylinder currently has an exhaust gas temperature of thirteen forty five degrees Fahrenheit and a cylinder head temperature of 305 degrees Fahrenheit I can also turn my engine monitor with this switch here from egt and see HT readouts to fuel related readouts showing us the fuel flow and as you can see here we're pushing about fifteen point five fifteen point six gallons per hour through the engine at this time and I can cycle through a few more related values such as this one here showing me how many miles per gallon we're traveling eleven point seven miles per gallon right now similar to the gas mileage of your car except this one here is in nautical miles now let's go Lena peak while I walk you through the process I want you to watch this readout here of the exhaust gas temperature while I'm leaning the mixture and reducing the fuel flow the mixture knob is down here so I'm reaching for this knob and slowly I'm reducing the amount of fuel going into the engine the engine sounds no different than before but what you can see is the mechanical fuel flow gauge he is slowly going down and the exhaust gas temperature the cylinder number five is going up and I'll just keep doing this 1440 43 44 47 and now watch this I keep reducing the fuel flow with the mixture knob but the exhaust gas temperature is reaching a maximum reaching a PG t here at fourteen forty five degrees and is now actually a reversing to lower values and that reversal tells us we're now on the deep side of peak the e GT is still going down further I'm gonna try to leave the mixture to a point where we get an e GT of about 1420 so about 25 degrees below the peak we saw earlier and we'll see what that does okay couple of minutes have passed giving me time for sip of coffee and time to the airplane to adjust to this new power setting on the lean side of PGD team so what has changed the e GT is still at about 1420 which is where we had said it 25 degrees below the peak EDT we observed and we call that 25 degrees lean of peak looking at my instruments I can see the true here speed is now 155 knots so we lost 10 knots our indicated airspeed is 135 knots ground speed is now showing us 171 dots our fuel flow has of course gone down because we pulled the mixture knob back now showing 12.0 12.1 gallons per hour and let's also look at the miles per gallon remember that was eleven point seven miles per gallon earlier when we were reached a peak we're now seeing much better gas mileage fourteen point three fourteen point four miles per gallon so we are a little slower than we were originally but we will use less fuel to get to our destination also our cylinder head temperature for CHT which was 305 degrees earlier is now stable at 285 degrees 20 degrees cooler than it was when we were 18 that by itself is a really nice improvement because when it comes to CHT cooler is better and that is all it takes we're now Elina peak simply by pulling the mixture back while watching the egt and at the expense of a little bit of speed I was able to reduce fuel burn and increase the range in gas mileage and reduce the cylinder head temperature by quite a bit now let's take a look at what's going on inside the cylinder and try to explain why all these changes are happening when we use the mixture control we change how much fuel is going into the engine without changing how much air goes in so it's the ratio of fuel to air that we change with the mixture control when a lot of fuel goes into the engine we call that a rich mixture when little fuel goes into the engine we call that a lean mixture with the mixture control we directly adjust a fuel flow expressed in gallons per hour or pounds per hour and the engine will actually run fine over a pretty large range of fuel flows while keeping other things like rpm and manifold pressure constant one thing that changes as a result of our mixture of fuel flow setting is the exhaust gas temperature or short egt that's the temperature of the gas coming out of the cylinder after the combustion cycle and we measure egt with little temperature probes in the exhaust deck such as this one here there's a separate probe installed for each cylinder so for my six cylinder engine I'm dealing with six separate exhaust gas temperatures for the moment though let's just look at one cylinder and one egt and ignore the rest in the flight you just saw we were at first flying with the rich mixture when I gradually reduce the fuel flow with the mixture control remember how the exhaust gas temperature is slowly increased and then after reaching a peak temperature it decreased as I further reduced fuel flow so in one continuous sweep of the mixture control from very rich to very lean the EDT first climbs then reaches a peak and from there goes down again that's what is depicted in this graph which shows on the horizontal axis the fuel flow you set and on the vertical axis the egt that directly results from that fuel flow note that there are no numbers on this chart the absolute numbers are not that important for what I'm trying to explain what is important is that there is a fuel flow somewhere in this range at which a maximum egt or a peak egt is reached well mark this with a bold line here in the chart from there when we make the mixture richer or leaner the resulting egt will be lower either way along those lines there are no good or bad numbers for exhaust gas temperature the specific temperature value itself is not directly responsible for whether you're going fast or slow or whether you're running the engine in a way that supports longevity or not instead think of the egt is something we can see directly in the cockpit which tells us where on this graph were operating in other words are we at peak egt are we rich of peak or are we lean of peak and as pilots we have complete control over where on this chart we run the engine simply by adjusting the mixture control watch the egt readout value chain the mixture when you're leaning the mixture and the egt increases we must be rich of peak if the EDT decreases we must be lean of peak so the egt helps us determine where we are on this range from very rich to very lean next we're gonna add two additional parameters to this chart the cylinder head temperature and the power produced Everett Norris power like before we're keeping this generic but there are no absolute numbers instead look at the peaks inclines and declines and how steep those inclines and declines are let's start with horsepower the amount of power produced by the engine cannot be directly read from any instrument or cockpit but it can be measured on a specialized engine test and plus you can observe a change of air speed as a result of the power change more power means more speed as you can see here the power curve is fairly flat with mixture settings that are on the rich side of peak egt peak horsepower is achieved at a point somewhat rich of peak egt that's the point where your engine develops the maximum possible power and if all else were equal that will be a great place to be but all else is not equal and as you'll soon see the point of best power is in fact quite often a very bad place to be on the lean of peak side engine horsepower output falls off noticeably as you lean the mixture as you can see from the steeper angle of the curve on the left side the lean side of the graph finally I'm adding the cylinder head temperature or CH T to the chart this is the temperature of the metal of the cylinder and it's important for two reasons both of which are related to the longevity of the cylinder first all metals lose strength with increasing temperature so a cooler CHT is better it means the metal of the cylinder is stronger and more durable second part of what creates the heat inside the cylinder besides just the high temperature of combustion is the pressure inside cylinder resulting from the expanding fuel-air mixture during the combustion event those two things high pressure and decreased strength of the metal are the enemy of all cylinders if they are too high they can weaken and damage the cylinder anything we can do to keep CHT slow is a good thing one important thing to know about CHT is that it changes slowly as opposed to the immediate changes receive the power and egt when changing the mixture the reason for the slow CHT changes is the thermal mass of the cylinder it takes time for all that metal to warm up or cool down and responds to changes of the combustion process on the inside remember this when you're looking for changes on your engine monitor the egt readout follows the mixture change is pretty much instantly whereas the CHT is trailing behind and can take a couple of minutes to stabilize at a new value now I'm gonna try to map the two scenarios we saw enough light earlier on this chart we started with an eg T of 13 45 degrees Fahrenheit and a CH T of 305 degrees Fahrenheit horsepower is not directly known instead I'll use the indicated airspeed in our case 143 knots as the one thing directly obtainable in the cockpit thats related to horsepower all this was the result of my mixture setting of fuel flow which as you saw in the video was fifteen point five gallons per hour when I started to lean the egt reached a peak of 14 45 degrees further leaning resulted in around 14 20 degrees the CH T then stabilized at 285 degrees and the indicated airspeed at 135 knots all this with a fuel flow of 12.1 gallons per hour comparing these two scenarios were going a little slower when lean of peak but were also burning quite a bit less fuel we will arrive if at our destination a few minutes later but with significantly more fuel left in the tanks so for maximizing arranged lean of peak is a great way to fly in addition our cylinder head temperature is lower which as you remember means we have stronger metal and less pressure inside the cylinder which are good things for the engine one more addition to this chart when pilots talk about power settings for the engines they often express that in how many degrees rich of peak or how many degrees lean of peak they are rather than fuel flow for example in the reach of peak as shown on the right side of this chart at fifteen point five gallons per hour fuel flow our egt was thirteen forty five degrees which is 100 degrees less than the peak egt of fourteen forty five degrees therefore we call this power setting 100 degrees switch of peak the equivalent for the lean of P case was a temperature of fourteen twenty or twenty five degrees below the peak of fourteen forty five so in this case we were running twenty five degrees lean of peak as you can probably tell I'm a big fan of lean of peak for the fuel savings and the cooler engine temperatures but history time went rich of peak is better yes there is anytime you want the best possible power or speed rich of peak is the way to go such as for takeoff for the best rate of climb or when your time of arrival and a particular flight is more important than your fuel costs just make sure you are far enough on the ridge site during high power settings to avoid the high CH T's and the high internal cylinder pressures that I mentioned on takeoff that means full throttle and mixture for rich unless leaning as needed for high density altitude thinking in terms of degrees rich of peak or degrees lean of peak is often more meaningful than the fuel flow fuel flow alone doesn't tell us very much if I only throw out a number say 14 gallons per hour depending on the engine I have depending on the altitude of fly at depending on how warm the outside air is depending on my manifold pressure and rpm those 14 gallons per hour could put me at peak egt on the lean side of peak or on the rich side of peak there's just no way of knowing from the number fourteen alone on the other hand saying I'm running 50 degrees lean of peak clearly puts us on the left side of the chart where as you can find 158 degrees rich if peak on the right side for navigating this chart degrees redshift peak and degrees lean of peak is very helpful I'm going to use this terminology now when we talk about power settings that should be avoided due to the thermal and mechanical stress they put on the engine thinking back of the flight you saw earlier I was in cruised at 9,000 feet with a wide-open throttle resulted in 20 the inches of manifold pressure on my normally aspirated engine the engine was making about 65% of its rated power and at that power below there is no mixture setting that will produce abnormal stress on the engine you can therefore vary the mixture and fly a lean off peak the best economy slightly rich if peak the best speed or a bit farther edge of peak for still good speed and cooler ch TS all without fear of the engine at higher power settings things are different that's because of the higher pressure inside the cylinder during combustion the combination of high internal signal pressure and high temperature is especially bad for your engine so at high power settings you should avoid a mixture that puts you in the area of this chart with high CH TS practically speaking at high power settings you should be at least 150 degrees rich if peak when on the rich side of peak or at least 50 degrees lean of peak when on the lean side of peak in between is an area sometimes referred to as the red box that's the area should not operate in the red box gets smaller when the engine develops less power for example when I climb with a normally aspirated engine and completely disappears around 65% power and below because of the red box it is recommended to make the transition from rich if peak to lean of peak quickly thereby avoiding spending more time than necessary in the harmful area associated with the red box so instead of reducing the mixture slowly from rich to lean like I did during the flight I showed you earlier I did that to show you the effect that mixture head on a GT you should pull the mixture in one quick motion not so far is to stop the engine of course but far enough to get on the lean side of peak you can then find peak a GT by enriching the mixture until eg t-piece then lean back to the desired number of degrees lean of peak that is better for your engine then looking for peak egt from the rich side of peak let me reiterate something about the red box because it is so important for you to understand it is perfectly fine to run an engine outside of the red box on either the Ridge or the lean side of peak but some people have gotten into trouble running the engine somewhat lean but not lean enough to be outside of the red box again because of the mechanical and thermal stress this is not a good place for the engine you can quickly transition to the red box to get from one side to the other but don't dwell here if you're flying clean of peak and your CH TS are rising tune uncomfortably high level your mixture is not lean enough and you does need to lean further if that doesn't help both full rich vena peak when done right results in lower CH TS than a comparable richer peak power settings as you've seen in the flight video earlier and if that's not what you're getting something isn't quite right you may have heard that not all engines can be run lean of peak and that is unfortunately a true statement why is that everything I've told you so far is accurate and applicable to virtually every cylinder ever made for any piston engine when lean of peak doesn't work it comes from the fact that we have more than one cylinder per engine all connected to the same crankshaft and while the idea is to give each cylinder the same amount of air and fuel in reality there will be some differences from cylinder the cylinder to understand why that's important for running lean of peak let's go back to our chart let's assume that we have a four cylinder engine everything we reviewed earlier still applies by it applies to each of the four cylinders separately in four slightly different places here's what they might look like when flying ridge of peak now I pull the mixture control back to bring all four cylinders to the lean side of peak look at the power produced by each cylinder in the rich FP case the power output of each cylinder is about the same and that's because of how flat the power curve is on this side of the chart now look at the same information on the lean of peak side because the power curve is steeper here our four cylinders now produce power with a lot more variation and that variation in power between the cylinders causes vibration or roughness when those four cylinders operate on the same crank shaft if the cylinders are spread over two large arranged on this chart you will likely not be able to operate lean of peak so what can you do if your engine becomes too rough to run before you have fully on the lean of peak side if you have a carbureted engine your options are limited carbureted engines unfortunately tend to suffer from somewhat uneven mixed to distribution and about the only thing that can make things better is to apply a little bit of carpet the warmer air will help create a more even mixture distribution which may be even enough to run clean of peak if you have a fuel-injected engine there's a better option since there's a separate fuel injection nozzle for each cylinder it is possible to adjust individual injectors thereby making the range over which the cylinders spread out in this chart much smaller Gami is the name of the company that makes these injectors and if you have a fuel-injected engine that isn't heavily running lean of peak odds are their gammy jack just can help one other thing when we say something like lean to 40 degrees lean of peak given that the cylinders reach peak EDT at different times which cylinder are we referring to the answer is the last similar to reach peak egt on their journey from reg to lean as shown on your digital engine monitor in my Bonanza that happens to be cylinder number five and that is why I had set my engine monitor to provide the readout for cylinder five in the flight I saw earlier different engine monitors of a different ways to identify when each cylinder crosses PE DT so consult its manual to understand how to best do that with your instrument the good news is you'll only have to go through this exercise once because it will always be the same cylinder in your aircraft with your engine at the beginning I promised you to quantify the fuel savings from flying Lena peak let's use the expected life of the engine for that and as human has a tbo of 2,000 hours let's be conservative and assume that we only spend 75% of those 2000 hours going Lena peak leaving the rest for takeoff climb are the richer peak operations remember Richard Piech we saw a 15 point 5 gallons per hour earlier as opposed to 12 gallons per hour when lean of beef times 1500 but that's up to 50 to 50 gallons of saved fuel over the life of the engine and with an average of price of $4 87 in the u.s. for a gallon of gas according to Yonhap com that means you save fuel in the amount of $25,000 in other words when your engine reaches tbo power of the overhaul is free thanks to flying Lena peak disrupt the fuel savings mean off-peak isn't the best way to operate all the time but for my kind of flying it's the best way to operate a lot of the time my fuel cost has gone down and my engine is running cooler saving money on every flight and reducing stress on the engine if this video has gotten you interested in trying beam of peak yourself I suggest that you team up with a flight instructor who is already familiar with lean of peak your type of airplane and with your type of engine together you can validate or tailor what you've seen here as needed to make it right and safe for your airplane if you would like to learn more there are many other resources available to teach lean of peak and engine management in general the two best ones in my opinion are John Deakins pelicans purge column available free of charge on the internet and an engine management class called advanced pilot which covers this and many related topics over the course of a weekend in a live seminar thanks for watching fly safe and see you next time [Music] as you can probably tell I'm a big fan of vegan the egt is still at about 14 20 which we had set with the mixture not 25 degrees and at the end we'll do a little math to achieve to see just how much fuel savings can up and I'll just keep doing this here and at the expense of a little bit of speed I was able to reduce food so we are a little slower than we were originally but we would so we are a little slower is to avoid the hi-c HTS and high internal pressure some were clean but not lean in love up to the outside of the red walls [Applause]

Channel: Martin Pauly

Views: 171,687

Rating: 4.9624104 out of 5

Keywords: LOP, lean of peak, engine, cylinder, rich of peak, ROP, LOP vs ROP, LOP vs. ROP, lean mixture, rich mixture, leaning, engine operation, fuel savings, EGT, exhaust gas temperature, CHT, cylinder head temperature, engine longevity, red box, peak EGT, degrees lean of peak, degrees rich of peak, degrees LOP, degrees ROP, fuel flow

Id: h3bATVXMHQg

Length: 25min 22sec (1522 seconds)

Published: Mon Jan 22 2018

Reddit Comments

[u/NorthWestApple]

Ugh.

So much crap spoken on this topic.

You can't beat physics/chemistry/laws of thermodynamics.

What is "the peak" of which people are rich or lean of, anyway?

Simple: it's the point where optimum fuel burn is occurring resulting in highest temperatures/greatest power.

So what is rich of peak? That is where there is more fuel in the combustion chamber than required. The excess fuel absorbs heat, reducing temperatures, and extends the burn. It results in more oxides in the exhaust, and more soot, as the result of incomplete combustion.

What is lean of peak? This is where there is less fuel in the chamber than required for combustion. The result is more oxygen vs. combustion products, resulting in a cleaner and more complete burn. Due to the reduced fuel mixture, the temperatures are lower (less overall work done), but the work that remains is sufficient to drive the engine without much loss of power.

The biggest thing to remember is detonation is the explosive expansion of fuel in the chamber, usually the result of too early timing before the mixture can be compressed sufficiently to increase the density.

If you pull the mixture back beyond the peak, into "lean", then if you pull off too much, you will lose airspeed (too much power is lost). Pull it back further still, and you get a rough running engine.

As long as the engine is running smoothly and temperatures are within limits, then running "lean of peak" will offer trouble-free operation and reduced fuel consumption in cruise phase, AND THERE IS NOTHING WRONG WITH IT!

You want slightly rich at WOT for cooling purposes.

[u/gbacon]

In the linked YouTube video, the speaker claims to realize savings in operating costs of more than $25k between overhauls with less engine wear due to lower CHT — at the expense of less than 10 KIAS lost — in a Beechcraft Bonanza.

• Engine TBO: 2,000 hours

• Net of takeoff, other ROP ops: 75% or 1,500 hours

• Fuel flow ROP: 15.5 gph

• Fuel flow LOP: 12.0 gph

• Hourly delta: 3.5 gph

• Fuel saved: 3.5 gph * 1,500 hours = 5,250 gal

• USD saved: avgas @ $4.87/gal * 5,250 gal = $25,567

[u/JasonThree]

I posted this video a few weeks back, but great video nonetheless. He's becoming one of my new favorite YouTuber's

[u/Whatever-whocares]

Hadnt seen video before, thanks for passing on, very interesting.