LOP & Percent Power for Dummies®

[gsxrpilot]

Yeah, I was just thinking about that. I don't know what "deeply" is.

I don't have the best GAMI spread with my engine. So 30° is about as lean as I can get. Therefore I don't run LOP above 65% power. This ensures there is no RedBox. 

In my estimation, this is the best combination of speed, fuel efficiency, and engine protection for my 252.

[jaylw314]

On 5/25/2020 at 3:30 PM, gsxrpilot said:

Sorry to be late to the party here but that's my post that you took the screen shot from. I got the multiplier from @kortopates specifically based on the compression ratio of an IO360 engine.

Ooops!  I stand corrected!

[jaylw314]

10 hours ago, jlunseth said:

Has it occurred to you, though, that if you run that far lean, at 65% power or less, you are essentially flying an Archer/Arrow class aircraft? I will grant you, your fuel flow will be better than an Archer. But the aircraft itself would be cheaper, less complicated to fly. 60% is approach speed for me. My engine flies around for hours at 70-71%, faster and it now has several hundred hours doing that with no ill effects, in fact, knock on wood, I am about 100 hours over TBO with the TSIO360LB.

A significant benefit of flying more efficiently is that you land with a larger fuel reserve on any given trip.  Given the number of accidents related to running out of fuel, I figure that slightly better safety margin on EVERY SINGLE TRIP I make will add up to better odds of avoiding such an accident over my lifetime... 

[MikeOH]

I flight plan for 10 gph, but run LOP at 8.5 gph.  Very comforting

[gsxrpilot]

8 minutes ago, jaylw314 said:

A significant benefit of flying more efficiently is that you land with a larger fuel reserve on any given trip.  Given the number of accidents related to running out of fuel, I figure that slightly better safety margin on EVERY SINGLE TRIP I make will add up to better odds of avoiding such an accident over my lifetime... 

That is one of two major benefits I see to LOP operations. Arriving at your destination with more fuel still in the tanks, is a safety factor and benefit.

The other one I see is speed. I hear everyone talking about LOP being too slow. But for those of us who like to fly our Mooneys far, nothing improves speed quite like skipping a fuel stop. 

[aviatoreb]

Well I’m all for saving fuel but I don’t see how it makes a guarantee or even greater likelihood of arriving at destination with more fuel / lowering likelihood of fuel exhaustion.  Those are caused by bad planning bad attitude and inattention.  With those bad traits but a better fuel burn a person can plan to arrive at their further away destination still with only 15 min of fuel and miss the mark just like they can screw up rop. Or vice versa with a good attitude and planning you can avoid fuel exhaustion rop.

[CharlesHuddleston]

FWIW, the JPI 700 can/will display %Power, but I think you have to add RMP and fuel flow modules ??? Mine displays it. Check in the User's Manual

[MikeOH]

1 hour ago, aviatoreb said:

Well I’m all for saving fuel but I don’t see how it makes a guarantee or even greater likelihood of arriving at destination with more fuel / lowering likelihood of fuel exhaustion.  Those are caused by bad planning bad attitude and inattention.  With those bad traits but a better fuel burn a person can plan to arrive at their further away destination still with only 15 min of fuel and miss the mark just like they can screw up rop. Or vice versa with a good attitude and planning you can avoid fuel exhaustion rop.

Well sure.  But, good planning allows for a reserve, right?  If we were all so perfect why have a reserve?  Why do we keep having fuel exhaustion incidents?

 So, I plan for 10 gph, and run LOP at 8.5 gph; I look at as a another 'reserve' on top of the hour I built into my flight plan at 10 gph.  No guarantees of course, but I absolutely think it "lowers the likelihood of fuel exhaustion."

[carusoam]

It’s like UPOD... under promise and over deliver.... (sales speak for a method to keep happy customers...)
 

In this case it is a method to keep happy plane owners, and their families....

Plan a higher FF that could happen under some conditions... then operate with tighter control....

For My M20C... we always used 10gph as the base line for fuel use... probably 15gph for T/O and climb...

We had no instrumentation beyond two wobbly fuel level indicators.... L & R...

Fuel planning that way works... it’s just sub-optimal with today’s technology being available...

There are two precise ways of measuring fuel used... FF/totalizer, and Cies FL instruments...

Good planning one way... you add a bunch of safety factor on top of the safety factor the FAA mandates...

Good planning with good instruments... your factor of safety is just the FAA mandates...

I really didn’t like flying for hours without knowing how much fuel was burned...

With MS... I realized how precise the FF of our engines actually is... It doesn’t fluctuate like I thought... or assumed...
 

Without decent instruments... I’d still be uncomfortable...

PP thoughts only not a CFI...
 

Best regards,

-a-

[ArtVandelay]

FWIW, the JPI 700 can/will display %Power, but I think you have to add RMP and fuel flow modules ??? Mine displays it. Check in the User's Manual

I think you need RPM, MAP and OAT sensors IIRC.

[aviatoreb]

6 hours ago, MikeOH said:

Well sure.  But, good planning allows for a reserve, right?  If we were all so perfect why have a reserve?  Why do we keep having fuel exhaustion incidents?

 So, I plan for 10 gph, and run LOP at 8.5 gph; I look at as a another 'reserve' on top of the hour I built into my flight plan at 10 gph.  No guarantees of course, but I absolutely think it "lowers the likelihood of fuel exhaustion."

I agree - you are using good planning strategies.  It’s you that is making you safer / not the lop itself.  Any good stuff.

[201er]

9 hours ago, aviatoreb said:

Well I’m all for saving fuel but I don’t see how it makes a guarantee or even greater likelihood of arriving at destination with more fuel / lowering likelihood of fuel exhaustion.  Those are caused by bad planning bad attitude and inattention.  With those bad traits but a better fuel burn a person can plan to arrive at their further away destination still with only 15 min of fuel and miss the mark just like they can screw up rop. Or vice versa with a good attitude and planning you can avoid fuel exhaustion rop.

When I was flying nonstop upwind from NYC to San Marcos TX, my enroute fuel calculations were showing me arriving with an uncomfortably insufficient fuel reserve. Of course I had several potential fuel stops planned and studied the airports short of the destination, but still I wanted to try to make it work. I was already LOP doing about 8.5gph but by slowing down to 8.0gph, that brought the estimated fuel reserve from 7 gallons to 11. Half a gallon an hour saved over 10 hours is a bunch of gallons. The headwind plus powering back tagged an extra hour on the flight, but hey it only cost me $87 in gas to fly to Texas.
 

 

[Ibra]

10 hours ago, MikeOH said:

I flight plan for 10 gph, but run LOP at 8.5 gph.  Very comforting

Same I do budget for 10GPH on 130GS, if I need to speed up or cool CHT down I have those 1.5usg/h and 30kts for the task, I like to have the option later on the flight when uncertainty on winds & route & level goes down, sometimes I do eat some of that fuel going faster at the end when Fuel Totaliser and gauges are sure of remaining fuel on board after landing

Once I landed dead stick in a field flying C172 close to it’s max range with 50kts headwinds by going too rich on old manufacturers gauges (should have planned for ROP fuel burn & way slower GS), if only I had extra 5 gallons or at least I did know halfway that I will not make it as winds turns out 20kts higher than forecasted 

Edited May 27, 2020 by Ibra

[Steve Yucht]

Hi all, new to this LOP vs ROP thought.  Have only 200hrs in my ppl and 100hrs in my Ovation 2.  Now that I can fly the plane well I added a JPI 830 to better manage the engine.  I like speed but definitely don't want to burn more avgas than necessary for that speed.  I have read the JPI manual countless times. Is there a post that has basic fuel flow settings for my IO-550 with corresponding MP and RPM's for 75% and 65% power.  I follow the visor settings (cruise power settings) for MP/RPM but this is ROP and doesn't really get to leaning ROP.  What I would really like is a simple approach to setting cruise at 2300 RPM (lower sound and presumably less wear on the engine in the long run) that gets me 75% or 65% power ROP and LOP out of the red box so I can talk to ATC and get everything all situated before spending head down time with the JPI to clean it all up as precise as possible. Thanks, I value your experience

[jlunseth]

Two things. On the running-out-of-fuel issue, I deal with that by keeping it simple.  Training is to change tanks every half hour or something similar, to keep the plane “balanced.” My Mooney does not care if it is balanced or not balanced, it flies the same.  I take off and climb to altitude on one tank, the climb might be in the neighborhood of 45 minutes if I am going to the flight levels.  Once I level off I make note on paper of the fuel used from that tank, then switch tanks.  Flying LOP, I have over three hours in the second tank. I stay on that tank until it is time to approach the destination airport, then switch to the first tank which has over two hours of fuel remaining.  I don’t switch back and forth frequently because, frankly, that is a recipe for forgetting. I just switch twice at major changes in the flight regime, no forgetting that way even at my advanced age.

And on the issue of skipping fuel stops, my 231 has six+ hours of fuel at LOP.  75.6 gallons divided by 11.1 is nearly 7 hours. To be conservative, I use 13.5. Fuel flow during the climb to altitude is going to be an average of 22 GPH, but then during the descent, about 10 GPH, so the 13.5 is to allow for that and be on the conservative side. That is over 5 hours of fuel with an IFR reserve. I have gone from Alamosa to Minneapolis, Peoria to Frederick MD, and Minneapolis to Asheville in one hop with plenty left over.  So why are we worrying about a fuel stop? My legs and bladder want a stop if the trip is longer than that.

I guess if you don’t have a 231 maybe you would worry more........

[gsxrpilot]

I use the same fuel tank strategy. Less switching, less times, less to forget.

All of our Mooneys benefit from being able to skip fuel stops when flying LOP, compared to brands C, P, B...

[jlunseth]

8 hours ago, Steve Yucht said:

Hi all, new to this LOP vs ROP thought.  Have only 200hrs in my ppl and 100hrs in my Ovation 2.  Now that I can fly the plane well I added a JPI 830 to better manage the engine.  I like speed but definitely don't want to burn more avgas than necessary for that speed.  I have read the JPI manual countless times. Is there a post that has basic fuel flow settings for my IO-550 with corresponding MP and RPM's for 75% and 65% power.  I follow the visor settings (cruise power settings) for MP/RPM but this is ROP and doesn't really get to leaning ROP.  What I would really like is a simple approach to setting cruise at 2300 RPM (lower sound and presumably less wear on the engine in the long run) that gets me 75% or 65% power ROP and LOP out of the red box so I can talk to ATC and get everything all situated before spending head down time with the JPI to clean it all up as precise as possible. Thanks, I value your experience

Steve, there is a way to get an accurate reading of how many degrees LOP you are running the engine, using the ROP lean function on the 830. Read that again, you can use the ROP lean function to get an accurate reading of degrees LOP.

First, though, if you want to fly LOP with a normally aspirated engine, just leave the throttle full open, set the RPM’s where you want them, and then manage your LOP power setting with the mixture knob. As everyone has said, power when LOP is the multiplier for your engine times the fuel flow in GPH. That’s it. It does not matter what the MP is, as long as the richest cylinder is a sufficient number of degrees lean of peak. The multiplier for your engine is directly determined by your compression ratio.  Maybe someone who knows the engine can tell us whether the multiplier is different from 15, which is pretty much the standard multiplier for an NA engine. Its that simple.

As for determing how many degrees LOP you are, the trick is to do the “big pull” first, to get over on the LOP side of peak. You do that by leaving the throttle wide open, setting the RPMs to what you want, and then smoothly pulling the mixture knob until you feel a pronounced drop in power. You are now operating LOP. To find out how many degrees LOP you are for a particular fuel flow, you then activate the JPI’s ROP lean function.  That’s the ROP lean function, not the LOP lean function.  The JPI lean function does not know whether you are rich or lean of peak. The ROP lean function shows how many degrees from peak the first cylinder to peak is, and that is what you want.  You are on the lean side of peak, so you activate the ROP lean function and then slowly enrich the fuel until the JPI finds the first cylinder to peak.  Then lean the fuel flow back again, and the reading the JPI will give you is the number of degrees lean of peak that first-cylinder-to-peak is.  

Its up to you at that point where you want to run your engine.  The “red box” is a theoretical model, not a fixed set of numbers. It is bigger for high power settings than for low. I would suggest you see if you can get 20 dF lean of peak with a fuel flow that gives you 75% power, then watch your CHTs to make sure they stay reasonably cool. As for a 65% setting, the GAMI/APS guys tell us you can’t hurt the engine at 65%, so you don’t really care how many degrees LOP that richest cylinder is.  What you want, is a fuel flow that, when multiplied times the multiplier for your engine, gives you 65% of the rated horsepower of your engine.

Remember that this setting you have just made is valid only for a particular altitude (or within a range of altitude). If you go higher the fuel flow may need to be reduced to stay lean of peak, because the MP is dropping with altitude.

It will take a little experimentation to get familiar with the fuel flow settings for you engine but not much. Once you have done that, it is just a matter of leaving the throttle open, setting the RPMs and pulling the mixture to the fuel setting for the power you want.

Edited May 28, 2020 by jlunseth

[Steve Yucht]

jlunseth

Since I don't have O2 in my O2 I never fly above 10,000 ft . Most of my trips are less than 1 hr so I'm usually at 8500 tops anyway.  I was taught to reduce MP to 25 after 1000 ft AGL on climb.  So when you say leave throttle all the way open that would mean I have to advance my throttle once in cruise prior to leaning.  Is that correct? 

[kortopates]

24 minutes ago, Steve Yucht said:

jlunseth

Since I don't have O2 in my O2 I never fly above 10,000 ft . Most of my trips are less than 1 hr so I'm usually at 8500 tops anyway.  I was taught to reduce MP to 25 after 1000 ft AGL on climb.  So when you say leave throttle all the way open that would mean I have to advance my throttle once in cruise prior to leaning.  Is that correct? 

That's not really good advice to reduce MAP to 25 after 1000'AGL. The engine runs more efficiently Wide Open Throttle (WOT) and so should you. Any power reduction is better done with RPM as opposed to Throttle/MAP. So i am sure John @jlunseth was expecting you would climb up to cruise altitude at WOT, and 8500' works fine, and set your normal cruise power level  based on WOT MAP and RPM. Then you can lean your engine with the big pull. 

But if you haven't run LOP before, you should first measure your gami sweeps and check the health of the ignition system with a LOP Mag check. Until your mixture distribution is at 0.5 or less and you know your ignition system is healthy your engine won't be happy running LOP. Plus virtually all IO-550 needed tuned injectors, either Gami's or Continental position tuned injectors before they have a adequate mixture distribution to support LOP ops.  I would encourage you to start there first. Here is a link to Savvy Test Profile instruction for collecting the necessary diagnostic data to measure you Gami spread and ignition system health. You can get a free account to upload your EDM data and use our Savvy tools to check your data.

https://resources.savvyaviation.com/resources/other-documents/flight-test-profile/ 

[jlunseth]

45 minutes ago, Steve Yucht said:

jlunseth

Since I don't have O2 in my O2 I never fly above 10,000 ft . Most of my trips are less than 1 hr so I'm usually at 8500 tops anyway.  I was taught to reduce MP to 25 after 1000 ft AGL on climb.  So when you say leave throttle all the way open that would mean I have to advance my throttle once in cruise prior to leaning.  Is that correct? 

You seem to be talking about so-called “square” operation, where the RPMs and MP would be pulled back to the “same” number, usually 2500 RPMs and an MP of 25 inches.  I learned the same thing in PPL years ago, it was the way things were done, apparently originally came from rotary engine ops. Paul is right, not necessary. I just fly to altitude at full throttle.  Here, turbo and NA operations are a little different (I fly a turbo). In the NA you would reduce fuel flow as you gain altitude, to manage EGT to a specific number, usually the number you had on takeoff. I will leave it to the NA guys to explain that because I don’t do it in my turbo and haven’t for quite awhile. What you are doing by leaning in the climb is keeping the fuel/air ratio about the same as it was at full power on takeoff.

In the turbo I just keep the fuel flow in all the way and the MP at full power all the way to altitude. Since I can go all the way to cruise altitude at full power, whatever that is (as long as it is less than the critical altitude of 22,500), there is no reason to lean the fuel.  In the NA you need to lean with altitude because the MP will ineluctibly fall. That said, there are turbo guys who swear by a reduced power climb.  If they can keep the airspeed up at about 120 and the CHTs low, it certainly doesn’t hurt anything. But that’s another story.

Do what Paul said though if you are interested in LOP, do your GAMI test and get your fuel flows within .5 GPH. 

Would be great if one of the NA guys could chime in and say how all this is done with their experience.  Its important to understand that turbo and NA ops are different though, especially important for turbo operators to not use NA lean-in-climb techniques, good way to hurt an engine.

 

[carusoam]

Steve Y...

Seeing if you have a few tools that will be helpful for what you are doing...

1) Do you have the POH for your plane..?

2) The O1’s POH has power charts that include both ROP and LOP. (Really well developed charts)

3) Do you have an analog EGT instrument.?   Does it have a blue box on the face? (Aka the ship’s EGT gauge)

Transition Training for the O, often includes a decent X-country... where you can learn the intricacies of..

• Setting best power for T/O above SL...
• Climbing ROP, using the blue box (white box if you have a G1000...)
• Accelerating and Setting power for cruise....
• Rough Leaning ROP or LOP...
• Fine leaning once in the neighborhood of peak...
• Setting RPM... (2500 rpm is a magical setting for many Ovations... Set it and forget it...)
• Setting up the JPI and learning best practices...
• downloading data from the JPI and sharing it...

4) Be ready to take notes... Peak will occur  somewhere between 13gph and 15gph (depending on MP, rpm, and Alt)

5) There is more complexity with the 310hp STC... it has the ability to use more rpm... and a FF will move with rpm...

6) when you get good at this... rough leaning is really quick... it gets you in the neighborhood...

7) Fine leaning takes a little longer, but you have the JPI to help... just know the TCs can take a few seconds to react... don’t spin so fast you miss the peak...   if you miss it, go back slowly... the peak doesn’t move...

8) If the peak appears to move... it is  a sign of not waiting long enough for the sensors to show the temp...

PP thoughts only, not a CFI...

Best regards,

-a-

 

[MikeOH]

M20F with NA 200 HP.  Here's the Cliff Notes of what I do:

1) Take off with all levers forward (DA less than 5000 feet)

2) Above 5000 DA I lean to maintain my take-off EGTs of 1350

3) Once at cruise altitude I set desired rpm, usually 2500-2600.

4) Pull mixture to set desired power (typically 8.5 gph and around 65%)  I do NOT use the engine monitor (EGT/CHT), only the FF gauge.  After things stabilize I'll check that CHTs are okay.  (Typically I don't even bother closing cowl flaps as I get virtually no speed increase and oil temp/CHTs rise)

Note the throttle stays at WOT.  Even in descent.  I just start enriching mixture as I descend.  That way I make up some of the time lost in climb.  I'll only pull power back when I get within a couple thousand feet of TPA in order to slow up.

Edited May 29, 2020 by MikeOH

[jlunseth]

29 minutes ago, MikeOH said:

M20F with NA 200 HP.  Here's the Cliff Notes of what I do:

1) Take off with all levers forward (DA less than 5000 feet)

2) Above 5000 DA I lean to maintain my take-off EGTs of 1350

3) Once at cruise altitude I set desired rpm, usually 2500-2600.

4) Pull mixture to set desired power (typically 8.5 gph and around 65%)  I do NOT use the engine monitor (EGT/CHT), only the FF gauge.  After things stabilize I'll check that CHTs are okay.  (Typically I don't even bother closing cowl flaps as I get virtually no speed increase and oil temp/CHTs rise)

Note the throttle stays at WOT.  Even in descent.  I just start enriching mixture as I descend.  That way I make up some of the time lost in climb.  I'll only pull power back when I get within a couple thousand feet of TPA in order to slow up.

That’s pretty close to what I do except no leaning during the climb for turbos. I also pull the power to a set fuel flow, but in my case I have done quite a bit of experimenting and I am comfortable that the 11.-11.3 fuel flow setting and 34” MP that I use are nicely lean of peak.  That produces 71% HP in my engine. From there I use Turbine Inlet Temp. to tweak the fuel flow, I don’t like TIT to creep above 1600 and if it does then I reduce the power by leaning a little bit.

[ArtVandelay]

Closing the cowl flaps on a J results in +5 knots.
If I’m going to an high altitude airport I make note of where I need the mixture in an earlier practice flight, so I can have it set properly without fiddling with it at runup, I quickly verify it by checking fuel flow.
By the time airspeed comes alive I only need to focus on controlling the plane, I’ve set everything and scanned the engine monitor for issues.
Running ROP can mask engine issues, I feel that a engine that can run LOP is a healthy engine.

[Bob - S50]

There are MANY good ways to run an engine.  I think we need to be careful about suggesting there is one best/easiest way to do that.  There are so many variables, that any time we recommend a specific technique, we should be sure to list all the qualifiers.  For example: above 6000', non-turbo, non-"D" engine, less than XX%, etc.

For example, do the WOT proponents do that at 2000'?  Run around at 28", 2400 RPM and 10 gph (for a 200 horse engine)?  Controlling power with mixture while WOT will probably require a mixture that is VERY LOP.  Maybe too lean for many engines to run smoothly.  And probably less efficiently than one run at best BSFC with a partially closed throttle.

Do you have an A3B6 engine timed at 20 BTDC or an A3B6D engine timed at 25 BTDC?  If the latter, maybe you don't want to run around over square (or maybe you do; I don't).

When we make suggestions here, we should not make any assumptions because we all know what happens when we assume.  Take everything we read here with a grain of salt.  Read the articles by John Deakin.  Educate ourselves and then make wise decisions.