Maintenance costs on Bravos

[Fly Boomer]

28 minutes ago, Rick Junkin said:

If not I can share it with appropriate credit to the original author.

If it's in there, I can't find it.  Zero hits on xls or lop.  I don't have very good luck finding things there.

[Rick Junkin]

7 minutes ago, Fly Boomer said:

If it's in there, I can't find it.  Zero hits on xls or lop.  I don't have very good luck finding things there.

Here's a link to the post from @Awful_Charlie where I believe I originally got the file, but the link to egtrends.com isn't working for me.

So here's a copy of the .xls file I have, noting THIS IS NOT MY ORIGINAL WORK. I've converted it to Numbers format for my personal use on my Mac, but I THINK this is the original .xls file I downloaded from the egtrends.com site.

LOPFFvsHP.xls

[Rick Junkin]

18 minutes ago, Rick Junkin said:

Here's a link to the post from @Awful_Charlie where I believe I originally got the file, but the link to egtrends.com isn't working for me.

So here's a copy of the .xls file I have, noting THIS IS NOT MY ORIGINAL WORK. I've converted it to Numbers format for my personal use on my Mac, but I THINK this is the original .xls file I downloaded from the egtrends.com site.

LOPFFvsHP.xls 28 kB · 1 download

Just in case this post goes away someday, I've also uploaded this file to the Performance Data category in the Downloads section of the site.

Cheers,
Junkman

[Fly Boomer]

56 minutes ago, Rick Junkin said:

Just in case this post goes away someday, I've also uploaded this file to the Performance Data category in the Downloads section of the site.

Cheers,
Junkman

That egtrends.com site appears to be defunct, but here is a similar downloadable version of the same LOPFFvsHP spreadsheet with a few comments and instructions;

https://twincessna.org/wp-content/uploads/attachments/LOPFFvsHP calculator.xls

[Pinecone]

With a turbo, you don't have to take a huge hit on speed running LOP.  You can run LOP at a similar power setting by increasing manifold pressure.

Here is a shot from the GAMI page showing an Aerostar with one engine ROP at 18.8 GPH and the other LOP at 14.3 GPH, but exactly the same power output (no yaw).

[Jetpilot86]

6 hours ago, Pinecone said:

With a turbo, you don't have to take a huge hit on speed running LOP.  You can run LOP at a similar power setting by increasing manifold pressure.

Here is a shot from the GAMI page showing an Aerostar with one engine ROP at 18.8 GPH and the other LOP at 14.3 GPH, but exactly the same power output (no yaw).

How does one set this up?  Start with the lower FF and add MP, or Higher FF and subtract it?

[Pinecone]

Once you know what your settings are for cruise, I pull the throttle back to my desired MP, then the RPM, then Big Mixture Pull from full rich to my LOP setting.

[Schllc]

11 hours ago, Pinecone said:

With a turbo, you don't have to take a huge hit on speed running LOP.  You can run LOP at a similar power setting by increasing manifold pressure.

Here is a shot from the GAMI page showing an Aerostar with one engine ROP at 18.8 GPH and the other LOP at 14.3 GPH, but exactly the same power output (no yaw).

With all due respect, I don’t care what the  photo suggests.   It doesn’t show where the yaw axis is in the photo, and the yaw on the Aerostar is minimal, even with an engine out. It also doesn’t show the airspeed difference. 
The io-540’s in my 601p will not produce the same power LOP and ROP, regardless of MP.

It is in the vicinity of 30knt penalty. That being said, I can easily run ROP closer to 16.8 gph per.  And the Aerostar is inexplicably fast at all altitudes. 
With the speed penalty running LOP and miles traveled per tbo, in my opinion, it doesn’t make financial sense to run LOP.  

[Pinecone]

Ask GAMI.  Airplane is N35LL.  IIRC, there used to be more info about the speeds and settings.  They stated that they set for 0 yaw, so same power output on each engine.

That fuel flow LOP should be about 195 HP.

https://gami.com/articles/baconsbonus.php

[Rick Junkin]

On 4/15/2025 at 10:53 AM, Pinecone said:

With a turbo, you don't have to take a huge hit on speed running LOP.  You can run LOP at a similar power setting by increasing manifold pressure.

I remember reading something like, "Set your lean of peak FF and then regain the power you lost by dialing the MP up 2 inches." All well and good, but only if you accept the fuel flow increase that occurs when you increase the MP. I believe Tom Haines even did a video demonstrating this in his Bonanza; unfortunately a quick google search for said video failed me. Everyone understood ROP operations so a lot of the early techniques of setting LOP were developed with a ROP mindset, if you will. Since there were no published power charts for LOP the only direct comparison power metric between ROP and LOP was airspeed. That's still true today for a lot of airplanes.

As I've come to understand it, power output when LOP is tied directly to fuel flow, agnostic of MP and RPM. As an example, I get 70% in my Bravo at about 35dF LOP with 13.2gph and 30"/2200RPM. If I dialed the MP up to 32" and didn't touch anything else, the fuel flow would also increase (to about 14.2gph), giving me more power (75% according to the LOPvsHP spreadsheet) and still about 35dF LOP, only with a higher peak EGT/TIT reference and commensurate higher CHTs. BUT, if I then dialed the fuel flow back to my original 13.2gph I would be back to 70% only now at 32"/2200RPM and closer to 60dF LOP.

I think what was happening when people advocated for this (adding back 2" MP) is they were starting with a known ROP power setting, pulling the mixture to the desired LOP value, then adding 2" of MP and accepting the fuel flow they got at that point and declaring equivalent power. So in reality what happens when you do this, you increase where the EGT/TIT value peaks because you're at a higher power setting, and you end up with a higher fuel flow while still maintaining about the same LOP offset. Nothing wrong with that, as long as the temperatures stay within limits and you're far enough LOP for the power you have set.

This post may have been a Mr MOTO thing, but I see folks say, without further explanation, that you can regain power LOP by adding MP.  That's true, but only if you allow the fuel flow to increase with the MP.

In simplistic terms, when operating LOP, power output is driven solely by fuel flow. As I understand it.

[Fly Boomer]

32 minutes ago, Rick Junkin said:

This post may have been a Mr MOTO thing, but I see folks say, without further explanation, that you can regain power LOP by adding MP.  That's true, but only if you allow the fuel flow to increase with the MP.

Takes more air (oxygen) to burn more fuel.

[Rick Junkin]

4 minutes ago, Fly Boomer said:

Takes more air (oxygen) to burn more fuel.

That's lost on me in this context. I'm sorry, I don't know what point you're trying to make.

[Fly Boomer]

1 hour ago, Rick Junkin said:

adding 2" of MP and accepting the fuel flow

Seems to me that if you add air (MP), you will have to add fuel to maintain the same mixture.  More air with the same fuel will change the fuel:air ratio.  More air has the same effect on the ratio as less fuel, making the mixture leaner.  As you know, one purpose/effect of running LOP is to stay (usually) off-peak but closer to a stoichiometric mixture than what has traditionally been described as "rich" (which could be 100 or more on the rich side of peak).  All I'm saying is that to keep the same fuel:air ratio, if you change one, you have to change the other.  I thought I was agreeing with you, but I'm always willing to learn.

[kortopates]

What @pinecone was describing is the alternate method of leaning available to just us Turbo pilots. Set the FF to your desired FF for the percent power LOP you want while still running ROP and then using 2 Hands, add MAP to lean while keeping FF constant with the other hand.
It’s harder to explain than do and takes a little practice.
Pretty much the same thing as starting with the higher MAP and leaning except by leaning from the higher MAP and FF your going through peak slowly with a higher % power generally putting you in the Red Box till you finish leaning sufficiently.

Of course once you have a target, previously verified MAP, RPM and FF you can do this very quickly e.g. the BMP. But this is the safer way to do it if your trying to also measure degrees LOP without exceeding your target % power - such as 65% which keeps your engine out of the Red Box.


Sent from my iPhone using Tapatalk

[Fly Boomer]

9 minutes ago, kortopates said:

It’s harder to explain than do and takes a little practice.

That's good news!  I'll have to ponder this for a bit.  Who teaches this?  I don't remember it from APS or Mike Busch.  Is this a PPP thing?

[Rick Junkin]

54 minutes ago, Fly Boomer said:

I thought I was agreeing with you, but I'm always willing to learn.

I thought you were too, but at first blush I had the RCA dog look on my face. 

[dkkim73]

2 minutes ago, Rick Junkin said:

I thought you were too, but at first blush I had the RCA dog look on my face. 

Wow. I thought I was the only one who used that image. Great minds? And apparently us, as well...

[Rick Junkin]

27 minutes ago, kortopates said:

What @pinecone was describing is the alternate method of leaning available to just us Turbo pilots. Set the FF to your desired FF for the percent power LOP you want while still running ROP and then using 2 Hands, add MAP to lean while keeping FF constant with the other hand.

@kortopates Ok, that's kind of what I was getting at, but you lost me with the part I bolded. How can I set my LOP fuel flow (13.2 in my case) and still be running ROP? Are you saying to initially set MP so low that 13.2gph is still ROP? Maybe an example will help me understand.

I climb full rich at 34/2400. My standard LOP cruise setting is 30/2200, 13.2gph. At top of climb after I've accelerated out to 140KIAS I set 28" and dial the RPM back to 2200RPM while still full rich, watching the MP climb to 30" as I reduce RPM. Once the CHTs start to drop I do a BMP straight to 13.2gph.

Using the method you described, would I initially set my cruise setting of 2200RPM after pulling the MP back to something like 20-25", set the FF to 13.2, and then increase the MP to 30" while adjusting the mixture to keep a constant 13.2gph fuel flow?

[PT20J]

3 hours ago, Rick Junkin said:

In simplistic terms, when operating LOP, power output is driven solely by fuel flow. As I understand it.

LOP increases the engine efficiency because the combustion gasses expand through a greater temperature change converting a greater fraction of the available chemical energy in the fuel to work. This is evidenced by the lower EGT when LOP. In theory, the BSFC (lbs/hour per horsepower) curve would decrease linearly with decreasing fuel/air ratio until the mixture was too lean to combust. However, in a real engine, at some point the mixture is lean enough that there are increased cycle-to-cycle pressure variations in each cylinder regardless of the quality of mixture distribution. This is why engines usually run somewhat rougher LOP than peak or ROP. Also, the burn time increases as the mixture gets leaner. Both of these effects tend to reduce efficiency. The effect is that the BSFC curve plotted against fuel/air ratio has a flat area centered somewhere around 50 dF LOP (varies with engine and combustion chamber design). In this region BSFC is approximately constant which means that the power will be a direct function of fuel flow.

[Rick Junkin]

8 minutes ago, PT20J said:

LOP increases the engine efficiency because the combustion gasses expand through a greater temperature change converting a greater fraction of the available chemical energy in the fuel to work. This is evidenced by the lower EGT when LOP. In theory, the BSFC (lbs/hour per horsepower) curve would decrease linearly with decreasing fuel/air ratio until the mixture was too lean to combust. However, in a real engine, at some point the mixture is lean enough that there are increased cycle-to-cycle pressure variations in each cylinder regardless of the quality of mixture distribution. This is why engines usually run somewhat rougher LOP than peak or ROP. Also, the burn time increases as the mixture gets leaner. Both of these effects tend to reduce efficiency. The effect is that the BSFC curve plotted against fuel/air ratio has a flat area centered somewhere around 50 dF LOP (varies with engine and combustion chamber design). In this region BSFC is approximately constant which means that the power will be a direct function of fuel flow.

Yeah that's what I said .

I crack myself up.

[hazek]

11 hours ago, Rick Junkin said:

As I've come to understand it, power output when LOP is tied directly to fuel flow, agnostic of MP and RPM. As an example, I get 70% in my Bravo at about 35dF LOP with 13.2gph and 30"/2200RPM. If I dialed the MP up to 32" and didn't touch anything else, the fuel flow would also increase (to about 14.2gph), giving me more power (75% according to the LOPvsHP spreadsheet) and still about 35dF LOP, only with a higher peak EGT/TIT reference and commensurate higher CHTs. BUT, if I then dialed the fuel flow back to my original 13.2gph I would be back to 70% only now at 32"/2200RPM and closer to 60dF LOP.

This exactly is also my understanding. You've stated it very clearly. I actually emailed Mike Busch what he thought about this approach to avoiding the red fin (never got a response). But my concern in general is and I'm still unclear about adding in more power while RPM is kept the same. To me this is analogous to a car in a high gear at low RPM and then further opening the throttle to develop more speed rather than shifting to a lower gear. The engine will struggle initially under high load as it gains RPM but is it actually bad for it? Especially if done slowly? I know this isn't what happens in our engines but it sorta is, isn't it?

In other words, my concern in general, not just when LOP, with increasing power without changing RPM is this: is going mixture rich, high RPM always always ALWAYS necessary to protect the engine before increasing power? Do I have to go full high RPM, or is 2400 enough? Or can I, except when going for climbing power, keep RPM unchanged and increase power very slowly, if the increase is a few inHg only, and it will not damage the engine?

But anyway, as you very well put as well Rick, the temps are the problem. Getting to LOP, EGTs will have to peak for the power setting one has. And that peak can put TIT much higher than desired. The higher the power setting one sets before leaning, the hotter it will burn at peak EGT. Once LOP the ~35dF drop in EGT might not be sufficient to lower the TIT to a safe temp which I understand to be max 1600dF. Basically the limitation on highest power setting LOP is which LOP power setting has a peak EGT minus ~35dF at an acceptable level so that TIT is below acceptable levels. -35dF or thereabout because it's the sweet spot and leaning further and deeper into LOP territory is also more inefficient!

But back to the topic. I'm on my first year of ownership. Well, co-owernship. I have no idea yet what the costs are, especially since it seems like the plane has been neglected for non essential things and has many little squawks that need fixing, not to mention it could do with a facelift in all areas. As for flying it as a low time, VFR only for now, pilot, as everyone says, if you can fly by the numbers, have a precise plan how to manage the engine and the speed, it's ok. In the beginning one can also just simply fly a bit less efficient and slow down much sooner before entering a traffic pattern and then it's not much different than flying a C172. Still a bit faster of course, but with gear down at 20" I'm usually at about 100kt which is perfectly manageable speed for VFR traffic patterns. I started with about 160TT and have now 40h on it and I find it perfectly manageable to fly and I consider myself safe. I also didn't need some extensive training to get checked out, only a couple of hours. But I did spend a lot of time reading about the plane and flying an Ovation in a sim at home to get a feel for timings before.

[Pinecone]

If you do the Big Mixture Pull, the EGTs don't have to time to get to the same peak as if you did it slowly.

When LOP started being talked about, they were advocating LOP climbs.  And John Deakin was freaking people out be doing the BMP at full throttle, high RPM at about 1000 feet in the climb.

And yes, if you want to make more power LOP you have to increase fuel flow.  But with a turbo you can increase fuel flow and keep the same span LOP.  With NA, if you are Wide Open Throttle, LOP, the only way to get more power is to get closer to peak or switch to ROP operation

[donkaye, MCFI]

8 hours ago, hazek said:

This exactly is also my understanding. You've stated it very clearly. I actually emailed Mike Busch what he thought about this approach to avoiding the red fin (never got a response). But my concern in general is and I'm still unclear about adding in more power while RPM is kept the same. To me this is analogous to a car in a high gear at low RPM and then further opening the throttle to develop more speed rather than shifting to a lower gear. The engine will struggle initially under high load as it gains RPM but is it actually bad for it? Especially if done slowly? I know this isn't what happens in our engines but it sorta is, isn't it?

In other words, my concern in general, not just when LOP, with increasing power without changing RPM is this: is going mixture rich, high RPM always always ALWAYS necessary to protect the engine before increasing power? Do I have to go full high RPM, or is 2400 enough? Or can I, except when going for climbing power, keep RPM unchanged and increase power very slowly, if the increase is a few inHg only, and it will not damage the engine?

But anyway, as you very well put as well Rick, the temps are the problem. Getting to LOP, EGTs will have to peak for the power setting one has. And that peak can put TIT much higher than desired. The higher the power setting one sets before leaning, the hotter it will burn at peak EGT. Once LOP the ~35dF drop in EGT might not be sufficient to lower the TIT to a safe temp which I understand to be max 1600dF. Basically the limitation on highest power setting LOP is which LOP power setting has a peak EGT minus ~35dF at an acceptable level so that TIT is below acceptable levels. -35dF or thereabout because it's the sweet spot and leaning further and deeper into LOP territory is also more inefficient!

But back to the topic. I'm on my first year of ownership. Well, co-owernship. I have no idea yet what the costs are, especially since it seems like the plane has been neglected for non essential things and has many little squawks that need fixing, not to mention it could do with a facelift in all areas. As for flying it as a low time, VFR only for now, pilot, as everyone says, if you can fly by the numbers, have a precise plan how to manage the engine and the speed, it's ok. In the beginning one can also just simply fly a bit less efficient and slow down much sooner before entering a traffic pattern and then it's not much different than flying a C172. Still a bit faster of course, but with gear down at 20" I'm usually at about 100kt which is perfectly manageable speed for VFR traffic patterns. I started with about 160TT and have now 40h on it and I find it perfectly manageable to fly and I consider myself safe. I also didn't need some extensive training to get checked out, only a couple of hours. But I did spend a lot of time reading about the plane and flying an Ovation in a sim at home to get a feel for timings before.

My friend at 160 hours TT and 40 hours in type, you don't know what you don't know.  A couple of hours of transition training is insufficient no matter what you think.  I say that having been a Mooney Specific Instructor for 31 years with over 7,100 hours of instruction given.

[hazek]

1 hour ago, Pinecone said:

And yes, if you want to make more power LOP you have to increase fuel flow.

1 hour ago, Pinecone said:

If you do the Big Mixture Pull, the EGTs don't have to time to get to the same peak as if you did it slowly.

If this was a response to me, then I think you are mistaken. Yes, obviously if you increase fuel flow while LOP, you would get more power. But you would also get higher EGTs and higher TIT, which could be higher than desired. At some power setting, these temperatures would simply be too high. So, there’s a clear limit to how much power you can achieve while operating LOP and still keep temperatures within safe limits. This is only feasible with a turbocharged engine, as without a turbo, typically at cruising levels there isn’t enough air available—adding more fuel would just push the engine back to the ROP side once higher up.

However, the big mixture pull doesn’t address the issue of higher temperatures. Its sole purpose is to reduce the time spent at peak cylinder pressures—that’s what the technique is designed for. By definition, LOP means operating lean of peak EGT. If we increase FF, the peak EGT will absolutely rise. This means that, in absolute terms, a relative setting like 35°F LOP will result in a higher absolute temperature than it would at a lower power setting, no matter how you reach that LOP point. Since going further lean of peak EGT than about 50°F is impractical—due to inefficiency and the engine likely running too roughly—we’re limited in how high our LOP power setting can go while keeping temperatures in the green. Whether you use the big mixture pull or another method, there’s an LOP power cap beyond which the engine runs too hot for the turbo and exhaust system.

Edited Monday at 03:43 PM by hazek
words

[hazek]

@donkaye, MCFI Could you maybe point out some of the gotchas that one might miss? Being based in Europe I have no clue who could be a reliable expert on the Bravo available to me. The instructor who signed me off is a captain on a 747, with extensive knowledge in general and also his own high performance light aircraft but I admit not Bravo specialist, and he was willing to sing me off. I must have displayed some competency. But you are right, I don't know what I don't know. So please, if you have any advice I'd happily receive it.