Lean of Peak

[Will.iam]

Another way to verify this is do a find peak at 2200 RPM and note the Fuel flow and MP then do another find peak at say 2500 RPM. Now do a Lean of Peak find at the 2500RPM and just when at peak stop and then change the RPM only back to 2200RPM to match the same MP and FF readings you had found earlier for peak at 2200 but now the JPI will say your are like at 50 LOP which isn’t true as setting known FF MP and RPM is repeatably the same power that’s how our charts are used. 

[jlunseth]

@FltBoomer. You would have to ask my A&P. They do it during the annual and I have not been there. Oasis Aero at Willmar MN

[Shadrach]

1 hour ago, Pinecone said:

When you change the RPM you change the amount of air moving through the engine.  More RPM, more air.

Over a given time period, yes, per combustion event, no. Reduction in RPM = reduction in piston speed. Reduction in piston speed increases the time from when combustion event begins to when exhaust valve opens.

[Pinecone]

1 hour ago, Shadrach said:

Over a given time period, yes, per combustion event, no. Reduction in RPM = reduction in piston speed. Reduction in piston speed increases the time from when combustion event begins to when exhaust valve opens.

Yes, the same amount of air per intake cycle.  But a different amount of fuel do to the change in time of the intake cycle.

[Will.iam]

So i went up this evening before sunset and ran some setting. I initially set 25” MP and my 9.5 fuel flow at 2500rpm. Then i added throttle until i got to 34”MP and my engine was running pretty rough but realized i was looking at the shadin FF which reads a little pessimistic once i looked at the JPI and increased the fuel flow up to 11.1 it was running just a very small amount rough. If i increased to 11.5 it smoothed out completely

here are my numbers:

FF.    RPM.  TIT.  TAS.  Altitude
11.5 2450 1574 154 @3k 

11.1 2450 1555 150  3k

then i realized my cowl flaps were still half open so i closed them and reran tests to get these values
11.1 2450 1575 154  3k

11.5 2450 1595 158  3k

i then just rolled back the RPMs at that last setup to see what 2300 would do. 
10.6 2300 1578 154. 3k

seemed i traded about a gallon of gas for 4 knots not too bad.

i have to admit @jlunseth i was really surprised at how little the TIT rose from 1550. I was expecting higher temps. And my cyl temps were 330 mostly with my highest being #3 at 359.  This was with a ground temp of 69 degrees F I estimated my temp at 3k at about 15C

[jlunseth]

Usually if my engine starts to run a little rough at lower fuel flow settings, it is time to get the mags looked at. Spark must be good to ignite the lean mix properly. I had fine wires and a new harness installed a few years ago and really have not had a problem since then. Some years I will start getting a little roughness if I have flown quite a few hours that year and as I approach annual. The mags get looked at and the fuel flows get reset at annual, then everything is back to normal and I can run down in the high 10s if I really want to. I have GAMIs. It saves 2-3 GPH over an equivalent ROP setting and nifty speeds.

[Will.iam]

4 hours ago, jlunseth said:

Usually if my engine starts to run a little rough at lower fuel flow settings, it is time to get the mags looked at. Spark must be good to ignite the lean mix properly. I had fine wires and a new harness installed a few years ago and really have not had a problem since then. Some years I will start getting a little roughness if I have flown quite a few hours that year and as I approach annual. The mags get looked at and the fuel flows get reset at annual, then everything is back to normal and I can run down in the high 10s if I really want to. I have GAMIs. It saves 2-3 GPH over an equivalent ROP setting and nifty speeds.

I too installed new harnesses gami injectors and a surefly and IRAN the other mag at annual. I put in fine wire tempest 50 hours before the annual and they now have 150 hours on them.  The last components are fuel and air. I did an IRAN of the fuel pump spider and throttle body. My gami spread is .2 could be better. My engine is at TBO and the cylinders have lost all cross hatch in the walls. I have blowby as my oil turns dark in just 3 to 5 hours after an oil change and she drinks a quart of oil every 6 hours but my compressions are all in the high 60’s to low 70’s. I think if my spread was a little tighter or if there is an airleak somewhere i could get the engine to run smoother at that setting. Nice to know if i need to push it up i have some room above. Was also surprised by the 2300setting as i would rather burn 10.6 than 11.5 and take the 4 knot loss, plus my TIT was lower too. 2300 did seem a little bit more “luggy” than 2450.  Might have been just psychological or maybe the pulsing power strokes through a 2 blade metal prop. I hear the MT composite 3 blade helps with that and wind noise. Do you have an intercooler on your 231?

 

[Shadrach]

37 minutes ago, Will.iam said:

I too installed new harnesses gami injectors and a surefly and IRAN the other mag at annual. I put in fine wire tempest 50 hours before the annual and they now have 150 hours on them.  The last components are fuel and air. I did an IRAN of the fuel pump spider and throttle body. My gami spread is .2 could be better. My engine is at TBO and the cylinders have lost all cross hatch in the walls. I have blowby as my oil turns dark in just 3 to 5 hours after an oil change and she drinks a quart of oil every 6 hours but my compressions are all in the high 60’s to low 70’s. I think if my spread was a little tighter or if there is an airleak somewhere i could get the engine to run smoother at that setting. Nice to know if i need to push it up i have some room above. Was also surprised by the 2300setting as i would rather burn 10.6 than 11.5 and take the 4 knot loss, plus my TIT was lower too. 2300 did seem a little bit more “luggy” than 2450.  Might have been just psychological or maybe the pulsing power strokes through a 2 blade metal prop. I hear the MT composite 3 blade helps with that and wind noise. Do you have an intercooler on your 231?

 

Not psychological, 2300 is indeed more "luggy". 

[jlunseth]

I have the Turboplus. I expect you have the factory intercooler. I can see the effect on my 930. I get both CDT (before intercooler) and IAT (after). The induction air temp drops between 75 and 125 dF, usually right around 100 at cruise.

Edited October 17, 2022 by jlunseth

[Will.iam]

6 hours ago, jlunseth said:

I have the Turboplus. I expect you have the factory intercooler. I can see the effect on my 930. I get both CDT (before intercooler) and IAT (after). The induction air temp drops between 75 and 125 dF, usually right around 100 at cruise.

Just wanted to make sure your 34”MP was close to the same density as mine. So do you use 36” for takeoff or do you go higher? I know without the precooler you are up to 40” to compensate for the less dense air due to heat. What do turbo plus state for T/O MP?

[jlunseth]

I have written about that. The recommendations for running the Turboplus equipped 231 seemed overly conservative to me. I looked into the Turboplus STC and found that it comes with special instructions to use SID-97x, which is the standard protocol, but to adjust the MP down from the factory 40” according to OAT. It varies by a few tenths, but essentially is 37”. The plane has more power than needed for takeoff, so I use 35-36, but there is a ram air effect as I roll down the runway so the MP climbs a little. I am fine with it getting to 37. Everyone seems to follow the 36” recommendation in an old article that basically said, “run it like a 252.” But that is not quite right for the 231. The problem isn’t so much takeoff power, its the fact that if the A&P follows the STC in setting up the engine, full power and thus max fuel flow will be at 37. You need all the fuel flow you can get in high hot conditions for climb, like out west, so the counterintuitive move is to increase MP. Usually it helps, sometimes it is just too hot and you have to do something else.

[Will.iam]

On 10/17/2022 at 9:18 PM, jlunseth said:

I have written about that. The recommendations for running the Turboplus equipped 231 seemed overly conservative to me. I looked into the Turboplus STC and found that it comes with special instructions to use SID-97x, which is the standard protocol, but to adjust the MP down from the factory 40” according to OAT. It varies by a few tenths, but essentially is 37”. The plane has more power than needed for takeoff, so I use 35-36, but there is a ram air effect as I roll down the runway so the MP climbs a little. I am fine with it getting to 37. Everyone seems to follow the 36” recommendation in an old article that basically said, “run it like a 252.” But that is not quite right for the 231. The problem isn’t so much takeoff power, its the fact that if the A&P follows the STC in setting up the engine, full power and thus max fuel flow will be at 37. You need all the fuel flow you can get in high hot conditions for climb, like out west, so the counterintuitive move is to increase MP. Usually it helps, sometimes it is just too hot and you have to do something else.

Would be interesting to dyno your engine. Since both our engines are essentially the same. I know mooney states and probably proved while flight testing that 36” MP gives me 210 hp. If your turbo plus is referencing 37” for T/O power then either that setting gives you 210hp and your intercoolers are a little less efficient Than mine or you are producing more than 210 hp on t/o. Would be curious which one that is.  

[MikeOH]

On 10/16/2022 at 3:52 PM, Pinecone said:

Yes, the same amount of air per intake cycle.  But a different amount of fuel do to the change in time of the intake cycle.

Not sure what you are really trying to say here.  There is MORE air per intake cycle at low RPM than at high RPM. Sure, the total amount (mass) of air per unit TIME is higher but the volumetric efficiency (amount of air mass per intake cycle/theoretical max) drops as RPM increases.  The amount of fuel is matched to the mass of air for a given desired fuel/air ratio which is dependent on VE and RPM.

[jlunseth]

3 hours ago, Will.iam said:

Would be interesting to dyno your engine.

I am certainly interested in any good empirical engine information, but my current engine is closing in on 500 hours over TBO and is going to be replaced in the next few months, as soon as the new engine shows up from Conti, so probably won’t be dyno’d in this lifetime.

But on the subject of actual HP output, I have often wondered how the 36” was established for the 252. Just for the sake of discussing theory, assume the engine operates at a stoichiometric mix or at least rich of peak, where there are insufficient molecules of air to consume the available fuel. Power can be added or reduced by adding or reducing the molecules of O2. The cooler the induction air is at a constant pressure, the more power is output. Cold air contains more molecules of air than hot air, assuming the pressure is constant. So the HP output at the beginning of the takeoff roll if the MP is 36”, is less than at the the end of the roll, even less than at cruise, and less yet at cruise in cold temperatures. This is because the efficiency of the intercooler improves with the flow of air over it and the temperature of the cooling air.  One would assume that the 36” power setting for the 252 probably makes some allowance for overboosting under some conditions of cold dense air combined with substantial airspeed that would improve the cooling by the intercooler; there probably is an engineered safety margin built in. Maybe the engineering calculations is that it is ok if the engine sometimes produces, say, 220 HP. Conversely, it also makes some allowance for production of less than 210 HP under hot conditions; there is still sufficient HP for a safe takeoff. In other words, the fact that MP is held at a constant 36” does not mean that HP is held at max rated HP under varying conditions of temperature and airspeed which improves the flow over the intercooler. It may seem that it is because the POH tells you to set 36” and the rated HP is 210, but what is actually happening in an intercooled engine is not a constant 210 HP under all conditions. 

We don’t actually have sensors that measure the number of molecules of air and of fuel in the mix so we use secondary measures like MP and GPH, but from an engineering standpoint one would assume that the engineers would allow for the fact that the measures we have are not direct measures.

[jlunseth]

I searched and found the Turboplus instructions for setting up the fuel flow in the TSIO360 with the Turboplus intercooler. I was talking earlier about the fact that it contains a chart to adjust MP during the run-up based on temp. I have attached the instructions for anyone who wants them. I got them from Turboplus. The table I talked about earlier that uses higher-than-36" MP settings in order to set max power is on p. 4, para. 1. As an example, at 59 dF (15 C) OAT the MP to achieve max HP is 38.4", or two inches higher than the commonly recommended 36". Bear in mind, however, that this is under static conditions, in other words the aircraft is not moving and airflow over the intercooler is limited. Been awhile since I thought about this, but am pretty sure that is why I downgraded my max MP number to 37". It could be lower at cruise altitude and cruise speed which would be in cool air with good airflow. 

 

TSIO360 Fuel Setup - NEW 08.pdf

[Will.iam]

1 hour ago, jlunseth said:

I searched and found the Turboplus instructions for setting up the fuel flow in the TSIO360 with the Turboplus intercooler. I was talking earlier about the fact that it contains a chart to adjust MP during the run-up based on temp. I have attached the instructions for anyone who wants them. I got them from Turboplus. The table I talked about earlier that uses higher-than-36" MP settings in order to set max power is on p. 4, para. 1. As an example, at 59 dF (15 C) OAT the MP to achieve max HP is 38.4", or two inches higher than the commonly recommended 36". Bear in mind, however, that this is under static conditions, in other words the aircraft is not moving and airflow over the intercooler is limited. Been awhile since I thought about this, but am pretty sure that is why I downgraded my max MP number to 37". It could be lower at cruise altitude and cruise speed which would be in cool air with good airflow. 

 

TSIO360 Fuel Setup - NEW 08.pdf 296.31 kB · 1 download

Thanks for the chart interesting how your chart shows at 36 inches manifold pressure which is what my automatic waste gate holds at I get 100% power at -15°C so realistically, I’m already at a detuned or D rated horsepower output even at standard day temperature and then in the summer I’m even further behind I just assumed in the summer it was because of the effect of density altitude on the wing and a on the prop, but the engine also has a pretty big performance drop just for not getting enough manifold pressure to get to the rated horse power output. or as you say, if the engineers set my aircraft for a standard day temp of getting 210 hp, then on those cold winter days I really should be taking off around 35 or even 34 inches of manifold so as to not be over, boosting the engine. 

[jlunseth]

Well, the chart is for a 231. The 231's LB and 252's MB engines are somewhat different. As I understand it, among other things, the intake system on the MB is improved over the LB. The LB's intake manifold is a straight pipe along both sides of the engine that ends in a flat cap. The three "droppers" to the cylinders are just 90 degree pipes off that main pipe. About as untuned as you can get, and pretty much guaranteed to set up back pressure waves off that end cap in operation. If you measure the MP upstream, then split the stream and send it down each side of the engine through piping that has restrictions and adverse pressure waves your measured 36" of MP before the split is not 36" at the cylinder. I believe the MB has a different turbo and definitely an improved wastegate design. Overall, cooling is supposed to be better. The point is that your MB may well make 100% at 36", within some range of engineering tolerance, while my LB may require somewhat more measured MP to make the same pressure as your MB at the cylinder, where it counts. I don't know for sure, I don't have a 252 and have not taken one apart.

Here is a statement from one article, if it helps:

"The -MB engine was a big improvement from previous TSIO-360s because it came with an advanced air induction system which alleviated most of the fuel injection and high CHT problems. An intercooler with a Garrett AiResearch turbocharger and automatic wastegate made this engine completely different from most other TSIO-360 engines. The -MB engine developed the same amount of horsepower as the -LB but did so at 36˝ of manifold pressure instead of 39.9'. " https://www.knr-inc.com/25-shoptalk/21-201012-flying-a-360

The article is comparing the factory configuration of the LB to the MB, and that would be the LB without an intercooler, so 39.9" is too high if the LB engine is intercooled, but the "advanced air induction system" would make a difference.

 

[Will.iam]

6 minutes ago, jlunseth said:

Well, the chart is for a 231. The 231's LB and 252's MB engines are somewhat different. As I understand it, among other things, the intake system on the MB is improved over the LB. The LB's intake manifold is a straight pipe along both sides of the engine that ends in a flat cap. The three "droppers" to the cylinders are just 90 degree pipes off that main pipe. About as untuned as you can get, and pretty much guaranteed to set up back pressure waves off that end cap in operation. If you measure the MP upstream, then split the stream and send it down each side of the engine through piping that has restrictions and adverse pressure waves your measured 36" of MP before the split is not 36" at the cylinder. I believe the MB has a different turbo and definitely an improved wastegate design. Overall, cooling is supposed to be better. The point is that your MB may well make 100% at 36", within some range of engineering tolerance, while my LB may require somewhat more measured MP to make the same pressure as your MB at the cylinder, where it counts. I don't know for sure, I don't have a 252 and have not taken one apart.

Here is a statement from one article, if it helps:

"The -MB engine was a big improvement from previous TSIO-360s because it came with an advanced air induction system which alleviated most of the fuel injection and high CHT problems. An intercooler with a Garrett AiResearch turbocharger and automatic wastegate made this engine completely different from most other TSIO-360 engines. The -MB engine developed the same amount of horsepower as the -LB but did so at 36˝ of manifold pressure instead of 39.9'. " https://www.knr-inc.com/25-shoptalk/21-201012-flying-a-360

The article is comparing the factory configuration of the LB to the MB, and that would be the LB without an intercooler, so 39.9" is too high if the LB engine is intercooled, but the "advanced air induction system" would make a difference.

 

I have seen the 231 intake “logs” as one a&p described them. That’s what made me wonder if 34”mp at 2450 RPM and 11.1 FF for your system might be too much air fir mine since my air intake was more optimized. Maybe set mine to 33” or so as an equivalent comparison to yours as my engine runs smooth at that trio of setttings compared to me using 34”mp. 

[Pinecone]

On 10/20/2022 at 10:42 PM, MikeOH said:

Not sure what you are really trying to say here.  There is MORE air per intake cycle at low RPM than at high RPM. Sure, the total amount (mass) of air per unit TIME is higher but the volumetric efficiency (amount of air mass per intake cycle/theoretical max) drops as RPM increases.  The amount of fuel is matched to the mass of air for a given desired fuel/air ratio which is dependent on VE and RPM.

Yes, more to intake, but less intakes per time.  Less intakes means less bangs.

And aircraft systems, longer intake cycle means longer fuel delivery, but it is truly linear and matched?

[Shadrach]

On 10/20/2022 at 10:42 PM, MikeOH said:

Not sure what you are really trying to say here.  There is MORE air per intake cycle at low RPM than at high RPM. Sure, the total amount (mass) of air per unit TIME is higher but the volumetric efficiency (amount of air mass per intake cycle/theoretical max) drops as RPM increases.  The amount of fuel is matched to the mass of air for a given desired fuel/air ratio which is dependent on VE and RPM.

Your thinking of autos with large rpm operating ranges. It’s probably a wash over the narrow and Low RPM spectrum where aircraft engines cruise.

[Will.iam]

@jlunseth i had an interesting phenomenon on yesterday’s flight. I was at 10k and normally i run 25” mp 2500 rpm and 9.5 fuel flow. But yesterday i thought let’s try your settings. So i pushed up the throttle and I couldn’t get 34” mp! At WOT it was at 30” mp. At first i thought i had a waste-gate leak and then thought well i got 36”mp on takeoff so maybe there is not enough heat going through the turbo so i went full rich. This made the manifold jump up to 33” then i increased the rpms from 2450 to 2700 and the mp went up to 35” mp not 36” though.  I thought i recalled there is an altitude test that you do to adjust on the wastegate if you don’t reach critical altitude but wasn’t that only for a fixed wastegate system? I. E. I should not have that problem with an automatic controlled wastegate right? I’m assuming you can get 34” LOP at 10k. How high can you go until you can’t maintain 34” LOP? Just curious how bad my turbo is not performing. The airplane is going into annual at the end of this month. Any tests i could do to help the A&P troubleshoot the issue before i drop off the plane? 

[kortopates]

2 hours ago, Will.iam said:

@jlunseth i had an interesting phenomenon on yesterday’s flight. I was at 10k and normally i run 25” mp 2500 rpm and 9.5 fuel flow. But yesterday i thought let’s try your settings. So i pushed up the throttle and I couldn’t get 34” mp! At WOT it was at 30” mp. At first i thought i had a waste-gate leak and then thought well i got 36”mp on takeoff so maybe there is not enough heat going through the turbo so i went full rich. This made the manifold jump up to 33” then i increased the rpms from 2450 to 2700 and the mp went up to 35” mp not 36” though.  I thought i recalled there is an altitude test that you do to adjust on the wastegate if you don’t reach critical altitude but wasn’t that only for a fixed wastegate system? I. E. I should not have that problem with an automatic controlled wastegate right? I’m assuming you can get 34” LOP at 10k. How high can you go until you can’t maintain 34” LOP? Just curious how bad my turbo is not performing. The airplane is going into annual at the end of this month. Any tests i could do to help the A&P troubleshoot the issue before i drop off the plane? 

Making throttle changes of that magnitude are going to work a whole lot better by starting from the right and going full rich, then prop full forward and lastly Map to what you want. Then reduce Prop and lean. It'll probably do just fine that way.  

[jlunseth]

I don’t know the 252 wastegate system well enough to really say what was going on, but my guess is that there is nothing wrong with your system, the issue is that your fuel flow was very low and therefore your power setting was low. If I were to try to run at 9.5 GPH and 34” I am sure the engine would be very rough if it could even get to that point at all. Probably you were generating so little power from the engine that even with the wastegate full open the turbo would not generate max pressure, it was running too slow. Running the 9.5 through the power formula for LOP you were making 61% power. 

LOP and ROP operations are air/fuel ratios. Your mix was quite a bit leaner -had much more O2 in it to burn the available fuel - than my 34” and 11.1 GPH. That slows the combustion cycle quite a bit.

Given that our two engines are different and yours can make max HP at a low MP than mine, if you want to try to copy my setting I would try a lower MP, like 33” and 11.0 GPH. If it were me, I would run some experiments to determine with the 930, how far LOP in degrees that puts the cylinder that is nearest to peak. 

[jlunseth]

I see that Paul K. posted and recommended that you lean over from the rich side to try new mixtures. Paul really knows his stuff and is dead right. Since your wastegate will hold MP at a constant number, start with a rich mix and say 33” of MP, then use your LOP function to set your degrees lean of peak. 

[Will.iam]

Thanks to both of you for your insight and suggestions. If i understand Paul’s method correctly going from the rich side to lop has the turbo already fully accelerated instead of me going from a lop setting and trying to increase the turbo output. I’m still concerned though when i went to full throttle full mixture and full rpm, basically everything firewalled like for takeoff, the highest mp pressure was only 35” instead of 36”. Seems to me i have an airleak or exhaust leak somewhere considering my critical altitude is 22k, i should be able to develop full boost at 10k. The fuel flow was higher than at takeoff but considering OAT was -5C i assumed that was matching the denser air going through the engine. In other words if i climbed to 20k as a test i should still see 36” especially on a standard temp day. Is there an adjustment my A&P make to increase the boost so the wastegate controller can achieve 36” at altitudes above 10k or is that only a sign of an air leak or worn turbo blades? It was overhauled only a hundred hours before i got the plane. 
 

will download the data later today and look more closely at it. Unfortunately i only have the jpi 711 so I don’t have MP or RPM recorded. But i forget what the fuelflow went to at 10k. 

Edited October 23, 2022 by Will.iam
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