Settings for 231 with Merlyn UDC and Intercooler

[whiskytango]

I will be picking up my new-to-me 231 in a week or two.  It has an -LB engine with a Merlyn Upper Deck Controller and an intercooler.  I have been reading an article from the MAPA site, and it indicated that the power settings in the 231 POH should not be used if you have a Merlyn and intercooler due to the risk of overloading the engine.  MAPA recommends the following settings:

Takeoff and climb: 2700 RPM, 36 inches MP, 1400 degrees TIT

Cruise: 2500 RPM, 28 inches MP, 50 degrees Rich of Peak TIT 

I was wondering if other MS owners of a 231 with a Merlyn and intercooler are using these settings or something else.

 

 

[carusoam]

Since the intercooler is responsible for changing the density of the compressed air making the MP more effective than before, it would be best to have the proper data for setting the power.  The proper data is usually supplied by STC.

Is there a reason you don't have updated ops data to go with the intercooler and MP Controller?

Stand by for some better help from a more TC knowledgable Mooney pilot...

Best regards,

-a-

[N5756v]

My intercooler lets me drop .5 for every ten degrees of cooling so if my mp is supposed to be 28 and my intercooler is cooling 60 degrees then I can drop 3 down to 25 . I have been told by other pilots , non mooney pilots that a drop of three is a little much . My intercooler usually is cooling right around 60 degrees . Now with all that being said if I am cooling 60 degreesish I usually drop right around 2 . I don't have a merlyn so on that end I am ignorant. 

[FBCK]

Takeoff looks ok, but don't operate the plane in cruise at those setting, you will find it runs hot, or at least hotter than it needs to be.  I have the same setup as you and you should shart reading the info on this site about lean of peak operations.  It greatly reduced the operating temperatures of my plane in cruise. I would run mind in cruise at 30-31 inches, burning10.5  gallons, which is about 68% power. 

[Zwaustin]

Intercooler has its own separate power chart so yes don't use the original POH or you will overboost. I think i posted the chart here once prior so look around on the site. Mine was an airflow systems intercooler. Take off is 37 inches at 2700 rpm with a fuel flow to be at 24.9 GPH, cruise climb is 31 inches 2600 rpm at around 18 GPH... if you can't find the chart let me know and ill send you one... Do you have the airflow systems intercooler or the turbo plus?

[Zwaustin]

Here is the link to the power settings i previously uploaded along with the POH supplement for airflow systems set up. I also had a Merlyn.

 

[whiskytango]

6 minutes ago, Zwaustin said:

Intercooler has its own separate power chart so yes don't use the original POH or you will overboost. I think i posted the chart here once prior so look around on the site. Mine was an airflow systems intercooler. Take off is 37 inches at 2700 rpm with a fuel flow to be at 24.9 GPH, cruise climb is 31 inches 2600 rpm at around 18 GPH... if you can't find the chart let me know and ill send you one... Do you have the airflow systems intercooler or the turbo plus?

It is a TurboPlus.  Thanks for the info, I will look for that power chart

[KLRDMD]

2 hours ago, Zwaustin said:

Take off is 37 inches at 2700 rpm with a fuel flow to be at 24.9 GPH, cruise climb is 31 inches 2600 rpm at around 18 GPH... 

I takeoff and climb to altitude with everything at red line (37", 2700 RPM, full rich at 24.9 GPH) which gives me about 800 fpm at 120 KIAS then I cruise at 30", 2500 RPM and 9.0 GPH which is 59% power LOP. Climb from my 2,000 ft field to 10,000 ft is only 10 minutes. I like 30" as it is essentially turbo normalizing the engine and I won't cruise a TSIO-360 above 65% power - that's just my preference. In the 10,000 ft range at 9.0 GPH that's about 160 KTAS and at 17,500 ft it is 175 KTAS. Paul K. recommended the takeoff and climb power settings be the same and he's right.

In the 10,000 ft range, 62% power LOP gives me 165 KTAS at 9.5 GPH and 65% power gives me 170 KTAS at 10.0 GPH. The 65% power setting is pushing my temperature comfort limits with CHT at 370-380ºF. The 59% power setting gives me CHTs around 310-330ºF and the 62% power gives CHTs around 350ºF.

Another way to look at the difference in 59-65% power, based on fuel burn, speed and fuel cost, is that is costs about $1/min to go from 160 to 170 knots.

[whiskytango]

11 hours ago, KLRDMD said:

I takeoff and climb to altitude with everything at red line (37", 2700 RPM, full rich at 24.9 GPH) which gives me about 800 fpm at 120 KIAS then I cruise at 30", 2500 RPM and 9.0 GPH which is 59% power LOP. Climb from my 2,000 ft field to 10,000 ft is only 10 minutes. I like 30" as it is essentially turbo normalizing the engine and I won't cruise a TSIO-360 above 65% power - that's just my preference. In the 10,000 ft range at 9.0 GPH that's about 160 KTAS and at 17,500 ft it is 175 KTAS. Paul K. recommended the takeoff and climb power settings be the same and he's right.

In the 10,000 ft range, 62% power LOP gives me 165 KTAS at 9.5 GPH and 65% power gives me 170 KTAS at 10.0 GPH. The 65% power setting is pushing my temperature comfort limits with CHT at 370-380ºF. The 59% power setting gives me CHTs around 310-330ºF and the 62% power gives CHTs around 350ºF.

Another way to look at the difference in 59-65% power, based on fuel burn, speed and fuel cost, is that is costs about $1/min to go from 160 to 170 knots.

This mode of operation is in agreement with recommendations from Mike Busch and also Tornado Alley Turbos.  They both say that maximum engine life is achieved by keeping peak cylinder internal pressures as low as possible, and CHT not to exceed 380 degrees F at any time.  LOP is the only way these goals can be achieved.  My 231 has GAMI injectors, so LOP should work.  Thanks for the info.

[jlunseth]

I have about 1000 hours in that combination with a JPI930.  Pretty much everyone will tell you that the intercooler requires reduced MP, but the adjustment charts supplied with the intercooler are aggressive, in other words, the engine does not require quite as much of an MP adjustment as the charts say.  

On takeoff, think of it this way.  The reason for the downward MP adjustment is that the intercooler cools the induction air, making it denser than what is expected in the factory tables in the POH.  However, the cooling effect is changing rapidly during the takeoff roll.  At the approach end of the runway the plane is standing still, so there is little air passing over the intercooler fins to cool the induction air.  On the departure end you are going somewhere in the 70-90 knot range, still much less than cruise.  At cruise you will find a drop of around 100 dF, on takeoff not so much, maybe 60 dF and highly variable.  In theory you could start the roll at 40" (the nonintercooled setting) and reduce during the roll, but you don't want to be messing with the MP at that point.  I use 36, and I don't worry about it if MP is 37-35.  Any of those power settings are ample power for takeoff and won't harm the engine.  

To make that power setting, if you have not flown a 231 before, you should be aware that the turbo will kick in and start to raise MP on its own during the roll, so you don't want to be aggressive with the throttle or you will find the engine overboosting once the turbo starts to work.  I put the throttle in about half way, let the turbo get going, and then adjust to 36 (or so).

The GAMI/APS people tell us that 50 ROP is just about the worst place to run an engine at cruise, if you want it to last.  And there have been lots of 231 engines that need a top at 1200 running on the POH settings.  I basically use two, a ROP setting and a LOP setting.  I don't use MP to make the ROP setting.  My JPI has a % power algorithm, it is about 8% conservative, but I use that as an indicator.  I run at least 100 ROP and usually 125.  I adjust to a fuel flow of 13.3 GPH.  That is not based on a guess, it is based on many times using the ROP lean function on my JPI and that is where it always lands.  I use 2450RPM, but that is just my own superstition, 2500 works fine.  MP is about 29".  Lots of people run at 12.5 and I believe that is where the POH wants you for "best power."  There is no doubt you will get more power and speed than at my 13.3 GPH, you will also be running in the "red box" and headed for a top at 1200.

The thing about MP is that it is not fixed, to generate a particular %HP, as many people assume.  Rather, the MP needed to achieve a particular power setting changes with air density and temperature, and since we are able to fly quite high in the 231, cruise MP can vary.  That is why I use the JPI %power algorithm, it adjusts for those variables.  

I climb to altitude full rich.  The engine needs to be making 22.5-24.0 GPH per the POH, and it really does.  You do not want to lean it out at full power.  That is an NA technique and not at all applicable to turbos.  That said, I know some turbo pilots who do lean during the climb, I suppose it is ok if you watch the temps like a hawk, but my experience is that especially on a hot day and especially out west, you will see temps you don't want to see.  I just climb full power full rich to whatever altitude is my target.  That is what APS recommends, and what I have done for quite a few hours now.  I know a very good PPP instructor with a 231, and he uses a cruise climb, setting power at 32".  That's nice, but what he doesn't understand and I can see on my JPI is that at some point in the teens, 32" is full power.

I did quite a bit of experimenting to get to a good LOP setting.  What I realized is that since LOP is a fuel/air mixture where there is more air than at a stoichiometric mix, there are two ways to get more LOP, fuel and air, duh!.  And in turbos we have the ability to change the air quite a bit more than the NA operators.  So that is partly what I do, add more air.  My normal LOP MP setting is 34" of MP, which would normally result in quite a high power setting if operating ROP, but I dial the fuel flow down to 11.0-11.1 GPH.  On the LOP side, %HP is governed by fuel flow and not by MP.  The formula for our LB engines is 13.7 x fuel flow = HP.  Divide HP by 210 (full rated HP) and you have percent HP while LOP.  A fuel flow of 11.0-11.1 results in a power setting of about 70-71%.  I can't stand flying the long trips I do at 65% or less, it is just too slow.  The plane gets cranky at 75% LOP which is about 11.5 gph.  Temps get persistently too high.  You want to keep the TIT at or below about 1600, and the CHT's as close to 380 as you can, and if they creep over 400 do something different, like to ROP or trail the cowl flaps.  So the 11 GPH setting is about as much power as I can generate without going over temp.

I find that I cannot generally fly LOP up high in the summer.  At some point in the mid-teens the temps just get too high.  Trailing the cowl flaps helps to a degree, but at some point I just go over to my dependable ROP setting.  I suppose I could do it if I went to 65%, which would be 10 GPH (9.96 to be exact), but it is too slow for me.

It may be that your LB won't run LOP very well.  That is true of many of them.  The induction system is very untuned, and it is possible to have some cylinders at peak, near peak or even over on the rich side, while others are quite lean.  So some engines will start to run rough at LOP.  GAMI injectors will generally fix that, they insure a more even fuel flow from cylinder to cylinder.

When I make my descent from cruise I don't mess with the red knob if I have been at LOP while cruising.  I make all my adjustments with MP.  You will find that descending from a high cruising altitude, say in the flight levels, and especially with a high tailwind aloft, will take some getting used to.  I pull off about an inch of MP and just tip the nose over and adjust to 500 fpm.  I pull an inch off the MP because it is going to rise about that much with the ram air effect.  If you were at a TAS of, say, 175, and had, say, a 50 knot tailwind aloft, you were cruising at 225 knots.  On descent you will now be at somewhere around 240 to 270, so you are coming in at a good clip.  Obviously if you are penetrating cumulus, you want to slow for turbulence, but that is not nearly as common as you might think.  If you were at 21,000 and your field is at 1,000, you have 20k to lose and at 500 fpm (to avoid popping ears) you will need 40 minutes.  At, say, 250 knots, you will in theory cover 165 nm.  I say "in theory" because the descent will slow because of two variables, adjustment to TAS with altitude, and loss of the tailwind.  The adjustment to TAS will be a constant, but the loss of tailwind varies quite alot with the weather patterns.  Sometimes you might have a 75 knots tailwind at cruise, which will be 30 knots at 12,000 and 10 or 15 at approach altitude.  Some days you will enjoy a good tailwind all the way down.  I normally start my descent at somewhere from 100 to 125 nm out, depending on what kind of wind change I expect on the way down.  It is as much art as math.  But the important point is that, just as you will need to adjust MP upward as you ascend, you will need to adjust it downward as you descend, but if you are at that 11.0 GPH LOP setting I just leave the fuel flow alone and do all the adjusting with the MP knob.  You will see some nice, low fuel flows and cool temps, and the engine will be happy with you.  Be sure to ask ATC to start your descent while you are a good ways out.  They will invariably take some time to clear the descent, so if you needed 125 nm when you asked and they mess around for several minutes you now might have 90-100, and then of course they will want to give you a crossing point 50 nm out, so you now need to descend at 1000 fpm or more. It is not a  big deal, just push the nose over further, but it will be harder on ears and a waste of all that energy you built up getting to altitude in the first place.

In fact, I keep that leaned out setting all the way to short final.  If the LB engine is properly set up, it will be very rich near the ground if you have the mixture in.  The result is "burbling," the engine will sound like it is missing because it is overrich.  The cure is to lean it out at the low power settings you will use during final approach, but when you are near the ground make it rich and just put up with the burbling.  That way you are set up for a go around.  

The Merlyn has practically nothing to do with fuel settings.  The Merlyn does two things for you.  First, it controls bootstrapping.  Bootstrapping is where you, say, add power, then the turbo spins up so you have more power, which makes the turbo spin faster yet, which makes more power, etc.  That was an issue with the factory engine but not with the Merlyn controlled engine.  The other is critical altitude.  CA is the altitude where the engine no longer makes full power.  In the non-Merlyn engine that is in the mid-teens, so climb after CA is a very slow affair.  In my engine with the Merlyn it is around 21-22k.  Although your service ceiling is 24k there is not much reason to go up that high.  The time of useful consciousness if your O2 system fails starts to drop sharply, 21-22 is all I find I ever need.  So the Merlyn will give you full power climb to a flight level cruise.  

One final note, when your mechanic sets the fuel flows up, double check and make sure you are getting 22-24.5 GPH at full power, and full power for you is 36-37, not 40".  There is information in the STC on how to do it with the intercooler installed.  Some modifications need to be made to the standard fuel flow method, which is a SID.  I don't remember the SID number off the top of my head but your mechanic will know.  Just be aware that there is a modification of the SID in the STC, and the mechanic needs to follow that.  I can't tell you how many times I have had mechanics set the fuel flow at annual or otherwise, and I find I can only get 19 GPH at full power.  Not enough.

[jlunseth]

PS One other thought on the intercooled LB.  You will find a redline for CDT in the POH.  Off the top of my head I don't recall it, I think it is 280.  With the intercooler you can safely ignore CDT and that redline.  The CDT redline is there to protect the cylinders from detonation due to high temperature induction air.  It assumes that CDT is the same as Induction Air Temperature.  But with the intercooler your IAT will be around 100dF cooler, especially at cruise.  I don't know how the original factory engines could ever get to the flight levels except maybe during the winter.  The CDT in my aircraft reaches redline somewhere in the upper teens.  But the IAT is cool because of the intercooler, so it is safe to ignore CDT.  I have separate CDT and IAT probes in my engine, so I see both of them.  CDT is not there to protect the turbo, TIT protects the turbo, so adhere to the TIT limitations.  My preference, as I said earlier, is to stay at or under 1600 in a LOP cruise, and at ROP you should never be near that number.  Never make the mistake of having the red knob leaned out on takeoff.  If you do, you will see TIT numbers that challenge those TIT limitations before your reach 1000 AGL.  My classic mistake is leaning at the hold short line while ATC takes time to clear me for IFR, then forgetting to push the red knob in when I do the takeoff.  Don't make that mistake.  

Edited January 22, 2017 by jlunseth

[topsun1]

Whisky Tango,

Attached is my 231's Airflow systems settings...I also have the Merlyn waste gate.

I installed the JPI 900 last year and all power settings at set MP/RPM's are automatically displayed so this is now redundant. 

Enjoy your 231!  We have for 11 years.

Rutherford Mooney 1152G Merlyn Intercooler Power Settings.pdf

 

[KLRDMD]

24 minutes ago, topsun1 said:

Attached is my 231's Airflow systems settings...

Rutherford Mooney 1152G Merlyn Intercooler Power Settings.pdf

13 gallons per minute (GPM), not very efficient 

[topsun1]

And this chart was done by an Engineer!

[Steve Dawson]

Great write up jlunseth.

Thanks for the information

[jlunseth]

23 hours ago, KLRDMD said:

13 gallons per minute (GPM), not very efficient 

You have a choice.  You can run ROP at 13.3 and 75%, or you can certainly run ROP at 50dF or even more efficiently right at peak, which is more or less a stoichiometric mix (perfect mix where all fuel and all O2 are consumed).   If you do the former you are less likely to be replacing parts, if you do either of the latter you can count on a top and probably more at 1200.  Efficiency is relative.  If I am running at 13.3 and 75% ROP it is because I am at a high altitude where the TAS is 170 or better and I likely am getting a nice tailwind.  13.3 at 230 kts. GS is 17 1/3 MPG.  If I stay lower down and run at, say 165 kts. GS and 11 gph, that is 15 MPG.  If the winds are favorable, high altitude flight is almost always worth the extra 2 GPH.  The highest I have ever seen was sustained 270 kts. on a trip from Williston ND to KFCM in the flight levels.  We had a 100 kt. tailwind.  At 13.3 that is better than 20 MPG. 

Some people with K's can fly LOP up that high, or say they can anyway,  especially pilots with the 252, which is a better engine.  It is a matter of cooling, the air being thin up there and not so good at cooling.  In a perfect world I would probably get the baffles re-done in an effort to improve cooling and might be able to make LOP up higher, but my engine is nearing TBO so probably I will wait until I put a reman in to try that.

The chart in my POH recommends 29.1", 2700 RPM and 11.1 GPH for 75% power at 22k, for "Best Economy."  It recommends 29.1, 2700 RPM, and 16.1 GPH for "Best Power or what it calls "Full Rich."  The reason for the 2700 RPM is that the prop is supposedly less efficient up high, so needs to be run at a higher RPM.  In reality, I haven't found it makes any significant difference, and 2450, or 2400, or 2500, are just fine.  I don't find I need 16.1 for good cooling when ROP, 13.3 does fine.  I also would be concerned about the 29" MP and 11 GPH setting for LOP.  Probably the engine is running right at peak or within a few degrees of it, in fact, from what I see on my JPI, probably you would have some cylinders LOP, one or two at peak, and some ROP.  You need to push the mixture further LOP than that, and the way to do it is to increase air (MP).  But that just does not work for my aircraft, at that altitude.  The POH has a CHT limitation of 460 dF and a green arc operating range of 250-460, so if you use those numbers you would think the POH mixture setting is just fine.  But from what we know now about metallurgy, sure you can run the engine there, but you are burning through the useful life of the cylinders pretty quickly.  Your goal CHT should be 380.

[mikeyhaley]

On 1/23/2017 at 2:36 PM, jlunseth said:

You have a choice.  You can run ROP at 13.3 and 75%, or you can certainly run ROP at 50dF or even more efficiently right at peak, which is more or less a stoichiometric mix (perfect mix where all fuel and all O2 are consumed).   If you do the former you are less likely to be replacing parts, if you do either of the latter you can count on a top and probably more at 1200.  Efficiency is relative.  If I am running at 13.3 and 75% ROP it is because I am at a high altitude where the TAS is 170 or better and I likely am getting a nice tailwind.  13.3 at 230 kts. GS is 17 1/3 MPG.  If I stay lower down and run at, say 165 kts. GS and 11 gph, that is 15 MPG.  If the winds are favorable, high altitude flight is almost always worth the extra 2 GPH.  The highest I have ever seen was sustained 270 kts. on a trip from Williston ND to KFCM in the flight levels.  We had a 100 kt. tailwind.  At 13.3 that is better than 20 MPG. 

Some people with K's can fly LOP up that high, or say they can anyway,  especially pilots with the 252, which is a better engine.  It is a matter of cooling, the air being thin up there and not so good at cooling.  In a perfect world I would probably get the baffles re-done in an effort to improve cooling and might be able to make LOP up higher, but my engine is nearing TBO so probably I will wait until I put a reman in to try that.

The chart in my POH recommends 29.1", 2700 RPM and 11.1 GPH for 75% power at 22k, for "Best Economy."  It recommends 29.1, 2700 RPM, and 16.1 GPH for "Best Power or what it calls "Full Rich."  The reason for the 2700 RPM is that the prop is supposedly less efficient up high, so needs to be run at a higher RPM.  In reality, I haven't found it makes any significant difference, and 2450, or 2400, or 2500, are just fine.  I don't find I need 16.1 for good cooling when ROP, 13.3 does fine.  I also would be concerned about the 29" MP and 11 GPH setting for LOP.  Probably the engine is running right at peak or within a few degrees of it, in fact, from what I see on my JPI, probably you would have some cylinders LOP, one or two at peak, and some ROP.  You need to push the mixture further LOP than that, and the way to do it is to increase air (MP).  But that just does not work for my aircraft, at that altitude.  The POH has a CHT limitation of 460 dF and a green arc operating range of 250-460, so if you use those numbers you would think the POH mixture setting is just fine.  But from what we know now about metallurgy, sure you can run the engine there, but you are burning through the useful life of the cylinders pretty quickly.  Your goal CHT should be 380.

I have a very similar setup as you in my 231 (Only diff is Turbo Plus Intercooler) and when I run LOP close to the power settings you outline, my CHT are around 310. I've only see 380/385 in the middle of the summer and just on take-off. Any idea for the big difference? Are the CHT's too low? (Prob a dumb question, ha). When I am ROP my CHT's are around 370 in mid summer. They are 330 this time of year. What is your TIT LOP & ROP? I run mine around 1575/1565 respectively. Great post!

[jlunseth]

My baffles are getting old.  I would do something about it, but like I said in an earlier post, my engine is near TBO so I am going to wait on the baffles.  But it does not take much of a reduction in fuel flow from the 11.0 I talked about, to reduce heat but also reduce %power and airspeed.  If you are "close to" the settings I mentioned, at say 10 or 10.5, you are quite a bit leaner.  10 is 65% HP.  

310 is not too low, I run in that area quite alot also when I am LOP.  Anything over 250 is fine.  I only occasionally see higher CHT's in the summer at higher altitudes.  I have one cylinder that is not well cooled, and I have a tendency to focus on that one, the others are generally much cooler.  As I said, I am not going to worry about it at this point, wait for when the reman goes in.  On a few occasions in our cold winter temps I have seen CHT's lower than that on one or two cylinders in cruise, but at that point the bigger worry is the oil temp, which needs to be at least 100 dF for the turbo bearings.  When OT or CHT gets that low, I have on a couple of occasions intentionally put the engine at peak just to generate the necessary heat.  But that is a rare thing, I have seen it only in our super cold winter temps and in the thick air at low altitude.

My TIT when LOP at 11.1 GPH and 34" is usually just under 1600.  I intentionally keep it at or under 1600.  I really don't even look at the number when ROP because it is irrelevant, what is relevant is how many degrees ROP the EGT's are in the first cylinder to peak.  But the TIT is low, in the range of 1475-1535.

[jrwilson]

On ‎1‎/‎21‎/‎2017 at 1:49 PM, whiskytango said:

I will be picking up my new-to-me 231 in a week or two.  It has an -LB engine with a Merlyn Upper Deck Controller and an intercooler.  I have been reading an article from the MAPA site, and it indicated that the power settings in the 231 POH should not be used if you have a Merlyn and intercooler due to the risk of overloading the engine.  MAPA recommends the following settings:

Takeoff and climb: 2700 RPM, 36 inches MP, 1400 degrees TIT

Cruise: 2500 RPM, 28 inches MP, 50 degrees Rich of Peak TIT 

I was wondering if other MS owners of a 231 with a Merlyn and intercooler are using these settings or something else.

 

 

No Merlyn yet, but I have the intercooler.  I use those power settings but I do 125 deg rich of peak in cruise...  That is usually around 1530 on TIT.