WOT LOP

[Tom 4536]

When cruising LOP, Mike Busch advocates running WOT and controlling power with only fuel flow. He says he even flies his turbocharged Continentals WOT. If, at say 15,000ft, we run our 231’s with Merlyn, GAMIs and intercooler WOT (or even 36 inches MP) won’t we have an overboost problem?

[kortopates]

2 hours ago, Tom 4536 said:

When cruising LOP, Mike Busch advocates running WOT and controlling power with only fuel flow. He says he even flies his turbocharged Continentals WOT. If, at say 15,000ft, we run our 231’s with Merlyn, GAMIs and intercooler WOT (or even 36 inches MP) won’t we have an overboost problem?

Of course you will! I know a thing or two about Mike's C310 and how he flys it. Mike's TSIO-520 has a real turbo controller with a hydraulically controlled wastegate which you don't have with just a turbo and manual pneumatic wastegate. Plus you missed he's also using RPM to control power - he's not running anywhere near redline rpm. Additionally his redline MAP is only 32" which is a far cry from yours and much more like a turbo normalized engine than most turbo's. The bottom line is that Mike power stetting is never above 65% unless he's in a real hurry - which is on blue moon since he has two of them.

Mike's turbo is rare compared to most, but he says this to underline the point more for the normally aspirated engines that should be run WOT at altitude using bith RPM and FF to control power. FF can only control power so far before your cylinders start missing, thus the need to also use RPM. But the engine breathes more efficiently and the reduced RPM aides in giving more time for the slowed lean combustion process to complete before the exhaust valve opens.

Edited February 12, 2023 by kortopates

[Tom 4536]

12 minutes ago, kortopates said:

Of course you will! I know a thing or two about Mike's C310 and how he flys it. Mike's TSIO-520 has a real turbo controller with a hydraulically controlled wastegate which you don't have with just a turbo and manual pneumatic wastegate. Plus you missed he's also using RPM to control power - he's not running anywhere near redline rpm. Additionally his redline MAP is only 32" which is a far cry from yours and much more like a turbo normalized engine than most turbo's. The bottom line is that Mike power stetting is never above 65% unless he's in a real hurry - which is on blue moon since he has two of them.

Mike's turbo is rare compared to most, but he says this to underline the point more for the normally aspirated engines that should be run WOT at altitude using bith RPM and FF to control power. FF is only going to so far in controlling power before your cylinders start missing, thus the need to also use RPM. But the engine runs breathes more efficiently and the reduced RPM aides in giving more time for the slowed lean combustion process to complete before the exhaust valve opens.

Thank you!

[exM20K]

51 minutes ago, kortopates said:

Of course you will! I know a thing or two about Mike's C310 and how he flys it. Mike's TSIO-520 has a real turbo controller with a hydraulically controlled wastegate which you don't have with just a turbo and manual pneumatic wastegate. Plus you missed he's also using RPM to control power - he's not running anywhere near redline rpm. Additionally his redline MAP is only 32" which is a far cry from yours and much more like a turbo normalized engine than most turbo's. The bottom line is that Mike power stetting is never above 65% unless he's in a real hurry - which is on blue moon since he has two of them.

Mike's turbo is rare compared to most, but he says this to underline the point more for the normally aspirated engines that should be run WOT at altitude using bith RPM and FF to control power. FF can only control power so far before your cylinders start missing, thus the need to also use RPM. But the engine breathes more efficiently and the reduced RPM aides in giving more time for the slowed lean combustion process to complete before the exhaust valve opens.

Interesting, Paul... So why do the power charts limit me to 65% ISH power at 2300 RPM and quite a bit less at 2200?  I’ve never really experimented in that RPM range.  If 2300x30.5 at 16.5 GPH operates smoothly, why not operate there?

-dan

[milotron]

1 hour ago, kortopates said:

 Mike's TSIO-520 has a real turbo controller with a hydraulically controlled wastegate which you don't have with just a turbo and manual pneumatic wastegate.

How does this controller compare to the SB or MB engines in the 252? Seems to be of a similar level of sophistication?

This raises some interesting questions on the dynamics of these intake systems and how hard the turbo is operating to maintain an upper deck pressure only to have it reduced by a low MP setting and disrupted by the throttle blades.

So long as the turbo can reasonably keep up, conceivably a lower rpm, high boost situation would be better, even if the MP was targeted around 30" and RPM/FF used to manage the power setting. That should be a fairly conservative approach for the 231/252 engines?

[kortopates]

Interesting, Paul... So why do the power charts limit me to 65% ISH power at 2300 RPM and quite a bit less at 2200?  I’ve never really experimented in that RPM range.  If 2300x30.5 at 16.5 GPH operates smoothly, why not operate there?
-dan

i can’t actually recommend any power setting not approved in your POH, so would suggest 2400 and 31.5”
But your welcome try with 2300 rpm LOP and report back


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[kortopates]

How does this controller compare to the SB or MB engines in the 252? Seems to be of a similar level of sophistication?
This raises some interesting questions on the dynamics of these intake systems and how hard the turbo is operating to maintain an upper deck pressure only to have it reduced by a low MP setting and disrupted by the throttle blades.
So long as the turbo can reasonably keep up, conceivably a lower rpm, high boost situation would be better, even if the MP was targeted around 30" and RPM/FF used to manage the power setting. That should be a fairly conservative approach for the 231/252 engines?

The MB and SB controller is different and even more advanced in that it doesn’t constantly maintain a UDP a couple of inches above redline like earlier designs but varies UDP to just above the MAP setting. Thus we’re not loosing the breathing efficiency like some of the more basic controllers.


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[carusoam]

Dan,

Add this one to the deep pile of variables…

The TopProp is reported to be most efficient at 2550rpm…

Would that change your thought process / selection any?

 

With my NA engine… at altitude… WOT is the norm (MP is only around 21”)… max power at peak EGT…

the only way for me to get more power is to increase RPM… with its normal increase in FF…

 

For Tom…  with a TC’d engine… it is really easy to run above 65% bhp… be sure to ask a lot of questions until you understand these topics really well…

CHT limits, TIT limits, BHP limits… big pull procedure…

Things get more complex with the added systems… the POH won’t know if a MP controller or intercooler were added later…  the STC should have the data and procedures for that…

 

Let’s include @jlunseth in the conversation…

Best regards,

-a-

[exM20K]

18 minutes ago, carusoam said:

Dan,

Add this one to the deep pile of variables…

The TopProp is reported to be most efficient at 2550rpm…

Would that change your thought process / selection any?

 

With my NA engine… at altitude… WOT is the norm (MP is only around 21”)… max power at peak EGT…

the only way to get more power is to increase RPM… with its normal increase in FF…

 

Let’s include @jlunseth in the conversation…

Best regards,

-a-

It’s all splitting hairs regarding performance in the big picture… I balanced the prop at 2400, and it runs acceptably smooth and cool.  2550 runs the TIT significantly higher, so I avoid that.  On the other hand, spinning the engine faster should effectively retard the timing a bit, so more efficient work?
 

it is fun to experiment, especially with the capability to record data.

[Ibra]

3 hours ago, kortopates said:

The bottom line is that Mike power stetting is never above 65% unless he's in a real hurry - which is on blue moon since he has two of them.

Indeed, that is the key takeaway, if you know the Fuel Flow that delivers less than 65% you will know how to run LOP 

The bottom line if you are smooth on 1GPH fuel flow, it does not matter if you areWOT & Max Rated RPM, you won’t have much CHT anyway 

[Ibra]

2 hours ago, exM20K said:

If 2300x30.5 at 16.5 GPH operates smoothly, why not operate there?

What does engine manual say? Airframe manual is not exhaustive on all MP, RPM, FF combinations, it does not mean it’s ok or not ok…at the end of the day, running smooth plus CHT/TIT have the final say, I would personally try it and closely watch engine instrumentation for operating limits

Edited February 12, 2023 by Ibra

[exM20K]

@Ibra that is the right question.

looks good:

[jlunseth]

8 hours ago, Tom 4536 said:

When cruising LOP, Mike Busch advocates running WOT and controlling power with only fuel flow. He says he even flies his turbocharged Continentals WOT. If, at say 15,000ft, we run our 231’s with Merlyn, GAMIs and intercooler WOT (or even 36 inches MP) won’t we have an overboost problem?

Yes, that’s an overboost. At ground level you would be well over 40 inches, which is the limit for the even the No intercooler 231 engine. You would be well over max HP. I don’t try to run at 36”, my feeling is that it just works the turbo too hard. Don’t have any hard evidence one way or the other, but back when I was experimenting I remember that temps start to climb pretty good at 35” (I.e. TIT and CHTs). We had one pilot on here from Europe that used higher MP settings though. Don’t know if he is still here and can add anything to the discussion.

One problem I think you would have if you run all the time at 36” is that you would probably have to run at a fairly high power setting to keep the engine from getting too lean and running rough.

[Tom 4536]

21 minutes ago, jlunseth said:

Yes, that’s an overboost. At ground level you would be well over 40 inches, which is the limit for the even the No intercooler 231 engine. You would be well over max HP. I don’t try to run at 36”, my feeling is that it just works the turbo too hard. Don’t have any hard evidence one way or the other, but back when I was experimenting I remember that temps start to climb pretty good at 35” (I.e. TIT and CHTs). We had one pilot on here from Europe that used higher MP settings though. Don’t know if he is still here and can add anything to the discussion.

One problem I think you would have if you run all the time at 36” is that you would probably have to run at a fairly high power setting to keep the engine from getting too lean and running rough.

Thank you!

[Pinecone]

13 hours ago, jlunseth said:

 Yes, that’s an overboost. my feeling is that it just works the turbo too hard. Don’t have any hard evidence one way or the other, but back when I was experimenting I remember that temps start to climb pretty good at 35” (I.e. TIT and CHTs). 

One problem I think you would have if you run all the time at 36” is that you would probably have to run at a fairly high power setting to keep the engine from getting too lean and running rough.

No, an overboost is running OVER rated MP.

The only two things that over work a turbo it to high of RPM, which can be approximated by too much difference between input air pressure and output.

And heat, as in too high TIT.  And this one is the real killer.

[jlunseth]

13 hours ago, Pinecone said:

No, an overboost is running OVER rated MP.

The only two things that over work a turbo it to high of RPM, which can be approximated by too much difference between input air pressure and output.

And heat, as in too high TIT.  And this one is the real killer.

I am pretty sure that is what I said. He has an intercooled 231. If he firewalls the throttle (WOT) at ground level, at least in my area where we are about 1,000 MSL for airport elevations, he will hit something over 40”. I have never done it, but I am pretty sure you could make it up to 45 or so inches. The limit in the nonintercooled 231 is about 37”, so hypothetically, if our OP were to firewall the throttle on takeoff, his MP would be about, say, 7 or 8” over max. At 37” at 1,000 MSL there is quite a bit of MP stick left to get to the firewall. The 231 is a different bird, it is capable of making well over max MP at ground level. It is up to the pilot to manage the throttle as the plane ascends, in order to keep the MP at a specific level. It is not like the automatic wastegate of the 252.

Simple point. In the 231 (with Merlin) you don’t go WOT unless you are up around 22,000.

[Pinecone]

OK.   Yes, if you go over the rated MP your are overboosting.  No matter how you get there.

The WOT,LOP was for NA engines, not turbos.

Mike Busch runs low boost engines, so it might still work for him.

In my 252/Encore I take off and climb at WOT (except when cold, it will overboost, up to 2 inches for up to 2 minutes is allowed), but cannot cruise at WOT, at least not until somewhere above the critical altitude.

[Will.iam]

16 hours ago, Pinecone said:

OK.   Yes, if you go over the rated MP your are overboosting.  No matter how you get there.

The WOT,LOP was for NA engines, not turbos.

Mike Busch runs low boost engines, so it might still work for him.

In my 252/Encore I take off and climb at WOT (except when cold, it will overboost, up to 2 inches for up to 2 minutes is allowed), but cannot cruise at WOT, at least not until somewhere above the critical altitude.

Actually i can go so lean that i can push the throttle all the way to WOT but there is not enough heat energy to spool up the turbo to make boost higher than about 30” but that makes the fuel mixture dangerously sensitive and was only an experiment I didn’t stay there long. At first i thought i had a boost leak issue until i started to increase fuel flow and the engine came to life. I read somewhere the 252 was designed manifold wise to be optimal at 28” of MP don’t know how true that is but my MB engine seems to like it there and i adjust fuel flow to 1550TIT which comes to 10gph. In the wintertime i can get 2500rpm for optimal prop efficiency but in the summer i have to dial down the RPM to keep the TIT below 1550 sometimes getting down to 2350 but my speed suffers then.