NicoN

Increase MAP after LOP-procedure

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My question may sound a little funny:

When doing the LOP-procedure , I set my engine to 65% ROP and wait for 1 or 2 minutes.

Then, I start leaning under control of the EDM830.

Doing this, I can see FF decreasing and MAP also decreasing. Completing LOP, I end up with -2.5 gals or more, reduced temperatures and reduced MAP.

Engine monitor says now 56-58% instead of 65% as before. Also I get a speed penalty of 6-8 knots. Of course I can lean more, Power is even more decreasing as the engine power is now mainly dependant on FF.

I never pushed the throttle in to raise my engine power back to 65%. But why ?

I found a continental document which also prohibits giving more MAP - but no explanation.

 

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Nico,

We have a couple of well written threads for LOP ops with TCs around here that are worthy of looking up....  The K’s engine is well designed to achieve excellent LOP numbers... The Bravo’s air intake system doesn’t have the flexibility/balance to do the same... we have a couple of MSers that have really defined the details of their engines....  See if you can find those authors...

 

Things to consider...

1) The whole idea of going LOP is to have excess air for cooler operations... where ROP uses excess fuel to do the same...

2) With a NA engine MP doesn’t change when the mixture is pulled through peak to LOP... the Tc’d Engine tries to change MP on its own...

3) The  challenge in a TC’d engine... Other things are changing as well in an autocatalytic sort of way.... (turbo rpm related)

4) The advantage of having a TC or TN... the pilot can add the MP back where it started...

5) Keep in mind... to keep track of %hp we measure the limited resource... ROP uses airflow, LOP uses fuel flow, your engine monitor might explain this in the documents... relying on the %bhp display without knowing what it is doing and how it is doing it can be very misleading....

6) airflow is hard to measure compared to FF... so comparisons are made to well instrumented engines under the same conditions in the lab.... in other words... we use MP and RPM to define what the airflow is...

7) Expect the following to occur.... proposed cruise flight, changing from ROP to LOP in cruise...

  • Flying ROP, Power is set according to the engine’s performance chart... MP and RPM are key, FF is supporting info...
  • to get some safe experience use 65% bhp to start... safe for the pistons, but turbo safety comes with watching TIT as well.
  • When going LOP, Power is set as a function of fuel flow... while keeping the MP and RPM where they were...
  • Realistically, LOP uses excess air flow... so an MP higher than the ROP numbers can be used....

8) The operational challenge is peak TIT... while doing this change from ROP to LOP, slowly, stepwise.... the TIT can get very hot before it starts to cool down... the peak is pretty strong...

9) To pass through peak as quickly as possible... pilots use something called the big pull method... they pull the mixture back in one quick step knowing where the FF and MP targets are...

10) Once LOP... with the TIT below your selected redline (1650°F for many people) you can adjust MP, and FF more slowly...

Now to find those threads.....  and MSers   @jlunseth  are you here?  :)

 

Thoughts of NA PP... not first hand experience of TC ops....

Best regards,

-a-

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I would not use C or L dated recommendations as strict guidance. This was before engine monitors.
If you have an engine monitor and cylinder head temperatures stay below limits, I think you’re good to go.

Can you even have detonation when LOP? I think the danger zone is from peak to 50° on the rich side.


Tom

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3 hours ago, NicoN said:

My question may sound a little funny:

When doing the LOP-procedure , I set my engine to 65% ROP and wait for 1 or 2 minutes.

Then, I start leaning under control of the EDM830.

Doing this, I can see FF decreasing and MAP also decreasing. Completing LOP, I end up with -2.5 gals or more, reduced temperatures and reduced MAP.

Engine monitor says now 56-58% instead of 65% as before. Also I get a speed penalty of 6-8 knots. Of course I can lean more, Power is even more decreasing as the engine power is now mainly dependant on FF.

I never pushed the throttle in to raise my engine power back to 65%. But why ?

I found a continental document which also prohibits giving more MAP - but no explanation.

 

Nico,

In most NA airplanes you target a LOP value such as 30 lop or 50 lop.  With the TSIO-360 GB/LB it's better to target a FF.  (10gph when LOP is about 65%. 9.2gph is about 60%.)  Any change in mixture will change MP, and vise versa.  Because of this its difficult (nearly impossible) to know how many degrees you are LOP but that really doesn't mater.  As long as you know you are well LOP or at a low enough power setting so it doesn't mater.  I typically fly at 32" and 10gph.   

When I fly LOP I treat the mixture control as my power lever and the Throttle (MP) becomes my mixture control.  I set the power I want by adjusting FF with the mixture.  I can lean the mixture further by adding MP (adding air) and richen it by reducing MP(less air).  So if you are LOP 10gph and 28" or LOP 10gph and 34" both are 65% power.  But the later is much further LOP.  So I run higher MP pressures and no more than 10gph so I can be confident I'm operating in a safe place. 

So if you increase your MP while adjusting the mixture to maintain your LOP FF your are not increasing power, but leaning further. 

What is your FF and MP when 65% ROP and what are they after leaning to LOP?

Cheers,

Dan

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