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Increase MAP after LOP-procedure


NicoN

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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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  • 5 months later...

May I come back to this pretty old thread ?

 

Recently  I was playing around a bit while being at 9000ft.

Already at LOP for several minutes, I started pushing the throttle in while leaving the mixture unchanged.

Indeed, my EGTs temperatures decreased by giving more throttle. I guess, I can bring my engine (TSIO360-GB) to quit  by simply advancing the throttle.

But, is it possible or does it make sense to fly LOP with throttle wide-open and controlling power with the mixture lever?

I have seen pilots flying their NA engines with throttle wide-open.

 

Thanky you!

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I assume you're flying a 231? The 231 is different than the other K, the 252. 

Once cruising at LOP, advancing the throttle just pushes you further away from Peak, or Leaner. In other words, pulling the mixture out or pushing the throttle in, will have the same effect while LOP.

You want to be flying at a specific distance, or degrees on the Lean side of Peak for best efficiency. If you increase the throttle, you'll have to increase the Mixture at the same time to maintain the optimal LOP setting. That results in LOP at a higher power setting. It's pretty well accepted that the safe place to run our TSIO360's LOP is at 65% power or below. Running LOP with a wide-open throttle in our turbo engines would be effectively running LOP at 100% power. That will kill the cylinders pretty quickly unless you are very deep LOP like 80° on the lean side of peak. The engine might not run that far lean.

The reason the NA guys run LOP at wide open throttle, is that they are already at reduced power because of altitude. WOT in the IO360 at 10,000 ft is probably close to 60% power already. My K at 10,000 is still making 100% power at 10,000 ft. 

Brian Lloyd flew his 231 around the world at FL210 and these engine settings. 31” 2450 10gph I would expect those to be the optimal settings for a 231.

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Yes, it's a 231 with the GB engine.

Thank you for clarification. So, no WOT, even not with more leaner mixture.

Hope, I can on time cross-check those numbers!

 

Let me continue with another question: Is there a specific descending technique after cruising ?

Let's say I was cruising for 2h in F100 with 28"/2500RPM/8.5-9gph and 50° dLOP.

At the moment, I compensate only for the increasing MAP to stay at 27-28" and keep the rest constant.

Is there anything better?

Of course, by reaching my lower altitude, e.g. for pattern, then I push in the mixture to be on the rich side as soon as I have to increase the power.

 

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11 minutes ago, NicoN said:

Let me continue with another question: Is there a specific descending technique after cruising ?

Let's say I was cruising for 2h in F100 with 28"/2500RPM/8.5-9gph and 50° dLOP.

At the moment, I compensate only for the increasing MAP to stay at 27-28" and keep the rest constant.

Is there anything better?

Of course, by reaching my lower altitude, e.g. for pattern, then I push in the mixture to be on the rich side as soon as I have to increase the power.

 

I think this looks fine. The only thing I do on the descent is to trim for 500 ft/min down. I leave the power settings the same. I usually go ROP once reaching pattern altitude.

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Yes, it's a 231 with the GB engine.
Thank you for clarification. So, no WOT, even not with more leaner mixture.
Hope, I can on time cross-check those numbers!
 
Let me continue with another question: Is there a specific descending technique after cruising ?
Let's say I was cruising for 2h in F100 with 28"/2500RPM/8.5-9gph and 50° dLOP.
At the moment, I compensate only for the increasing MAP to stay at 27-28" and keep the rest constant.
Is there anything better?
Of course, by reaching my lower altitude, e.g. for pattern, then I push in the mixture to be on the rich side as soon as I have to increase the power.
 

There are as many descent possibilities as there are pilots. I personally come down at cruise power at a few hundred ft/min as long as I get cleared to descend early enough at Pilot Discretion; which is more typical than not.
But Whether your coming down LOP or ROP, it's easiest with your 231 without a hydraulic controller, to just use TIT as your guide to maintain mixture. So if you're coming down ROP, which will be a TIT likely in the 1450 to 1550 range, don't let it creep up, enrichen just enough to keep the same TIT throughout the descent. If your coming LOP with a TIT, hopefully just below 1600 rather than above, you can reduce the air to keep TIT from going down. The latter step is mostly done automatically by a 252 with a hydraulic controller, but not with manual waste gate.
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Okay, thnak you!

Normally I try to keep MAP constant.

These days I had seen the effect, that TIT was going  up rapidly. I pulled back MAP and enriched, that cured the situation.

You do it by only enriching?

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Okay, thnak you!

Normally I try to keep MAP constant.

These days I had seen the effect, that TIT was going  up rapidly. I pulled back MAP and enriched, that cured the situation.

You do it by only enriching?

Yes and no, I enrichen only because I have the automatic wastegate. You don't and will have to stop the MAP from increasing in descent manually. Sorry, left that out.

 

 

Sent from my iPhone using Tapatalk

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Some additional thoughts...

Sort of an MS summary.

 

1) With LOP we are already burning all of the available gasoline and getting the most power out of the fuel available.... 

2) This occurs right around peak.... give or take...

3) Going further LOP... we are using excess air to help lower EGT and / or TIT... all good... a side effect also occurs by slowing down the reaction rate of the fuel burn...

4) There is a limit to how far or deep LOP one wants to operate...

5) If EGT And TIT are well controlled, Going deeper LOP won’t add any additional benefit... except for coolness factor... (as in that’s wicked cool! :))

6) Deeper LOP essentially compresses additional air and will generate a small percentage of mechanical energy loss... how cool do you want to run your engine?  CHTs and TITs have Have temps to stay under for best parts life...

7) Really deep LOP... The viable fuel/air ratio gets exceeded... too many N2 molecules getting in the way of O2 and 100LL molecules finding each other...  Random walk theory, interrupted... :)

8) An engine with a tight Gami spread will discontinue running as the air / fuel ratio increases with more air...

9) Higher MPs and their associated °F LOP are related... a well balanced, NA, IO550 can go 90°F LOP around 5k’ of altitude... before it shuts off...

10) @10k’ of altitude the ability of the NA IO550 to go deep LOP is limited to about 50°F LOP... before it shuts off...

11) A poor Gami balanced engine will be shutting down one cylinder at a time and running rough when that occurs...

12) Having a TC or TN there are two ways to control the fuel / air ratio... you get to adjust MP and mixture... and some of that is going on automatically too...

13) Running deep LOP... runs out of advantages... once temps are under control...

14) the biggest disappointment of deep LOP... less fuel is being burned so %bhp is pretty low with a resulting lower number on the ASI...

15) If you are on an efficiency run... and Vz is your target on the ASI... and cool cylinders or TIT are the target CHT... deep LOP is fantastic...

16) Expect at the deep LOP end where the viable F/A ratio starts getting exceeded... there may be some fuel that doesn’t get burned... before the exhaust valve opens... the burn rate gets slowed down as the ratio falls to the edges of the envelope...

17) One way to goof things up... At high BHP%, the chances of pre-ignition are increased, and not really easy to notice... >65% BHP is the typical cut-off point to keep from accidentally experiencing pre-ignition related challenges...  keeping things cool, either ROP or LOP, is another way to avoid pre-ignition...

18) Avoid running high CHT, TIT and BHP% at the same time... often, the big pull is used to get through the transition... it can be a challenge to sneak up past peak into LOP...

19) TIT can be challenging to control...

20) With excellent instrumentation... it is possible to keep a good eye on the MP/FF and temps...

PP summary only... not an original thought in there anywhere... :)

Best regards,

-a-

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As an interesting adjunct to this discussion, I have a TSIO-360 LB with an intercooler and Merlyn. Recently, I went out to do an IPC with my CFII. As we know, IPC's are not necessarily representative of real world IMC approaches since the CFII usually throws several approaches at the pilot during the flight. At least, this is what happened to me. A problem I found (and was pointed out to me by my CFII) was that I was spending too much time on engine management after each approach. A Merlyn requires a "deft" touch on the throttle as it can easily get over boosted and I am transitioning from ROP during final approach to a Missed then reconfiguring to setup for the next approach flying LOP. Moving from ROP to LOP while getting the correct Approach loaded and buttons pushed while under "foggles" is a big load on the pilot. I am thinking that the next IPC (and all the rest after) will be done ROP so I dont mess with the engine at all other than prop. What techniques do others use?

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2 minutes ago, 231LV said:

As an interesting adjunct to this discussion, I have a TSIO-360 LB with an intercooler and Merlyn. Recently, I went out to do an IPC with my CFII. As we know, IPC's are not necessarily representative of real world IMC approaches since the CFII usually throws several approaches at the pilot during the flight. At least, this is what happened to me. A problem I found (and was pointed out to me by my CFII) was that I was spending too much time on engine management after each approach. A Merlyn requires a "deft" touch on the throttle as it can easily get over boosted and I am transitioning from ROP during final approach to a Missed then reconfiguring to setup for the next approach flying LOP. Moving from ROP to LOP while getting the correct Approach loaded and buttons pushed while under "foggles" is a big load on the pilot. I am thinking that the next IPC (and all the rest after) will be done ROP so I dont mess with the engine at all other than prop. What techniques do others use?

I teach the LOP stuff, but I am also a bit anal about setting it up, but I don't use it till after climbing up for a longer x-country where I'll be at cruise for sometime. Although I am sure there are pilots that may set up LOP between airports when doing IFR currency training, I wouldn't consider doing so myself when doing a series of approaches since the workload is too high with so much going on. I strictly use and practice a series of ROP PAC's (by the numbers). Except for going missed, all of the power settings are low power anyway.

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Yep, I'm with @kortopates on this. I use LOP all the time... but only in cruise. And if I know I'm descending towards an Instrument approach, I"ll go back ROP prior to even getting into the approach environment. Even though engine management is much easier with the 252, I still don't want to be trying to fine tune the engine while also trying to keep needles centered on an approach. 

LOP is for those long stretches at altitude where nothing else is going on.

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