Contentious ROP

[PTK]

And target climb takes very little leaning, it appears. To 8000 feet target EGT climb shows a delta ff of about 1.5 gph!! Am I reading this right?

 

[Txbyker]

Quote: testwest

Hi Russ

Byron mentioned, "climb at target" in other words the Target EGT method - see the attached pictures from KSMooniac's airplane. This is a Target EGT climb at WOT/2700 from KAAO, up to 8000'. Folks, this is how you do it. Russ, does "Target EGT" have meaning for you?

 

 

 

 

Norman, thanks!  By Target EGT I am thinking you refer to leaning to the highest EGT observed at sea level takeoff and continously lean to that during climb, am I right?  I plan to do that on my next flight.  

I did not perform the GAMI test prior to ordering new injectors but always wanted to add them so will do so and ensure I can run LOP evenly.

 

[PTK]

Quote: allsmiles

 

 

[Parker_Woodruff]

Quote: txbyker

Thanks everyone!  Just ordered a set of GAMIs.  After reading everything figured I would try the other contentious leaning method.  $700 should get my money back in about 20-30 hours of flying.

[Hank]

Quote: txbyker

[stevecampbell]

Just a thought...

From attending some seminars where peak cylinder pressure is plotted vs mixture, the "red box" is the area where pressures are highest. Now, in the red box EGT range, CHT's are also the highest (mostly as a byproduct I think).

So when the engine mfg's say "peak EGT is ok, but only below 75% power".  So it seems like they are mainly concerned with CHT and not cylinder pressures.  As I could get roughtly the same cylinder pressures running the same mixture at 2700 rpm as I could at 2200 rpm (although the 2200 rpm would give me less power, and lower CHT's).  In actuality the 2200rpm pressure would possibly be higher due to the piston not moving down as fast.  (Although this would depend on the state of the cylinder charge after top dead center..is it all burned or still burning? ) ...so how much does cylinder pressures really play in engine longivity..or is it mainly just CHT? 

[Txbyker]

Quote: Parker_Woodruff

 Having trouble with a stock IO-360?

You still MUST perform a GAMI test prior to ordering.  How would they know how to modify the injectors for size?

[Parker_Woodruff]

Try flying LOP with the stock injectors first.  Most Lycoming IO-360s don't require GAMIs to run LOP.

The fact is that you may not need GAMIs at all...and any cylinder that's way out of line on a GAMI test with stock injectors may first point you to something else, such as an induction problem.

[testwest]

Parker is right....and I added him to my list above in an edit.

[Immelman]

Quote: testwest

Parker is right....and I added him to my list above in an edit.

[DaV8or]

Quote: stevecampbell

 ...so how much does cylinder pressures really play in engine longivity..or is it mainly just CHT? 

[Txbyker]

Quote: Immelman

Just curious, do you have an issue with what I posted above in this thread? Always looking for suggestions on being a better pilot...

[KSMooniac]

Quote: DaV8or

Good question. I don't think anyone really knows for sure. It is just assumed that high pressures are bad, but I don't think there has been too much quantitative study on the subject. In real world flying, CHTs we can easily quantify, cylinder pressures, not so much. Best to keep both down IMO.

[KSMooniac]

Quote: allsmiles

And target climb takes very little leaning, it appears. To 8000 feet target EGT climb shows a delta ff of about 1.5 gph!! Am I reading this right?

 

[KSMooniac]

Quote: txbyker

 Having trouble with a stock IO-360?

You still MUST perform a GAMI test prior to ordering.  How would they know how to modify the injectors for size?

[Immelman]

Discussion point on GAMI as a company: I spoke with one of their reps at OSH a couple years ago. We got into a discsussion about the characteristics of the stock injectors in lyc IO-360's. He did not strike me as the type who would want to sell a set of injectors to someone who didn't need them. I appreciate that business ethic (I still haven't got GAMIs myself.. I can run LOP 'ok' with my stock injectors, but would perfer a tighter spread).

[testwest]

I-man you are correct. There are some folks not on this thread who aren't fully convinced about what LOP means.

We don't have GAMIs on ours yet. Our plan when the JPI 930 is installed is to do the following:

Check for any induction leaks, fix as necessary

Do a GAMI Lean Check and LOP mag check at 8000' DA

Pull our old Champion spark plugs, measure and record all resistances, then install new Tempest fine wires

Do another GAMI Lean Check and LOP mag check at 8000' DA

Determine if there is any change to the GAMI spread due to the spark plugs. There sure "seemed" to be an improvement on our Aerostar left engine when we did this, but I didn't do a good baseline first, so I don't have hard data. The steps above will be my atonement.

We'll post the results. If our GAMI spread is more than .5 gph, we get GAMIs.

[Parker_Woodruff]

Norman,

The Tempest Fine Wires helped me significantly at FL210 the other day.  11.6 GPH LOP (31.5", 2525 RPM, -10 OAT) without a single stumble on the TSIO-360-MB/SB.

[danb35]

Russ, as you've no doubt observed, this is a subject that gets pretty emotional.  It's not too unusual for claims to be repeated without the surrounding context, which results in quite a bit of confusion.  Here are a few factual data points, which can be confirmed with Lycoming's own charts (you can find them in the operator's manual for your engine):

• 
  
• Best power is 80-100 ROP.  IOW, this mixture setting gives you the most possible power for a given MP/RPM setting.
  
• Best economy is about 20-50 LOP.  "Best economy" means that the engine uses the least possible amount of fuel to produce power.  Power will be lower than at 100 ROP (with the same MP/RPM), but fuel flow will be more lower (and yes, that's a correct usage of that construction).  Put differently, any other combination of engine settings that yields the same power output will burn more fuel.
  
• A mixture of 40-50 ROP yields the highest CHTs and peak ICPs.
  

It's this last fact, I think, that contributes so much to the emotional nature of many of these discussions, probably because it's often phrased as "50 ROP is the worst place to run your engine".  In a sense, that is true--after all, higher temperatures and pressures aren't generally a good thing.  Whether it's really a problem in the O-360 series, though, is another question.  It seems that those engines have a history of bottom-end (especially camshaft) problems, not top-end problems that would be more likely to be attributed to mixture management.

[Cruiser]

Very well said Dan.  Concerning the RED BOX........

 "There is a limit ot the amount of compression and the degree of temperature rise that can be tolerated within an engine cylinder and still permit normal combustion. When this limit is exceeded, detonation can take place. Piston engines are vulnerable to detonation at high power output because combustion temperature and pressure are, of course, higher than they are at low or medium powers. Leaning the mixture at high power can cause it."

and.... 

"Preignition, as the name implies, means that combustion takes place within the cylinder before the timed spark jumps across the spark plug terminals. This condition can often be traced to excessive combustion deposits or other deposits (such as lead) which cause local hot spots. Detonation often leads to preignition. However, preignition may also be caused by high power operation at excessively leaned mixtures." Lycoming Flyer - General

If you look carefully at the attached image, rotate it 90° counterclockwise and you can approximate the size and shape of the RED BOX. Although I have never seen a description comparing the two, it is pretty easy to see why you would want to avoid these areas.  Extracting the Safe Operating areas from the chart shows you can run

80% power @ 150°F ROP and

75% power @ 100°F ROP or

about 75% power @ 50°F LOP and

at 100°F LOP as much power as you want and not worry. 

At less then about 72% power you can run the mixture pretty much anywhere you want. (sound familiar? Lycoming says 65% others say 70%.) In addition to all the other good things that happen to your engine at lower ICP and CHT, detonation and/or preignition are not among them and that IS a good thing also.

Finally, there have been tests run that show our O-360 series engines are virtually impossible to get into a pressure/tempurature combination that will allow either preignition or detonation under normal operating conditions. Improperly set ignition timing being the biggest offender. Large bore and turbocharged engines are entirely different animals. LOP is often discussed in generic terms so many times these specifics are neglected and applied universally to all operations. There is a huge difference in how different engines can be effected because of their abilities to make power.

[M016576]

This forum is full of much bigger brains than I... Please correct me if I'm going wrong here...

I was under the impression that any time you are ROP you are sending excess fuel required for the combustion event out the tail pipe, thus retarding the combustion event if enough air is displaced (thus loss of power at higher altitudes). Any time you are LOP you are operating in the exact opposite sort of regime: you are not providing enough fuel to the combustion event to maximize power.  By that definition, if all cylinders were of an unlimited strength and had a perfectly balanced gami spread then Peak EGT would indicate maximum power.  Maximum economy would depend on the airframe a bit, but would occur at some point LOP.  My understanding, though, is that we do have CHT's and material strength to worry about, therefore the Red Box.. And ROP operation.  Below a certain power percentage (different for each motor), since all cylinders aren't perfectly balanced, the 50 degree ROP rule of thumb for best power exists (as per deakin): that way you know all cylinders are operating at or near peak, rather than straddling the line so to speak: ie all cylinders are producing maximum Power while sending the least practical amount of excess fuel out the exhaust.

Where am I going wrong with my logic train?

Edit: already found one hole: I failed to account for preignition/detonation.  So my simplified thought process is clearly flawed a bit!

[DaV8or]

Quote: KSMooniac

The concern with the higher PEAK intra-cylinder pressures that occur due to ROP ops is that it places a higher load on the engine/cylinder components.  Metals fatigue due to heat and load (force) applied to them over and over, so whatever we do to reduce the heat and force on them will prolong their lives before they crack and fail.

[jetdriven]

You cannot measure ICP but you can measure CHT.  You can exceed the rated ICP on a very cold day at low altitude with a perfectly fine 330 CHT on an IO-360.  So, CHT as a long term trend for mixture setting is a good idea, except low altitude on cold days. As long as you obey the 10.0 GPH LOP fuel flow limit, that will for the most part, keeps you out of trouble regarding ICP.

[jetdriven]

Quote: KSMooniac

I may be going about it backwards but you can install new GAMI's and do the test afterward and they will tweak to the test results. New GAMI's can't be worse than 25 year old, probably dirty, stock injectors I am thinking.

[danb35]

Quote: M016576

I was under the impression that any time you are ROP you are sending excess fuel required for the combustion event out the tail pipe, thus retarding the combustion event if enough air is displaced (thus loss of power at higher altitudes). Any time you are LOP you are operating in the exact opposite sort of regime: you are not providing enough fuel to the combustion event to maximize power.