LOP & Exhaust System Life

[jetdriven]

Byron, or someone with a J, what is your speed loss at 60 to 70 degrees LOP, compared to 15 to 20 degrees LOP, so about a 50 degree delta?

At 10-15 LOP the speed loss from 80 ROP (maximum speed) is around 3 knots true. At 50-75 its massive, around 10-11 knots, a little leaner and the NMPG is actually worse than around peak.  You save 0.8 GPH but run 12 knots slower, its a bad trade.

 

Now below 3K to get it lean enough to run 10.0 GPH WOT it is around 75 LOP, but you are limiting HP with FF.

 

This photo is garbage data, I will get something better with the GAMI injectors. But it seems that any leaner than 25 LOP is only economical due to lower TAS and total drag from that.  Even the Beechtalk guys caught onto this and now 15-25 LOP is SOP for them as well. Even the 95% power TAT TN A36 guys. What a hell of an airplane.

 

 

now how about some carbon fiber!

[fantom]

.... I think the ADDITIONAL speed loss for another 50 LOP would be pretty significant... in the 5-7 knot range.

 

 

At 10-15 LOP the speed loss from 80 ROP (maximum speed) is around 3 knots true. At 50-75 its massive, around 10-11 knots, a little leaner and the NMPG is actually worse than around peak.  You save 0.8 GPH but run 12 knots slower, its a bad trade.

 

.....Even the Beechtalk guys caught onto this and now 15-25 LOP is SOP for them as well. Even the 95% power TAT TN A36 guys. What a hell of an airplane.

 

 

Thanks, guys....that's my experience also, although I've only tried 75 degrees LOP once, and that was enough. Around 20 degrees LOP is my usual target.

[KSMooniac]

Again, there is no need to fly more than 20 LOP in a J at normal/optimal J altitudes (7-9k').  I usually try for peak to 10 LOP and then lean more if CHTs get to 380 or higher.  

 

If/when I add the turbo normalizer, then I plan to be in the 60-70 LOP camp regardless of altitude running 85% power all the time.  

[Flymu2]

At 10-15 LOP the speed loss from 80 ROP (maximum speed) is around 3 knots true. At 50-75 its massive, around 10-11 knots, a little leaner and the NMPG is actually worse than around peak.  You save 0.8 GPH but run 12 knots slower, its a bad trade.

 

Now below 3K to get it lean enough to run 10.0 GPH WOT it is around 75 LOP, but you are limiting HP with FF.

 

This photo is garbage data, I will get something better with the GAMI injectors. But it seems that any leaner than 25 LOP is only economical due to lower TAS and total drag from that.  Even the Beechtalk guys caught onto this and now 15-25 LOP is SOP for them as well. Even the 95% power TAT TN A36 guys. What a hell of an airplane.

IMG_2833.jpg

 

 

now how about some carbon fiber!

photo-70.JPG

 

15-25 LOP at high power settings is definitely *not* SOP.

 

15-25 LOP *is* the peak of the brake specific fuel consumption (BSFC) curve. At high power settings, however, it is solidly within the "red box" as described by the GAMI people. At the aforementioned 95% power setting, available mostly to the TN airplanes, the "red box" is large, and one needs to be either about 150 ROP or about 80 LOP to stay out of it. As power setting decreases so does the size of the red box, to the point where at 65% power or less there is *no* red box, and one can do anything with the mixture control and not hurt the engine.

 

All of these concepts are very well described by a graph that Advanced Pilot Seminars publishes. The graph shows the relationship of EGT, CHT, BSFC, power, and ICP (internal cylinder pressure). It's the heart of the APS course. You can see it at http://www.advancedpilot.com/redbox.html. It succinctly states everything one needs to know about leaning spark fired piston engines.

 

None of this has anything to do with exhaust system life as far as I can tell.

.

[DaV8or]

The topic is does LOP affect exhaust life , and the answer at least on my planes is NO They are made of Alconel and don't corrode.....They crack , from vibration mainly ....... 

 

Actually, they do corrode. Stainless steel oxidizes just as most metals do. It's just much more resistant than ordinary steel. Try this- polish your tail pipe until it looks shiny like chrome. Then go fly and see how long that shine lasts.

 

It is a reasonable supposition that a oxygen rich, high temperature environment will accelerate oxidization. Yes, even stainless steel. Now if you run LOP at 80 degrees, that will cause less oxidization than say if you run 10 degrees LOP. Higher temperatures excite the oxygen molecules and they react faster.

 

Since there have been no scientific studies of LOP ops on aircraft exhaust systems all we have is anecdotal evidence. Many exhaust systems may very well fail from cracks long before they burn out. Others may very well burn out early if they are operated at a high EGT LOP setting as SOP. There may also be differences in exhaust system designs that either promote, or discourage corrosion. We'll never know for sure until it's tested in a lab some day.

 

In short, I think it all just depends and there may be more than one right answer to this question.