God I hate it when I'm sucked in by a troll.

You are correct, oggers. :ok: Best wishes for the rest of your life. :ok:

oogers:
The 600 to 3600 hour TBO information came from "Basic Theory", a publication by Wright Aeronautical (known as the WAD manual). It was published in (IIRC) 1957, and was based on 400 million flight hours of data collected by American Airlines. This has been confirmed by pilots and flight engineers who flew these engines during their heyday.

The US Military ran 'em ROP. As a general rule, changed one or two cylinders after every ocean crossing (according to Ralph Requa who flew them) and American Airlines did the same--until running them with a 10% BMEP drop (about 50dF LOP) when the TBOs extended to 3600 hours (according to the WAD manual and Captain John Miller who had 80,000 hours flying them, four at a time.)

Lead Balloon:
I guess I got sucked in by the troll as well. The difference is that over the last 15 years we have educated more than few by dealing with the trolls.

So far in summary...

The only data posted in this thread that has real measurements of exhaust valve temps is the naca report below.

It makes the point that mixture has the biggest effect of valve temp. It notes that a mixture of 0.66 results in the highest temp observed and the graph shows this very close to peak EGT. A mixture of .112 (indicative of full rich) give the lowest valve temp and the lowest EGT. While a lean mixture of 0.52 gives a substantial reduction of valve temp, EGT and also power (if knock is to be avoided) verses .066.

It also shows that both CHT and EGT do not always correlate with Exhaust valve temp, but in the case where mixture is varied alone there is strong correlation between EGT and exhaust valve temp.

That seems pretty conclusive, perhaps they made some errors...

Yet the Lycoming data posted, while they have not measured the valve temps, they have measured the guide and seat, these support the measurement provided in NACA-754.



Perhaps my summary is all rubbish, if so there must be some scientific data, with actual valve temp measurements to show its rubbish?

Would be nice to see that data, but it appears entirely plausible given that it appears this engine was designed for LOP at cruise power.

I would suggest your explanation leaves an important bit out, spark advance. Those engines had variable timing, albeit operated by the FE and he had two choices 30 and 20 degrees. At the cruise setting 30 degree BTDC and a mixture close to peak EGT, combustion would start and finish too early. Using the data from NACA-754, 30 degree and mixture at .08 results in CHT and EGT higher than at 20 degree.

***
Would be nice to see that data, but it appears entirely plausible given that it appears this engine was designed for LOP at cruise power.
***
It was operated ROP for a number of years. Poor results lead to the understanding that if operated with a 10% BMEP drop, the engines would last longer... six times longer to be exact.

***
I would suggest your explanation leaves an important bit out, spark advance. Those engines had variable timing, albeit operated by the FE and he had two choices 30 and 20 degrees. At the cruise setting 30 degree BTDC and a mixture close to peak EGT, combustion would start and finish too early. Using the data from NACA-754, 30 degree and mixture at .08 results in CHT and EGT higher than at 20 degree.
***
I explained that earlier. Please reference the explanation as to higher EGT very late in the combustion stroke and poor valve life. The spark advanced was added to the TC-18 variant, not originally present in the 3350.

BTW, our flat engines were DESIGNED to be run LOP. They have not been until recently since, as delivered, they had poor F:A balance and would run rough on the lean side. Since GAMI fixed that, they run as they were designed to be run. See the Malibu TSIO-520 history on that fubar.

Alcoa's development of the EGT probe allowed us to see that the 10% BMEP drop was about 50dF LOP. It allowed for more accurate leaning on engines without torque converters.

FWIW, when the crank is 20dBTDC on the up-stroke, the piston is very, very close to TDC--it's not 20 degrees more travel up. The piston movement is very, very small from 20dBTDC to 20dATDC on the crank. It's so close that it's hard to tell that it's not AT the top. Another thing we have shown to the many APS students. These things help in one's understanding.

http://www.pprune.org/newreply.php?d...reply&t=573902
I would say your not acknowledging important details... An earlier version of the engine, run ROP lasted 600 hours operated by the military, and a later model that incorporated at least variable timing operated by an airline operated LOP lasted 3500 hours.

Who was the physicist that said ?

'Everything should be made as simple as possible, but not simpler'

I would believe that, if I had the skills and was asked to design an engine I would design it LOP as well, doesn't mean when it got built there might be some limitations not intended that are either inherit in the design and/or manufacture that now must be observed.

***
I would believe that, if I had the skills and was asked to design an engine I would design it LOP as well, doesn't mean when it got built there might be some limitations not intended that are either inherit in the design and/or manufacture that now must be observed.
***

That's a weird approach. If you thin that might be true, and intellectually honest, you should say why that *might* be the case. It's not the case. The only issue was that they did not provide the product with balanced F:A ratios like the design called for. Had they, we would have been running these engines for 50 years like they were intended to be run--LOP. GAMI fixed that and a small group of pilots don't seem to be able to "get it."

Be well. Go on as you see fit.

i has discussed this technickal question at length about the whys and wherefores of operating reciprocating piston powerplants of various type with my good friend Delmar O'Donnel and he says, "I'm with you fellers."http://www.wearysloth.com/Gallery/Ac...04-25320-0.jpg

yes, i have done the APS course, even though the engines i operate have no mixture controls, i still find these conversations with "trolls" entertaining and learn a little bit, or refresh previous learned knowledge.

Walter Atkinson

In your opinion.

The graph Alcor produced:

http://www.pprune.org/members/125420...0-alcoregt.png

...is validated by the data from the NACA series of tests:

http://www.pprune.org/members/125420...ve-v-power.png

I hate to muddy the waters further, but I looked for information on BMEP change with mixture.

3 different sources I found show 10% BMEP drop from best power putting you at peak EGT or just lean (maybe 10F). Right at the best economy mixture.

10% additional BMEP drop from peak EGT looks closer to 50F lean (which the same sources suggest is 20-25% less BMEP than best power).

I am not trying to troll, just trying to relate what APS is teaching to data from other sources - which is what science is supposed to be about.

I don't get all this troll talk!

I am being honest, I would design it LOP, I can understand that when it got built it might not work out like that, maybe one day I would get a chance to fix it... I have designed and built complex stuff as a team and seen that pattern before.

I applaud your efforts to improve education, and advance technology appreciating that part of it is 'back to the future'...

However there are some important statements in this thread that relate to safety, that are in conflict with the verifiable data presented!

Pilots sometimes do the right thing for the wrong reason, what's important is they do the right thing! That is why I would suggest that if you want to do something different that relates to safety you need some scrutiny to ensure that the real reason that perhaps the pilot was blissfully unaware, is still not a concern.

My last statement also applies to engineers equally.

Who said 'to err is human'?

a good source of peer reviewed journals, and scientific texts on pretty much anything
ScienceDirect.com | Science, health and medical journals, full text articles and books.
just got to know the search terms
Assessment of Flame Transfer Function Formulations for the Thermoacoustic Analysis of Lean Burn Aero-engine Combustors

Walter Atkinson; the "torque converters" transmit the turbine power to the crankshaft. The BMEP was measured by torque gauges.

He is talking of the means by which the torque on a shaft is converted into a signal that can be measured on a gauge. It's a really simple piece of gear, at least the theory behind the concept.

Effectively a load cell in todays language. The gauge indicates the torque, not measures it. To be pedantic.

megan

Nope. A "torque converter" is not a torque meter, it is a fluid coupling like that in an automatic transmission that is used to transmit drive. A torquemeter does not transmit the drive - though it is of necessity in the transmission. The old TC18 engines he was referring to had fluid couplings (torque converters) to transmit drive from turbine to crankshaft. Those torque converters had nothing whatsoever to do with the torquemeter that was “indicating” BMEP.

http://www.pprune.org/members/125420...econverter.png

http://www.pprune.org/members/125420...orquemeter.png

I have learnt a few things from the NACA report presented in this thread, along with Cpt Deakin's articles and have been reflecting on my own professional experience operating some of these engines, though that was a long time ago and unlikely to be repeated.

Someone said earlier something to the effect of, which is better?
I would agree that if everything is working and you can safely get ALL cylinders to 30 degrees from a peak, 30 LOP is probably better than 30 ROP for your engine in cruise, Probably at least.

But as an example of possibly not thinking through ALL factors, what mistakes might you make from the descent onwards that might make 30 ROP better than 30 LOP? i.e. which might be more error tolerant?

Or perhaps to put it another way, what mistakes might you make from descent onwards that might make operating at a best power mixture with higher cylinder temps, higher ICP and maybe higher valve temps at say perhaps 100 ROP etc compared to say a safe LOP of perhaps 50 LOP.

Perhaps in my example, you might just consider a turbocharged example like a chieftain, or a big normally aspirated engine with alt compensation fuel pump, such as found in baron or bonanza, though the same problems or different problems may apply with smaller training aircraft.

foobar,

With a better understanding of things it would be easier to explain, but a forum post will not do your inquisitiveness justice. In terms of error tolerance on descent? LOP, far more tolerant in every case.

Abridged version;
In a conforming engine take off, full rich, climb leaning to a target EGT (Turbos full rich the whole way up, same for ACFP), level out, big mixture pull (another story) leave red knob alone until at the hangar door or if you must for your own desires, full rich when you put the gear down or turn final or whatever you prefer.

There are some extra comments and in the class room it is easy to discuss. Or pick up the phone and call me.

Is that answering your question? Hope it helps