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Old 28th Apr 2007, 16:02   #1 (permalink)
huv
 
Join Date: Feb 2006
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Any pilots of Piper Dakota with an engine analyzer?

I own 1/6 share of a Piper PA-28-236 Dakota with a newly overhauled engine, but without an engine analyzer. The other co-owners don't feel they need such a thing, but I am concerned about the health of the engine. The POH gives settings for 85% power, and a corresponding fuel flow for 50F rich of peak, inviting to a setting that is running CHT to an absolute maximum. So this is my question to you Dakota pilots with an engine analyzer:

Does the engine run hot in cruise? Where do you put the EGT to keep CHT's down? What are the CHT's you get?

BTW, our Dakota runs fairly smoothly when a little lean of peak, which I believe is unusual for a carburetted engine. Any experience with that, any of you?
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Old 28th Apr 2007, 16:41   #2 (permalink)
Final 3 Greens
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Are you sure your Dak has a carb?
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Old 28th Apr 2007, 16:56   #3 (permalink)
 
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I would recommend not running your engine lean of peak without an engine analyzer. I wouldn't be without the EDM-700 I bought for my continental TSIO-360-FB.

Run rich of peak if you are restricted to just an EGT guage. Just because the engine runs smoothly lean of peak does not mean you are not causing damage.

www.piperowner.org is where you will find excellent advice from other Dakota owners with Lycoming experience.
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Old 28th Apr 2007, 18:34   #4 (permalink)
 
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Quote:
I would recommend not running your engine lean of peak without an engine analyzer. I wouldn't be without the EDM-700 I bought for my continental TSIO-360-FB.
Are you suggesting it's safer to run the engine at 50 degF ROP based on the EGT of a single cylinder than it is to run the engine LOP?

If so, what is the logic of that argument?
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Old 28th Apr 2007, 20:25   #5 (permalink)
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No answers to my specific question yet, but thanks anyway.

Final 3 Greens, yes, it has a carb. Why do you ask?

Kiltie, thanks for the suggestion to go to piperowners.org. I had been there, but for some reason I got the impression that the forum was for paying members only. I checked again, it isn't, and now I have put my question on that forum too. But your reservations about LOP puzzles me. As you have an analyzer in your own aircraft, you have surely observed the CHT drop when running LOP? My concern is high CHT's, and as manufacturer's recomended best pwr mixture (50F) is also the setting giving the highest CHT, I am interested in LOP as that means lower CHT. So, along with Islander2, I would like to ask you what kind of damage you are envisioning in relation to LOP - vibration due to uneven fuel distribution is the only problem I can think of.

But, first and foremost, and as stated in my original post, I would like to know if the engine as installed in a Piper Dakota is a hot-running engine or not.
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Old 28th Apr 2007, 23:37   #6 (permalink)
 
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Lycoming 0-540 your PA-28-236 runs I think, from memory. Worked on them as a LAME quite a bit, and flown them once or twice as well.

The engine is not working that hard, as it is installed in a basic PA-28 airframe, but provides better cruise & climb performance. This would indicate that extra power that is installed up front from a standard 0-320 would make it a cold running engine, though their exhaust type system is weird that it does not remove the heat quickly from the cylinder.

The engine actually sounds like a tractor on start-up and idle, but smooothes out in cruise. I think that there is a different exhaust set-up that can be purchased and fitted as an after-market item that could increase effeciency and operating limits on your aircraft. I did fit one to a similar piper aircraft, with excellent results, better fuel burn, quieter, and colder running.

I do not remember much about the CHT's or EGT's, as it was a six place digital system, but did not read figures, only yellow, green and red lights.

Maybe you should have gone the SMA Jet-A (diesel concept) engine as per www.aero-diesel.com as this would have been far more effecient than what you have now!

Cheers, KP
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Old 29th Apr 2007, 11:42   #7 (permalink)
 
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huv

Since you haven't had adequate answers to your questions from people with 0-540/Dakota experience, here's my tuppence worth (from someone with zero experience of either your engine or your aeroplane!).

Without a multi-cylinder engine analyser, your options for safe leaning are very limited. This is the case for any large (235hp+) injected engine, and the more so with a carburetted engine like yours where the mixture difference between cylinders is likely to be substantial.

The single cylinder EGT gauge gives you but one sixth of the picture, which is close to useless! You say your engine runs smoothly LOP, but how do you know? If the EGT probe is on the leanest cylinder (and that would have been the intention), the other five cylinders may well all be running ROP! That's not LOP operation.

With just the one-channel EGT gauge, if the engine were mine I would run it as follows:

1. At the 85% power you quoted, I would strongly advise leaving the mixture in full rich. Any rich setting less than 250 degF ROP could have one or more cylinders in dangerous territory. 50 degF ROP is the worst place to be! A weak setting with all cylinders leaner than 90 degF LOP would be fine, but you have no means of knowing that they are all sufficiently lean ... and it is near certain in your engine that with the richest cylinder leaner than 90 degF LOP, one or more of the leanest cylinders will be producing so little power that the engine will be as rough as old boots if it will run at all!

2. At 75% power, where for many of their engines Lycoming say it is alright to run 50 degF ROP, I would still run full rich. There is a strong body of opinion in the USA based on work at GAMI's engine test facility to suggest 50 degF rich at 75% power is highly inadvisable. If you're comfortable that the EGT probe is on the weakest cylinder (not sure how you achieve that), you could run safely at, say, 150 degF ROP. LOP is not an option since you will have no idea where the richest cylinder is running.

3. At 65% power and below, you can safely set the mixture anywhere. To go fast, I'd set the mixture at 50 degF ROP since some or all of the cylinders should then be around peak HP. To go far or save money (and at these power settings you can ignore Kiltie's recommendation only to run ROP), I'd lean the mixture as far as you can with the engine continuing to run smoothly. As you've observed, you'll probably be able to get at least some of the cylinders running LOP. A tip for LOP operations from some pilots that fly behind O- engines at altitudes where full throttle is giving 65% or less power is to back the throttle slightly off from its fully open position. Apparently the turbulence from having the carburettor butterfly valve at a small angle to the airflow improves mixing and reduces the mixture spread between cylinders. A further tip for LOP operation at these lower power settings is to use partial carb heat, which has also been observed to improve mixing.

If the engine were mine, however, I would unquestionably fit a multi-cylinder engine analyser. I've had an EDM-800 in my IO-550 now for 4.5 years, and I view it as: a) a real potential life saver; b) tremendous for reducing fault diagnosis time and therefore maintenance costs - I've been able to tell the engineers specifically which plug out of the 12 was defective, and which fuel injector was partially blocked); and c) an eye-opener to engine management that has significantly altered my practices, given more flexibility for 'go fast' and 'go far' power settings and I'm sure is extending cylinder life.

Last edited by Islander2; 29th Apr 2007 at 17:46.
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Old 29th Apr 2007, 12:32   #8 (permalink)
 
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Without the like of GAMIjectors fuel flows are more often than not uneven across your cylinders making lean of peak operation imprecise. I have been advised by engineers and other owners alike that they all run slightly rich of peak with only an EGT guage (as this only tells the tale from one only of your cylinders).

Try the Lycoming website for more thorough advice as I am not an engineer and can't give you the full technical reasons for it; I have however a couple of thousand hours experience operating Lycoming and Continental IO-470/520/540 but not much on carburreted variants.

Feel free to accept or decline advice on these forums with your own judgement; I shall not be instructing you to ignore other poster's advice as I consider that to be quite rude.
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Old 29th Apr 2007, 14:13   #9 (permalink)
 
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Without the like of GAMIjectors fuel flows are more often than not uneven across your cylinders making lean of peak operation imprecise.
Yes, but uneven fuel flows make ROP operation equally imprecise.

And the crucial point (not understood by >90% of pilots) is that a cylinder operating 'slightly rich of peak' is in a much, much more critical operating regime than one run LOP. A mixture setting of around 50 degF ROP means you are forcing the engine to run with the highest internal cylinder pressures, the highest cylinder head and valve temperatures and the greatest chance of detonation. All of these adverse factors diminish as you weaken the mixture further through peak EGT to LOP.

All of the hard data (rather than 'marketing fluff') contained in aircraft piston engine manufacturers' manuals over many decades show this to be factual. Unfortunately, power diminishes as you weaken the mixture from 50 degF ROP, adversely affecting speed. I wonder why aircraft marketing departments don't like that? Equally, as you richen the mixture from 50 degF to 150 degF ROP, which is the minimum advisable for any of the cylinders at say, 75% power (250 degF ROP for 100% power), fuel consumption increases significantly for almost no increase in power. Not surprisingly, the aircraft marketing departments don't like that either.

So, despite the hard data to the contrary from the engine manufacturers together with decades of experience from piston airliners, G.A. has ended up believing that engines should be operated at the worst possible mixture settings from the perspective of engine longevity.

For the larger engines at power settings above 65%, if you run ROP you must run strongly ROP on all cylinders. To have any cylinders around 50 degF ROP is the worst place to be.

Kiltie, don't consider it rude if you wish to suggest that posters should ignore my advice ... just give them the technical reasons for doing so.

That engineers and other pilots alike advise operating the engine in the worst possible way isn't of much help. Precisely why do those people think that slightly ROP on one cylinder is a good place to be at high power settings? Try asking them to sketch a chart graphing EGT, CHT, ICP, HP and Valve Temp against mixture to see if they have any technical basis for their argument (or, indeed, any knowledge at all of the subject!). Then find some engine manuals (the earlier Lycoming and Continental manuals contained much more test-stand data than the later ones) to see what that chart really looks like. If you want the most comprehensive data, find a manual for one of the old Pratt & Whitney radials. These engines were traditionally run LOP yet, thermodynamically, they were just the same as our flat fours and sixes.

Last edited by Islander2; 29th Apr 2007 at 17:48.
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Old 29th Apr 2007, 16:34   #10 (permalink)
 
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I have absolutely no intention of instructing anyone to ignore your advice Islander2.

"That engineers and other pilots alike advise operating the engine in the worst possible way isn't of much help."

Again Islander2, you are completely dismissing other people's theories on the strength of your own opinion. You clearly have more technical knowledge than I, but you crudely assume the others I mention don't know what they are talking about. It is you that has interpreted "slightly" rich of peak to mean less than 100 degrees richer.

Disagreement is part of healthy debate; dismissal is self-righteous.

huv I would suggest you consider Islander2's well explained theories and compare with the wealth of knowledge on piperowner.org. They may well be the same.
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Old 30th Apr 2007, 19:42   #11 (permalink)
 
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Not a Dakota but a Maule M5-235C with an O-540.

Most Dakotas (?all) have a carburetted engine and so has the Maule.

Sticking a 15k new or overhauled engine in an aeroplane but skimping on an engine analyser is incomprehensible in my estimation.

Unless you are very lucky you will not be able to run the engine LOP.

But an analyser gives important information and if you go for the option with the fuel flow bits you gain some very valuable insights on what is what.
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Old 30th Apr 2007, 20:36   #12 (permalink)
 
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I think Islander2 is right. I have the old P&W radial engine manual, purchased from John Deakin.

Just a couple of things:

One could run a carb engine LOP but would need a means of balancing up the air and fuel delivery to individual cylinders. This is done in competition engines (1 carb per cylinder, perhaps, or the old radials?) but if you have just one carb, you are stuffed.

GAMI injectors are standard Lyco injectors which have been measured up (or drilled out) by GAMI for a specific flow rate, and they sell you a set of them, selected to match up your (uneven) air delivery figures, such that all cylinders reach peak EGT at the same common fuel flow figure. This enables smoother running, but not everybody needs it to be able to run LOP. Some people are lucky. But that's a fuel injected engine. I've never heard of anybody being able to run a single-carb aircraft engine LOP - it shakes too much.
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Old 30th Apr 2007, 20:58   #13 (permalink)
 
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I've never heard of anybody being able to run a single-carb aircraft engine LOP - it shakes too much.
I'm sure as a generality that's true. But Deakin and Co at Advanced Pilot Seminars have examples of Cessna 182 pilots flying behind Lycoming O-470s with multi-cylinder engine analysers that routinely operate LOP. That's where the tips have been promulgated of slightly closing the throttle from WOT and using partial carb heat at the higher altitudes. Whether you can truly get all six cylinders LOP and still running smoothly on many of these engines is another question!
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