LOP or ROP, which do you run?

[RV10inOz]

Q&A debate...hopefully educational.

Quote:
Originally Posted by RV10inOz View Post
allbee

If you are motoring along all nice fat and happy, LOP and you see on your dynon EMS with its EGT display start flashing a rising and falling EGT, what would that mean to you? A disaster? Lets ask the question with more details to help, the EGT starts rising and stays up, maybe the odd retraction but its fluctuating above 1500F, and likely the CHT is dropping a bit. What does that tell you?

DB
I had this very thing happen, the problem. The exhaust plugged up on the left side for cylenders 1 and 2. did this same very thing. At the time my response was to rich the mix and pull back on the throttle, turn back to the airport. If at any time the exhaust temp climbs up from norm I take it seriously, yes higher exhaust temps mean to lean which can burn the exhaust temp. I've seen it many times on a vehicle with fuel injection, fuel injector plugs up and the result every time if left alone is a burned exhaust valve.

So what does "the exhaust plugged up" mean? If you had said a spark plug/s had plugged up with lead balls and carbon and were firing less effectively I would agree with you. Even spark plug gaps that are too wide will yield this as the spark is not ideal. Its like switching a mag of on jst that one or two cylinders , the spark is poor, the combustion event is lethagic and retarded, some of it continues as the exhaust valve opens and out past your EGT probe and the temp at the probe rises. As a result the HP produced falls and so does the CHT ever so slightly. If you meant something else I would love to know, I can't imagine you plugged up the whole exhaust pipe.

As for the notion of high EGT readings burning exhaust valves, can I suggest you read up on some of George Brayly, Walter Atkinsons or John Deakins writings, clearly you do not believe me but these guys you should.

As for comparing your EGT numbers and mine, or anyone elses, that is pointless. If I move my probe another inch or two away from the head, I could get numbers like yours too. Fact is its all about relative changes not exact numbers.

I see you don't really understand what you are saying here. I check my system out all the time this way. If you turn off one mag, in my case a pmag, I have exhaust temps go up, no more than 100deg. for me that's about 1430, no where near your 1500+. All cylenders go up the same across the board. Now you turn that mag back on and all temps normalize. Now do the other mag. I do this on a reutine basis to check my system out. If a cylender doesn't change in conjuction to the others I note the cylender and go fix it. the last time I had that happen I ended up with a bad spark plug. doing mag checks on the ground is a worthless operation in my book. I do it just to let me know the mag is "working".

I do not see what on earth it is you think I do not understand what I was saying???? If you leave your one mag off long enough, you will generally see at least 100F rise based on probes 2" from the head, but here agin, the actual numbers mean nothing. Its the relative changes that matter.

What you are doing is correct and for the right reasons.

Just as a side comment, your EGT numbers suggest your criuise power setting LOP yields 1330F +/- which is absolutely fine with me. For the benefit of all readers could you measure where in the exhaust pipe your probe is and let us know.

Just for the record, if you had 6 cylinders and placed the probes at 6 different distances, the closer ones will read higher, the further lower, generally speaking assuming well matched cylinders, and you could still fault find and use LOP ops. Its all about relative change. Mind you its far easier on our brains to keep them all in a simlar zone.

DanH

I'm surprised at the number of respondents who use LOP operations to control CHT.

Here's a take-it-to-the-bank fact about a fixed exit cooling system: If the components are sized, fabricated and installed to provide proper cooling under climb conditions, the system will have considerable excess cooling capacity in cruise.

So....take this the right way, please, because I'm not saying it to insult anyone: If you must use LOP to maintain an acceptable cruise CHT, you have problems elsewhere. There are thousands of well constructed dead stock RV's whose builders enjoy nice cool cylinders while cruising at best power or peak EGT.

Great post, I have never noticed that point. And so true, low CHT is a benefit of a good cooling system and LOP ops. I'll second that

RV8R999

If you are LOP and need to advance the throttle in a hurry to max blast what happens?

Lets paint a picture, at 2500', poking along doins something scenic, say throttle back at around 20-21"MP RPM wherever you like thats smooth, 2319RPM, and LOP or at this power setting at peak to 10LOP, and all of a sudden you realise the football game is on in half an hour and you better scoot back home. There is nothing you can do over 3-5 seconds that can harm your engine......So, here is the answer, and I suggest its burnt into your brain for a good reason.

Red Knob, Blue Knob, Black Knob.

I do nothing with mixture from the FL's all the way down to parking it at the hangar. Then I use ICO And in the event of a Missed approach, its red/blue/black. It takes about 1.5 seconds max and what can go wrong? Nothing.

If you are at 7000' WOT 2200RPM and LOP and after a long time being held down by ATC you are cleared to 9000', you could gently climb LOP if you wanted, change nothing you will slowly creap closer to peak and best power, but why not do this, richen up a bit, then set 2700RPM for the climb, which will pump more fuel anyway, and then adjust mixture to your climb power TARGET EGT. You do still remember your Target EGT of course, because that was in use only 15 minutes ago before ATC held you at 7000'. Does it matter if you went a little too rich and have to tweak back a bit, not at all.

Then at RV speeds with a fast cruise climb 3 minutes later you are at 9000', leave MP where it was all along, pull back the RPM to where its happiest and then set LOP by using a known fuel flow and watching the EGT's roll over or by doing it a bit slower but watching them roll over with the aid of a Lean Find mode or however you do it.

Of course don't take my word for it..............
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[AlexPeterson]

I'm surprised at the number of respondents who use LOP operations to control CHT.

Here's a take-it-to-the-bank fact about a fixed exit cooling system: If the components are sized, fabricated and installed to provide proper cooling under climb conditions, the system will have considerable excess cooling capacity in cruise.

So....take this the right way, please, because I'm not saying it to insult anyone: If you must use LOP to maintain an acceptable cruise CHT, you have problems elsewhere. There are thousands of well constructed dead stock RV's whose builders enjoy nice cool cylinders while cruising at best power or peak EGT.

Dan, we might need to calibrate what acceptable cht's means. In my case, summer cruising, if ROP "best power", might put the cylinders in the high 300's, perhaps 380. Many consider that ok, which it might be. However, I prefer to get them down into the low 300's. Everything one reads is that cylinder life is related to cooler running. I can dial the cht's from 380 down to 320 or 330 by going from 8.5 or 9 gph down to 7.5, at 22"/23 settings. Speed penalty might be 6 knots or similar. MPG goes up a fair bit, as does range.

Many people have tried to putz around with baffling because they have one or more cylinders which run much hotter than others. While the baffling may be at fault, it is often the result of one cylinder's mixture being out of whack as compared with the others. But, they cannot lean any more owing to the leaner cylinders running poorly, causing roughness. So, one cylinder runs along much warmer than the others. I've done enough fuel flow vs cht's on other planes to know this is often the case.

I'm also not convinced that the standard Van's design does indeed provide enough cooling for sustained climb, nor should it necessarily. Most I know have to use some other control mechanism for keeping cool on climbs on hot days (slobbering fuel in, stair step, LOP, cruise climb speeds, etc.). Again, I do not let mine go above 400 on climbs, just my way.

I also think the lower power one tends to cruise at, the warmer the engine will run. If I cruise at 24/24, it will run cooler than at 22/23, similar mixtures. I tend to cruise almost exclusively at the lower of these two. I have not taken extensive data to compare these though...

Those with EI seem to notice a more profound cht vs mixture relationship as well.

 

[RV10inOz]

Using the TARGET EGT method we climb all the way to 10K and have CHT's around 350-365F in the climb and 300-310 in cruise when LOP.

Good baffling is not hard. Variations of 10-20F are nothing serious imho.