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  #11  
Old 08-02-2021, 07:27 PM
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DanH DanH is offline
 
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Lycoming's standard best economy mixture setting is peak EGT at 75% power or below. Power is manifold pressure and RPM, not some arbitrary altitude. Set power and run at peak or lean of peak right down to sea level.

As for best power mixture, again there is no arbitrary altitude. Assuming good temperatures, it's perfectly OK to lean to best power (aprox 100 ROP) at WOT and 2700, at any altitude.
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  #12  
Old 08-02-2021, 08:45 PM
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Approach/Landing
Donít go full rich on final, it is very hard on engine

Why is this? It's hard to think any movement of the mixture control at all is "very hard on the engine" at idle power. What's so special about final?

- mark
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  #13  
Old 08-02-2021, 09:01 PM
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jcarne jcarne is offline
 
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Quote:
Originally Posted by newt View Post
Approach/Landing
Donít go full rich on final, it is very hard on engine

Why is this? It's hard to think any movement of the mixture control at all is "very hard on the engine" at idle power. What's so special about final?

- mark
It would be almost equivalent to taxiing around with full mixture. Fouled plugs/ deposits.
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  #14  
Old 08-03-2021, 01:27 AM
GlennBfromOz GlennBfromOz is offline
 
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Originally Posted by jcarne View Post
It would be almost equivalent to taxiing around with full mixture. Fouled plugs/ deposits.
Sorry, I have to add $A0.02 here.

The plugs aren't going to foul in the short time spent in the circuit or on final. Even if they did, that'd be inconvenient but not "hard" on the engine. Unless the pilot is in the habit of making long power-off approaches, things in the chambers will be hot enough not to leave any deposits.

Additionally, if a go-around is needed, it'll probably be at short notice so it's best the engine be ready for it. For the same reason, we move the prop control fully forward once the RPM have started to drop.

Yes, it's possible to leave that stuff until the go-around actually happens. But the pilot will suddenly be busy, and it's too easy to miss something. That would be tough for the engine.
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  #15  
Old 08-03-2021, 06:33 AM
Strikhedonia Strikhedonia is offline
 
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Quote:
Originally Posted by newt View Post
Approach/Landing
Donít go full rich on final, it is very hard on engine

Why is this? It's hard to think any movement of the mixture control at all is "very hard on the engine" at idle power. What's so special about final?

- mark
Mark, the issue is running the engine rich, which due to the lead is really hard on the engine. Same goes for why Mike recommends aggressive leaning on the ground/taxi. His position is that if you forget to enrichen and the engine runs rough as you descend (or are on final) that a properly trained pilot will push power, prop, and mixture full forward.
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  #16  
Old 08-03-2021, 06:40 AM
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Originally Posted by Strikhedonia View Post
I didn't ask that follow up question. I plan to cover a small portion of the top of the fins on both 3 and 4 wrapping an inch down the sides. And I'll keep blocking off until the CHTs are within 10-15 degrees of each other.
Cylinder temperature and cylinder head temperature are not the same. Typically there is no instrumentation for cylinder temperature, and the thermal path from the hot head to the cylinder is inefficient anyway. It has to cross the screw joint, into a material (steel) with a far lower coefficient of thermal conductivity. The head sheds the vast majority of the waste head.

Point is, covering some portion of the cylinder to raise CHT is a lot like warming your ears by putting on your shoes.

Why raise a CHT anyway? Why not lower the hot ones, and gain some headroom for climb?
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  #17  
Old 08-03-2021, 06:51 AM
Strikhedonia Strikhedonia is offline
 
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Originally Posted by DanH View Post
Cylinder temperature and cylinder head temperature are not the same. Typically there is no instrumentation for cylinder temperature, and the thermal path from the hot head to the cylinder is inefficient anyway. It has to cross the screw joint, into a material (steel) with a far lower coefficient of thermal conductivity. The head sheds the vast majority of the waste head.

Point is, covering some portion of the cylinder to raise CHT is a lot like warming your ears by putting on your shoes.

Why raise a CHT anyway? Why not lower the hot ones, and gain some headroom for climb?
I'm still learning and I would say my baffling is 97% of the way there but at some point if there are no leaks I don't see how it is possible to bring all of the CHT temperatures lower. My hottest cylinders 2 and 6 are around 385 maximum during climb except on hot days when they can reach 400 before I use fuel to keep them from going higher (climbing at 130 kts). My understanding is that by blocking off some of 3/4 it will push more air over 1/2/5/6 and provide some help cooling them. Is that incorrect?
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  #18  
Old 08-03-2021, 07:50 AM
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Originally Posted by GlennBfromOz View Post
Sorry, I have to add $A0.02 here.

The plugs aren't going to foul in the short time spent in the circuit or on final. Even if they did, that'd be inconvenient but not "hard" on the engine. Unless the pilot is in the habit of making long power-off approaches, things in the chambers will be hot enough not to leave any deposits.

Additionally, if a go-around is needed, it'll probably be at short notice so it's best the engine be ready for it. For the same reason, we move the prop control fully forward once the RPM have started to drop.

Yes, it's possible to leave that stuff until the go-around actually happens. But the pilot will suddenly be busy, and it's too easy to miss something. That would be tough for the engine.
I agree that the word "hard" as used by Mike was not the best choice of words. Go full rich on final and watch the EGTs, if they are low enough (which they will be) the lead scavenging won't be there. Do it especially at a high density altitude airport and you will eventually foul an aviation spark plug. Ya it will be missing a time or two and you can clear it up but I would just rather avoid it which is why I don't go full rich in the pattern. First thing I do when I apply full power to my engine is look at the EGTs, if I forgot to push the mixture in I would know very quickly.
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Last edited by jcarne : 08-03-2021 at 07:52 AM.
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  #19  
Old 08-03-2021, 07:59 AM
lr172 lr172 is offline
 
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Originally Posted by Strikhedonia View Post
Mark, the issue is running the engine rich, which due to the lead is really hard on the engine.
where do you guys come up with the stuff. Lead is only an issue when rich???

Lead is lead and is always present. If you want to talk about what temp lead bromide will become vapor, that makes a lot of sense, but concerned about lead when ROP, but not LOP makes no sense to me. From my research, aside from deposits, lead is good for your engine. It lubricates, cools, and increases detonation margin. There is a reason that they put lead in the gas originally.

Larry
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Last edited by lr172 : 08-03-2021 at 08:22 AM.
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  #20  
Old 08-03-2021, 08:02 AM
lr172 lr172 is offline
 
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Originally Posted by jcarne View Post
I agree that the word "hard" as used by Mike was not the best choice of words. Go full rich on final and watch the EGTs, if they are low enough (which they will be) the lead scavenging won't be there. Do it especially at a high density altitude airport and you will eventually foul an aviation spark plug. Ya it will be missing a time or two and you can clear it up but I would just rather avoid it which is why I don't go full rich in the pattern. First thing I do when I apply full power to my engine is look at the EGTs, if I forgot to push the mixture in I would know very quickly.
lead bromide becomes vapor around 800-1000 degrees and will typically not deposit above those temps. I have never seen my EGTs lower than 1200 in the pattern. Maybe my engine is different. At idle, the temps can get into that range and that is typically when lead deposits are made.

IMHO, leaning aggressively in the pattern is an accident waiting to happen. If I need power in the pattern, I likely need it NOW. Having to remember to go full rich increases the odds of becoming a statistic. There is a reason that pretty much EVERY certificated airframe manufacturer recommends full rich in the landing phase. I landed a couple of weeks ago with serious wind shear (10 kts surface/60 knots at 1500 AGL). My IAS was jumping between 75 - 100 MPH. I needed several LARGE throttle movements to stay safe. You just don't know when you will need aggressive throttle, but I promise that you will appreciate that it works when you need it when near the ground.

Larry
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Last edited by lr172 : 08-03-2021 at 08:12 AM.
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