At altitude, which throttle setting?

[Pinecone]

Good analogy. I remember it from my Cirrus days.

There’s an acronym many Cirrus pilots use for cruise settings - WOTLOP (Wide Open Throttle Lean Of Peak). Maximum efficiency by not impeding the flow of air to the engine, and controlling power with the mixture. This, of course, pretty much requires fuel injection with reasonably balanced injectors.

That saying predates Cirrus.

WOTLOP is the mantra of Advanced Pilots Seminars and related to GAMI and GAMIjectors.

 

[Pinecone]

I'm old school I guess. I don't even run my lawnmower that way and it specifically says to in the manual. I wouldn't fly with a partially clogged air filter because I wouldn't take off with partial throttle. Closing the throttle in cruise extends the range, saves gas and is quieter. It HAS to be better on the engine — think about it. When you need to wear the rings into brand new cylinder walls you use wide open throttle. Less wear, lower temps, increased volumetric efficiency, less piston-miles per flight. Now, I'm sure someone is chafing at the bit to set me straight, so I might as well say that "squared" power settings are a nice and convenient way to operate an NA airplane during climb.

On NA aircraft, as you climb your maximum power is lower. So if you cruise up high, WOT may be 75% power or less, or even less than 65%. WHY would you close the throttle to make the power even lower??????

At low altitude, YES, you do not cruise at WOT as that is a fairly high power setting.

 

[FastEddieB]

Closing the throttle in cruise extends the range, saves gas and is quieter. It HAS to be better on the engine — think about it.

Not necessarily. Within an engine’s normal operation range, there should be virtually no metal-to-metal contact - if there is, the engine will grind to a halt in very short order. Lower RPM in some cases can yield higher combustion chamber pressures, itself not healthy for the engine.

I think your break-in analogy is flawed. During break-in there does exist a tiny bit of metal-to-metal contact between the rings and the cylinder wall. Higher pressures during that phase allows them to be worn down just enough so the rings can float on a thin film of oil without making contact with each other. Once that threshold is reached, there’s not much if any evidence that lower RPM = less wear.

 

[mandm]

You might have a sluggish MP gauge, or something off in the throttle subgroup of parts?

I’m not sure if/how extremes of mixture would affect how linear or non-linear the throttle position is to MP.

Are you 100% that’s what’s happening?

I’m a newer pilot (2020), I’m not 100% sure nor an expert, I’m just learning, I have opinions learned from various mechanics, CFI’s, DPE’s, other pilots of varying experience, and my experience. The only thing I’m 100% sure on, is that everyone will have a different viewpoint/opinion.

 

[Kitch]

In this thread we find that none of us know what we are talking about…

To be fair couldn't that be every thread on POA....

 

[Martin Pauly]

Closing the throttle in cruise extends the range, saves gas and is quieter. It HAS to be better on the engine — think about it.

I did think about it. What creates wear and tear on an engine is primarily its temperature (hot metal is weak metal) and the pressure created inside the cylinders. Throttle setting is only one of many factors which determine temperature and pressure. Mixture, RPM and ignition timing are other important ones. "But I don't control ignition timing", you say? Indirectly you do, through RPM.

Case in point: many of our engines get a little bit of extra fuel when running full throttle, to keep CHTs and internal cylinder pressure under control during take-off and to provide an increased detonation margin. Trying to "help" the engine with a slight throttle reduction during the initial climb deprives it of that extra fuel, making the mixture leaner - not a good place for the engine at high power. Which shows that what is and what is not good for the engine isn't as simple as looking at the throttle position.

For anyone seeking a better understanding, you are welcome to join my "Lean of Peak & Mixture Management" presentations in Oshkosh on the topic:
- Monday 10AM, EAA Forum Stage 4
- Tuesday 11AM, American Bonanza Society (near the Theater in the Woods)

- Martin

 

[dtuuri]

Within an engine’s normal operation range, there should be virtually no metal-to-metal contact...

Something wears out those cylinder walls and causes higher oil consumption and low compression, just sayin'... I bet it varies with the number of piston strokes.

 

[dtuuri]

On NA aircraft, as you climb your maximum power is lower. So if you cruise up high, WOT may be 75% power or less, or even less than 65%. WHY would you close the throttle to make the power even lower??????

Why? Better range.

"What we call 'cruising' is from the engineering point of view barbaric waste." - Wolfgang Langewiesche, "Stick and Rudder" pg. 376.​

 

[dtuuri]

I did think about it. What creates wear and tear on an engine is primarily its temperature (hot metal is weak metal) and the pressure created inside the cylinders. Throttle setting is only one of many factors which determine temperature and pressure. Mixture, RPM and ignition timing are other important ones. "But I don't control ignition timing", you say? Indirectly you do, through RPM.

Case in point: many of our engines get a little bit of extra fuel when running full throttle, to keep CHTs and internal cylinder pressure under control during take-off and to provide an increased detonation margin. Trying to "help" the engine with a slight throttle reduction during the initial climb deprives it of that extra fuel, making the mixture leaner - not a good place for the engine at high power. Which shows that what is and what is not good for the engine isn't as simple as looking at the throttle position.

For anyone seeking a better understanding, you are welcome to join my "Lean of Peak & Mixture Management" presentations in Oshkosh on the topic:
- Monday 10AM, EAA Forum Stage 4
- Tuesday 11AM, American Bonanza Society (near the Theater in the Woods)

- Martin

LOL, well played! Used my post to plug your seminar, good shot. Now, y'know, I'm talking about "squared" power settings during climb after takeoff. Comes in handy often enough if you don't have a better set in mind. Also, I can't think of a lot of fixed pitch planes with MP gauges, though I knew someone who had one in a Tri-Pacer once, so I wasn't talking about using less than full throttle in those. As for constant speed, higher HP planes, I think most manufacturers would advise making a power reduction after takeoff for a normal climb. I'm not inclined to argue with them on that point. Some other things, maybe, not that.

 

[FastEddieB]

Something wears out those cylinder walls and causes higher oil consumption and low compression, just sayin'... I bet it varies with the number of piston strokes.

I believe the majority of wear occurs on startup, before oil pressure builds enough to avoid metal scraping against metal. I'll see if I can find a source.

First grab - From Continental (regarding cold weather starts):

Another area of concern is engine starting. This is where most engine wear occurs, due to a lack of lubrication on the frictional wear surfaces inside your engine. The longer the engine sets without running the more gravity will cause the engine oil to “fall off” the engine parts.

 

[dmspilot]

Looks like the 25"/2500RPM climb recommendation was removed with the Arrow II.

 

[dtuuri]

From Continental (regarding cold weather starts):

Another area of concern is engine starting. This is where most engine wear occurs, due to a lack of lubrication on the frictional wear surfaces inside your engine.

Can you express that in an equivalent number of chest x-rays?

 

[Pinecone]

Why? Better range.

"What we call 'cruising' is from the engineering point of view barbaric waste." - Wolfgang Langewiesche, "Stick and Rudder" pg. 376.​

65% power is 65% power. If you are flying low, then you might close the throttle some to get the desired power.

Also, engines are most efficient at full throttle as there is the least amount of loss in pumping the air into the engine. There might be a slight assistance with a small reduction in a carb engine to even out air flow to the cylinders to allow running leaner.

 

[dtuuri]

65% power is 65% power. If you are flying low, then you might close the throttle some to get the desired power.

Also, engines are most efficient at full throttle as there is the least amount of loss in pumping the air into the engine. There might be a slight assistance with a small reduction in a carb engine to even out air flow to the cylinders to allow running leaner.

Max range on a C-172 is at less than 65% power. I happen to have the chart on my hard drive.
Volumetric efficiency is less at high RPM; to get lower RPM with a fixed pitch prop you need to close the throttle, but maybe you're referring to a constant speed propeller airplane? In that case, you still increase your range by flying slower than "normal cruise" for more efficient airframe L/D. And I know YOU know this, so let's just agree to agree?

 

[dtuuri]

Can you express that in an equivalent number of chest x-rays?

In other words, @FastEddieB , did they start it up and run it in a test cell at full throttle until overhaul and determine the wear was exactly the same as a brand new engine started only one time? Of course not. So, without knowing how "starting wear" relates to hours of operation at various power settings, such a comment is without value to me. Then there's flight school wear, jump school wear and pipeline cross country wear. Is an hour of takeoff and landing practice less wear than starting the engine? How do they know? Just saying, "Most engine wear occurs...(during start)" is a nebulas statement that needs context, like one engine start is equal to X-hours of cruising flight at X-% power or equal to X-number of takeoff and landings.

 

[Rgbeard]

How confident are you in your tachometer? The magnet likes to make the needle lazy after a few decades.

Might want to invest in a laser tach, or download Video Tachometer for a smartphone.