Low Power Cruise settings

[A64Pilot]

1 hour ago, ArtVandelay said:

They use to have an app, but I think it was removed?

That would be what I’m looking for, be nice to have a cheat sheet.

‘Who was they?

Edited March 3, 2021 by A64Pilot

[ArtVandelay]

That would be what I’m looking for, be nice to have a cheat sheet.
‘Who was they?

Apple App Store.

[A64Pilot]

2 hours ago, Fry said:

I wonder why (apparently) everybody agrees that wear is proportional to "piston travel", i.e. higher RPM converts to proportionally higher wear per hour.

To me, this is absolutely not obvious, and I don't "buy" it.

Just think about this: at the same power, lower RPM means higher torque and thus higher forces. Why should that mean less wear?

I am running my engine at lower than the 2700 RPM (max. specified continuous RPM) for noise reasons. But by doing so, I get less air (at the same MP) into the engine, thus have to choose a lower FF, and I get less power. But flying is about speed (for me), so I don't want to go lower than 2600 RPM.

Your partially correct, within limits. for example you wouldn’t want to run a motor at 30” manifold pressure and 2000 RPM, nor would you want to run one at 15” and 2700 RPM.

If you want to run one hard, it’s your airplane and as long as y9u stay within published limits, it ought to make TBO.

‘There are times when I want to go fast too, but there are times that to use a phrase we had in the military just OFO, Out **** Off, and since your flying just for the fun of flying and don’t have a destination, why hurry?

Thst was the point of this thread, what power settings do those who are just OFO run, and why?

The guy who posted the 120 kts came in my opinion the closest to answering the original question, and backed up his answer with logic, an explanation of where 120 kts came from.

So I think next time I’m out just goofing off, I’ll likely pull it lean of peak and set a power to get 120 kts.

[testwest]

Hi AH64pilot

I'm the guy that wrote the Vz thesis that was referenced earlier in this thread. For 120 knots or so you will be about 45-50% power. You did mention that 2350 rpm or less was problematic, so 2400 rpm and about 19" MP will get you 120-125 KIAS or so. That will be about 7 1/2 gph leaned roughly to peak. This information can be gleaned from your POH (1223E, I think), performance pages, Best Economy at 2000 feet. But no one like to interpolate tables, so....

I ran the Benchmark engine model for 2000 feet and 30 deg C for a jaunt around Lake Weir, the temperature was chosen to provide a good opportunity for sightseeing the, uh, personnel likely to be on boats and what they are wearing (or not) under those conditions. I know how you Army rotorheads think.

And here is a better performance prediction for those conditions, how about 2500 lb GW on the airplane:

There is a massive amount of information in this model, and it touches nearly every aspect of the discussion in this thread thus far. If your airplane is pretty close to the drag of the baseline used to create the POH (where this Benchmark model is derived from), you will be going about 125 knots indicated or so.

Hope this helps. LMK if I need to run the model for a higher gross weight airplane, e.g. you are having a squadron reunion and there are 4 retiree Apache vets on a ....reconnaissance mission....in the plane instead of just one. :-)

 

[A64Pilot]

Where did you get that model?

The other day if memory serves I was at 130 true and 7.5 gph.

 I remember that specifically as 130 kts is 150 MPH, and divided by 7.5 is 20 MPG, which is the fuel mileage my C-140 gets with its C-85 burning 5 GPH but only traveling at 100 MPH. Mooney is efficient, but can’t be that efficient.

I probably had a little tailwind to get the 130 kts, I didn’t look at it very hard.

‘But I’m interested in that software

 

Oh, and after Retirement I worked at the Test Activity as a contract test pilot, that was when we would cruise around looking at personnel in the boats etc, believe it or not but a favorite place to cruise below the tree tops down the river was called the Pee river.

Thwt was its name, honestly.

Edited March 4, 2021 by A64Pilot

[PT20J]

6 hours ago, A64Pilot said:

Volumetric efficiency of greater than 100% is common in high performance engines, usually at full throttle and at the specific RPM that the exhaust and intake are tuned for, exhaust wise you have the restriction of the exhaust to occur just before the exhaust pulse goes though and as the exhaust valve opens, that makes the pressure in the exhaust be below atmospheric and the exhaust is sucked out of the cylinder.

‘On the intake side you design the intake so that the inertia of the gasses in the intake will have a higher than atmospheric pressure before the intake valve opens, so your pushing air into the intake and sucking it out of the exhaust and you have greater than 100% efficiency, but only at a narrow RPM range and usually only at full throttle, partial throttle’s purpose is to block incoming air.

Race motors have exceeded 100% for decades

https://forums.autosport.com/topic/94318-more-than-100-volumetric-efficiency-on-a-na-motor/

Well, I have to admit that I'm not up on race engine tuning - All my textbooks are about stock engines. But, I'm always interested to learn because there is so much I don't know. Unfortunately, the forum you posted didn't provide any real information and the link provided in one post to the NASA Technical Reports Server was for a non-existent document ID.  I did search the server for "Volumetric efficiency" and "intake tuning" but didn't find anything about increasing VE above 100%.

If you have a link to a paper on the subject, please post it as I'd really be interested in reading it. Thanks.

Skip

[PT20J]

6 hours ago, jlunseth said:

Well, I don't find the last statement to be true in my 231. First, yes, a turbo is an exhaust driven turbine, not quite accurate to say it is heat driven.  What is it about the heat that drives the turbine, as opposed to the exhaust flow through the turbine.

It's thermodynamics. Heat is a form of energy. The turbine extracts heat energy from the exhaust gasses and converts it to mechanical energy to spin the compressor. The effect is that the temperature of the exhaust leaving the turbine will be lower than the turbine inlet temperature.

There are, of course, details to actual process by which the energy transfer takes place, and there are additional factors like the kinetic energy of the exhaust gas. But the basic idea of thermodynamic processes is that energy cannot be created or destroyed (First Law) and so the heat energy and mechanical energy of a system and it's environment must balance.

Skip

[PT20J]

8 hours ago, Fry said:

I wonder why (apparently) everybody agrees that wear is proportional to "piston travel", i.e. higher RPM converts to proportionally higher wear per hour.

To me, this is absolutely not obvious, and I don't "buy" it.

Just think about this: at the same power, lower RPM means higher torque and thus higher forces. Why should that mean less wear?

I am running my engine at lower than the 2700 RPM (max. specified continuous RPM) for noise reasons. But by doing so, I get less air (at the same MP) into the engine, thus have to choose a lower FF, and I get less power. But flying is about speed (for me), so I don't want to go lower than 2600 RPM.

The cylinders and camshaft/lifters (unless you have roller lifters) are the major parts that have sliding friction and they get most of the wear. If you look at a cylinder that has been run a long time you will see a wear step at the top. But really, as has been pointed out, the difference in travel is only about 4%/100 rpm, so not a big difference. The optimum rpm is really more a question of efficiency vs power. Lower rpm is more efficient because the friction losses in the engine are lower. But, with a normally aspirated engine, you lose manifold pressure as you climb and the only way to get the power back is to increase the rpm since the higher rpm will produce more power strokes per minute and thus more power.

Checking the POH power charts, the fuel flow is lower at lower rpms for the same power.

Skip

[Fry]

@PT20J  @ArtVandelay

I believe both the app and the POH are ROP. There, power is determined by airflow, which in turn is determined by RPM and MP.

LOP, power is determined directly by FF - unless you are extreme LOP and thus inefficient.

The reason I am using my "calculator" is simply to be more or less at that optimum point.

@A64Pilot:

Of course, running the engine at lower power will result in less wear PER HOUR. But when going places at a slower speed, that will use MORE HOURS, so again, I don't find it obvious that I'm being nice to the engine going slower.

Plus, as pointed out before, over 4000ft or so (and I don't usually cruise below that unless it's a short flight and/or airspace restrictions above me), power is limited to 75% or so anyway. So less power, less wear.

And I don't think I am running my engine "hard". Not at all. When reading Mike Bush, I understood what is destroying engines (besides corrosion when not flying) is high CHTs. My usual cruise CHTs are 300-320 at this time of the year, and only somewhat higher in summer.

Of course, turbocharged engines are different. But we are talking M20J here.

[M20F]

I run my TN F with 10” of boost and 300 degrees LOP, get about 200KTs true at sea level.  

[A64Pilot]

12 hours ago, PT20J said:

Well, I have to admit that I'm not up on race engine tuning - All my textbooks are about stock engines. But, I'm always interested to learn because there is so much I don't know. Unfortunately, the forum you posted didn't provide any real information and the link provided in one post to the NASA Technical Reports Server was for a non-existent document ID.  I did search the server for "Volumetric efficiency" and "intake tuning" but didn't find anything about increasing VE above 100%.

If you have a link to a paper on the subject, please post it as I'd really be interested in reading it. Thanks.

Skip

No, I don't have any papers etc, I’m just an old engine builder and A&P etc. In my earlier years I raced most anything on wheels, and built the motors.

‘Even though I’ve always said that we fly behind our Grandfather’s engines, they are more advanced than many realize. It’s the exhaust more than anything that “kills” most existing aircraft installations. The engine manufacturers have little to nothing todo with exhaust design, it’s supplied by the airframe manufacturer and almost often ease of manufacturing / cost  / weight / fitting into existing space etc take precedence over performance.

‘Still I wouldn’t be surprised if our engines aren’t operating close to 100% volumetric efficiency at full throttle openings, and if they had an honest tuned exhaust, they should.

There are a whole lot of misunderstandings about our motors and even more marketing selling “improvements” for them that more often than not offer little actual improvements and or bring out their own sets of problems.

Edited March 4, 2021 by A64Pilot

[A64Pilot]

If you read Lycomings literature, they even state pretty often that engines operated at 65% power or lower will last longer.

‘Ever heard of TANSTAAFL? It’s from one of my favorite Science Fiction writers, it’s “There Ain’t No Such Thing As A Free Lunch”

Simply stated it says there are advantages and disadvantages to every single way that you can operate an engine, so pick a way that fits your desires and to Hell with all the supposed experts, most of us fly less than 100 hours per year. my aircraft is 41 years old and has 2200 hours on it, and that’s not all that unusual. Engine was overhauled 10 years ago and has about 400 hours on it, It may never reach overhaul while I own it.

So it’s likely that for most of us that we won’t ever fly an engine for a full overhaul period, so making changes to the way we want to fly to get 10% longer life from an engine does what?

‘But for instance I’m going flying today, the mission is just to fly, and hopefully to introduce our little dog to flying, so why bore around at high speed, burning fuel? Slow down burn less fuel, make less noise and make the turbulence more comfortable? 

[AH-1 Cobra Pilot]

13 hours ago, PT20J said:

The turbine extracts heat energy from the exhaust gasses and converts it to mechanical energy to spin the compressor.

When you tell people that, you will, deservedly, get a blank stare, because you are completely ignoring the intermediate actions/processes.  For instance, are these processes at constant pressure?  Constant volume?  Adiabatic?  Changing conditions?  Heat may be the fundamental input to result in the spinning of a turbine, while pressure is the direct cause.

There are several abstractions between gasoline and thrust, and breaking them out will go a long ways to understanding the whole process.  That is why earlier in this thread, I suggested thinking in terms of pressures as the more direct cause of conversion to rotational energy rather than 'heat'.

[AH-1 Cobra Pilot]

2 hours ago, A64Pilot said:

Ever heard of TANSTAAFL? It’s from one of my favorite Science Fiction writers, it’s “There Ain’t No Such Thing As A Free Lunch”

Unfortunately, I think only about 5% of people understand that, or maybe accept it.  I, perhaps perversely, enjoyed talking about the Volkswagen scandal of a few years ago.  Someone would say how horrible it is to be releasing all those nitrogen oxides into the atmosphere.  I would then ask, "So, you are okay with those cars releasing 30% more CO₂?"  After explaining how the mileage improvement was a trade-off between NO_x and CO₂, I would watch their heads melt.

[PT20J]

3 hours ago, A64Pilot said:

No, I don't have any papers etc, I’m just an old engine builder and A&P etc. In my earlier years I raced most anything on wheels, and built the motors.

‘Even though I’ve always said that we fly behind our Grandfather’s engines, they are more advanced than many realize. It’s the exhaust more than anything that “kills” most existing aircraft installations. The engine manufacturers have little to nothing todo with exhaust design, it’s supplied by the airframe manufacturer and almost often ease of manufacturing / cost  / weight / fitting into existing space etc take precedence over performance.

‘Still I wouldn’t be surprised if our engines aren’t operating close to 100% volumetric efficiency at full throttle openings, and if they had an honest tuned exhaust, they should.

There are a whole lot of misunderstandings about our motors and even more marketing selling “improvements” for them that more often than not offer little actual improvements and or bring out their own sets of problems.

It is my understanding that the M20J has a reasonably good exhaust system. Lopresti had a marketing goal: >200 mph on 200 hp. All the drag reduction gets the press, but I read that he spent some time optimizing the engine installation as well. As I recall, the Powerflow guys that market the tuned exhaust systems admitted that they don't do much for a M20J when they presented at MooneyMax a couple of years ago. In fact, they said that they get much more improvement on 6 cyl engines than 4 cyl in general because of more power pulses/min.

Some time back,  I took the Sea Level and Altitude Performance chart for the IO-360A (from the Lycoming Operator's Manual) and calculated a power chart like in the POH. This would presumably be based on measurements in a test cell. Comparing it with the chart from the POH I observe that higher manifold pressures are required to achieve the same power when installed in the airplane.

 

 

 

 

[PT20J]

55 minutes ago, AH-1 Cobra Pilot said:

Unfortunately, I think only about 5% of people understand that, or maybe accept it.  I, perhaps perversely, enjoyed talking about the Volkswagen scandal of a few years ago.  Someone would say how horrible it is to be releasing all those nitrogen oxides into the atmosphere.  I would then ask, "So, you are okay with those cars releasing 30% more CO₂?"  After explaining how the mileage improvement was a trade-off between NO_x and CO₂, I would watch their heads melt.

It seems that this area is where most of the IC engine research has been focused in recent years. It's easy to get the efficiency up if you don't care about emissions (that's why aircraft engines can be so efficient), and it's possible to minimize emissions if you don't care about gas mileage. With mandated targets for both, it becomes a challenge, in the automotive world. 

Skip

[A64Pilot]

1 hour ago, PT20J said:

It seems that this area is where most of the IC engine research has been focused in recent years. It's easy to get the efficiency up if you don't care about emissions (that's why aircraft engines can be so efficient), and it's possible to minimize emissions if you don't care about gas mileage. With mandated targets for both, it becomes a challenge, in the automotive world. 

Skip

I’m not arguing with you, but in fact HP, fuel economy and emissions have never, ever been better. Today’s cars are the most powerful ever produced, pollute the least, and are capable of phenomenal mileage.

‘My Wife’s car is the fastest four door coupe that’s ever been mass produced, a CTS-V Cadillac. We get almost 25 MPH on the road, spark plugs last 100,000 miles so no tune ups for 100,000 miles, and it passes emissions, idles smooth etc.

Our other car that the Daughter has in College is a 2010 Toyota Prius that’s closing in on 300,000 miles, and when I drive it, it gets close to 60 MPG, my best was 72.3 MPG hypermiling it.

Autos that will easily last over 250,000 miles carrying four passengers and luggage while getting in excess of 60 MPG and exceedingly low emissions is easy, was done over a decade ago.

But it’s not what people want, if you built it, it wouldn’t sell. People want huge impressive four wheel drive SUV’s that may on a good day get 20 MPG. Even the last generation of the Prius when Toyota was faced with making it way more efficient chose instead to make it bigger, heavier and with a larger more powerful engine and leaving fuel economy the same.

Now People want big impressive four wheel drive electric SUV’s that will use at least three times the energy of an efficient sedan would.

Edited March 4, 2021 by A64Pilot

[PT20J]

3 minutes ago, A64Pilot said:

I’m not arguing with you, but in fact HP, fuel economy and emissions have never, ever been better. Today’s cars are the most powerful ever produced, pollute the least, and are capable of phenomenal mileage.

I agree with you. My point was simply that everything is a compromise and engineers have to try to get the best fit for all the variables rather than just optimizing a single one. Increasing gas prices, competition and emission standards have fueled a lot of innovation.

I don't understand electric cars or airplanes. The energy density of batteries is low compared to a tank of gas and there are more energy conversions (each with less than 100% efficiency) and transport losses between the power generation and the wheels.

But, then again, I've never been an early adopter, and I'm probably missing something. I probably wouldn't have thought light bulbs were a good idea when my gas light worked just fine 

Skip

[PT20J]

3 hours ago, AH-1 Cobra Pilot said:

When you tell people that, you will, deservedly, get a blank stare, because you are completely ignoring the intermediate actions/processes.  For instance, are these processes at constant pressure?  Constant volume?  Adiabatic?  Changing conditions?  Heat may be the fundamental input to result in the spinning of a turbine, while pressure is the direct cause.

There are several abstractions between gasoline and thrust, and breaking them out will go a long ways to understanding the whole process.  That is why earlier in this thread, I suggested thinking in terms of pressures as the more direct cause of conversion to rotational energy rather than 'heat'.

I must admit a bias toward thinking about work and heat rather than pressure since in a heat engine, pressure is a function of work and heat. And, discussions of pressure cause me to drift off into thinking about combustion pressure and "red boxes" and my head starts to hurt 

When I took the APS course, I got all excited about cylinder peak pressure and the crankshaft angle at which is occurs. But after deeper thought, I realized it didn't really explain the shape of the curves: Why does the power curve have a broad peak, Why do peak combustion temperature, power and EGT occur at different mixture strengths? Why does BSFC flatten and then rise again as the mixture is leaned? A lot of thought and study later, I have figured out some of this, but I understand why it's not in the APS course - it gets complex quickly.

As a byproduct, I've come to believe that the attention given to the peak pressure is somewhat misplaced-- kind of like when we all used to worry about shock cooling. It's really a design consideration rather than an operational consideration and some of the characterizations of it are questionable. For instance, one of the purported benefits of LOP operation is that the pressure peak is lower and flattened compared to ROP. (This is sometimes described as a sharp impact vs a gentle push. This is not accurate since all the non-detonating pressure curves are smooth. Some just have greater rates of change and higher peaks.) But from a design standpoint, one wants high combustion pressures (within design limits, of course). Much of the change in magnitude and location of the peak cylinder pressure LOP comes from slowing of the combustion process which makes the fixed timing farther from optimum and reduces power. If timing is advanced back to MBT (maximum brake torque), the pressure peak will increase and move closer to TDC. This is why a Surefly improves LOP power and efficiency somewhat. 

I ran across this old NACA report that has a description of a this stuff without having to dredge up a lot of thermodynamics.

NACA-TN-772.pdf

Skip

 

[A64Pilot]

Before you guys go buying devices to advance timing etc., might want to give Hartzell a call and ask what they can do to propellers.

‘Ask their opinion 

[A64Pilot]

Went out this afternoon, she woud run fine at 20” and 2200 up to 6 GPH, any less and it would pickup a little roughness. 7,500 ft

6 GPH is still awfully good though

Object of today’s flight was to see how our little dog took to flying, he did OK,a little apprehensive, but he will do fine given a little time. How do you rotate a image because the forum software rotated it.

 

Edited March 4, 2021 by A64Pilot

[PT20J]

1 hour ago, A64Pilot said:

Went out this afternoon, she woud run fine at 20” and 2200 up to 6 GPH, any less and it would pickup a little roughness. 7,500 ft

6 GPH is still awfully good though

Object of today’s flight was to see how our little dog took to flying, he did OK,a little apprehensive, but he will do fine given a little time. How do you rotate a image because the forum software rotated it.

 

Nice copilot you have there 

One of the nice things about having an efficient airframe is there are lots of options for speed/economy tradeoffs.

 

[carusoam]

Ransom...

Tell us the dog’s name and breed...

... And our hangar elf will orient his pic.

-a-

[PT20J]

10 minutes ago, carusoam said:

Ransom...

Tell us the dog’s name and breed...

... And our hangar elf will orient his pic.

-a-

Anthony, we need to change your handle to Pix Rotator 

[A64Pilot]

He is a Havamalt, it’s a “designer” breed, half Maltese, half Havanese. We were living on a sailboat when we bought him a year or so ago and he doesn’t shed, which is a desirable trait in small quarters.

His name is Mikey

How are you rotating the photo’s?