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Carson number and contiounous RPM

Yep

"...I think most of us choose to spend more on gas to go faster, e.g., we value our time more than the gas cost. So I really don’t understand all the hoopla about this. iMHO it’s just an interesting calculation for one set of preferences..."

Definitely agree with this! That's why my RV-10 is a Time Machine!
 
In Carson’s paper V is true airspeed. He assumes no wind so he can equate V as inversely proportional to the total trip time. If you look in his equations (2,3) for the parasitic and induced drag you’ll see the air density (rho) explicitly written out. It’s common to eliminate rho by using (rho V(true) squared)=V(indicated) squared but he explicitly carried the air density along, and used true airspeed.
Remember that Carson was trying to approximate people’s behavior toward money: Efficiently in his paper means minimum cost, weighting gas cost the same as everything else that is time-dependent (maintenance, engine reserve, your time, etc).
 
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Carson's approach is interesting. Here is another and it's described as a real-life approach by the man who was the flight director for Rutan's flight around the world on one tank of gas.
image311.jpg

http://www.propellersexplained.com/LogicOfFlightCover.jpg
http://www.propellersexplained.com/LogicOfFlight.pdf
 
I'm still learning my RV-8/IO-360/Hartzell/Pmags/AFP-200 and so far it seems happiest high (8-10k DA), full throttle, 2300 RPM, leaned to peak.

This gives me just about 170TAS at about 8.7GPH at DA 9000.

HB-YMM - EHGG-LSGY - 20220703.png

I like going fast!
 
Can you expand on this?

I am only trying to be helpful. Everything that I have read about this has seemed to say that peak temperatures are neither the most powerful, the most efficient, or the best for the engine. I think you should look into it independently if you are interested. You might start with GAMI.
 
Lycoming states you can run at peak EGT for best economy at 65% power or less. There is no time limit at peak EGT as long as CHT and oil temps stay in line. This has been a recommendation from Lycoming for decades - I was curious if you are aware of something new that I did not know.

Personally, I use peak EGT for normal cruise and will go to 25 LOP if I'm not in much of a hurry.
 
Lycoming states you can run at peak EGT for best economy at 65% power or less. There is no time limit at peak EGT as long as CHT and oil temps stay in line. This has been a recommendation from Lycoming for decades - I was curious if you are aware of something new that I did not know.

Personally, I use peak EGT for normal cruise and will go to 25 LOP if I'm not in much of a hurry.

I am not expert enough to argue with either Lycoming nor GAMI but I am pretty sure that if you run at 65% you will get some significant advantages by doing it at LOP per GAMI vs Lycoming's advice. of course, you will need real-time engine data to get that right. I used GRT instrumentation. Others are also good. The BSFC at LOP is better than at peak.

In my limited experiments with my Superior, a Lyco-clone, there was no doubt about this. GAMI's data is published and seems very persuasive to me. I could easily see the improved results while in flight.

But if you want to run at peak then, again, I suggest limiting the power. I was cautioning, earlier, about higher power settings. Is 8.7 GPH only 65%?

Even at safe power settings, GAMI's information demonstrates that the power pulses are smoother and longer at LOP. That is hard to dismiss as insignificant.

I have no idea what you know so I cannot claim to have new information for you. But GAMI's stuff is at least 20 years old as far as I know. I wish you well and only meant to give you a heads-up.
 
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Mickey indicated that he was operating at peak EGT between 8 - 10k altitude. Assuming he's running NA, that altitude is well within the safe range for leaning at power.
 
LOP operation will both lose power and cause PCP to occur later than ROP at the same rpm and MAP. CHTs and EGTs also drop. All these things mean less stress on the engine.

Best BSFC occurs at roughly 30-50F LOP, depending on ignition timing.
 
You might start with GAMI.

Every source seems to trace back to GAMI. Is there anyone else who has done similar work?

I have some doubts about GAMI's claims.
- I don't believe that Lycoming don't understand their own engines
- Many of their demos are invalid, e.g. they show LOP and ROP at different speeds, or LOP vs best power rather than the Lycoming recommended economy settings
- Some of their chemistry is very doubtful, and ultimately ROP vs LOP is chemistry - they should be able to get that right.

To me, "don't run at peak even if Lycoming recommend it" seems the same as saying don't do aeros in your RV because the G load fatigues the wings. Technically it might be correct, but you have to trust the designer to take it into account, and the real question is whether it affects the life in any measurable way in the real world.
 
GAMI

Every source seems to trace back to GAMI. Is there anyone else who has done similar work?

I have some doubts about GAMI's claims.
- I don't believe that Lycoming don't understand their own engines
- Many of their demos are invalid, e.g. they show LOP and ROP at different speeds, or LOP vs best power rather than the Lycoming recommended economy settings
- Some of their chemistry is very doubtful, and ultimately ROP vs LOP is chemistry - they should be able to get that right.

To me, "don't run at peak even if Lycoming recommend it" seems the same as saying don't do aeros in your RV because the G load fatigues the wings. Technically it might be correct, but you have to trust the designer to take it into account, and the real question is whether it affects the life in any measurable way in the real world.

Some of us want to believe that Continental and Lycoming must be the most authoritative. Others choose to not only believe GAMI but to operate their engines LOP. I can no longer experiment with the issue because my 12's engine does not have mixture control.

I can only reiterate that when I experimented with peak vs. LOP using my Superior IO-360 180 HP engine in my RV-7A my GRT instrumentation made it very clear that LOP gave lower temps and greater economy at the same power and performance. Anyone of you with comparable panels could do the same. My panel was in the minority when I built it but now I would guess that most of the builders have the ability to monitor EGT, RPM, MPG and fuel flow while maintaining the same alitude and airspeed.

Try it for yourselves and let's stop speculating on manufacturer vs GAMI and the other authors who agree with them.
 

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My C-150 POH said..

Some of us want to believe that Continental and Lycoming must be the most authoritative. Others choose to not only believe GAMI but to operate their engines LOP. I can no longer experiment with the issue because my 12's engine does not have mixture control.

I can only reiterate that when I experimented with peak vs. LOP using my Superior IO-360 180 HP engine in my RV-7A my GRT instrumentation made it very clear that LOP gave lower temps and greater economy at the same power and performance. Anyone of you with comparable panels could do the same. My panel was in the minority when I built it but now I would guess that most of the builders have the ability to monitor EGT, RPM, MPG and fuel flow while maintaining the same alitude and airspeed.

Try it for yourselves and let's stop speculating on manufacturer vs GAMI and the other authors who agree with them.


CESSNA SECTION 4 MODEL 150M NORMAL PROCEDURES
For best fuel economy at 65% power or less, operate at the leanest mixture that results in smooth engine operation or at 50 RPM on the lean side of the peak RPM, whichever occurs first. This will result in approxi- mately 5% greater range than shown in this handbook.


It was a Continuental O-200 in case anyone did not already know that.
 
You might want to re-think operating at peak. Just saying..

I asked you to expand on this statement because it can be received very differently in the aviation community.

Some pilots still believe that LOP ops can "burn up" an engine. And my retort to this is the long standing Lycoming guidance that operating at peak EGT is perfectly acceptible given certain circumstances. So if the hottest possible EGT is OK according to the manufacturer, then how is a cooler EGT (LOP) going to harm the engine? Based on your cautionary tone, I thought you might be one of "those guys".

Another line of thought is the debate over how fast the power drops off once you are lean of peak. In my experience, its pretty fast, and even with optimized timing the chemical power just isnt there. So yes, I fully agree that operating at peak EGT delivers less economy than slightly LOP, but it does no harm to the engine. I am rarely looking for maximum economy anyway - Im looking for the best economy possible for a given speed. Personally, I need to see 200KTAS or I'm not happy. I would RATHER see 10GPH than 12 GPH, but I'll do whatever it takes to post 200 on the boards.

To return to this thread, I'm certainly looking at max economy numbers because I just might find myself over water on min fuel someday and need to play that card, but for the most part I want to go fast, whatever the cost.
 
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Lycoming conveniently seems to ignore all the radial powered aircraft flying in the '50s where LOP operation was well proven over millions of hours. GAMI wasn't anywhere near the first to document all this, just suggesting it could be applied to opposed engines. Conti has embraced it and there are no significant differences compared to Lycomings.

Michael hits it here- how can cooler than peak EGTs and CHTs damage the engine?

Hasn't Pete Howell here on VAF proven that LOP doesn't hurt Lycs yet? Just passed 2550 hours without being touched if I recall.

Most of my customers (hundreds of them) embrace and use LOP every flight. Don't hear about a bunch top overhauls happening and some of these guys fly over 250 hours per year.

Glass panels give us the tools to do this properly and easily these days. If you want to save some fuel at the cost of the few knots, it's the way to go.
 
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Lycoming conveniently seems to ignore all the radial powered aircraft flying in the '50s where LOP operation was well proven over millions of hours.

I found a document describing the procedures used for radial engines, it is very interesting. They didn't lean by EGT, as I'm sure you know.

The leaning procedure it describes (summarized):
- lean to a 10% torque drop from best power (I think this is pretty close to peak EGT)
- advance spark timing from 20 degrees to 30 degrees for longer exhaust valve life
- Add 1" MP and lean again to the original leaned torque ('m guessing that's about another 2-3% torque reduction)

Wait a minute - advance spark timing when LOP to maximize exhaust valve life? I thought GAMI said LOP didn't affect valve life??

LOP is pretty common in engines trying to extract maximum efficiency. But I think (outside manual mixture control i.e. aviation) it is rare or nonexistent without variable spark timing.

I don't think Lycoming is ignoring radial engines - they just know that there ARE differences.

For that matter, GAMI says that one advantage of LOP operations is slower combustion and lower PCP occurring later - but don't we have people selling ignition systems to advance the spark at cruise power for earlier PCP - exactly the opposite of what GAMI is telling us?

Keeping it cool

The maximum cruise CHT was 470F. For maximum cylinder life, they adjusted cowl flaps to maintain CHT at 445F.

Michael hits it here- how can cooler than peak EGTs and CHTs damage the engine?

The EGT measurement is an average over time measured in the exhaust pipe. I think the value that really matters is the combustion gas temperature at the instant the exhaust valve opens, when the boundary layer breaks down and the high pressure, high temperature gas hits the valve sealing surface. Finishing combustion earlier and extracting energy into the propeller over a longer time surely makes that gas cooler, even if the average over the whole cycle is higher.

And all the chemical reactions in the engine e.g. lead scavenging work better at high temperature.

(The operating procedure notes I found are here:
http://www.enginehistory.org/Operations/R-4360Ops/r-4360ops1.shtml
If you have anything else similar I would be interested to read them)
 
I found a document describing the procedures used for radial engines, it is very interesting. They didn't lean by EGT, as I'm sure you know.

The leaning procedure it describes (summarized):
- lean to a 10% torque drop from best power (I think this is pretty close to peak EGT)
- advance spark timing from 20 degrees to 30 degrees for longer exhaust valve life
- Add 1" MP and lean again to the original leaned torque ('m guessing that's about another 2-3% torque reduction)

Wait a minute - advance spark timing when LOP to maximize exhaust valve life? I thought GAMI said LOP didn't affect valve life??

LOP is pretty common in engines trying to extract maximum efficiency. But I think (outside manual mixture control i.e. aviation) it is rare or nonexistent without variable spark timing.

I don't think Lycoming is ignoring radial engines - they just know that there ARE differences.

For that matter, GAMI says that one advantage of LOP operations is slower combustion and lower PCP occurring later - but don't we have people selling ignition systems to advance the spark at cruise power for earlier PCP - exactly the opposite of what GAMI is telling us?

The EGT measurement is an average over time measured in the exhaust pipe. I think the value that really matters is the combustion gas temperature at the instant the exhaust valve opens, when the boundary layer breaks down and the high pressure, high temperature gas hits the valve sealing surface. Finishing combustion earlier and extracting energy into the propeller over a longer time surely makes that gas cooler, even if the average over the whole cycle is higher.

Yes, there are differences between the typical atmo opposed engines most RVs have and supercharged, turbocharged or turbo compound radials however fundamentally, these are Otto cycle engines and combustion dynamics are similar between types.

A 10% drop in torque would be well LOP. I'll try to illustrate this fact later with a graphic I don't have available at the shop here.

Advancing timing reduces EGT and recovers some of the lost torque as lean mixtures burn a lot slower than rich ones. Lower EGTs running LOP can't reduce valve life and there is no evidence that excess oxygen affects life either. Peak and average combustion pressures and temps are lowered LOP, EGTs must necessarily be lower all through the cycle in all parts of the system.

While most of the big radials had torque meters, that's something we don't have. Modern glass panels provide more information overall than they had back in the '50s though they had some cool other stuff like scopes onboard to check spark plug firing in some cases (saw this demonstrated on a military DC-3 once). We can't add MAP on naturally aspirated engines to gain back torque as we're already WOT in most cases. The average pressure over the whole cycle is certainly lower LOP, not higher.

People have been flying opposed engines LOP for years now and life doesn't seem to be affected from what I've seen. I mentioned Pete Howell as a real world example where he's documented his journey with frequent updates and borescope photos.

Variable ignition timing brings a few more knots into the LOP equation. Flight verified. I've seen it with my own eyes as have my customers. Now after much flying in the RV-10 experimenting, the gains flying LOP are less than most think at the same speed. LOP results in a drop of power, thus speed. Drag is lower at that speed and that must be accounted for. My experiments showed around a 5-7% increase in MPG at the same speed running LOP with optimized timing. Fixed timing would result in lower gains LOP as you mention.
 

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This isn't the chart I was looking for but it illustrates how far you'd have to lean to have a 10% loss in torque. Well lean of Stoich and peak EGT.
 

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Wait a minute - advance spark timing when LOP to maximize exhaust valve life? I thought GAMI said LOP didn't affect valve life??

I'd believe that advancing the spark improves valve life as compared to not advancing the spark at the same mixture setting. LOP setting, mixture burns slower, so want less burning gas going past the valve both for power and valve life. Advance the timing, again still at the same LOP setting has more of the gas burn inside the cylinder and not on it's way past the exhaust valve.

If we compare LOP to ROP, I believe GAMI. But I'm comparing different ignition settings both LOP.
 
Combustion is complete in a Lycoming engine well before the exhaust valve opens. By the time the engine has completed the expansion (power) stroke and the exhaust valve opens, gas temperatures are far below peak combustion temps and far below the temperature limits of the exhaust valve materials typically employed.
 
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In doing the performance data collection and modeling for my -7, I found a neat method: Constant TAS. It works out to Carson's speed at sea level for a given weight and temperature. After takeoff, I establish my pre-determined TAS for the cruise climb (I made a spreadsheet that does a lot more than figure that out). Of course IAS decreases as I climb. If you make Carson's speed a constant IAS (I think it's supposed to be a TAS anyway, but Carson's speed (TAS) varies with altitude IIRC), you will not be able to reach service/absolute ceiling. But when I scheduled my cruise climb IAS to converge on Vy with altitude, I found I was maintaining a constant TAS, to the knot. It results in the very best cruise climb speed and rate all the way as high as I want to go. Check out the Enroute Climb section if you are interested. The only potential downside is as you climb higher and IAS decreases, the engine gets warmer. This hasn't been a problem, but it bears watching. I'm never going to climb anywhere near my estimated absolute ceiling (around 21k) anyway, so this shouldn't be a problem for me.
https://1drv.ms/b/s!Avy__ATKb7AWjrYp-Ru4l20K2gF8QQ?e=fs9il4
 
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In doing the performance data collection and modeling for my -7, I found a neat method: Constant TAS. It works out to Carson's speed at sea level for a given weight and temperature. After takeoff, I establish my pre-determined TAS for the cruise climb (I made a spreadsheet that does a lot more than figure that out). Of course IAS decreases as I climb. If you make Carson's speed a constant IAS, you will not be able to reach service/absolute ceiling. But when I scheduled my cruise climb IAS to converge on Vy linearly at my estimated absolute ceiling, I found I was maintaining a constant TAS, to the knot. It results in the very best cruise climb speed and rate all the way as high as I want to go. Check out the Enroute Climb section if you are interested. The only potential downside is as you climb higher and IAS decreases, the engine gets warmer. This hasn't been a problem, but it bears watching. I'm never going to climb anywhere near my estimated absolute ceiling (around 21k) anyway, so this shouldn't be a problem for me.
https://1drv.ms/b/s!Avy__ATKb7AWjrYp-Ru4l20K2gF8QQ?e=fs9il4
Hi Ed, the link does not work for me - is it a PDF? If so, you can attach it with the paperclip. Thanks!
 
Yes, it’s a PDF

It is a PDF, a fairly sizable one. I just tested it and it does work. I used the paperclip to post the link. Did you give it some time to download before giving up? I don’t normally have problems sending files this way. Depending on what device you are using you might need to open it in a browser. Just paste the link into the address bar. It’s stored on OneDrive. If it doesn’t work I can try Google Drive or Dropbox, just let me know.
 
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Interesting posts without doubt and some great info, but you guys need to be very happy with your lot and just go fly WOT.

Down here Avgas peaked at $15.06 per US gallon last month. It's backed off to about $14 for now, but its slated to skyrocket in the next three months. If I was paying your prices I'd be overjoyed and flying daily.
 
Works now

It is a PDF, a fairly sizable one. I just tested it and it does work. I used the paperclip to post the link. Did you give it some time to download before giving up? I don’t normally have problems sending files this way. Depending on what device you are using you might need to open it in a browser. Just paste the link into the address bar. It’s stored on OneDrive. If it doesn’t work I can try Google Drive or Dropbox, just let me know.

Thanks Ed, it works now. I think I just didn't wait long enough.
 
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