(LOP) Experts Are Everywhere – The Rebuttal By John Deakin ©June, 2013

Discussion in 'Flight Following' started by alfadog, Jun 30, 2013.

  1. azure

    azure Final Approach

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    I wouldn't doubt it. But the question is, if I buy a set from GAMI and they test out at 0.4 at my preferred cruise power, will they overnight me a new one to tweak the spread down another tenth or two? "0.5 or better" is what their literature claims, so I'm assuming that as far as they're concerned, anything better than that is gravy.
     
  2. Henning

    Henning Ejection Handle Pulled

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    I wanted to do 180kts, so I got a plane that does 205kts and run it leaned so far back that my exhaust residue on my augmentors is pure white lead. I get 9nmpg and have clean valves, rings & jugs, if I could get unleaded gas I'd have clean augmentors and exhaust pipes as well. Much of the engine maintenance expenses aircraft see are due to carbon deposits that stick to the valve seating surfaces and stems along with the rings.

    What running LOP gains you is more $$$ in your pocket at the end of any usage cycle. If I slowed down to 160kts, I'd be using about the same fuel you do for less engine maintenance money loafing 2 lean and clean just on the pipe vs running one hard, hot and dirty. Some engine manufacturers are now rating engine life in total fuel flow through the engine, i.e. "It's a 250,000 gallon engine, run it any way you want."
     
    Last edited: Jul 12, 2013
  3. GeorgeC

    GeorgeC Administrator Management Council Member PoA Supporter

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    I was looking at Lycoming's charts of fuel consumption as a function of BHP for the IO360C. There is one set of curves for best power, and another set for best economy. If I draw a vertical line at the 65% mark, it intersects the 2400 rpm curves at around 54 and 64 lb/hr. That makes sense; best power burns more gas than best economy.

    This may be a semantic nit, but isn't 65% power 65% power, in this case, 130 BHP? In the Arrow IV POH, I also see references to "65% best power" and "65% best economy" with different associated airspeeds, which implies to me that the percent power changed. Am I missing something, or just overthinking? If we're set up for 65% with a best power mixture, and I pull the red knob back to a best economy mixture, I would expect to land at around 55% power.

    It seems to me that the best power and best economy curves should not be plotted on the same X axis.

    Related: Say you are in level cruise at a given RPM and MP, at full rich. You lean to best power, and then keep on leaning to best economy. Does the MP needle move?

     

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  4. Jaybird180

    Jaybird180 Final Approach

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    Interesting question and I'm sure the experts will chime in, but I can state that the MP gauge <> %power. It's indirectly related. MP gauge per Deakin measures the plenum vacuum and as we know more air at a certain fuel setting yields more power.
     
  5. kgruber

    kgruber En-Route

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    Manifold pressure is a poor indication of power. Even if the engine is not running it will read ambient. And, if you're flying, the tach will still indicate the last RPM selected on the prop control.

    Best indications of power is fuel flow and EGT.
     
  6. Ted

    Ted The pilot formerly known as Twin Engine Ted

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    On a King Air, yes. On a piston, it's a host of things.

    Lycoming's power/economy tables use the MP/RPM as a power setting because it makes the math easy when you aren't nit-picking. So correct, at 65% power best economy you'll make less power than at 65% power best power following the Lycoming charts.
     
  7. kgruber

    kgruber En-Route

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    With your piston engine out, how is MP/RPM going to show power?

    KA doesn't have EGT.
     
  8. coma24

    coma24 Line Up and Wait

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    198ktas ~50ROP, 191ktas at ~50 LOP.

    12.5gph ROP, around 10gp LOP.

    I throw in the tilda because I'm cursed with a carburetor and am doing the best I can. #4 goes lean way before the others, #1 has to be dragged kicking and screaming.

    I can only do it with the throttle wide open, then backed off about 1/3" to 1/2", otherwise the vibration is significant thanks to the pitiful fuel distribution. *Casts a glance at #4* Thanks, buddy.

    Deakin's articles have been pure gold...I discovered them shortly before buying the airplane, read them 4-5 times, then went and did it. If you can visualize the curve and know where you are along the curve, then life is good.
     
  9. petrolero

    petrolero Pattern Altitude

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  10. Capt. Geoffrey Thorpe

    Capt. Geoffrey Thorpe Touchdown! Greaser! PoA Supporter

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    I suspect that the POH refers to a rpm / manifold pressure combination as 65% which is not actually 65% of the rated horsepower. At a fixed RPM / Manifold pressure, as you pull the red knob leaner than best power, you get less power.

    Not much. Manifold pressure is primarily a function of how much is sucked out of the manifold (function of engine speed) and the restriction on the inlet to the manifold (throttle angle) and the pressure upstream of the throttle (pressure altitude). Changing the amount of fuel supplied to the manifold will have only a very minimal effect on the manifold pressure.
     
  11. Ted

    Ted The pilot formerly known as Twin Engine Ted

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    That's why I said it wasn't one particular item, but a host of several.

    ITT is close enough. Still measures the temp of that hot stuff coming out of the engine.
     
  12. kgruber

    kgruber En-Route

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    What are the "host of several" besides to two I mentioned, EGT and fuel flow?
     
  13. coloradobluesky

    coloradobluesky En-Route Gone West

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    My engine wont run at peak EGT, it runs rougher and rougher and the EGT keeps going up if you keep leaning until its so rough, no one would want to run it there. It runs fine if you lean it to max rpm and lean it a bit more. So I guess Im running a different kind of lean of peak. Lean of peak RPM!
    Lycoming 360 180hp carbed
     
    Last edited: Oct 21, 2014
  14. Capt. Geoffrey Thorpe

    Capt. Geoffrey Thorpe Touchdown! Greaser! PoA Supporter

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    Once you get lean enough you get into combustion issues like slow burns and even misfires - those will drive EGT back up as you get leaner and result in engine roughness (and increase the fuel consumed per unit power output).
     
  15. Henning

    Henning Ejection Handle Pulled

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    I measure % power by IAS/Alt. Any combination of settings that gets me that speed is that % power. I prefer to reduce my power by reducing fuel flow first, fuel is what wears an engine out. The most work for the least amount of fuel you can put through the engine will give you the most cost effective use of that engine along with the least maintenance hassles.

    There are three ways I can choose to effect power reduction, or any combination of, my order of choice is fuel, RPM, MP.
     
  16. dans2992

    dans2992 En-Route PoA Supporter

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    I'm a bit of a newbie on LOP stuff, but if you reduce fuel flow at a high(ish) MP, aren't you risking detonation? Do you need to get to below 75% before you start leaning?
     
  17. GeorgeC

    GeorgeC Administrator Management Council Member PoA Supporter

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    Thanks, gents.
     
  18. kgruber

    kgruber En-Route

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    Thanks.......I am writing of engine out indications.

    With an engine out and windmilling:
    MP....good
    Tach.....good
    Oil pressure.....good
    Oil Temp.....good
    Only fuel flow and EGT will be out of a normal range.
     
  19. Ted

    Ted The pilot formerly known as Twin Engine Ted

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    MP and RPM
     
  20. Henning

    Henning Ejection Handle Pulled

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    No, I don't stay in the detonation prone (high power ROP) mixtures long enough to get into detonation, plus I leave my RPM high buying me extra margin. MP becomes irrelevant to the power equation LOP, you are limited on the fuel end so MP won't really change with power until the engine dies from being too lean, then MP will increase given no turbo. I grab the mixture aft until the engines fall off then bring them back up on the pipe. After you find that the first time, you can be more precise by pulling back to the right fuel flow number. You can check on what's going on by richening up and seeing what the EGT does. The key indicator of what is actually going on though is CHT. If your heads aren't getting hot, you are not operating in a condition conducive to detonation. Detonation is a high pressure/high heat issue. If you see CHTs below 350°, you're looking just fine.
     
  21. Henning

    Henning Ejection Handle Pulled

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    And CHT. I use CHT dropping off to govern my enrichment during descent. RPM will usually drop though, and MP rise, on a dead naturally aspirated engine.
     
  22. kgruber

    kgruber En-Route

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    With an engine out, RPM and MP are in a normal range. Only fuel flow/EGT tells the whole truth and nothing but the truth.
     
  23. coloradobluesky

    coloradobluesky En-Route Gone West

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    Torque x speed = Horsepower
     
    Last edited: Oct 21, 2014
  24. coloradobluesky

    coloradobluesky En-Route Gone West

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    12 horsepower per gallon per hour. So if you are burning 10 gallons per hour, that is 120 horsepower. (for gasoline engines) True for cars and motorcycles too.
     
  25. Hank S

    Hank S En-Route

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    Sound and level speed tell tales, too! Both decrease . . .
     
  26. Jaybird180

    Jaybird180 Final Approach

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    Busted fuel line will continue to flow:D
     
  27. FastEddieB

    FastEddieB Touchdown! Greaser!

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    Maybe worth noting that in some aircraft, the fuel flow gauge is actually a fuel pressure gauge, albeit shown in gph.

    Can make it difficult to discern what's really going on with clogged injectors.
     
  28. Ted

    Ted The pilot formerly known as Twin Engine Ted

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    Depends heavily on your engine. Not all engines have the same detonation characteristics. In fact, most engines are vastly different.

    If you're looking only at an engine out, EGT is all that matters since FF may still be full and not working properly.

    But for the rest of operation, MP, RPM, and FF are important. EGT is less important other than as an aid to leaning. EGT is far from an aid for telling the whole truth and nothing but the truth.
     
  29. GeorgeC

    GeorgeC Administrator Management Council Member PoA Supporter

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    I know the real relationship is not linear, but I used matlab to fit y=ax to the Lycoming 65% economy 2400 rpm curve and came up with 14*gph ~= hp, at least for the io360c, which seemed to line up reasonably well with reality. Presumably this is how Deakin came up with his magic number of 14.9 for the larger engines.

     
    Last edited: Oct 22, 2014
  30. coloradobluesky

    coloradobluesky En-Route Gone West

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    That 12 gallons per hp per hour has worked pretty well for me with my Lycoming 360 A1A, carbed and constant speed. But Ill admit, it may not be perfect for every engine.

    One thing, if the engine is high compression and needs the high octane, it will be higher. High compression engines get better gas mileage (all else being equal).
     
  31. Henning

    Henning Ejection Handle Pulled

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    Kinda, it makes a simple rule when you ignore supercharging and the pressure limits of the fuel.
     
  32. James_Dean

    James_Dean Pattern Altitude

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    This is exactly how I've been running. I have to bring power back by 1000 AGL to keep Cht's below 400 even with fuel flows set at redline. Then it is a 75% climb to 5000agl full rich. At 5000 throttles come back to full and will stay there until desent. I will pull fuel in the remaining climb keeping hottest cht at 370-380. Once I level off I do the big pull until I feel a substantial deceleration. Park them that way for a few minutes to let them stabilize and cool down. Then add fuel back to get speed while keeping CHTs at 340-350 or less depending upon mission and winds. RPM's come down to 2350 below 7,000 and 2450 above for the extra power.

    Oil is still golden at 25 hours and exhaust tips are pure white.
     
  33. flyingcheesehead

    flyingcheesehead Touchdown! Greaser!

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    What do you do for engine management during descents?

    Personally, I don't enrich the mixture at all - I maintain cruise MP by slowly pulling the throttle in the descent, and I leave the mixture as it was in cruise until I'm turning final and the red and blue knobs go forward.

    The engine doesn't know whether it's running at 23" MP because I'm at altitude or because the throttle is pulled back, with the slight caveat that there are minor losses to pumping action. Mixture doesn't need changing unless you let the MP go up.
     
  34. Henning

    Henning Ejection Handle Pulled

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    See, I just pulled back mixture around 500' to 12.2/side at sea level, leave WFO throttles and 2675 RPM for the climb out then pull back to 2450 and end up at 10.5 at cruise altitude.
     
  35. GeorgeC

    GeorgeC Administrator Management Council Member PoA Supporter

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    For posterity, the magic coefficient for the o470r is around 12.35.
     
    Last edited: Jan 19, 2016