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  #11  
Old 12-16-2017, 03:32 PM
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Jesse Jesse is offline
 
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I understand that the equation gives you an approximation, but Manifold Pressure plays a bigger part in power than does RPM, does it not? For example, to get 75% power, the number 48 assumes 24 squared, I guess. However, if you increase RPM to 2700 and reduce MAP to 21, the number 48 does not yield 75% power. Likewise, 30 of MAP and 1800RPM would likely yield more than 75% power (while not advisable to fly that far over squared. Is there an equation somewhere that gives a weightingvto RPM & MAP that are more true to life than the even weighting?
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  #12  
Old 01-12-2018, 06:24 AM
svyolo svyolo is offline
 
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Power is also a function of how fast you are producing work. So RPM definitely matters.

Anybody got a resource for what this all means LOP? 24/24 at SL is 75%. I think Lyc doesn't want you to lean above 70% or something like that. Lets take 65%. What is the "square" power setting for 65% ROP, and what is it LOP. I assume the 22/22 ROP is more power than 22/22 LOP. Or maybe I am wrong.
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  #13  
Old 01-12-2018, 06:27 AM
svyolo svyolo is offline
 
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So I can't believe a bunch of RV guys haven't done this. Fly 8000' 170 KIAS, ROP. Then fly 8000', 170 KIAS, LOP. What was the difference in MP and rpm? I have been searching for this for a long time. Can't find it.

Thanks in advance for any help.
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  #14  
Old 01-12-2018, 07:25 AM
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rv6ejguy rv6ejguy is offline
 
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On a Lycoming, power is very approximately proportional to both rpm and MAP (within the normal limits of cruise flight) at a given air/ fuel ratio but there are several other factors involved as has been discussed many times here.

LOP will cost you between 4% and 8% over best power mixture, depending on how lean and how well spark advance is optimized for the lean mixture.

Altitude and intake air temperature also have rather significant effects on power output if you are comparing to SL, standard day conditions.
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  #15  
Old 01-12-2018, 08:06 PM
svyolo svyolo is offline
 
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HI Ross;
I guess my question is this. Are 22/22 ROP, and 22/22 LOP, the same amount of power? My assumption is not.
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  #16  
Old 01-12-2018, 08:12 PM
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No, depending actual air/fuel ratio and ignition advance, you'd see a reduction of 4-8% running LOP at the same MAP/RPM.
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Turbo Subaru EJ22, Marcotte M-300, IVO, RV6A C-GVZX flying from CYBW since 2003- 418.1 hrs. on the Hobbs,
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  #17  
Old 01-13-2018, 07:46 AM
svyolo svyolo is offline
 
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I was expecting something like that. But I never heard an actual %. So with a CS prop, running the same MP/rpm either LOP or ROP, the plane flies slower LOP, and the CS prop compensates by using a finer blade pitch.

Thanks.
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  #18  
Old 01-13-2018, 06:00 PM
n816kc n816kc is offline
 
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Default LOP HP

If’n I recall correctly, when lean of peak, multiply fuel flow by 15 to get horsepower, roughly. For instance, 6 gph x 15 = 90 hp. 50% power for an O-360. Or 60% for an O-320 (150). Always used the rule of 48 at best power in my Pacer to get 75%, 45 for 65%.
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Last edited by n816kc : 01-13-2018 at 06:06 PM.
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