LOP convinced and converted!!!

[Tommy]

Finally got a chance to play with mixture setting with a long haul flight in almost nil wind condition after owning a M20J for 2 months.

With 50F or more LOP, the CHT temperature is actually a lot cooler than 100F ROP! And the speed difference is almost negligible! The engine runs smoothly in both!

Now I am truly convinced!

My annual is coming up and hopefully my exhaust and my sparks will be in clean condition to finally put a nail in the coffin in this debate! *gasps*

[rbridges]

My annual is coming up and hopefully my exhaust and my sparks will be in clean condition to finally put a nail in the coffin in this debate! *gasps*

 

 

but if anything unrelated breaks, your mechanic will probably blame it on LOP operations.  

[Bob_Belville]

 finally put a nail in the coffin in this debate! *gasps*

Dream on.

 

But I would check that speed loss claim. I been flying LOP about half the time but the speed lost is typically more like 8-12 knots. LOP is more economical with much cooler CHTs & Oil Temps but the reduced HP affects TAS.

[WardHolbrook]

Does anyone still argue against LOP? That's so 2008. 

[Bob_Belville]

Does anyone still argue against LOP? That's so 2008. 

Dream on. 

[Tommy]

8 to 12 knots? Really? Ok! Maybe I will test it out in the next flight!

[PTK]

LOP?! Think again!

 

You will burn exhaust valves, cause detonation, pre-ignition, your pistons will melt and your engine will cease!   

 

Some wives just get old become mother-in-laws and live forever!

[Bob_Belville]

8 to 12 knots? Really? Ok! Maybe I will test it out in the next flight!

Same day, ignore GS, one was east the other west, look at TAS on Aspen. 146 vs 158. (1966 M20E with essentially the same engine as your J.)

[jetdriven]

Anything leaner than ~25 LOP is detrimental to economy. Yes the airplane goes (slightly) further at 50 LOP but it's drag loss from flying slower. But you are flying 8-10 knots slower for the same NMPG. Just set it to 15-25 LOP which results in a 3 knot IAS loss, and run leaner only for CHT control. If 65% power or less, you can run a little richer to recover the lost speed as needed.

[jetdriven]

8 to 12 knots? Really? Ok! Maybe I will test it out in the next flight!

the speed curve gets a real bend in it below about 25 LOP. 20 degree engines see this sooner than 25 degree ones, too. You can set it to 25 LOP, get it all stabilized,then lean it .2 GPH at a time and you will quickly find a 5-8 knot further loss in TAS for a .2 GPH lower FF. that's when you know you have gone too far. Generally around 50 LOP or a bit past that.

[PaulB]

What do you guys use to find your LOP setting? Lean find or just the big mixture pull until you feel it decelerate?

[jetdriven]

BMP, where it feels like going down the highway at 70 MPH when you let your foot off the gas. Detectable deceleration.

In a car not a Jeep or 1 ton dually.

[pinerunner]

If you're talking about power loss LOP vs ROP at the same MP and RPM then you're missing an important point.

 

On the ROP side oxygen (air) is the limiting combustion ingredient and RPM and MP (and also absolute temperature a little bit) define how much oxygen you're pumping through and therefore how much power. To someone who remembers PV=nRT from freshman chemistry/physics its no surprise that pilots use MP and RPM to set power (assuming running rich).

 

On the LOP side fuel is the limiting reagent and power is set by fuel flow. Simple as that. 14.9 HP per gallon per hour works pretty well. So of course power goes down as you lean further at a given MP and RPM.  It doesn't mean LOP is less efficient.

 

If you want to compare power generated by the two modes we have another parameter that we don't usually think of as a power gauge, the airspeed!  Carefully tweek your settings around to get the same airspeed in each of the two modes and you can KNOW that you're comparing at the same power.  You can test for yourself that 14.9 number. You don't need to take anybodys word for any of it. 

 

Caveat added: Of course at the more extreme LOP settings the engine sputters and dies so we know the 14.9 rule of thumb stops working somewhere. I did my comparison with 20-70 LOP ( my GAMI spread about 0.5 GPH) vs 100 ROP about 1-2 inchs less MP. I fiddled with it to get the same airspeed averaged over about half hour each mode, maintaining constant altitude. I used the tables we all use to get the  the ROP mode power (it was about 70%) and then used that HP along with the GPH on the LOP side to get the HP/GPH and it was close to the 14.9 number occasionally quoted here.  Of course simple rules of thumb fall down if you push them too far; I acknowledge that.  The simple logic here would predict no loss of power as you go further and further ROP and we all know there's a slow drop in power as you enrich past 100 ROP but with the benefit of decreased danger of detonation. So we put up with that loss during takeoff and high power-poor cooling scenarios.

[jetdriven]

I know for fact that at 1500', 10.0 GPH WOT with an EGT of 1400 is 5-7 knots slower than the same 10.0 GPH with 27" of MP and the EGT at 1480. Pulling the throttle back to go faster sounds crazy but I read it here first. Lean of peak isn't the same HP at all points on the curve for a given FF. HP output falls off precipitously below 50-100 LOP depending on % power and timing.

[Danb]

Bob there's a 200 difference in prop. comparing the two TAS #'s

[jetdriven]

~6 or 8 knots can be explained by the lower prop RPM. Another 3-5 knots for LOP.

[Bob_Belville]

Bob there's a 200 difference in prop. comparing the two TAS #'s

Yes, I don't run LOP above 65% power so I either had to pull back the throttle or the prop. (The 70% was WOT + RAM AIR, 2550 RPM which is my practical all she's got cruise @ 9500'.) The 12 k difference is largely due to the difference between 65% and 70%

 

But that's the real world options. I can go 158 k on 10.3 gph or 146 k on 8.2 gph. At least for the conditions that day. Strictly thinking economy: 15.34 ROP vs. 17.80 LOP nm/gal. That's 16% cheaper (fuel cost) running 8% slower.  

[jetdriven]

The Lycoming operators manual shows around 23" and 2500 RPM as 65%. I wouldn't put too much trust in that engine monitor to give an accurate % of power. Nobody knows what formula they use either.

[Bob_Belville]

The Lycoming operators manual shows around 23" and 2500 RPM as 65%. I wouldn't put too much trust in that engine monitor to give an accurate % of power. Nobody knows what formula they use either.

Byron, the '66E Owners Manual has 21 & 2500 @ 10,000' as 69%. That's very close to my (calibrated) monitor calling 21.5 & 2550 @ 9500 70%.

 

Forget about the monitor, why is the Lycoming info you cite so different from the Mooney Manual? The manual shows 23/2500 as 71% @ 2500'; 73% @ 5000'; 76% @ 7500'!

[Steve Dawson]

Same day, ignore GS, one was east the other west, look at TAS on Aspen. 146 vs 158. (1966 M20E with essentially the same engine as your J.)

Your RPM is 200 off

[jetdriven]

the LOM shows 21"- 2500 RPM 10,000' as ~130 BHP, which is 65%. 

23" - 2500 RPM @ 7500' is ~140 HP, or 70%

 

performance chart page 3-37.

 

the chart must be corrected for standard atmosphere. so hotter than std temp (-1% power for each ten degree warmer than std) or lower than 29.92 is less power.

[Super Dave]

What do you guys use to find your LOP setting? Lean find or just the big mixture pull until you feel it decelerate?

Both. I do a BMP until I feel the deceleration to get on the lean side, then I use the engine monitor to find peak on the richest cylinder, and lean 15-20 from there.

Depends on the monitor you are using, but for the JPI 700 things are a little backward when finding peak from the lean side.

[John Pleisse]

Does anyone still argue against LOP? That's so 2008. 

 

 

Yes.....

[Bob_Belville]

Both. I do a BMP until I feel the deceleration to get on the lean side, then I use the engine monitor to find peak on the richest cylinder, and lean 15-20 from there.

Depends on the monitor you are using, but for the JPI 700 things are a little backward when finding peak from the lean side.

 

the LOM shows 21"- 2500 RPM 10,000' as ~130 BHP, which is 65%. 

23" - 2500 RPM @ 7500' is ~140 HP, or 70%

 

performance chart page 3-37.

 

the chart must be corrected for standard atmosphere. so hotter than std temp (-1% power for each ten degree warmer than std) or lower than 29.92 is less power.

The Mooney OM shows 21"/2500RPM @ 10,000' as 138 HP = 69%. The Mooney chart is labeled Standard Atmosphere.

 

My flight data shows is was 39F vs. 25F standard @ 9500. Baro was 30.35. So what was my %HP @ 21.6/2550? JPI says 70%. 

[Tommy]

Haha guess I am too quick to say that the verdict is out! Wonderful to see such passionate discussion!

I am running 22" and 2500rpm. LOP 50-100 and my CHT Is steady just covering the right side of "F" sign.

I don't have a Fuel flow meter. Also I am yet to compare the speed of 100 ROP.

But I am definitely not running 50 ROP as advocated by http://www.mooneypilots.com/mapalog/cruisepower.html

The CHT is a lot higher!