Economy Power Settings

[MooneyNate]

Hello all, 

I've owned my C model for over a year now and starting to stretch my legs. Does anyone have any opinions on the 17-1800 economy setting in the manual? I included a pic of the manual at 2500 (I'd be flying higher of course, just an example).

A few weeks ago I tested out the 17-1800 setting because I had nice tailwind and... well.... it did not sound or feel natural. Maybe I'm just used to the sights and sounds of going faster but the prop control was almost in my lap to get to 1800 and I didn't want to put too much pressure on the prop. Does anyone else routinely use this setting? Do you get book results in GPH and MPH? I don't plan on using this setting often but its nice to know I could. I looked around a few other threads but couldn't quite find what I was looking for. Any thoughts or advice appreciated. 

[carusoam]

Power charts from the 60s lack a lot of reality.  Use caution using them.

Most people around here develop personalized fuel burn data for the various aspects of flight.

without FF instruments and a real EGT gauge, it can be a challenge to collect.  It can be done.  It is just a challenge.

Collect a lot of data on each flight. 

Was that chart 50°F ROP?  At 37% bhp operating at peak won't be a problem. staying a loft might be. The chart seems to be avoiding operating over square by too much..?

as far as operating at the low end of the power performance envelope... make sure you are out of the yellow rpm arcs or whatever color you are supposed to avoid.  

Low power has different vibrations than more power. Cylinder and oil temps can be on the low side.  You can turn a little gas into a lot of hours this way.  Add some wind and a ridge, you can be a Mooney soaring team member.

yes I have done it with my C.  Not a lot.  I like speed and efficiency...

Best regards,

-a-

Edited April 26, 2017 by carusoam

[Hank]

I've flown my C at its published 20"/1950, and don't care for the mushy control feel.

When I need to fly slow, like giving rides on Airport Day a d staying in line with several 172s, I use 2300 and whatever MP is required to match their speed (16-17" usually), and yes, I lean her out, too, for the flights at 1500 agl or less. Fuel burn is pretty low, but I don't have a meter . . . .

I prefer to cruise fast, and high, using the 2500 line from these charts, a d back the throttle off just enough to make the MP needle move. 

What year is your C? Mine is a 1970, and these are from my Owners Manual. FWIW,  my cowl flaps are fixed, not adjustable. 

[Yetti]

feels mushy.  When I needed to slow to take some pics.   Went to landing configuration. gear out, half flaps

[MooneyNate]

It's a 1965 and you guys are right, it felt mushy. I need to go out and do some experimenting. Giving rides I do about the same: 18-20 MP and 2300 RPM. For me I'm intrigued with the endurance at the low setting. Book says I can get 9 hours out of it which i think is awesome..... but I don't want to put too much pressure on the hub and seals, a high MX bill isn't worth the cost savings in fuel. This is more out of curiosity for me than anything. 

[carusoam]

The important thing is to know that you are actually getting that low of a fuel burn...

Start with a full tank on one side to run the test.  Take of and fly on the other tank.  When ready, set you power, rpm, mixture, then switch to the full tank.  Time the fuel burn for 15 minutes or more change the tank head back and fill the tank the same way you did before.  Calculate the fuel used/hour of your test with your plane.

Since the prop is like a wing and a coarse setting is like a high AOA.  Selecting a low rpm doesn't scream better efficiency...

The TopProp uses 2550 rpm for cruise.  Part efficiency, part sound, part it is different than 2500 limit of other props....

Setting a low MP to get a low FF is most of the efficiency.  The rest comes with slow flight.  Running low power, use peak for the mixture. Or as LOP as you can smoothly go...

For interesting reading look up Vz, for Carson's speed...  it is a relative of Vx and Vy. Slow cruising...

As you go slower, the AOA starts to increase ruining the ficiency you gained by going slow.

Message for 201er:  hmmmmm.  Hey Mikey, have you ever graphed FF vs. indicated AOA vs. airspeed?  There is probably a measurable Carson's speed that can be determined with the proper instruments. It is slow... IFR approach slow...

Best regards,

-a-

Edited April 26, 2017 by carusoam

[aaronk25]

Only thing I'd add is that if you go more than 20f LOP the mpg falls off due to the timing being fixed as a leaner mixture takes longer to burn. Yes the display may say a higher mpg because the aircraft slowed and there is less parasitic drag from the lower speed. Try setting a lower MP setting and then re-lean to 20f LOP (that yields the same previous IAS) and you will see a improvement in MPG or less fuel at the same speed. 50lop should be used to cool a hot motor or continued a cruise setting.


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[Raptor05121]

I haven't gone that low.

Local flying: 23 squared
Somewhere in the general vicinity: 24 squared
Flying long distance: 2500rpm/WOT.

All leaned out

[Hank]

3 hours ago, aaronk25 said:

Only thing I'd add is that if you go more than 20f LOP the mpg falls off due to the timing being fixed as a leaner mixture takes longer to burn. Yes the display may say a higher mpg because the aircraft slowed and there is less parasitic drag from the lower speed. Try setting a lower MP setting and then re-lean to 20f LOP (that yields the same previous IAS) and you will see a improvement in MPG or less fuel at the same speed. 50lop should be used to cool a hot motor or continued a cruise setting.


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You have a carbureted Mooney that will run at 50ºLOP?

[Cyril Gibb]

23 hours ago, aaronk25 said:

Only thing I'd add is that if you go more than 20f LOP the mpg falls off due to the timing being fixed as a leaner mixture takes longer to burn.

True about a lean mixture burning more slowly than a richer one.   I back the rpm off to about 2300 in LOP cruise to compensate.  It brings the peak cylinder pressure back closer to the optimum crank angle and (for me) results in a small but noticeable increase in airspeed.

MPG, of course, is more complex when the wind component is taken into consideration. Into a headwind, I usually get a higher mpg using a closer to peak mixture and a higher rpm because the increased airspeed more than compensates for the increased fuel flow.  For a tailwind I go deeper into LOP.

[tigers2007]

Can someone remind me what Mike Busch's percent BHP limit for leaning is? Was it lean under 75% or 70% or 65%? I get an anxiety attack when I lean WOT below 5000. I don't care about the fuel burn - I just don't want to grenade the motor.

[MyNameIsNobody]

Learn to fly a Cub if you want to fly slow/sight-see, burn a little fuel and have fun doing it.  In a Mooney?  Meh.

[Raptor05121]

44 minutes ago, tigers2007 said:

Can someone remind me what Mike Busch's percent BHP limit for leaning is? Was it lean under 75% or 70% or 65%? I get an anxiety attack when I lean WOT below 5000. I don't care about the fuel burn - I just don't want to grenade the motor.

 

Someone else can chime in with the rule of thumb, but its like if your MP & RPM combo are less than 48, I think you are less than 75% power.
 

[Hank]

5 minutes ago, Raptor05121 said:

Someone else can chime in with the rule of thumb, but its like if your MP & RPM combo are less than 48, I think you are less than 75% power.
 

That varies by model, due to engine differences. Your number is correct for our C models. 

[Mooneymite]

1 hour ago, tigers2007 said:

Can someone remind me what Mike Busch's percent BHP limit for leaning is? Was it lean under 75% or 70% or 65%? I get an anxiety attack when I lean WOT below 5000. I don't care about the fuel burn - I just don't want to grenade the motor.

Perhaps not as authoritative as Mike Busch, but the O-360 POH power tables assume leaning below 75% for endurance and range numbers.

[jetdriven]

They will run at 83% LOP as well. At 30F LOP the cylinders are in the 320-350 range.  

[Andy95W]

I thought Mike Busch's recommendation is that below 65% power, there was no "Red Box".  I think that equates to about 43 or less (about 20"/2300 rpm.)

[carusoam]

1) 70's M20C POH says to lean below 75% bhp.

2) with regards to the red box, go LOP below 65% bhp, the red box ends there...

3) There are other ways to avoid the red box, but it takes some more knowledge of what you are doing...

Best regards,

-a-

[FloridaMan]

I run ROP and try to get as much speed as possible as I am of the mindset that cost per mile traveled is not just based on the miles you get per gallon, but also the number of miles traveled between maintenance intervals. 

[Hank]

19 hours ago, Andy95W said:

I thought Mike Busch's recommendation is that below 65% power, there was no "Red Box".  I think that equates to about 43 or less (about 20"/2300 rpm.)

When I'm high end ought to only get 20", I run 2500 and generally indicate ~145 mph. This is generally 9000-10,000 msl, which puts me 170+ mph. Can't argue with that . . . I'm usually right around 9 gph block time, with near Vy climbs and power on 500 fpm descents. Climb is usually limited by Oil Temp.

[Hector]

I thought Mike Busch's recommendation is that below 65% power, there was no "Red Box".  I think that equates to about 43 or less (about 20"/2300 rpm.)

The MAPA manual indicates the key number for the C at 65% power is 46 (47 for the J). So for example 2400 RPM and 22 MP (24+22=46) should yield 65% power. However, when I look at the tables in my POH it does not seem to work out. Anybody know why?


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[MooneyNate]

I really need to get a MAPA manual. I hear a lot of people quoting it. Not to open up another giant can of worms but I spent some time this morning debating with myself on LOP vs. ROP. I just found it comical that Flying mag recommends 50 ROP while AV web recommends LOP, AOPA took a refreshing stance in their "Dogfight" article debating both sides. I finally gave up and went straight to Lycoming and pulled their recommendations. For performance it recommends leaning until theirs an increase in airspeed. For economy it recommends leaning until engine roughness then increasing until smoothness returns. It also recommends for maximum service life to fly 65% power or less, CHT 400 and below ad Oil Temp 165-220.

I normally fly 21-2300 and probably use the economy leaning procedure. I have a EGT but use it for more of a reference rather than using it solely for leaning.

A little off topic but I duck hunt and I swear the only reason they invented duck calls is to give duck hunters something to do. I mean, who knows what your really saying to those ducks. Based on my success last year I'm sure I told them "the food sucks here guys." I think the same thing applies to the LOP vs ROP argument. Gives us good foder for hanger talk.

[tigers2007]

From the 1977 M20C Ranger POH. Note the differences.

 

 

What MooneyNate posted:

 

 

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[Hector]

From the 1977 M20C Ranger POH. Note the differences.
 

 
What MooneyNate posted:
 

 
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Looking at both tables it would still seem that the key number for 65% power is 45, not 46. I'm missing something I think. I doubt the guys that wrote the MAPA manual made a mistake.


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[Andy95W]

It sure looks like 65% power equates to a 45 to me.