Common cruise settings

[MIm20c]

I’m currently flying within a 250nm radius of my home airport gaining experience and time as I work towards my instrument rating.  Needless to say I’m not really in a hurry to get anywhere. Normally I set the engine at 2400/20 and enrich just past roughness.

Lately I’ve been testing the aircraft at different altitudes and power settings to stretch its legs.  I’m finding the JPI % power is fairly close at some settings and off a little at others. 

What power settings (MP/RPM/PresAlt) do you run (C-J)?  For staying well outside the red box can the o-360 run % power of 200 vs 180?  I’m kind of thinking eagle vs O3 - 240 vs 310 hp what percent power do you use for staying out of the red box?

I’m trying to run peak egt at the highest speed possible for a given altitude while being kind to the cylinders. 

[steingar]

For local "I'm in no hurry" flights I run 2300/2100.  For longer "I want to get there" flights below 5K feet I run 2300/2300.  For longer flights above 5K feet I pull out the POH and see what works best in the prevailing conditions.

[Mooneymite]

I suspect that every individual engine/prop has its own particular sweet spot where it runs smoothest.  For me, picking a wind/ride favorable altitude and a power settind below 75% determines what I set in my C.  There are those on Mooneyspace who advocate high power settings.  I am not one of those.  I loaf along at 2350 rpm a lot.

[Andy95W]

14 minutes ago, Mooneymite said:

I suspect that every individual engine/prop has its own particular sweet spot where it runs smoothest.  For me, picking a wind/ride favorable altitude and a power settind below 75% determines what I set in my C.  There are those on Mooneyspace who advocate high power settings.  I am not one of those.  I loaf along at 2350 rpm a lot.

+1.

Exactly what I do.

[MIm20c]

So do you set power via the POH or fuel flow?  I agree about the loafing around. That’s easy to set fuel flow just lean to just rich of rough (ROR). However, I also like the speed of 2400/22  which is a couple % hp lower than 23/23.  

Anything above 24/22 does not net much as far as speed goes.  I find my plane likes the 146-148 TAS and I have to add a lot more power to get another 5 kts.

If I take the data from the POH at 5k the 24/22 setting gives me 72% of 180hp or 65% of 200hp. One power setting is theoretically able to run at almost any fuel flow the other should be 100 ROP. 

I guess my real question is for C/G owners what is the highest power setting you feel comfortable running peak (or as close as you can get) egt vs 100 ROP?  Also do you think because the displacement/components are very similar to the IO-360 that 200 can be used in the percent power basis?

[TonyK]

Burning fuel for entertainment and burning fuel for getting somewhere.  19.5 / 19.5 when I am just wallowing along for fun.  I get about 120mph which is still way faster than my C172G on close the same fuel burn as the O-300 wfo.  Getting somewhere changes depending but I have been aiming high WOT and as close to 75%hp as I can get

[Hank]

mlm, our engines are 180 hp, so ignore any figures that start with 200, 'cause we ain't got it. I also ignore all the advice from our fuel-injected brethren, 'cause we ain't got that, neither.

Engine management is fairly simple in our C models. MAPA teaches that our Key Number is 47, and that's simply adding the numbers for MP + RPM straight off of your dials, which yields 65% power. I generally run 46 or 47 total, but I do confirm with the Performance Charts [I added them to my checklist, which lives on my kneeboard].

For loafing around or making short, low trips, I generally run 23" / 2300 [which is 23 + 23 = 46], which gives me ~135 knots ± winds. Giving rides on Airport Day with a bunch of 172s, I set 2300 and reduce throttle enough to hang back with them, which can be 16-17" if it's not too windy.

For medium range trips [less than an hour], I generally climb to 5000-7000 and run 22" / 2400 [or 22 + 24 = 46 again]; if I'm in a hurry, I can add either another 1" of MP or 100 RPM.

Traveling is done 8000+, and it's also simple:  reduce throttle until the MP needle just starts to move, and leave it there, set 2500 and lean away. This will often leave me ~145 mphi, which on my fingers computes to faster than book speed, so I'm happy. With 143 mphi at 9500 msl, that's 143 + 19% = 143 + 14.3 + 14.3 - 1.4 = 143 + 28 - 1 = 170 mph true. [NOTE:  170 mph = 148 knots, pretty good for what is widely reputed to be a 140 knot plane!]

Regardless of trip length, I do not reduce throttle to descend, I just push on the yoke for 500 fpm and trim the forces out, and walk throttle backwards and mixture forward periodically to maintain my cruise MP and EGT readings. This makes up for the slow climb on departure, improves my block speed and leaves my block fuel burn right around 9 gph.

Edited November 10, 2017 by Hank

[gsxrpilot]

What @Hank said.  That's how I ran my C.

[Hank]

Really wish I'd met you at Summit, Paul!

I'll be in El Paso on business next week, probably as close as I'll come to Austin.

[carusoam]

JPI %power numbers for ROP are generally inaccurate...  they are based on calculations that can't match every engine or operator.

For LOP, the JPI Numbers are a much better match, but it requires FF to do the math...

+1 for The MAPA key numbers that Hank referred to above...

65% hp is a generally a nice way to operate whether cruising around or cruising traveling...

When building time.... 18” MP is a pretty good way to increase time while burning fuel slowly...

When covering distance 20" at a high altitude is a nice way to minimize air resistance....

Works for both the M20R and the M20C...  except the M20R can easily run LOP.  

I usually run near peak at this altitude, which is good for the C as well...

PP thoughts only, not a CFI or mechanic...

 

Best regards,

-a-

[gsxrpilot]

3 minutes ago, Hank said:

Really wish I'd met you at Summit, Paul!

I'll be in El Paso on business next week, probably as close as I'll come to Austin.

Likewise. I actually asked around for you one day, and then just never made it happen.  Unfortunately I'm in Dubai and Bahrain on business next week.

[ArtVandelay]

I generally ignore MP in my J, I use JPI HP%, RPM 2300-2500, at 2200 the engine just doesn’t sound as smooth. I only use MP to stay out of the placarded warning range.

[Raptor05121]

x3 what Hank said. 2300/23 is my local "burning holes in the logbook but not the wallet" setting.

[MIm20c]

1 hour ago, Hank said:

mlm, our engines are 180 hp, so ignore any figures that start with 200, 'cause we ain't got it. I also ignore all the advice from our fuel-injected brethren, 'cause we ain't got that, neither.

Engine management is fairly simple in our C models. MAPA teaches that our Key Number is 47, and that's simply adding the numbers for MP + RPM straight off of your dials, which yields 65% power. I generally run 46 or 47 total, but I do confirm with the Performance Charts [I added them to my checklist, which lives on my kneeboard].

For loafing around or making short, low trips, I generally run 23" / 2300 [which is 23 + 23 = 46], which gives me ~135 knots ± winds. Giving rides on Airport Day with a bunch of 172s, I set 2300 and reduce throttle enough to hang back with them, which can be 16-17" if it's not too windy.

For medium range trips [less than an hour], I generally climb to 5000-7000 and run 22" / 2400 [or 22 + 24 = 46 again]; if I'm in a hurry, I can add either another 1" of MP or 100 RPM.

Traveling is done 8000+, and it's also simple:  reduce throttle until the MP needle just starts to move, and leave it there, set 2500 and lean away. This will often leave me ~145 mphi, which on my fingers computes to faster than book speed, so I'm happy. With 143 mphi at 9500 msl, that's 143 + 19% = 143 + 14.3 + 14.3 - 1.4 = 143 + 28 - 1 = 170 mph true. [NOTE:  170 mph = 148 knots, pretty good for what is widely reputed to be a 140 knot plane!]

Regardless of trip length, I do not reduce throttle to descend, I just push on the yoke for 500 fpm and trim the forces out, and walk throttle backwards and mixture forward periodically to maintain my cruise MP and EGT readings. This makes up for the slow climb on departure, improves my block speed and leaves my block fuel burn right around 9 gph.

Hank, thank you for the detailed answer.  The highest power setting I’ve used for any length of time has been the 2400/22 which gives me the 46. My POH shows 74% power at 7500 ft at that setting. I’m assuming the 46-47 rule means 100 degrees ROP?

I’m seeing the 46 number close to 65% when looking at the io-360 charts vs 70%+ when looking at my POH. That’s why I was wondering about using the 200hp info for leaning. 

[Hank]

Lean using your Owners Manual, not the POH for a higher powered, fuel injected, angle valve engine.

I routinely fly ~70%, and lean 50° Rich. Up high enough to not reduce MP, it's generally safe to run at or near peak for a little lower fuel burn and speed. 

[jetdriven]

On 11/10/2017 at 2:54 PM, MIm20c said:

Hank, thank you for the detailed answer.  The highest power setting I’ve used for any length of time has been the 2400/22 which gives me the 46. My POH shows 74% power at 7500 ft at that setting. I’m assuming the 46-47 rule means 100 degrees ROP?

I’m seeing the 46 number close to 65% when looking at the io-360 charts vs 70%+ when looking at my POH. That’s why I was wondering about using the 200hp info for leaning. 

I don't see how 2400-20" is 74% power. Maybe 55-60%. 

[yvesg]

Here is the 7500 feet table for the C.

Yves

 

[MIm20c]

14 minutes ago, jetdriven said:

I don't see how 2400-20" is 74% power. Maybe 55-60%. 

That’s why I’m asking, hard to find a consensus on this.  24/22 @7500 shows 74% from the owners manual.  I would think 100 degrees ROP would be appropriate. However, would 2350/21 be low enough to run peak egt (first cylinder to peak, rest are on the rich side)?

From testing done so far I can get one to two cylinders to peak before the engine starts to get a little rough. I’m going to play with throttle position/ carb heat / or maybe a slight amount of turbo to see if I can get them all to peak. 

[jetdriven]

Usually around 2500-25" is 75% power.  23" is 65%. 

[Hank]

This is the 7500 msl page in my Owners Manual. 20"/2400 is 66% power, lean wherever you want.

[Hector]

According to the MAPA manual the key number for a C model for 65% power is 46; however, the tables in the POH suggests otherwise. Is the MAPA manual wrong?


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[Hank]

7 minutes ago, Hector said:

According to the MAPA manual the key number for a C model for 65% power is 46; however, the tables in the POH suggests otherwise. Is the MAPA manual wrong?


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I thought our Key number was 47. Memory also says tbey developed it from the original 1962 Owners Manual.

[Hector]

I thought our Key number was 47. Memory also says tbey developed it from the original 1962 Owners Manual.

46 for the C. 47 for the J. Page 8-4 in my copy of the MAPA manual.


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[Hector]

46 for the C. 47 for the J. Page 8-4 in my copy of the MAPA manual.


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Here is a PIC of the MAPA manual key numbers as well as a PIC from my POH. According to the MAPA manual a key number of 46 should yield 65 percent power for my C. If you look at the performance table from my POH at 7500 feet, a combination of 2400 RPM and 22 inches (46 key number) yields 74 percent power. Am I reading this wrong? Can someone explain the discrepancy between the two sources?

[Andy95W]

I've noticed the same thing so I made my own chart, based on key number and altitude.

I love the concept, I just thought the published numbers were overly simplified.