-C and -G Model Power Settings

[Raptor05121]

9 hours ago, steingar said:

Been running my M20C at 23 squared or 23/21 in cruise.  Don't like high power settings, I'm told by an airplane engineer that it isn't good for the engine.

Read your POH. Mooney says otherwise.

[ryoder]

Much of what the POH says is refuted by people here and MAPA.

[steingar]

14 hours ago, jetdriven said:

What is your definition of a high power setting 

Pretty much anything over 75%, and I prefer to keep it down around 65%.  The guy who told me this was an engineer for Lycoming, so I do tend to take his word for it.

 

[Shadrach]

1 hour ago, steingar said:

Pretty much anything over 75%, and I prefer to keep it down around 65%.  The guy who told me this was an engineer for Lycoming, so I do tend to take his word for it.

Is said engineer a former Cherokee 6 driver and current V-tail Bonanza driver? 

If so, his buddy with the RV-6 is one of the propulsion engineers to which I was referring...

[steingar]

Guy flies twins mostly and rescues dogs for which he has a nonprofit.  He is an engineer and a CFI.  

[M20F]

35 minutes ago, daver328 said:

Wouldn't the aft CG improve your cruise performance? 

Thinking you have three bladed prop? Wonder if that changes things and/or Bob's premise no longer applies? 

I get about 2 knots when I push my seat all the way back in cruise aft CG definitely brings the speed and on long trips I will ballast the baggage.

For everyone saying they fly WOT for power settings that doesn't tell much.  Are you flying WOT at 2000 feet, 5000 feet, 9000 feet, etc.  

[steingar]

19 hours ago, Raptor05121 said:

Read your POH. Mooney says otherwise.

Just did, POH says nothing.  Gives RMP/MP settings with all the attendant data, but that's it.

[Hank]

2 hours ago, steingar said:

Just did, POH says nothing.  Gives RMP/MP settings with all the attendant data, but that's it.

That works well. You just have to apply some Kentucky windage to MP unless you happen to be at an altitude shown. That's where I came up with 23/2300 down low; still haven't made my mind up on 22/2400 for mid-level flight and stepdowns; seems like 7500 and up I'm always at 2500 and WOT minus enough to move the MP needle (this cuts off the additional fuel flow at WOT, and hopefully creates turbulent flow in the carb body for better fuel droplet atomization and more uniform fuel/air mixing).

You just need to pick some settings for altitudes you fly that give the power or speed that you want, and test them. How do they work for your plane? How does it feel--vibration, noise, bumps, comfort? How about fuel burn?

Play with your charts for your frequent altitudes and see how well they match up with the MAPA equation. Adjust the target to suit yourself. If the engine performs better and lasts longer, you come out way ahead. These are just ways to keep from flipping through the Manual when ATC brings you down in three steps instead of a steady descent. I have the interesting portions on my kneeboard for quick reference without destroying my fragile 1970 booklet, whose center sheet has already torn loose from one staple.

[jetdriven]

5 hours ago, M20F said:

For everyone saying they fly WOT for power settings that doesn't tell much.  Are you flying WOT at 2000 feet, 5000 feet, 9000 feet, etc.  

All those altitudes although I will set it to 28" below 2000' because it's faster at 30-50 LOP than 100 or more. 

[Shadrach]

8 hours ago, M20F said:

Are you flying WOT at 2000 feet, 5000 feet, 9000 feet, etc.  

Yes!

[xrs135]

I fly high in my C. Typically 9,500 - 12,500ft. I'm always WOT since my engine isn't producing much power up high, and 2300-2400RPM for smoothness and low fuel flows. I'm all about getting 7.5gph! 

On the rare occasion that I'm down low, I stick to the 23" 2300 technique or keep the sum of the two at or below 46.

[jetdriven]

You may find the NMPG actually lower below ~ 2450 RPM.  

[Hank]

Just went 254 nm at 9000 msl, 2500, WOT pulled back enough to make the MP needle move, right at peak. Indicated a steady 145-148 mph. I'll find out the fuel burn on Saturday.

[Hank]

On November 22, 2015 at 2:09:20 PM, Hank said:

At the last Summit, Bob K. Recommended running my C WOT/2500. Tried that this week (the data is still in the plane . . . ).

In a nutshell, I cruised 2.7 hours at 9000 msl with a killer tailwind, groundspeeds exceeding 200 mph. Nice! When I refueled at the Class C where I stayed, it was 26.3 gallons or 9.7 gph. Way higher than normal! He said to expect a 40 nm loss of range. To be fair, I was close to gross and certainly had an aft CG.

Came back into stiff headwinds, making 111-125 knots over the ground, for 3.5 hours. Power was 23/2400, a little more than normal (I like MP + RPM = 46, a little conservative). Fuel burn was 36.9 gallons or 10 gph.

but since my last annual, when the carb heat box was rebuilt and a new muffler installed, I seem to go faster and use more fuel. Ten or more mph is nice, but not at a 10% fuel penalty. What really worried me was I climbed out on the left tank, switched every hour religiously (L-R-L-R), and the left and took 25 gallons to refill!

think I'm going back to my normal regime, climb to altitude and if high enough per the Owners Manual, pull just enough throttle out to make the MP needle move, set 2500 and lean. Although whatever changed at annual now let's me run up to 25 LOP, may play with that some. When not high enough (I.e., 6000 msl), it's back to 22/2500, and below ~4000 msl it's 23/2300. But maybe LOP? 

Got out another trip next week, we'll see what we see . . . Look for updates here.

Back to my normal cruise settings. Just went to the SC coast, flew 2:15 getting there at 9000 msl. Didn't track the climb, it was gusty and bumpy from field (264 msl) to over 3000'. Here's the brief summary:  fuel used was 18.6 gallons, or 8.3 gph. Power was WOT backed off just enough to move the MP needle, 2500, and 50° ROP. 

So it seems that running a carbureted Mooney WOT costs about 1.4 gph, for maybe a knot or two of speed. No thanks!

I remembered to bring my kneeboard home, so look for both flight profiles in the Time to Climb thread soon, since if was able to record data coming back from the coast at 10,000 msl, WOT backed off just enough to move the MP needle, 2500, and at peak. 

[gsxrpilot]

18 minutes ago, Hank said:

Back to my normal cruise settings. Just went to the SC coast, flew 2:15 getting there at 9000 msl. Didn't track the climb, it was gusty and bumpy from field (264 msl) to over 3000'. Here's the brief summary:  fuel used was 18.6 gallons, or 8.3 gph. Power was WOT backed off just enough to move the MP needle, 2500, and 50° ROP. 

So it seems that running a carbureted Mooney WOT costs about 1.4 gph, for maybe a knot or two of speed. No thanks!

I remembered to bring my kneeboard home, so look for both flight profiles in the Time to Climb thread soon, since if was able to record data coming back from the coast at 10,000 msl, WOT backed off just enough to move the MP needle, 2500, and at peak. 

Question Hank... At 9000 ft. you wouldn't be getting 25". You'd probably be closer to 21" or so. Do you still back the throttle back just a smidge? Or are you finally at WOT at 9000ft? I'd certainly give up the 1 or 2 kts in exchange for 1.4 gph.

Thanks,

[Hank]

15 minutes ago, gsxrpilot said:

Question Hank... At 9000 ft. you wouldn't be getting 25". You'd probably be closer to 21" or so. Do you still back the throttle back just a smidge? Or are you finally at WOT at 9000ft? I'd certainly give up the 1 or 2 kts in exchange for 1.4 gph.

Thanks,

Paul--

I made one trip each way at 9000 msl, both eastbound. Flew 2.7 hours with a tailwind, WOT, 2500, 50° ROP, for 9.7 gph. 

Six days later, the wind had calmed down and I went 2.2 hours, WOT backed off enough to move the MP needle, 2500, and don't remember if I was 50° ROP or at peak (that's what notes are for!), 8.3 gph.

My notes will clarify both mixture and IAS. I know I came home at 10,000 msl, 2500, WOT minus, at peak, but I didn't top off yet.

Yesterday at 10K, I was just under 20", so that would make 9000 msl right around 21".

[Urs_Wildermuth]

Nice thread. I'd like to pick your experiences here on a few things I've been mulling over. Being a former airline dispatcher and generally a bit of a flight planning nut, I tried to reorganize the somewhat lacking figures in my POH (1965 C model). I came up with some funnies there, which I'd like to run by you for comments. Obviously, I should go out and fly more and try them all out, which I will, but maybe some of you have comments.

First of all, the ever "important" top speeds.

Reading out of the book, the top speed a C model should be able to achieve would be around 160 kts @ 7500 ft with obviously WOT and 2600 rpm, at a fuel flow of about 12 GPH. I never tried that, but it looks pretty ambitious to me. On the other hand, on departure in Zürich, where you get very short enroute segments during the climb to stay below the CAS, I took this pic:

This was at 6500 ft with 2500 RPM and leaned to about peak EGT. That is about the fastest I've seen my C model go. I wonder if 100 RPM more can make such a difference, but I'll eventually try it.

What is quite a bit more interesting to me is max range figures.

I don't like to use the range figures in the POH's as they are most of the time pure marketing. One of the first things I did when I got my POH is to derive Time/Fuel/Distance to climb and descend tables which I later verified in flight. Range in my book is calculated like follows: Final Reserve of 45' at the respective cruise fuel flow is deducted from the total fuel available. On the basis of the available trip fuel, I add up distance for climb + desc, deduct fuel for climb and descend, then divide the rest by the cruise fuel flow and multiply the time resulting with cruise TAS, which results in cruise distance. Using this method, I have calculated most "usual" regimes of 75%, 65% and finally tried to work out a long range cruise which will return a decent TAS vs FF relation without going into the low speed Mooney proposes for the long range flights. That is what I wanted to ask you about:

The POH gives figures for a long range cruise at 1800 RPM. I don' t know if anyone has actually tried that, they reduce fuel flow to about 6 gph and give speeds of about 105 kts TAS at 10k ft. Obviously nobody buys a Mooney to fly that slow.

The maximum range I calculate using this regime is 760 NM at 10'000 ft, using 1800 RPM, 16.6 MP and 6.15 gph fuel flow but with a measly 106 kts TAS.

When I started maximizing the 2300 RPM Tables however, I found that at 10'000 ft with 17" MP, 7.8GPH and 135 kts TAS I can reach a figure of 770 NM, so practically the same range but with much better speed. I did try the power setting and it round about worked out with about 134 kts and 7.7 GPH indicated, but was not really able to fly a longer track on that. Again, on the to do list.

So has anyone ever tried that? 770NM is a pretty nice figure for a 52 USG airplane.

For completenes sake:

At 75% the POH figures calculated the same way above gives me 153 kts @ 10'000 ft, 2300 RPM, 20.25"MP and 10.6 GPH fuel flow for a range of 639 NM.

At 65% at 10k ft and 2300 RPM, the POH would suggest 141kts TAS @ 19.5" MP and 9.2 GPH, for a range of 685 NM

 

What are your experiences?