-C and -G Model Power Settings

[3914N]

I just purchased a G model (for those unfamiliar, the medium-length fuselage with the C-model's O-360 180HP carb'd engine).

My issue is with the correct power settings to use.  I came across this article by Bob Kromer that makes a pretty compelling case for cruising at full-throttle, 2500rpm, 50 degrees ROP all the time above 3,000 feet.  Seems like decent advise.  I flew a M20F before I bought the G model and it seemed to work well.

My issue is that I'm pretty unhappy with the CHT's these settings give me in my G.  I don't have any of the cowling mods (nor does the G model have cowl flaps) so the engine definitely runs pretty hot.  My normal procedure has been to lean to 400 degrees CHT, which is usually richer than 50 degrees ROP.  As a result, my fuel burn is not exactly wonderful.

Recently I've been trying my cruise at 2,400 RPM instead of 2,500.  My temperatures are WAY better, it allows me to lean out quite a bit more, and I've noticed the fuel savings.  I think it's costing me a knot or two, but I feel a lot more comfortable with it.

I do not have a fuel totalizer nor digital engine monitor (just the factory analog single-probe EGT/CHT gauge), so I can't really run a detailed comparison.  Has anyone had similar experience, and what do you think of the lower RPM in cruise?

[gsxrpilot]

I fly a C (same engine) and have to keep the prop under 2500 to keep the temps under control.  I generally run full throttle, 2450 to 2480 RPM, lean as much as I can get away with.

[BigTex]

I personally cruise at 2400 and WOT when at altitude.  Seems to work well for me.  I also had my prop dynamically balanced at 2400 and it seems to make a much smoother running engine.

[DXB]

+1 for 2400-2450 rpm at altitude.  I tried to follow that article's recommendations too- I didn't like the greater noise and vibration at 2500rpm, and I can lean much more at 2400 while keeping CHTs in line.   I hate my CHT issues in climb, but at 24 squared, in cruise at 7500 MSL, I can lean to 25-50 ROP and still limit my leanest cylinder CHT to the 380s, while consistently seeing 150-155kt TAS at 10.5-11gph.  Not exactly an objective criterion, but this is just where my plane seems "happiest" to me.

[Hank]

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.

[Raptor05121]

I havent studied the cruise charts enough, but what difference from these settings are the charts? I printed out the Mooney 2500/5000/7500/10,000/12,500 charts and have them in a sheet protector next to my custom checklist.

[Seanhoya]

Hey - I fly a 1968 Mooney M20G, and I fly most of the time at altitude at 22" and 2400 RPM.  When I want to go fast, I fly at 24" and 2400 RPM.  Rarely, I fly at 25" and 2500 RPM (I reserve this for sustained climbs).  At 22" and 2400 RPM, I lean to roughness, then back off the fuel mixture just a bit.  At 24" and 2400 RPM, depending on altitude, I might lean just a bit.  I know that the manuals say I can use all the way up to 2500 or 2600 RPM sustained (depending on the manual), but I simply don't - it's a bit loud, and I don't see much improvement in airspeed for the increase in burn.  

A bit about cooling and the G model - I run a bit hot in the summer months in the climb (sometimes running ~420 until I level off).  Most of the time, this is after an extended taxi.  I have never had problems in cruise (Usually no hotter than 350-380 on hottest cylinder), but i never push the prop or engine like you are talking about.  

Look - the G is a great airplane, but it is a little underpowered in the climb and in my experience, is prone to cooling issues.  I run between 700 and 1200 fpm in the climb generally, but on a really hot day, it can be pretty bad (like being in a sustained descent at altitude despite having full throttle due to downdrafts).  I rarely fly at gross weight, and can count on one hand the number of time I have had more than 2 people in the plane.  As a 2-person cruiser, though, it is great!  Finally, fuel = cooling.  So if you are hot, enrichening the mixture a bit should help.  And at the power settings you are talking about, you can't lean much (if at all).  In terms of cooling issues with the G model, I have replaced the oil cooler, did the Lake Aero cowling mod, and rechecked my doghouse multiple times, and the cooling still is not great.  

My experience is that you will burn about 9-10 GPH and you should see around 130-135 KIAS in a G.

Clear skies!
Sean

[Sabremech]

Although I just met Bob Kromer at the last Mooney Summit, I have been flying my C at WOT and 2500 continuously for the 5 years that I've had it. I've never had any issues with CHT's except for a little warm on climb and they settle down nicely at cruise. I installed an Insight Avionics G1 engine monitor 2 years ago and I'm more comfortable knowing what temps are versus the single old factory gauge. I don't pay much attention to how much fuel I burn per hour. I want to fly and get to my destination. 

David

 

[Hector]

67C with same engine as yours. My cruise setting is usually 22 and 2400. This would typically be between 8k and 9K WOT and then back off Just enough to move the MP gage. It runs very smooth there but actually it runs just as smooth at 2500. 2400 is just less noise and better fuel efficiency. I have a JPI and lean to peak or 20 degrees ROP. A 65 percent power that is ok and my CHTs are 330-360 range. I will add this, I read some folks here had switched to Tempest UREM37BY plugs and had noticed lower CHTs. After one of my Champion plugs failed (very easy to identify with a JPI) I swapped all the plugs with the Tempest UREM37BY and immediately noticed lower CHTs. Frankly, I swapped them mainly because I wanted to go with Tempest (most of the Champion plugs in my engine measured extremely high resistance) and really did not expect temps to change. I was very pleasantly surprised. In the summer months here in Florida it was very hard to climb and keep temps below 400 even at 120 mph. It was not unusual to see 420 or so. Now I have no problems climbing at 120 mph and 380 CHT.

The G does not have cowl flaps? Did not know that. One thing I learned during the Mooney summit is that the C with the original guppy mouth will actually cruise a bit faster with the cowl flaps open a couple of inches.

[bonal]

2500 seems where mine is running in its sweet spot. I can't remember if I have ever been able to get 24 inches at 7500 feet as for power once it's in cruise and all nicely trimmed I pull just enough throttle to make the MP needle move then once CHT gets down close up the cowl flaps. As much as I like to think of a C doing 150 to 155 knots true I'm not so sure those are achievable speeds but then every one of these old birds is different. Any thing above 6000 you can run WOT without being able to make enough power to hurt anything at least that's what I've been taught.

[DXB]

2 hours ago, bonal said:

As much as I like to think of a C doing 150 to 155 knots true I'm not so sure those are achievable speeds but then every one of these old birds is different. 

I'll have to see if these numbers hold up- probably stated with far too much confidence by me above.  This is from a single trip at 7500ft, WOT, 2450rpm, with my newly installed Aspen PFD calculating the TAS figures.   They were corroborated somewhat by some very high ground speeds arising from a 20kt or so tailwind that day:  http://flightaware.com/live/flight/N2971L/history/20151031/1802Z   Only thing I have that might be considered a significant speed mod is the Top Prop.  Still, a little incredulity is in order, as you suggest .   I was so surprised that I had the pfd installer recheck both ASIs for consistency, and they were pretty close.   

[bonal]

If those hold up you got one fast C I don't know how those GPS devises calculate TAS I had to do a 3 and 4 heading test and they were within 1 knot at 149 at 8000 feet two on board WOT 2500 but I can't recal my MP.  The best ground speed I ever noted was 210mph

[Sabremech]

I was at 148 TAS on my 66 C before my cowling mod. I'm making some induction changes and tightening up my baffle seals then I'm back to testing some more. I'll be doing a performance flight to determine speed improvements in the near future. Maybe I'll break into the 150's. 

David

[jetdriven]

How do you measure tas david

[kpaul]

42 minutes ago, jetdriven said:

How do you measure tas david

Here is a calculator that you can run to convert IAS into TAS http://indoavis.co.id/main/tas.html I cannot confirm its accuracy though.

Or if you are still old school and use an E6B:

1. Set the pressure altitude in the window opposite the outside air temperature in Celsius.

2. Without moving the computer’s scales, read the true airspeed on the outer scale opposite CAS on the middle scale.

[ryoder]

I fly at 2300 and 19 inches and burn 6 GPH at about 130mph indicated.

[jetdriven]

Just now, kpaul said:

Here is a calculator that you can run to convert IAS into TAS http://indoavis.co.id/main/tas.html I cannot confirm its accuracy though.

Or if you are still old school and use an E6B:

1. Set the pressure altitude in the window opposite the outside air temperature in Celsius.

2. Without moving the computer’s scales, read the true airspeed on the outer scale opposite CAS on the middle scale.

but how do you know the ASI is reading right, or that your CAS is showing what its supposed to be? Or that you lined up the C and the PA exactly opposite each the other in the airspeed indicator. Or correct for nonstandard air temperature. For example, the book shows CAS about 2 knots less than IAS in cruise.

[carusoam]

Summary of some ideas that I captured in this thread...

1) Bob K wrote performance articles for many of the Mooneys around Y2k.  Inspiring enough to me to buy an M20C.

2) It is a good idea to have an engine monitor for all four CHTs and EGTs.

3) All C pilots deserve a carb temperature sensor as well.  This helps to maintain power without full carb heat, still avoiding carb ice.

4) Fuel flow is an incredibly important piece of data to have.

5) The O360 uses a second fuel nozzle in the carb that is open at full throttle.  It stays open at slightly less than FT.  The FF gauge should be sensitive enough to show the second nozzle being on.

6) Old Champion plugs can have issues with high internal resistance.  Fine wires are nice to help keep plugs from fouling. They are made by the not-champion company.

7) Lean a lot on the ground.  This will keep large lead balls from forming in the lower spark plugs.

8) Cowl closures have been very helpful at improving airflow in and around the old C and G cowls.

9) A new cowl is being developed by Sabremech and company.  Better than the previous cowl closures.

10) Electronics used to be so expensive that even simple data collectors were unheard of in M20Cs and Gs.  Now they are in every plane.  The used market makes it possible for the youngest Mooney driver to be able to afford some really good stuff. Some Cs and Gs are loved enough to be forever planes.  They get Aspens, or have really nice paint, and sleep indoors.

11) There are a couple of methods people use to maintain a safe (out of red box) power setting.  Hank mentioned the MAPA method of MP + RPM/100 = 46.  Bonal mentioned using 6k' and above to achieve the same effect.

12) Taget EGT, FT climbs are often part of this discussion.

13) Somebody must have mentioned climbing out at 120mph IAS for best climb with good CHT control.

14) I am looking forward to the day when David is able to publish some data.  I bet Mr. Kromer will be impressed by the results.  David has published some pictures in this site if you want to see what a modern C is going to look like.  

15) Include as much technical detail with your data as you have. Specially when speaking of Mooney performance improvements.  TAS, density altitude, OAT are always going to be important. Pictures are always appreciated...

Welcome aboard 3914N, welcome back to Mooney ownership.

Welcome aboard KPaul.

Best regards,

-a-

[kpaul]

9 minutes ago, jetdriven said:

but how do you know the ASI is reading right, or that your CAS is showing what its supposed to be? Or that you lined up the C and the PA exactly opposite each the other in the airspeed indicator. Or correct for nonstandard air temperature. For example, the book shows CAS about 2 knots less than IAS in cruise.

Since CAS is  IAS corrected for instrument and position error, you have to know what the error is (i.e. flight manual).  Although, depending on the system, EFIS, IAS=CAS since the computer applies the corrections before the IAS is displayed.

As for PA while crushing at any altitude, change you altimeter to 29.92, the new reading is your pressure altitude.  All of this assumes your instrumentation is calibrated correctly.

[goterminal120]

18 hours ago, Sabremech said:

I don't pay much attention to how much fuel I burn per hour. I want to fly and get to my destination.

David

 

+1

[steingar]

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.

[Hank]

23/23 is more power down low than 21/2300 is up high. My target is 70% or less by the Owners Manual. Or I cheat and use the MAPA formula of MP + RPM <= 47. But since I don't cruise faster than 2500, often I'm at 45 or 46.

[jetdriven]

8 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.

What is your definition of a high power setting 

[Shadrach]

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.

A propulsion engineer would be a better source of advice. I know 2, they both fly RVs and run them WOTLOP unless they are in climb or approach to landing. Both aircraft are equiped with parallel valve IO360s.

[jetdriven]

22 hours ago, kpaul said:

Since CAS is  IAS corrected for instrument and position error, you have to know what the error is (i.e. flight manual).  Although, depending on the system, EFIS, IAS=CAS since the computer applies the corrections before the IAS is displayed.

As for PA while crushing at any altitude, change you altimeter to 29.92, the new reading is your pressure altitude.  All of this assumes your instrumentation is calibrated correctly.

How do you know the IAS is, corrected for position and instrument error, displaying the exact CAS?  Since we're measuring to a knot or two accuracy, how can you say that 140 KIAS is really 135 KCAS at 1000' ? I don't think IAS is all that close for measuring TAS   A 4-heading GS divided by 4 is close,  but still wrong.  The 3-track NtPS spreadsheet seems accurate to about a knot.