What are your cruise fuel flow settings for your Turbo?
 

Last Sunday was cold and rainy, so I started compiling various engine and airframe performance charts into something useful.

While there are billions and billions of tables, does anyone really fly using them?

I think in reality we

1) set manifold pressure, then
2) RPM, then
3) lean, ...and away we go!

Beyond that is just obsessive diddling with things

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One 'constant' is INDICATED airspeed at SEA LEVEL for a given power setting.

From that INDICATED airspeed one can then use math to determine TRUE airspeed, adjust for pressure altitude, temperature etc. But we can only adjust power for a shown IAS.

The TCM engine manual has tables for rich to lean, for example.

The table below shows the limits from the TCM engine manual for my TSIO 360ABs

QUESTION #1: With GAMI do you lean BELOW the 'lean' values in the TCM manual? or...

QUESTION #2: With GAMI do you just run smoothly at the SAME TCM lean settings?



Below is the user table I derived from the various tables and manuals.

Next time I have time to spare I will flight check reality vs tables.

The efficiency values to right are MPG and speed, vs baseline of 75% at ROP.

For example, running the engine 75% power LOP would get you 20% better MPG than ROP with no loss in speed. Running 65% power LOP is 24% better MPG, with a loss in speed of 7%, etc.

Comments? Comparisons?

SET IAS @ altitude GAL/HR KNOTS/GAL LOP LOP
MP RPM PWR MPH KTS 5k 10k 15k ROP MID LOP ROP GPH LOP +EFF -SPD
32 28 100% 178 155 - - - 42 40 ---
28 25 75% 173 150 160 169 177 28 24 23 5.4 6.3 6.5 20% ---
24 70% 169 147 156 165 175 26 23 22 5.7 6.4 6.7 24% 2%
26 26 70% 169 147 156 165 175 26 23 22 5.7 6.4 6.7 24% 2%
24 65% 161 140 150 159 169 24 23 21 5.8 6.1 6.7 24% 7%
22 55% 151 131 143 152 162 21 19 18 6.2 6.9 7.3 35% 13%
24 22 50% 143 124 135 144 155 18 17 16 6.9 7.3 7.8 44% 17%

I've never given it the level of thought shown in your post, but I flight plan 26 gph total in my P337H. That's at 75% where I usually get pretty close to the book cruise numbers. Close enough anyway.

I do not have GAMIs.

I fly pretty much the way you described: I set FF via the JPI to about 13 GPH each initially, then "diddle" with it as the flight progresses. The JPI has a "Lean Find" feature that I find very un-intuitive, so I hardly ever use it. I will lean back as I get to altitude if I can keep my CHTs under about 380 and turbine inlet temps under 1500.

I just had the baffling repaired on the rear engine and haven't yet made any flights of consequence, but before I had to give the rear a bit more fuel in order to maintain the same CHTs. I would often fly with FF of 12.5 up front and 13.5 for the rear. We will have to see if the baffling fixes change that.

Tangentially related, anyone else try seeing what the minimum possible fuel flow while staying aloft is for your plane? I needed to build a bunch of hours for insurance reasons while not going anywhere in particular very quickly, so I spent some time playing with this and got it down to about 12.5 GPH total (10500', 6.5 GPH front, 6 GPH rear at about 21" and 2250 RPMs). Couldn't get it much leaner without intermittent missing. 1975 P337G, no GAMI injectors on here. Photos attached showing EDM-960 display and airspeed.

Single engine with the front prop feathered at 10500' (while loitering over a rural airport with a 5000' runway) actually took more GPH to maintain altitude than with both engines running.

-Ryan

That's good info on the min fuel flow. I see you were doing C172 type speeds but with an extra 50% fuel flow (vs the 8 gph of the 172).

I have the EDM 760 FF gauge installed. My understand is the 960 is a plug-and-play replacement for the 760 (won't fit in the same mounting spot though!) I think with trade-in, the upgrade only costs about $1500! I would have already done it, but it would require almost a complete redesign of my panel, so I've held off. Would LOVE to have one though!

I bet you could cut it down even more by caging the front engine. I hear that the Skymaster is the only airplane that EXTENDS its range when operating on only one engine! :p

Found the photos from my single engine minimum fuel flow test. Photos attached, looks like I ended up at 14.7 GPH on the rear engine to just barely maintain altitude close to Vx.

I'll try it again during the winter months sometime soon and see if I can get it down any further with cooler air available. And maybe see if I can maintain altitude at Vy for a little less drag.

Thanks for the pics Ryann! I always say, if there's no pics then it didn't happen! :D

Low observable loiter
 

Once upon a time, I heard that a three letter agency has a 337 that provides top cover comms coordination, during certain circumstances, that powers waaay back, with low RPM, and goes for hours and hours and hour