Gentlemen -

It's been a busy week and I've slept since then, so I don't remember exactly how the conversation got to that point, but I don't think that's quite what I said.  Perhaps I said it poorly.

The salient point of this subject is that the fuel flow indicated on airframe-mounted instruments is not a parameter to be set.  It is a result.

The absolute physics of the fuel-air-power equation are not in dispute.  In the abstract, a technical discussion centered on the math of fuel/air/humidity/density/RPM/et al can be both educational and entertaining.  But the typical ready-to-fly engine installation is not a laboratory-quality environment and the sharp-pencil, hair-splitting numbers derived on paper and adjusted in the test cell may not apply in the real world.

We set MAP and RPM per the charts to achieve the desired percent power. Then lean to achieve the recommended EGT (typically 75 deg F ROP or 50 deg F LOP).  Finally, observe the RESULTING fuel flow.  And either accept it or start over with a different target for resulting power.

In other words, no matter how many times you have run the experiment in your airplane and no matter how accurate and repeatable you believe your engine monitor to be, DO NOT lean to a target fuel flow.  EGTs are the parameter for leaning. Fuel flow is the result.

Neal George
Continental Motors
Technical Support
Sent from my iPhone

> On Oct 14, 2013, at 7:14 AM, "Walter Atkinson" <walter@advancedpilot.com> wrote:
>
> Jeff:
>
> **Interestingly, the TCM guy said that LOP operations is not correlated to HP, and that the fuel conversion HP/GPH is not a value measure of HP output.  His advice: best to use the graph provided in the manual (which is limited in RPM and not depicting LOP operations with precision).  He was saying that 19 GPH fuel flow at 34"/2500/19GPH is not the same HP engine output as 31.5"/2500/19GPH (still LOP at 19 GPH but closer to peak); this is different from what our friends at GAMI have said.**
>
> His comment is simply not in harmony with the laws of physics with which all scientific sources agree.
>
> He seems to be confused between HP production ROP in which RPM (mass airflow) is associated with HP production and LOP HP production in which only FF is a factor.  If you would be so kind as to provide me with his name in a PM to the email below, I will help Bill Ross (VP at TCM) improve his knowledge on the matter.
>
> Walter Atkinson
> <walter@advancedpilot.com>
> (225) 939-7508
>
>
>
>
>
> On Oct 12, 2013, at 6:00 PM, jeffrey liegner wrote:
>
> LML PIlots,
>
> At LOBO Greenville, I discussed engine management with the team from Continental Motors.  They provided their slides from their presentations (which I have reviewed) and I asked them many questions.  I communicated to Jeff Edwards that the group would definitely benefit from a group open forum discussing engine management settings commonly used, with opportunity for others to listen and others to explain why they do what they do, perhaps moderated by a Continental guy or GAMI people and/or an exemplary Lancair authority.  Old wives tales would be debunked, poor techniques would be scolded, and new settings could be integrated into all phases of flight for each individual.
>
> One thing that was clearly stated by TCM: we should cruise at power setting no more than our Maximum Recommended Cruise.  If you don't have access to the TCM engine manual for turbocharged TSIO550 series engines, here's the link:
>
> http://www.tcmlink.com/pdf2/MaintenanceManuals/OI-18/OI-18.pdf
> CONTINENTAL® AIRCRAFT ENGINE PERMOLD SERIES ENGINE
> ENGINE INSTALLATION AND OPERATION MANUAL
>
> In my TSIO-550E, the maximum recommended cruise is 262 BHP @ 2500 RPM, which is 75% of 350HP.  Elsewhere in the manual, this Rich of Peak (ROP) operation (75%) is listed to be at 29GPH fuel flow (ROP).
>
> Based on prior LML discussions with help from GAMI experts, and engine compression calculations, the Lean of Peak (LOP) fuel flow (GPH) to horsepower (HP) conversion ration for my TSIO550E is 13.73 HP/GPH (for 7.5:1 compression ratio).  So LOP operations at 75% cruise (263HP) would be 19.15 GPH.
>
> I will occassionally cruise at 2500/34.0"/19GPH, when the flight is three hours or less, which some at LOBO felt is TOO MUCH cruise power (not that this is still below 75% power).
>
> I also occassionally cruise at 2500/31.5"/18 GPH, which is an OK setting for speed and economy.
>
> For long flights (and super economy), I will cruise at 2350/31.5"/16.3GPH (64%).  If facing a headwind, I'll give it more gas to 17.1GPH (67%).
>
> I have noticed through a detailed study of indicated airspeed (IAS) at different prop RPM settins (2500-2540-2400-2350-2300) that the Hartzell Simitar 3-Blade prop's highest efficiency seems to be at 2350 RPM.  That is, IAS is best at same LOP fuel flows when the prop is turning 2350 RPM, independent of MAP.
>
> I'm sharing these engine settings in case anyone has comments.
>
> Interestingly, the TCM guy said that LOP operations is not correlated to HP, and that the fuel conversion HP/GPH is not a value measure of HP output.  His advice: best to use the graph provided in the manual (which is limited in RPM and not depicting LOP operations with precision).  He was saying that 19 GPH fuel flow at 34"/2500/19GPH is not the same HP engine output as 31.5"/2500/19GPH (still LOP at 19 GPH but closer to peak); this is different from what our friends at GAMI have said.
>
> Comments welcomed.
>
> Jeff L
>
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