[Bob Cook]

Originally posted by Walter Atkinson
First, it is important to understand that when ROP, the only variables in HP output are those which control mass air flow.
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Walter ..... just a minute here. I DISAGREE! HP (and airspeed) can change with fuel flow ROP.

Since there is no vaccuum advance or change of timing as in an automobile engine (it's fixed), then detonation is controlled by fuel flow (fuel cooling and super rich). On take-off we are wasting fuel and of course, highest possible chance of pre-ignition of extra fuel was not thrown into the cylinder. Therefore the engine has been set up rich to avoid detonation and burning of valves. This hold true as you back off power with full mixture -- it's rich!

Now we are dealing with controlling the fuel for optimum;
1) Climb power,
2) cruise- best power,
3) cruise best economy (depends on %hp) and then
4) best Economy (<65% power (more or less).

Then there is max range or endurance. All based on fuel flow assuming mass airflow remains relatively the same. since we cannot play with Air other than increasing throttle (air controller). Now we are down to two variables,
1) fuel and
2) AIR!.

Based on playing with these two variables you can blow your engine up in seconds.... right?

Bring in the turbo ---- more air.
bring in the intercooler ----- more cooler air.
(UNCHARTED TERRITORY)

Using the TCM manuals and charts for the TSIO360 or any flat head air cooled engine you have charts that define HP based on fuel flow. We know there are barometric and temp influences that need to be thrown into the equation to absolutely determine power at given altitude and/or density altitude.

When reducing fuel flow from full mixture we increase temps, increase efficiency (less fuel burn) and increase potential for detonation or burning of the valves DEPENDING ON % HP.

One other thing, at some point we do get to a point where the fuel goes down, temps go down, and power goes down. What is this; it's PEAK.
***You can add air but you cannot add power without adding fuel***

Things run better as the peak compression occurs later as the fuel flow is retarted (cyl is further away from TDC when peak compression occurs). After peak it definately is retarted. Your TIT peaks differently based on how much unburned fuel gets burned in the exhaust..... none when you are at peak or LOP.

So what I have learned and varified over the years is that running 60-100 ROP is best HP (with some fuel wastage). 50 LOP is getting close to dangerous depending on hp. And it is safe to run peak or even 50 ROP at <65% or thereabouts. The questionable territory is between peak and 50 ROP... right?

Between 100/60 rop and peak you see very little difference in cruising speed; but there is a very SLIGHT difference. There is about a 10% reduction in fuel flow. Once you are over the hill (peak) then speed drops, fuel flow drops, temp drops and it takes longer to get where you are going.
**You sacrifice speed for range**

Cessna and TCM say 10% increase in range between 60 ROP and Peak. They both say Peak is best range. They also say best power is 1 gph (6 pph) above 60 ROP. I concur unless you go LOP and sacrifice another couple of knots for engine longevity and fuel saving. You can also save fuel by flying slower. BTW in a skymaster this can add up to 17 hrs duration. Try that in your 3 wheeled Baron <G>,

**LOP or just running lean where possible is great assistance in keeping the engine CLEAN. **

So whats the point ?

1)I agree with what you say, however, running LOP does sacrifice speed for performance.

2) Peak is best economy without sacrificing speed (or little) at <65% hp.

3) Decision to run below 60 ROP is strickly based on temps, hp settings, and level of comfort (pucker factor)... but only at cruise!

4) Adjustments must be made to the mp to correlate with the POH and TCM curves and only at PEAK can you determine your hp at that point in time (has nothing really to do with density altitude). At this point fuel flow/hp can be gleened from the tcm chart or the numbers I transposed in an earlier conversation. At this point power is LINEAR below 65% or below possible occurance of detonation.

It is not an issue if Cessna or TCM endorses or does not endorse LOP or Peak operations. If you have proper engine monitoring you can more accurately determine hp and avoid the bid "D" work (detonation). Burning valves is strickly a high hp issue and rarely occurs at sensible cruise if at all.

It would be nice each cylinder is optimized using GAMI injectors, or better yet FADEC control just like the automobile mfgrs. Better yet it would be nice if TCM had better tolerances in the engine and fuel setup.

I understand that Compression (better yet cylinder pressures) changes with fuel flow settings or rop/lop settings. The leaner you go the more you retard the compression stroke or flatten it out past TDC.. BUT our issue was HP and how do you quickly set it for what you are trying to accomplish?

Sunday afternoon sight seeing trip or I must be in NYC by 10?

Therein lies the difference and more so the operational differences in how you treat the engine.

From Fuel flow at peak you can figure out power quickly and accurately knowing the fuel flow. Thats all... So with intercoolers and no "published" curves how do you set you engine for the correct HP? Answer: by doing the peak fuel flow measurement and correlating. If you have a more accurate method sure would like to hear about it. This is not a LOP discussion, it is a hp discussion.... WITH INTERCOOLERS.

And one last issue, what happens when you blow a TURBO? How do you relight a turbo engine? How do you set power after a turbo fails? Can you fly with a blown turbo or do you need to shut the engine down? How do you adjust proper hp / say at +50 ISA and -50 ISA with or without intercoolers?


sorry to ramble but I wanted to work thru it in my own mind and insure we are on the same wavelength. Partially this is a benefit (hopefully) for those owners who's wives, girffriends or companions will not allow them to attend OSHkosh.... Oh my gosh!
sorry fella's but it's true. Yea, gotta work?.... yea,,, gotta find and excuse ? right! It's all right, we all understand, and we will have one minute of silence as we sit around under the stars with a sud's in hand, and talking afterwards about what you are missing........

I have NEVER heard a proper technical explanation in setting power with aftermarket intercoolers other than dragging back the mp a "notch or two". Well; I prefer to try and do it the correct way to save a rediculously expensive engine and make sure it reaches TBO +500. Without FADEC you are on your own!

bob