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I found on M20J leaving prop at 2500rpm from takeoff to final while maintaining 140ias with throttle (or keep 23MP), this does it for me and usually lean LOP for CO & fuel bill (or richer depending on CHT), above 8kft I may have to fiddle with prop/mixture to 2650 & ROP but rarely go up there, so flying is far more easier, except takeoff/landing I am just flying a “fixed pitch” (well constant prop speed :D)

Only issue is that throttle (to set % power) does not accelerate you quickly in cruise IAS or cruise climb VSI as quickly advancing prop for the same extra power, it just feels like a dog dragging behind but I am happy to wait for it...

Edited by Ibra
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13 minutes ago, Ibra said:

 except takeoff/landing I am just flying a “fixed pitch” (well constant prop speed :D)

Constant RPM is not fixed pitch, but I guess you know that...

Also, 2500 RPM on _takeoff_ is risky. The engine will not develop full power at that RPM setting. But I guess you know that as well...

Edited by Fry
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10 minutes ago, Ibra said:

I said from takeoff and before landing, these need 2700 :D

Ok, thanks for clarification.

I set full throttle from the beginning of takeoff, reduce just the RPM to 2600 at 500 feet AGL (throttle stays wide open), and continue climbing. When passing 4000ft (I never cruise below that), I do the "big mixture pull" to 10.1 gph (throttle/prop untouched) and continue reducing the mixture according to the "key"->LOP gph relationship at the bottom of my table. When reaching cruise altitude, I accelerate and then close the cowl flaps. Descents are planned well ahead, and usually the throttle stays wide open until preparing for an approach or closing in on the destination airfield. It is just so much fun to see this little airplane do 200 KTAS when descending :-)

My CHT stays below 380°F (Lycoming limit is 500°F, Mike Bush recommends 420°F as a limit). On my last longer flight, the maximum CHT during climb was 360°F briefly. In cruise at 8000ft I had between 270 and 300°F, no more. Okay, that was in winter...

Edited by Fry
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IMO those POH tables just give too much choices, one just has to find an easy way to fly their aircraft within limits without getting to check POH data for every move, in transition lot of instructors put lot of rituals on “over-square/speed/lean” which are more conservative than POH and then there is what seems to works for your cylinders ;)

I used to rent a C182, in POH 22rpm/25mp & ROP, it had the best bang for the buck for long trips (we paid on tach engine revs and they paid for fuel & Mx :lol:)

 

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5 hours ago, Fry said:

Hi there,

The following is my understanding and approach to leaning, and I would be happy to get your comments on that:

I refer to the M20J and the Lycoming IO-360. (The airflow in turbocharged engines is different, therefore the thoughts below do not apply).

Rich of Peak EGT

 

Lean of Peak EGT

Combustion process limited by the air/oxygen flow into the engine.

Combustion process is limited by the fuel flow into the engine.

Air flow is proportional to power.

Fuel flow is proportional to power.

Air flow is approx. proportional to the product of MP times RPM, for a given engine displacement.

For the IO-360, fuel flow (in gph) times 7.5 yields power in % of rated power.

(The lines of constant MP x RPM are almost identical to the lines of constant MP + RPM/100. The latter is easy to compute and is called the "key”.)

(To multiply by 7.5, simply multiply by 5 and add 50% of the result).

A given key is a "code" for power.
57=100%, 54=90%, 50=75%, 47=65%, etc.

With a given fuel flow, a higher "key" from the ROP just means more air and thus a cooler engine. The only way you can do that is by going further LOP.  Is that what you were implying?

Excess fuel does not participate in the chemical reaction and thus cools the engine. Push the mixture in, you get a cooler engine.

Excess air does not participate in the chemical reaction and thus cools the engine. Push the prop and/or throttle in (and readjust the mixture for the same fuel flow), you get a higher “key” and thus a cooler engine.

For the last row:  I think it isn't the actual excess fuel or air that is making the engine run cooler, I think in both cases it makes the mixture burn more slowly which causes peak pressure to occur further after TDC which in turn makes the engine run cooler.  That may or may not be what you were saying.

With that in mind, I fly LOP like this and get a cool and clean, hopefully long-lasting engine:

  •      Below 4000ft with full power (typically in climb), full rich. In the climb, I lean to a target EGT and that usually starts happening within the first 2000' of climb for me.
  •      The following applies only to 4000ft MSL or more, when %BHP is <=75%.
  •      Full throttle, RPM as desired, and use the mixture to control power. Tune it to a fuel flow not higher than that indicated by the table. That is certainly one way to do it.  However, as you go richer or leaner than about 50F LOP (approximate best BSFC), the engine becomes less efficient.  I prefer to keep my engine leaned to something close to that point and use throttle to adjust my power for maximum efficiency.
  •      A quick and easy way is to push the throttle wide open, read off the available MP, choose RPM as desired, compute the "key" RPM/100+MP and then look up the corresponding LOP fuel flow from the table at the very bottom (the two rows in the bubble). It's just important to keep below 10.1 gph as that corresponds to 75% BHP. Above that, go full rich.
  •      I do not check EGT for leaning in cruise anymore, instead simply use the table. And watch my CHT. I usually end up with 300-340°F in cruise, cowl flaps closed.

grafik.thumb.png.e21861a6b1e62edeee056a997b8f1ef1.png

Remarks:

  •         At Peak EGT, the chemical reaction is complete, no excess air or fuel leads to a maximum thermal efficiency.  Being nit picky, in theory that is correct.  However, I believe that in reality, since the mixture is not ideally distributed, at peak EGT we end up with both a little unburned fuel and unburned oxygen.  In my opinion, that's why best BSFC happens at about 50 LOP.  Because at that point you have finally essentially burned all the fuel without slowing the combustion process too much.  And that's also why best power happens at about 50 ROP.  Because at that point you have essentially used up all the oxygen without slowing the combustion process too much.
  •          I do not believe that a faster prop shortens the engine lifetime, at least not for the IO-360, where 2700 continuous RPM is permitted, and because faster means lower forces. Nevertheless, I don't like the noise with 2700 RPMs continuously, so I typically use 2600 in cruise and even lower when flying low.  I too like 2600 RPM because I think my engine is happier there.  That's because it is a "D" engine that is timed to 25 BTDC and keeping the RPM up moves peak pressure further past TDC.
  •          When flying LOP, you should also get less CO (since the combustion tends to be more complete) and thus also lower risk from CO intoxication in the cabin due to a broken heat exchanger or cabin leak.
  •           While I do not use EGT for leaning in cruise, it is critical for something else: the mag check at runup. When switching from both mags to a single mag, EGT must rise on all four cylinders. If it doesn't, check the mag and/or the corresponding spark plug.

Feel free to comment on this approach. I hope I'm not preaching to the choir.

Nice summary.  I put my comments in red above.

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20 hours ago, whiskeyone2 said:

I took a quick look at OpenAsApp. It does not like the format of the spreadsheet. I think that is because I built the front page as a graphical user interface (GUI) already and not just raw data. It would probably work if I stripped the raw formulas out and uploaded that to be converted to an app. 

You are correct, I could only do a tabular format. The app works pretty well though.  Here is an image of my takeoff app.  LeeF00DD6ED-EA30-4405-A1DE-9CC54AE5DF0D.thumb.png.9120024942b37b8fa7333be0e17f85ad.png

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@patrickf

Inviting Patrick to visit this thread...

He showed me his T/O calculator for the O1...

Seeing Lee’s was a great reminder...

Everyone should have a reliable one...

Much better than moving your finger around a chart in the POH.... hoping you got it right...

Hope makes a lousy flight plan.... :)

PP thoughts only, not a CFI...

Best regards,

-a-

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7 hours ago, carusoam said:

@patrickf

Inviting Patrick to visit this thread...

He showed me his T/O calculator for the O1...

Seeing Lee’s was a great reminder...

Everyone should have a reliable one...

Much better than moving your finger around a chart in the POH.... hoping you got it right...

Hope makes a lousy flight plan.... :)

PP thoughts only, not a CFI...

Best regards,

-a-

Yeah (and I love complex spreadsheets), but when I start seeing MP and GPH measured in 10ths, I begin wondering whether we are measuring a football field with a micrometer.

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43 minutes ago, midlifeflyer said:

but when I start seeing MP and GPH measured in 10ths, I begin wondering whether we are measuring a football field with a micrometer.

(Joke) wish NFL footballers made those measurements on their ball, they would have call it soccer :lol:

I agree on the required level of MP/GPH accuracy, main drivers of my MPG while flying 1/ winds and turbulence aloft (not even temperature) and 2/ route and altitude zigzag when hand flying and trying to manage and lean engine accurately fiddling with those 3 knobs like it is my first time every time, complexity/accuracy of procedure is useful to keep busy when the flight is boring but harmful when the flight is overwhelming :D

Edited by Ibra
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Every now and then we get caught with the math challenges of Significant Figures...

My POH uses a single decimal point often... to indicate there is a tenths column.... MP, IAS...

Many of my gauges are digital.... but their presentation is only an analog needle... (go 90’s :))

Stall speed in a 30°bank... 63.5 kias....

 

What instrument in the panel do I use to avoid falling out of the sky that is that accurate?  Or precise?

Twofer...

  • Significant figures...
  • Accuracy vs. Precision...

 

Looking forward to the digital age.... :)

Best regards,

-a-

 

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Here an analog tool that I created with a 3D printer. The middle ring can be turned, inner and outer are fixed. You tune your RPM opposite the current OAT in °C and read off the optimal fuel flow and corresponding power output (in %BHP) opposite the MP. Between 10.1 gph and 13 gph is the transition LOP<->ROP, basically the right side should be (almost) full rich.

Not yet "flight tested", but looking forward to it.

Needless to say, this tool is only correct for the Lycoming IO-360-A3B6D and maybe slight variations of it.

The idea is, on the LEAN side (left of the arrow "FULL RICH"), the gph values are a maximum (to avoid getting near the peak LOP). On the RIGHT side (right of the arrow "FULL RICH"), the gph values are a minimum.

Comments welcome. And a disclaimer: I've just created this, it may still contain errors.

Lean Calculator.jpeg

Edit: if someone wants to make the same tool for himself, here is a printable graphic of the final version I am using.

 

Lean-Rechner.jpg

Edited by Fry
added second graphic
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1 hour ago, Fry said:

Here an analog tool that I created with a 3D printer.

Nice, I think we can create an app with that as well? (like rotating a touch screen E6B wizzwheel app on iPad :D)
 

 

Edited by Ibra
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Very nicely done, whiskeyone2.  Works like a charm.  I used to create Excel sheets and tools like this during flight training.  I remember how much work it is to make those formulas work.  Great job.  Thank you so much for sharing.

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On 5/10/2020 at 2:45 PM, carusoam said:

@patrickf

Inviting Patrick to visit this thread...

He showed me his T/O calculator for the O1...

Seeing Lee’s was a great reminder...

Everyone should have a reliable one...

Much better than moving your finger around a chart in the POH.... hoping you got it right...

Hope makes a lousy flight plan.... :)

PP thoughts only, not a CFI...

Best regards,

-a-

Thanks Anthony,

Still working fine, and I do have working versions for the 310 STC and the J's.

Need to clean them up and issue. Busy at the moment completing an IFR rating - can't get distracted!

@midlifeflyer - couldn't agree more. My sheet uses plenty of significant points to do the calcs but back to one decimal to output - to match the POH numbers.

In practice I know a couple of the numbers and go to adjust to close unless I am in cruise and have plenty of time. I do check landing speed, and takeoff distance if I haven't had that config, or that strip before.

Then again we aren't the guys that carry rulers onto a football pitch ? :)

regards, and stay safe.

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