Common cruise settings

[Mooneymite]

20 minutes ago, Andy95W said:

I love the concept, I just thought the published numbers were overly simplified. 

It just isn't that hard to reference the book in cruise.  (Assuming the POH is correct.)

[MIm20c]

46 minutes ago, bluehighwayflyer said:

The more time you spend analyzing the POH performance tables the more discrepancies you will find and the less confidence you will have in them.  MAPA's key number method makes more sense to me, and it is easy to apply once you realize that in our 4 cylinder Mooneys, at least, 1" of manifold pressure or 100 rpm are each worth about 3 1/3 percent power.  LOP operations based on fuel flow are even simpler still. 

I like the key number keep it simple concept. I’m just looking for the number (44, 45, 46, or 47) that I can run with just the first cylinder peaking (all the others will rich of that, in the red zone if the engine is at 75 percent power). I know I can run 24/20 at 7-7.3 gph and 24/22 at 8.7-9 gph and the cylinders are all happy in the 350-370 range. What I don’t know is if the 24/22 is really in the red box based on percent power. 

[Hector]

I know our POH from the late 60’s is far from perfect but 65 to 74 percent difference between the MAPA manual and the POH is a bit much. Which do you trust for the sake of your engine?

 

 

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[Hector]

It just isn't that hard to reference the book in cruise.  (Assuming the POH is correct.)

Agree. I have laminated copies of the performance charts in the cockpit for easy reference. The key number is dead simple and I would prefer to use but I’m not confident they are correct, at least for a C model.


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[Hector]

I like the key number keep it simple concept. I’m just looking for the number (44, 45, 46, or 47) that I can run with just the first cylinder peaking (all the others will rich of that, in the red zone if the engine is at 75 percent power). I know I can run 24/20 at 7-7.3 gph and 24/22 at 8.7-9 gph and the cylinders are all happy in the 350-370 range. What I don’t know is if the 24/22 is really in the red box based on percent power. 

If you run 24/22 you will be in the red zone if you believe your POH and lean as described in your post. You are at 74 % power. My C runs nice and cool at that power setting, in fact other than climbing, my C runs below 370 in just about any power setting and leaning combination. I would like to avoid the red zone, but that requires a decision to follow either the MAPA manual or the POH. One of these two appears to be wrong.


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[jetdriven]

45 minutes ago, Hector said:

 

If you run 24/22 you will be in the red zone if you believe your POH and lean as described in your post. You are at 74 % power. My C runs nice and cool at that power setting, in fact other than climbing, my C runs below 370 in just about any power setting and leaning combination. I would like to avoid the red zone, but that requires a decision to follow either the MAPA manual or the POH. One of these two appears to be wrong.


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24-22 is not in the red zone.  It’s about 60-63% power.  And remember the red zone on a Lycoming is 76% power and up. Lycoming themselves authorize peak EGT at 75% and below. 

[Hector]

24-22 is not in the red zone.  It’s about 60-63% power.  And remember the red zone on a Lycoming is 76% power and up. Lycoming themselves authorize peak EGT at 75% and below. 

 

According to the POH 24/22 is 74% power at 7500 feet. Again, if the MAPA manual is correct the yes it is 65% power and no need to worry about the red box no matter how you lean. If you believe the POH then you may have something to worry about as you will have one cylinder at peak EGT and the rest probably in the red box

 

 

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[MIm20c]

So if the displacement, compression ratio, ignition timing, intake/exhaust efficiency, and cooling designs are all about the same would the red box be any different from engine to engine?  Talking o360 vs io360 here. 

[Hector]

So if the displacement, compression ratio, ignition timing, intake/exhaust efficiency, and cooling designs are all about the same would the red box be any different from engine to engine?  Talking o360 vs io360 here. 

Not sure but the O-360 and IO-360 are not exactly the same. The IO is a higher compression engine so the red box will be slightly different. Probably why the key numbers for he J are a bit different than for the C


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[FloridaMan]

I run 2500 RPM and ROP to around 11 GPH between 6,000 and 8,000ft (the ram air adds about 1GPH and 1-2" MP for a few kts extra; with the LoPresti cowling's ram air closed, I'm just under 10GPH). At higher altitudes above 15,000ft I sometimes run as high as 2700 RPM. The last engine got over 2100 hours (I put the last 900 on it) and 23 years on it before lifters spalled. I don't care about fuel burn unless going slower gets me to my destination sooner by saving me from a time consuming fuel stop. I watch my CHTs and I found it interesting that when I installed the EDM-900 that the ROP setting was the same that I was feeling with the old analog EGT gauge.