Hi everyone,
I've been on a bit of a kick lately about proper piston engine care and management. I've been doing a lot of reading especially about in-flight mixture settings, and how they affect CHTs and internal pressures. I broke open the C172 PIM today and read a bit about proper leaning techniques while in cruise. My school has always taught "50 degrees ROP," even during cross country training flights where the students will calculate fuel burn using the tables in section 5 of the PIM. I'll admit that I've taken that a bit for granted and never really looked into it until recently. Now that I have, I've noticed a bit of an inconsistency in what the PIM recommends for leaning the mixture during cruise flight.
The first paragraph that grabs my attention is this:
That was a bit surprising to me, actually. I've been hearing everyone drone on about "50 ROP" for so long, but it seems that Cessna is actually recommending LOP operations for cruise planning when fuel burn is a concern (i.e. cross countries). It seemed at first as though that what I'd learned was inaccurate, until I turned the page.
The next page then says that if operating at or below 75% power, the EGT gauge may be used to lean the mixture instead. It then shows a chart that has two mixture settings: "Recommended Lean," and "Best Economy." "Recommended Lean" is shown on the chart as 50 degrees ROP, and "Best Economy" is shown as Peak EGT. Now, my question is, why would Cessna on the first page publish that LOP is appropriate for cruise when using the Section 5 cruise charts, but then on the next say that ROP is appropriate for cruise with an EGT gauge? My feeling is that the LOP setting is for use with those cruise charts, whereas the ROP setting may be just a "general" setting for when cruising around in general. Would I be correct in that assumption?
This POH isn't written extremely well, and I want to make sure that my students are taught cross country flight planning correctly, so I'm just trying to get to the bottom of this. I personally like the LOP idea, considering it's cooler and uses less fuel, but I want to make sure that they are getting the published fuel burn and performance numbers when in-flight.
I've been on a bit of a kick lately about proper piston engine care and management. I've been doing a lot of reading especially about in-flight mixture settings, and how they affect CHTs and internal pressures. I broke open the C172 PIM today and read a bit about proper leaning techniques while in cruise. My school has always taught "50 degrees ROP," even during cross country training flights where the students will calculate fuel burn using the tables in section 5 of the PIM. I'll admit that I've taken that a bit for granted and never really looked into it until recently. Now that I have, I've noticed a bit of an inconsistency in what the PIM recommends for leaning the mixture during cruise flight.
The first paragraph that grabs my attention is this:
That was a bit surprising to me, actually. I've been hearing everyone drone on about "50 ROP" for so long, but it seems that Cessna is actually recommending LOP operations for cruise planning when fuel burn is a concern (i.e. cross countries). It seemed at first as though that what I'd learned was inaccurate, until I turned the page.
The next page then says that if operating at or below 75% power, the EGT gauge may be used to lean the mixture instead. It then shows a chart that has two mixture settings: "Recommended Lean," and "Best Economy." "Recommended Lean" is shown on the chart as 50 degrees ROP, and "Best Economy" is shown as Peak EGT. Now, my question is, why would Cessna on the first page publish that LOP is appropriate for cruise when using the Section 5 cruise charts, but then on the next say that ROP is appropriate for cruise with an EGT gauge? My feeling is that the LOP setting is for use with those cruise charts, whereas the ROP setting may be just a "general" setting for when cruising around in general. Would I be correct in that assumption?
This POH isn't written extremely well, and I want to make sure that my students are taught cross country flight planning correctly, so I'm just trying to get to the bottom of this. I personally like the LOP idea, considering it's cooler and uses less fuel, but I want to make sure that they are getting the published fuel burn and performance numbers when in-flight.
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