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Today during the ground portion with my instructor he asked me "why did you choose to cruise at 2300 rpm flying at 1990 ft pressure altitude?" I didn't have an answer for him, and I couldn't find anything in the POH or online that could answer that question.

All I was able to find and surmise is "cruising should be done between 55% and 75% power, it is up to the pilot's discretion to choose the power setting in this range for the planned route"

So now I'm stuck with this in my head:" As long as my power setting allows me enough range and endurance to reach my destination with reserves in mind and that my cruising speed is not ridiculously slow any power setting between 55% and 75% should do"

However, previously another instructor told me for a C172 a power setting between 62% and 65% is the best balance between performance and engine care.

what is the right way of going about this?

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    $\begingroup$ Seems like an opinion-based question, but if you are looking for maximum endurance choose a power setting that will provide that (see the POH). If you're looking for the best speed power setting choose that. As long as you're referencing power settings identified in the POH you should choose what works best for your circumstances. Also, I am wondering about the 1990 altitude as well. Just my opinion. – $\endgroup$
    – user22445
    Commented Jun 25, 2022 at 2:30
  • $\begingroup$ Look at gallons per hour vs speed and altitude in the POH. Then decide if range, terrain, time, weather, or local rules affect the planned route. $\endgroup$
    – Robert DiGiovanni
    Commented Jun 25, 2022 at 9:59
  • $\begingroup$ I think there may be a typo or grammatical error here. Was this really the word you wanted to use? en.wikipedia.org/wiki/Digression . Feel free to roll back my edit if your word choice correctly reflects your original source-- but consider providing a citation-- $\endgroup$
    – quiet flyer
    Commented Jun 26, 2022 at 18:27

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While the choice of altitude and power is indeed at your discretion, you should be able to explain why you made the choice you did.

Best Speed

Assuming range isn’t a problem, you typically want to get to your destination as quickly as possible, especially when you’re paying a wet rental rate.

Look in the cruise performance table to find the best TAS for each potential altitude, and then factor in the head/tail wind for each altitude according to the winds aloft forecast. The altitude and power setting with the best ground speed wins!

(Technically, you also need to factor in the extra time it’ll take to climb to a higher altitude, but it’ll only be a few minutes, so you can skip that for now.)

Best Range

Flying faster burns fuel faster. If you’re going a really long distance, it may burn so much fuel that you won’t make it! Maybe you’re better off flying slower to get more range. Or maybe you’re renting dry and just want to save fuel. Or you’re the person paying the maintenance bill.

Do a similar calculation to the above, but instead of maximizing ground speed, you’re minimizing fuel per mile. Or at least getting it low enough that you can make it to your destination (plus reserves).

Note that even if you can stretch the plane to fly five-plus hours per leg, do consider whether you can handle being cooped up for that long without a break. You may prefer to fly faster with fuel stops that will double as an opportunity to get out and stretch—and use a toilet.

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  • $\begingroup$ Or a smart compromise between the two. $\endgroup$
    – Jim
    Commented Jun 25, 2022 at 5:35
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    $\begingroup$ Bottom line: if it's a wet rental and you just want to get from A to B on as little hobbs time as possible, wind it up to max cruise. If it's your airplane and you're paying for the gas, fly at best MPG if you're not in a hurry. I cruise my own plane at about 50% most of the time. $\endgroup$
    – John K
    Commented Jun 25, 2022 at 14:41
  • $\begingroup$ Re "Look in the cruise performance table to find the best TAS for each potential altitude, and then factor in the head/tail wind for each altitude according to the winds aloft forecast. The altitude and power setting with the best ground speed wins!" -- so this would always be redline RPM, or full throttle, whichever comes first, right? If not, can you expand your answer to say why not? $\endgroup$
    – quiet flyer
    Commented Jun 26, 2022 at 18:45
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    $\begingroup$ @JohnK -- if you are really not in a hurry, why not fly at best gallons per hour? After all, the real point of most of the flying that many of us do, is simply to spend time in the air, right? $\endgroup$
    – quiet flyer
    Commented Jun 26, 2022 at 18:47
  • $\begingroup$ @quietflyer Lower altitudes usually aren’t WOT at cruise power. $\endgroup$
    – StephenS
    Commented Jun 26, 2022 at 18:54

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