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Procedure to fly for Endurance

Asked by: 1419 views General Aviation, Private Pilot, Student Pilot

Hi   I am confused on the proper procedure to fly for endurance. Can someone clarify? I was taught the following way: METHOD 1

  1. Start from high RPM and indicated airspeed.
  2. Decrease 100RPM (add in carb heat if necessary).
  3. Re-adjust angle of attack and retrim.
  4. Record indicated airspeed.
  5. Repeat steps 2 to 4 until indicated airspeed no longer drops constantly.
  6. Increase RPM back to right before the increased airspeed drop.
  7. Lean the engine.
My observation:
  1. 90kts @ 2300RPM
  2. 85kts @ 2200RPM (Carb heat in)
  3. 80kts @ 2100RPM
  4. 75kts @ 2000RPM
  5. 70kts @ 1900RPM
  6. 65kts @ 1800RPM
  7. 57kts @ 1700RPM (drop of indicated airspeed is more than before)
I was then told that the airspeed to fly for best power is at 65kts @ 1800RPM (point 6). This is where I should lean out my engine with the mixture control.   However, I have been hearing about another method and it goes like this: METHOD 2
  1. Start from high RPM and indicated airspeed.
  2. Decrease RPM until higher RPM is required to go to a lower indicated airspeed.
  3. When RPM is lowest, that is the airspeed and power for best endurance.
  1. 90kts @ 2500RPM
  2. 86kts @ 2400RPM
  3. 78kts @ 2300RPM
  4. 74kts @ 2200RPM
  5. 70kts @ 2150RPM
  6. 65kts @ 2075RPM
  7. 61kts @ 2250RPM
Note that at point 7 (61kts @ 2250RPM), power needs to be increased in order to go to a lower airspeed. This where I have entered slow flight. So before this would be best endurance which is point 6 (65kts @ 2075 RPM). This is where I should lean out my engine with the mixture control.   It seems to be that the 2nd method makes more sense to me. Can someone verify if 1st method is correct as well?   Thanks, Alan

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2 Answers

  1. Nibake on Nov 24, 2015

    Airspeed for maximum endurance (Vbe) is the point at which airspeed increases or decreases will require additional power and hence more fuel flow. Reference the PHAK 10-10 for more info. Here is a visualization –

    So I would say your second method is an accurate way of determining best endurance speed, although many airplanes already have best endurance speed and endurance charts published in the POH.

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  2. Jim F. on Nov 28, 2015

    I disagree with Nibake, in that the second method is probably not the best endurance; In method 2, you needed a lot more power to achieve 65kts than with method 1. Now, I’m not commenting on which is correct, because I don’t know. However, for the same speed (assuming no other factors change such as flaps or gear) if one uses a lower power setting, and thus less fuel, then that is the defacto the higher endurance power setting.

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