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2 Answers

Effect of Temperature on Range

Asked by: 2020 views Aerodynamics

Hello,

A sample best power mixture range graph mentions to add 0.6 NM for each degree Celsius above standard temperature and subtract 1 NM for each degree Celsius
below standard temperature. This is what I do not understand. I was under the impression that with hotter temperatures an engine becomes less efficient and produces less power and hence less range. Or to put it differently, I was under the impression that most aircraft have the best range with higher density altitudes. I know ultimately range depends on L/D max but my question is what is indeed the effect of temperature and altitude on range? Thank you :-)

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2 Answers



  1. John D Collins on Dec 06, 2020

    It all depends on how the chart is constructed. If one assumes the chart is showing a constant power setting, the air will be less dense at higher temperatures and is sort of equivalent to flying at a higher altitude. I don’t have range charts on my Bonanza that include the note you refer to to adjust range for temperature, but I do have constant power performance charts that definitely suggest the range would be enhanced at a higher temperature, assuming I am developing the identical power and consuming the identical fuel flow in gallons per hour. Here is one point at 75% power for 5000 feet pressure altitude, all the fuel flow are stated as 15.2 GPH.

    ISA – 20C, TAS 167 IAS 161
    ISA, TAS 170 IAS 158
    ISA +20C, TAS 175 IAS 156

    Note that the TAS increases with temperature, but the IAS decreases, so you feel worse about the IAS, but get farther and use less fuel at the increased TAS.

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  2. Nima on Dec 06, 2020

    Thank you Mr. Collins for your answer. It now makes sense. I appreciate it. I was referring to figure 11.29 from the PHAK (Pilot’s Handbook of Aeronautical Knowledge) book.

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