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I recently Stumbled on this Why Planes Don't Fly Faster on youtube and it talked about how less speed is more economical for airlines and he also said something that plane above and below speed of sound will face less air drag, in the region of speed of sound maximum air drag will be experienced. I am not quite able to understand what he meant there?

Question In the first part :
1. Why planes fly at M .8?
2. Why there is less drag above and below M 1 ?.

Also in one of the comment someone said

What generates the most thrust in a turbofan is the bypass air and not the turbine. Usually the fan generates around 80% thrust and the turbine generates around 20%. There are some rare cases where the turbine generates more thrust, but in most high bypass turbofans (which are the most we use today) the fan is what generates most of the thrust.

Question Here : Why turbofans generate most of the thrust with the cold flow?

And that the video is mostly incorrect, can someone guide me here, I am sort of confused.

Lastly : Is that youtube video wrong? , I want to know this because I really liked his way of explaining , and I really want video to be right, but I am confused by the some comments, if one could guide me if video is wrong or right, it would highly appreciated?

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  • $\begingroup$ @fooot Sir, I want to confirm about that video, if that would not be the case i would have not asked . $\endgroup$
    – Suraj Jain
    Mar 4, 2017 at 17:24
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    $\begingroup$ @SurajJain I am not sure if I understand your question(s). Could you maybe highlight them in your entry? Are you interested in the factors which have an impact on the economy of an air plane, or are you interested in the thrust-generation in a high-bypass-ratio-jet-engine? $\endgroup$
    – rul30
    Mar 4, 2017 at 17:47
  • $\begingroup$ @rul30 Updated. $\endgroup$
    – Suraj Jain
    Mar 4, 2017 at 18:36
  • $\begingroup$ @RalphJ Sir Could You Help me with that youtube video ? $\endgroup$
    – Suraj Jain
    Mar 4, 2017 at 18:38
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    $\begingroup$ In addition to everything else, there's a point of diminishing returns. Even now, for a lot of short to medium distance flights, actual flying takes less time than getting through security, boarding, taxiing, deplaning, &c. Cut flying time in half, and you spend lots more money on fuel for very little time saved. $\endgroup$
    – jamesqf
    Mar 4, 2017 at 19:40

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