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Least amount of trip fuel req

• Posts: 86

MissSoph created the topic: Least amount of trip fuel req

Hey everyone... just a question about review question set 1....question 4 talks about the min trip fuel required for the 500nm...
so p104 states that for the echo it will be either 45 or 55 per cent power except in the most unusual of circumstances....
So just wondering why? Is it just a casa thing with this infamous echo plane... and is it true in real life.... would using 35% power be Ridiculous... it would always be higher...
Oh... and how’s this storm... I’m on nth side of brissie... it’s a ripper... but kinda cool....

• Posts: 2164

bobtait replied the topic: Least amount of trip fuel req

Minimum trip fuel is achieved by flying at the power setting that gives the best ground nautical miles per gallon. If you divide the ground speed by the fuel flow you will get the ground nautical miles per gallon for each power setting listed in the TAS table.

If you try that for each power setting in the cruise TAS tables and introduce various headwind or tailwind components, you will find that, with a strong headwind the best ground nautical miles per gallon occurs at a higher power setting, while a strong tailwind requires a lower power setting.

To make 65%mcp the best miles per gallon, you would need to introduce a headwind of over 80kt, and to make 35% the best miles per gallon you would need a similar tailwind.

So, to get the power setting for best specific ground range for the ECHO, under anything but exceptional circumstances, you would need to check 55% and 45% only . Note that the examiner often gives you the power setting to use for a given trip, so in that case, you would use the power setting given in the question of course.