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I am doing an univeristy project to do initial sizing of an electrical vtol drone. Using the aircraft design book from Raymer, I have gotten the battery mass fraction for the cruise, loiter, and climb segment of the mission. However, I can't find a useful value for takeoff and landing battery mass fraction in the book or anywhere else. Is it that climb and takeoff can be count as the same flight segment and the battery mass fraction for landing segment is just a little bit higher than the climb segment?

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I'm a bit late here but... have you seriously calculated the battery mass fraction?

The "weight fractions" method is a quick & dirty method to evaluate how much fuel is burned during each flight phase and get the relevant change in weight. For example Raymer suggests a value of 0.97 for the "warmup and takeoff" phases: that value simply means that, due to the burning of fuel, the weight of the aircraft has diminished of some 3% (i.e. the airplane weights now 97% of its MTOW). And so on for all other phases of the mission.

So, what about a battery driven aircraft? Well, the weight of a battery does not change if the battery is full or depleted and therefore the relevant weight fraction is always 1! An electrical aircraft doesn't change weight due to electricity being consumed!

Hopefully your university project didn't contain this mistake at the end...

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  • $\begingroup$ I read it as the fraction of MTOW that is taken up by the batteries. If you have a range requirement, calculation of the mass fraction can be done. $\endgroup$ Commented Nov 24, 2023 at 8:22
  • $\begingroup$ @PeterKämpf: the op state that they found the mass fraction for "cruise, loiter, and climb segment of the mission" but not the one "for takeoff and landing" so they are clearing doing the wrong thing here... Plus, these latter values are definitely given in Raymer, I've even used one of them in my answer... $\endgroup$
    – sophit
    Commented Nov 24, 2023 at 8:57
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It would seem quite reasonable to assume that for a vtol drone (or any other vtol acft) takeoff can be considered to be insignificantly different from climb segment. Only difference would be the short time the drone would operate in ground effect, this phase would last for no more than 5 second.

The same would apply for descent/landing.

I'm not familiar with the concept of battery mass fraction, but the ground effect would work in favour of the drone, making it consume less battery capacity.

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