Mavic Battery and Speed efficiency chart

[bjohnson]

Yesterday I flew 2 10000 feet flights the first full speed in p mode the second at full speed in sports mode in the sports mode flight I came home with 25 percent battery in p mode 38 percent. I got several high wind velocity warnings. I think the sweet speed for distance in about 20 mph.

Correction p mode full throttle 28 mph ish give me best distance

 

[mavicpro1000]

So what is the max extra weight it can carry without hitting duration too hard!

 

[vashon100]

Th

Correction p mode full throttle 28 mph ish give me best distance

FYI, Posts can be edited and deleted, rather than just adding another.

 

[Andrew F]

Guys, this is all pretty vanilla aerodynamics. The same physics principles apply as for any aircraft: Thrust balances drag => constant speed, lift balances weight=> constant altitude.

In the case of a quad, energy is being used directly for both lift and forward thrust as the single thrust vector from each prop.

The reason there is an optimal speed for distance efficiency is for two reasons:

1) Energy is being used to simply maintain altitude. Because of this, at very low speeds energy consumption is distance inefficient -- most of the energy is being consumed hovering. Obviously the degenerate case -- simply hovering without moving for the entire battery -- is most inefficient in terms of distance traveled per unit Ah consumed... ZERO. So obviously efficiency increases as you go faster -- you'll end up with a higher efficiency figure for ft/Ah running an entire battery moving along at 0.025mph; even better at 1mph; 2mph; and on and on. All of these runs would take about the same time, because the energy going into horizontal translation is trivial -- all of it's essentially going into hovering.

If you gather a ton of experimental data doing careful runs incrementing 1mph each time, you'd find that at first the increase in efficiency vs. speed would be linear, up to the point thrust going to forward motion was below 3 or 4 percent. At that point, more and more thrust is going to forward motion in addition to what's being consumed hovering, so the curve starts to bend toward flattening as speed increases.

2) Air resistance (drag) increases as the square of speed. Because of this, the curve starts to bend downward, with efficiency actually decreasing with higher speed. This is because to go twice as fast requires 4x the forward thrust to overcome the increased by squared drag. Obviously, at very low speed changes (1 mph to 2mph) the double of drag (from 0.1oz to 0.2oz) is completely inconsequential compared to the total forces the aircraft is countering with thrust -- basically the weight of the aircraft.

Now, lets go 15mph. Drag is 2lbs. double to 30mph, now drag is 4lbs. A lot more power (energy/time) is needed to push against this drag.

The knee of the curve -- the point of peak efficiency -- will not be at the aircraft's maximum speed, because aircraft always have much more power than just that necessary to fly at peak efficiency -- it's a necessary safety margin.

Did you look at my real test data? Did you note the hypothesis - similar to your analysis, was proven wrong.

 

[TTFullTimer]

Lift thrust etc are all part of the equation. A large part is the efficiency of the whole drive train from the peukert curve for the battery, the ESC efficiency, motor efficiency, wire losses, and prop efficiency. Any and all of those can change with varying speed of the bird. My humble opinion on the OPs results and this is just a guess is that the props are more efficient at higher rpms. Battery will be less efficient at higher current draws, ESC is a crap shoot to guess at as we have little knowledge of the electronics functions, motor could have a better efficiency at higher speeds, and cooling of the whole mess may be better at higher speeds yielding less losses from resistance. Some of the other postulations about lift and thrust have validity as well. Just an efficiency of the props sort of thing.

Me I just fly and enjoy. Never been in sport mode my main usage is for pictures and videos of the places around me as I move from place to place in my full time travels.

 

[OzoneVibe]

Just bumped into this thread ...
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I have to question the "This was tested on a 1,500 foot route out and back (for a total of 3,000 feet) to offset any wind effects at 4 MPH increments on both a calm day and a windy day."

Perhaps I'm missing something, but I can't see how the slowest flying speed of 4mph was tested on a "windy" day.
Surely it would never have got out, or back, or whichever it was that wasn't downwind.
​

 

[Andrew F]

Just bumped into this thread ...
​

I have to question the "This was tested on a 1,500 foot route out and back (for a total of 3,000 feet) to offset any wind effects at 4 MPH increments on both a calm day and a windy day."

Perhaps I'm missing something, but I can't see how the slowest flying speed of 4mph was tested on a "windy" day.
Surely it would never have got out, or back, or whichever it was that wasn't downwind.
​

It wasn't particularly windy but if we only tested "with the wind" for one speed and "against the wind" for the next speed we would have gotten false results. Going out and back and calling that "one circuit" neutralized the wind effect (small though it was.) And even in a strong wind, you can still fly at 4 MPH with or against the wind. The Mavic would just be fighting it and using more energy to even stay still.

 

[OzoneVibe]

It wasn't particularly windy but if we only tested "with the wind" for one speed and "against the wind" for the next speed we would have gotten false results. Going out and back and calling that "one circuit" neutralized the wind effect (small though it was.) And even in a strong wind, you can still fly at 4 MPH with or against the wind. The Mavic would just be fighting it and using more energy to even stay still.

Ah. Ok. GROUND SPEED ... then that makes a lot of difference.
It also makes interpretation far less easy.
In plane flying terms, one would never quote any performance figures in terms of ground speed.
Thanks for clarifying.

 

[byedaway]

Thanks for this experiment. However it doesn't seem to quite square with this guy's results: Experiment: Battery Drain in Flight