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Probable reason for 500m altitude limit

Xtreme Drone Pilot

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At 6m/s descent rate Mavic consumes about 4-5% of battery from 500m to 0 (test done at 4500ft AMSL). I didn't test at the default 3m/s (too lazy), but since it would take 2x the time, and the props spin at almost the same RPM (after all, if descending at constant speed, lift equals to weight regardless of speed; there are small differences in efficiency due to downwash and body drag), it's not unreasonable to expect it would take ~8-10% of battery. So if there was no 500m limit, and some pidiot (pilot idiot) flew it super high and ignored low battery warning (and disabled Smart RTH, too) and flew until 10% remaining, still at more than 500m up, Mavic won't have enough energy remaining to reach the ground via critical battery RTH and would fall out of the sky, possibly hurting innocent people or causing damage to property.

Just a hypothesis on how they came up with this seemingly arbitrary number - 500m - that doesn't have any analog in aviation airspace altitudes.
 
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At 6m/s descent rate Mavic consumes about 4-5% of battery from 500m to 0 (test done at 4500ft AMSL). I didn't test at the default 3m/s (too lazy), but since it would take 2x the time, and the props spin at almost the same RPM (after all, if descending at constant speed, lift equals to weight regardless of speed; there are small differences in efficiency due to downwash and body drag), it's not unreasonable to expect it would take ~8-10% of battery. So if there was no 500m limit, and some pidiot (pilot idiot) flew it super high and ignored low battery warning (and disabled Smart RTH, too) and flew until 10% remaining, still at more than 500m up, Mavic won't have enough energy remaining to reach the ground via critical battery RTH and would fall out of the sky, possibly hurting innocent people or causing damage to property.

Just a hypothesis on how they came up with this seemingly arbitrary number - 500m - that doesn't have any analog in aviation airspace altitudes.
Interesting. I never thought about that but it totally makes sense! Makes me a little more forgiving of having that limit in place. -CF
 
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Is that a new limit ?
I saw video of people going way higher with it. (But never tried to, or want, or will..)
 
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I thought the limit is because a lot of light aircrafts' low height limit is just a little above that, outside of NFZ. Just to ensure no incidents outside populated areas.
Correction: I initially thought it was 500ft, instead of 500m.
I've heard at 500m, the wind up that high can be crazy and unpredictable
 
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@Xtreme Drone Pilot

1. The auto-landing battery percentage is somewhere between 20-30% if the drone goes above 250m (from my experience). I believe it would be in the 30s or even 40s when the altitude is near 500m.
2. After flight parameter changes via DJI Assistant 2, the descending speed can be adjusted to as high as 10m/s.
3. Many that I know hacked the DJI altitude limit of 500m on earlier versions of the firmware. They were able to go up over 4000m and came down with 5% battery left.
 
@Xtreme Drone Pilot

1. The auto-landing battery percentage is somewhere between 20-30% if the drone goes above 250m (from my experience). I believe it would be in the 30s or even 40s when the altitude is near 500m.
2. After flight parameter changes via DJI Assistant 2, the descending speed can be adjusted to as high as 10m/s.
3. Many that I know hacked the DJI altitude limit of 500m on earlier versions of the firmware. They were able to go up over 4000m and came down with 5% battery left.

1. Smart RTH can be disabled by pidiot.
2. Yep. I did a simple test in GPS+ mode at 7m/s up, 6m/s down. Too lazy to do another test.
3. 4000m - good to know (and impressive). I've gone up 1200m, just getting comfortable. ;)
 
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At 6m/s descent rate Mavic consumes about 4-5% of battery from 500m to 0 (test done at 4500ft AMSL). I didn't test at the default 3m/s (too lazy), but since it would take 2x the time, and the props spin at almost the same RPM (after all, if descending at constant speed, lift equals to weight regardless of speed; there are small differences in efficiency due to downwash and body drag), it's not unreasonable to expect it would take ~8-10% of battery. So if there was no 500m limit, and some pidiot (pilot idiot) flew it super high and ignored low battery warning (and disabled Smart RTH, too) and flew until 10% remaining, still at more than 500m up, Mavic won't have enough energy remaining to reach the ground via critical battery RTH and would fall out of the sky, possibly hurting innocent people or causing damage to property.

Just a hypothesis on how they came up with this seemingly arbitrary number - 500m - that doesn't have any analog in aviation airspace altitudes.

Seems like a good analogy. The reason for 400ft is because commercial airplanes are not allowed to fly 500ft or lower of any object, person etc. that leaves 100ft of space between drones and airplanes to prevent any accidents. Still have to watch out for private license planes. I have some here like when they drop to about 100ft to spray the crops.
 
Enough time to reach terminal velocity on the way down when it runs out of battery :)
i wonder how long it would take to hit terminal velocity...i mean, in theory, wouldn't it hit that if it fell from 500m? so if it fell from 1,500m, it won't do any more damage than it would at 500m.
 
i wonder how long it would take to hit terminal velocity...i mean, in theory, wouldn't it hit that if it fell from 500m? so if it fell from 1,500m, it won't do any more damage than it would at 500m.

Exactly. I'm a skydiver and BASE jumper, so know well what terminal velocity is. For human body in plain clothes falling stable in belly-to-earth position with arms and legs spread out, it's about 120mph at 4000ft AMSL (it varies according to air density, of course) and if falling from a big cliff, is achieved in about 1000ft of altitude loss; somewhat less if jumping from an airplane since you start with ~100mph airspeed already and have forward throw.

Mavic is not so dense, has a lot of parasite drag (arms, props, tumble), also the ratio of weight vs surface area (aka "wingloading") grows as a cube volume vs. square area (i.e. 3rd order of size vs. 2nd order of size), so I would hazard a guesstimate of 100-150m for Mavic to achieve it's terminal speed which is probably in ~60mph range. Any higher than ~150m, Mavic won't be falling any faster.

Uneducated journalists write these silly dramatic stories about people surviving falling out of an airplane (there were at least 2-3, during WWII and in the 70s, I think a Serbian flight attendant) from huge heights as if you fall from these alittudes, you'd hit the ground harder... NOT. Not above 1000ft. Extra altitude will just add more time for horror and praying. :D
 
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Mavic is not so dense,
Disagree.
The human body is close to that of water ... which is why we just float.
There's no way all that metal and battery are lighter than water .... not that I intend proving by an attempt to make it swim.
 
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I'd say it's probably more likely that the mavic has no sense of how far above ground level it is at any given point other then it's barometer. If you fly 500m above a 400m structure then your not really flying 500m AGL at that given point, but only 100m. In which case 500m gives the pilot some leeway on clearing tall structures.

Not so good when your trying to scale a 500m+ structure.
 

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