Guys, any idea what will happen if pick up a dron to 1500 meters, and then turn off engines. Wait till it fall to 600-700 meters and then turn motors on? I just sitting here and drinking beer, and this idea come to my head for some reason.

I am sorry, now this idea in your heads too....

Any thoughts?

Only one thought - It is not legal to fly above 100m.

Imo, you need to sober up.

I got an random thought reading this,  (wondering if this thread is infecting my brain)    What if I turn the motors on  and let it register a home point, then CAREFULLY carry it to particular location, hover it then hit record, then RTH.  Easy way to fly...no?   LOL.  

:@. SORRY, seemed like an appropriate response to this.

One too many beers sir.

Never post when you're toast!

You probably shouldn't be flying that high but hey, you're in Bulgaria so maybe there's a place where you are that it wouldn't be an issue?
If that's the case or let's say you were "authorized" to fly at that altitude......

It might be the ONLY way to get back on the ground safely from that altitude if for example your batteries were almost exhausted?
I do it sometimes from 300ft with my cheap quad.   Never tried it with my Phantom.

Give it a try and let us know what happens. Might be OK if you get a restart.

Drink two more beers. Take the props off the quad. Crank it up and in the DJI pilot app, click HELP (we all need help when we're drinking). Now start the Flight Simulator and take off. CSC at whatever altitude you want and test your reflexes... Drink two more beers and repeat.... Let us know how it goes... But don't fall/crash onto your P3.....

I tried that this morning after breakfast from 400 feet. A few seconds later I CSC'ed to restart and it recovered at about 200 feet. I think I'll use that method to quickly descend from now on, providing there is nothing within a good 200 meters of a possible landing point.  

Can you provide us with a video when you do the CSC at 400ft and then restart?
Thanks in advance!

ScottyT Posted at 2015-7-25 14:56
I tried that this morning after breakfast from 400 feet. A few seconds later I CSC'ed to restart and ...

Do you have a video of this?
Would be awesome.

PerlanSwed Posted at 2015-7-25 15:17
Can you provide us with a video when you do the CSC at 400ft and then restart?
Thanks in advance!

Probably not a wise move to post such a video online - but I'll think about it. I had prop guards on which on review likely helped level out flight sooner, so will try again in the daylight hours without them on.

ScottyT Posted at 2015-7-25 17:11
Probably not a wise move to post such a video online - but I'll think about it. I had prop guards  ...

Its definitely not worse than flying 10,000ft out. If there's nothing around you, the only thing in danger is your Phantom. I'd be curious to see if this is possible.

That a good question!
I tried to answer in theory :
Regarding spec of the drone Vmax = 15-20 m/s depending scenario : this is the maximum falling speed whatever altitude.
So what is the power needed to recovery at this speed ??? Hard to evaluate it,  but if you try using embedded simulator altitude of "no return" is 120m at this speed. 40m are lost just to switch on propellers and 60m are needed with maximum throttle to stabilize at 20m.

Yeah but with P3's getting stress cracks, I can see a motor ripping right out when it restarts the props.

Stress for motors is exactly the same whatever you climb at 2 m/s or you try to stop the fall. This only a question of power (vector), not direction of translation.

lord Posted at 2015-7-25 20:13
Stress for motors is exactly the same whatever you climb at 2 m/s or you try to stop the fall. This  ...

It might be tumbling at restart and cause a much greater load - so not true.

Not a daft question, at all. In fact, it's quite interesting.

Provided the Phantom 3 can right all manner of tumbling... and anecdotal evidence suggests most quads, mostly will... then the biggest potential downsides will be down to the timing of pilot inputs and excess stresses on the airframe due to harsh braking of the descent.

Terminal velocity for a Phantom will be around 50 to 55m/s and it will approach this after about 8 seconds of free-fall. By rapidly spooling up to full power in the opposite direction to free-fall at these speeds, say 30-50m/s (depending on how long it's been in free-fall), the problem will be abnormally high g-force stresses to the rotors and the motor-mounts due to abnormally rapid decelerations.

These will be far in excess of any g-forces encountered in the Phantom's normal performance envelope (and therefore, design spec).

So my guess is, anyone doing this who leaves reasonable margins for timing, will probably get away with it (and perhaps get away with it many times). Sooner or later however, I reckon a motor-mount structure or a rotor will fail sooner than it otherwise would.

So yeh... interesting... and for those who like to push stuff for fun, this technique might just be the difference between landing gently or landing in a heap.

REBELimgs Posted at 2015-7-25 18:18
Its definitely not worse than flying 10,000ft out. If there's nothing around you, the only thing i ...

Well, going above 120 meters / 400 ft or whatever your country's laws and regulations says is actually pretty serious .  

I would say it is much worse than going far out. If you go far out while keeping a sensible altitude then at least you can still see what is below at all times and easily avoid flying over e.g. crowded areas and not risking peoples health, property, and privacy.

So, just  try to keep it below 120 meters / 400 ft or whatever your country's laws and regulations says.

020667@gmail.co Posted at 2015-7-25 06:13
Only one thought - It is not legal to fly above 100m.

Not true - Depends on which country you are in.
In my country the limit is 120 meters.

heclectic Posted at 2015-7-25 23:18
Not a daft question, at all. In fact, it's quite interesting.

Provided the Phantom 3 can right all  ...

How do you get 55 m/s as Vmax ?!
with propellers, arms, body... there is a huge air resistance during the fall.

Terminal Velocity (Vmax) = square root ( (2*m*g ) / (C * P * S)) = ~15 m/s
m= 1.3 kg
g = 9,81
C = 1.2 (hypothesis of disc)
P = Volumic Mass of air = 1,3
S = surface in opposition (disc of 15cm radius hypothisis) = pie x r2
r=0,15m

In the simulator Vmax = 20 m/s so this result 15 m/s seems relevant.

aek Posted at 2015-7-26 00:07
Not true - Depends on which country you are in.
In my country the limit is 120 meters.

still some way t go for the 1500m. he asked for

drink some more...

lord Posted at 2015-7-26 01:49
How do you get 55 m/s as Vmax ?!
with propellers, arms, body... there is a huge air resistance dur ...

Your figures and methodology aren't realistic.

In free-fall, these things tumble wildly and anecdotally at least, spend much of their time "side-sliding" downward. In doing so, the drag from the propellers could never be construed as a disc that will spool enough to produce the element of auto-rotational drag against gravity your calculation suggests. In all other respects, the cross-section of the machine is relatively aerodynamic (quite obviously) and would likely accelerate beyond 55m/s with no props.

I confess however, my approximation wasn't scientific. I took the example terminal velocity of a human sky-diver in the classic (high drag) belly down attitude; i.e. approx 120mph or 53m/s as a guide. Incidentally, I'm sure I don't need to tell you that a sky diver accelerates way beyond this figure if they tumble.

Perhaps my method is a little "back of a fag packet" as we say here in the UK, but even allowing for a gross error in this estimation, having seen video evidence of so many quads tumbling out of the sky with little, if any propeller induced drag, I'm going to stick my neck out and predict 50-55m/s is closer to reality than 15m/s.

I did not tell that propellers will be considered as a disc. In my calculation, I consider the overall surface opposed to the fall as a disc with a radius of 15cm (that is not so irrealistic) - arms+body+propellers+feet.

Your assumption is based on a 75 kg skydiver... with a surface of 1m2 in "crepe" position... 0,3m2 in "candela" position.
I would agree on the moon but not in our atmoshphere. Mass of skyDiver is 58x drone. Surface of friction is 20x drone... Ratio is 1/3...

We need experimentation

lord Posted at 2015-7-26 17:58
I did not tell that propellers will be considered as a disc. In my calculation, I consider the overa ...

"Your assumption"

I think it was more, as I wrote, "back of fag packet" approximation.

"I would agree on the moon but not in our atmoshphere. Mass of skyDiver is 58x drone. Surface of friction is 20x drone... Ratio is 1/3..."

This point would hold more weight if we didn't consider the drag coefficient of a jump-suited skydiver compared to that of an aerodynamic airframe.

So where does this leave us...

"We need experimentation..." ;)

heclectic Posted at 2015-7-26 20:01
"Your assumption"

I think it was more, as I wrote, "back of fag packet" approximation.

Thanks guys.... I now have a migraine.

This can definitely be done with a P2...  A few months ago had a friend visiting who did it a couple of times..

No camera/gimbal on his P2 though.

He said 'ever seen a tumble with a Phantom?  Of course I said the NAZA wont do it...

So he goes up high, tips it into full speed backwards flight and the CSC's it....    Lets it tumble for a second or two then CSC's again.

It lost a _lot_ of height though, and something I'd definitely not be doing with mine..  Although I quite regularly cut the power on my miniquad at height, falls like a stone, then full power from 10m up stops it, most of the time....  But then it doesn't break like a phantom does. :-)

Remember to shoot a video of doing this experiment, really wanna see that

Test message.

gregg1r Posted at 2015-7-24 17:33
One too many beers sir.

Never post when you're toast!

Why? This is hilarious, lol

This really is rather funny.... And I raise the bs flag on the guy that posted saying he did this after breakfast this am. There would be no reason not to film if u didn't peak 400'. I also do this rather often with my toy syma quad and it works like a charm. Except for once? But i do wonder if the added weight that the phantom has would cause any issue with its ability to turn itself upright once you hit the throttle again....?

I'm assuming the fall would be upside down due to the weight distribution.