Can you fly under bridges if you are on one?

[Buel]

Hi,

Naïve question from a relative newbie - there is a bridge over a river where I live (hundreds of feet high), I would love to fly under it whilst being on it but how dangerous is this re losing wifi and reverting to Go Home?

 

[fificap]

Hi,
First check wifi signal on the app when you're on the bridge, if there is not too much disturbance (select manualy the better chanel, i.e. the lower bar!), it can be a good idea to configure (in the app) the action in case of signal lost to "stay in place" (not sure it is the exact wording). Then if you lose the signal, the MM will stay in place and you can move yourself to regain signal.

 

[Buel]

Wow! I didn't know that 'stay in place' was an option?

 

[fificap]

With the official app, You have the choice to : RTH, Stay in place, or land! Stay in place saved me ( at least the mini) when i sent it around a big tower, when the mini was on the opposite side, i lost connection, and if it was setup as RTH, it probably crash on the tower trying to go back.... Hopefuly i've setup "stay in place" and i was able to walk closer to the tower and found the connection again!

 

[SkyeHigh]

Hi,

Naïve question from a relative newbie - there is a bridge over a river where I live (hundreds of feet high), I would love to fly under it whilst being on it but how dangerous is this re losing wifi and reverting to Go Home?

If it is a concrete bridge it will be full of rebar that is likely to affect your compass if you take-off from the bridge. If you get far enough to pass under the bridge you may lose signal but it will also be beyond your visual line-of-sight.

 

[Buel]

Thanks so much, both. Losing your visual line-of-sight is a big no-no then?

 

[WooZie]

and if it was setup as RTH, it probably crash on the tower trying to go back

that's because you didn't setup RTH properly, always you have to look around you and set the RTH higher than highest building, or for more security, you can put 30 meters above

 

[fificap]

You're right, it is a choice that i use often, but in this particular situation ( realy hight tower) it was safer to stay in place, as i was able to come closer to the drone, and in the case of flying under something, it can be tricky to setup the right RTH altitude.

 

[Olav van Gerven]

There is a way to avoid the problem. No not the obvious, not flying under the bridge, but using waypoints (I use Litchi). It would take some preparation (to get the exact flightpath and altitudes) but then it should work. A lithcimission is continued even if the contact to the controler is lost. So if you are on the bridge and sent the drone out on the mission, getting away from the bridge first, then heading exact where it has to go, planning a path with relativ short distances between the waypoint and setting the action after finishing the mission to hold the last position, it could work. You can have flightfootage before and afterwards flying completly manual, just using the mission to go around the moment you are under the bridge. (which ofcourse is illegal if you are on the bridge without VLOS, so I am sure you would not do it...)

 

[Buel]

Wow, what great answers, thank you. I have never used a waypoint......seems I have some learning to do!!!

 

[Meta4]

Naïve question from a relative newbie - there is a bridge over a river where I live (hundreds of feet high), I would love to fly under it whilst being on it but how dangerous is this re losing wifi and reverting to Go Home?

If you are a relative newbie, don't try this.
There are a number of ways it could end badly.

Losing your visual line-of-sight is a big no-no then?

If you were on the bridge and flying under it, the controller signal would have to pass through the bridge.
And unless it's a wooden bridge (it sounds like it isn't), you would lose signal and not be able to control the drone until you got to somewhere that gave you a clear, unobstructed line of sight to the drone again.

If you had set your loss of signal action to hover that would prevent the drone rising and crashing under the bridge, but how would you reconnect?
If the bridge deck was wide and you were relatively close, your drone could also lose GPS, causing some other issues for you to deal with.

There are other potential issues as well.
Don't attempt this until you understand them ... and when you do, you might know enough to avoid it anyway.

 

[WooZie]

A lithcimission is continued even if the contact to the controler is lost.

Are you sure of that? Here we talk about mavic mini which its firmware does not support missions if the signal is lost, but the drone will do RTH

 

[new2mavic]

Whether the drone can remain connected in the presence of obstacles depends very much on the environment. I have tested it with my M2P in FCC mode inside my apartment. With the drone placed in a room and me holding the controller, disconnection occurred as soon as I got out of the apartment.

The other day I tested again outside with my M2P in CE mode ( radio transmit power much lower ) and the drone remained connected even when there was a big concrete-and-steel building standing in the way :

There is no way that the radio signal could shoot throught that big building. I believe the signal reached the drone by means of reflection off nearby buildings / structures.

I don't know the environment surrounding the bridge so I am not sure whether you can rely on reflection to maintain the connection. One thing you may try to do is to get your Mini to run in FCC mode. The signal is much stronger.

 

[superfunkmojo]

There is a way to avoid the problem. No not the obvious, not flying under the bridge, but using waypoints (I use Litchi). It would take some preparation (to get the exact flightpath and altitudes) but then it should work. A lithcimission is continued even if the contact to the controler is lost. So if you are on the bridge and sent the drone out on the mission, getting away from the bridge first, then heading exact where it has to go, planning a path with relativ short distances between the waypoint and setting the action after finishing the mission to hold the last position, it could work. You can have flightfootage before and afterwards flying completly manual, just using the mission to go around the moment you are under the bridge. (which ofcourse is illegal if you are on the bridge without VLOS, so I am sure you would not do it...)

Good points but I don’t think Litchi does waypoints on the Mavic Mini?

 

[new2mavic]

One thing you can try is to set the home point to somewhere away the bridge and the RTH height to be lower than the bridge so that if disconnection occurs, the drone will automatically get out by itself. Of course you have to make sure that the GPS signal will be good enough under the bridge.

 

[manjosh2020]

you can set it to whatever you want either to go home if signal lost is lost and visual is disconnected or rather hover and remain on its spot till you regain your singal.

 

[manjosh2020]

funny... hahahahaha ?? better to have than to loose isn’t it???

✌?love from ??

 

[SkyeHigh]

Thanks so much, both. Losing your visual line-of-sight is a big no-no then?

Correct, it is a regulation requirement to maintain VLOS at all times.

 

[MavicAir2Marc]

A quick question that maybe @Meta4 could answer...how much buffering of the GPS signal would the drone do if you just flew underneath the bridge at a reasonable speed? Would it have enough buffered signal to keep from triggering a RTH and does anyone have a figure on how much buffering drones would do with the GPS signal in terms of time?

 

[SkyeHigh]

A quick question that maybe @Meta4 could answer...how much buffering of the GPS signal would the drone do if you just flew underneath the bridge at a reasonable speed? Would it have enough buffered signal to keep from triggering a RTH and does anyone have a figure on how much buffering drones would do with the GPS signal in terms of time?

The GPS signal is real-time. As soon as it is lost, it is lost until a valid signal is received.

With loss of GPS the flight controller will switch to attitude mode, which will lead to drift until the signal is regained.

That said, if the pass under the bridge is quick you may get away with a brief loss. However it’s still not a wise path to take.