Can you fly under bridges if you are on one?

[MavicAir2Marc]

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.

I have satellite radio in the car, that seems to be buffered as it will give me about 5-10 sec under the bridge before I get the "No XM Signal". I didn't know if perhaps the same was true for GPS on the drone.

 

[SkyeHigh]

I have satellite radio in the car, that seems to be buffered as it will give me about 5-10 sec under the bridge before I get the "No XM Signal". I didn't know if perhaps the same was true for GPS on the drone.

Satellite radio is completely different. GPS uses extremely precise time signals from multiple satellites in real-time to provide a fix at the receiver location.

 

[hiflyer201]

If the bridge is hundreds of feet high it shouldn't be very difficult flying under it. It couldn't be all that wide. Post the video

 

[EyesWideShut]

Last December when I first got my mini, I did a wide 1 minute Circle/Orbit in Quickshots around a small old chapel with a steeple. Being a newbie I was surprised that I lost video for 5 seconds as the mini went behind the church and the "DJI Fly lady" started her warning about RTH. If I remember correctly it takes about 10 - 11 seconds of lost signal before RTH actually kicks in and in those few seconds the mini had continued doing the circle and regained the signal on the other side of the chapel and then finished the quickshot video.

My point is that the mini continued it's Quickshot path during those lost 5 seconds rather than stopping. So that makes me wonder in your case, if it would continue on a regular flight path in the "stick" direction during those 10 seconds RTH countdown or stop dead and wait before going into it's RTH instructions.

 

[hiflyer201]

Sorry..I forgot you said you were standing on the bridge..forget all of the above..not worth it. There would be no way out of a signal loss and a RT....the base of the bridge..yikes!

 

[chazzm]

Well you could, however the only potential problem would be the AC losing its sats! also there's ALOT of magnetic interference due to the rebar in the bridge1 IF YOUR flying line of sight in ATTY mode its cool though!!

 

[Meta4]

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?

Although GPS cannot buffer like satellite radio, it could appear to for the operator.
If the satellite signals to the GPS receiver are blocked there is an instant loss of GPS data.
However the drone will continue for a few seconds on "dead reckoning" in case the signal loss is just temporary.
I've not tested to know how long this will go for.

Also, the height and width of the bridge as well as how far below the bridge deck would be important factors affecting how much of the sky (and satellites) is visible to the GPS antenna.
If you flew half way between the water and the bridge under the Golden Gate bridge, the drone would probably maintain GPS signal all the way but if it was 30 ft below the bridge deck, GPS signal would be quickly lost.

But if the operator is on the bridge he's still going to have control difficulty when the control signal is blocked by the bridge deck.

 

[Thomas B]

I routinely fly under a 5 lane wide reinforced concrete road bridge in my FAA approved practice area.

I have never hovered beneath the bridge, but have done slow passes as well as full throttle passes with my M2P. No problems, no changed mode. After passing the bridge I do climb. I have done this essentially standing on the bridge (after visual invite inspection to rule out any hanging wires, etc). I’ve also done it while standing in the drainage canal that runs beneath the bridge...most of the time it’s essentially dry except a 2-3 foot stream of water.