How Far Can A Drone Fly In a Tunnel



This week’s “Ask Rob” visitor question from Google Search is “How far can I fly a drone in a tunnel?”
Fortunately I can answer that one because I have extensive current experience in researching how to use radio communications in difficult environments. And that is exactly what you are trying to do with controlling a drone in a confined space.

Quick Answer

The quick answer is the distance depends on the length of the straight section of the tunnel between you and your drone, and the strength of the radio control signal. If you have a really long straight tunnel, you could get 3km or more, as long as your batteries last. The video feed range is usually only 100 metres though.
This video of drone racing in a football stadium makes me wonder what their communication set up is, because the drones fly into the concrete tunnels beneath the stands. The most likely solution is to install radio repeaters throughout the tunnels to make sure the signals connect.

Video of Drone Racing in Tunnels

Detailed Answer

For a detailed explanation of how far can you fly a drone into a tunnel you need to consider four aspects to this challenge:
1. The radio control link to control your drone
2. The radio link providing the video feed
3. Avoiding hitting anything solid
4. How long the power supply lasts
You need the radio control link to move your drone into the tunnel and control where it goes. For most drones, this requires a permanent communication link between your controller and the drone. For a single radio control unit, this has to be line of sight. If there is any obstruction between you and your drone, the radio link will get blocked.
The control link on a consumer drone such as one of the DJI Phantom Drone will reach between 3km and 5km. You next challenge is being able to see where the drone is using the video feed.
The video feed usually uses wifi, which will only give you up to 100m reliable communications. Beyond that things get patchy. If the tunnel is dark you may not even be able to see where you are flying. Have you got lights on your drone?
You could program your drone to fly on its own flight path, but it will need to have that capability, and how will it know where it is if there is no GPS or position markers?
Even if you are an ace drone pilot, the width of the tunnel dictates how easy it is to fly in A narrower space will of course cause more challenges. If you have a drone with collision avoidance on it, that will greatly help.
Also, if you are in a tunnel then there is no GPS signal, which means that the position stabilisation that most drones use will be useless. Without acoustic positioning such as on the DJI Mavic, flying indoors in a confined space is a nightmare.
If there is not a direct line of sight link between you and the drone, you can still control it and get a video feed back using MANET radio systems. A Mobile Ad-Hoc Radio Network comprises of several radios scattered around your area you are flying in which act as radio signal repeaters. They recieve and retransmit the control and video signals. If you have these in place, the only limitation is where you place them for total radio coverage, and the power life of the drone.
Most drone batteries only provide about 10 to 15 minutes of flight time. You can get high capacity drone batteries that will last up to 30 minutes. With battery technology constantly improving battery life is getting better all the time.
So, I hope that answers the question sufficiently for you. Just remember, you will need to stick to the legal rules for drones where you are, and if you lose control of your drone in a tunnel, how are you going to get it back?

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