I’m not sure what you mean by Viaduct but I can give you some tips. Oh, and I have never flown a drone, but I am thinking of buying one. I just signed up to answer your question.
1. Walk to the end of the Weir Track (it’s a bit rough so wear good shoes). Once you get to the weir you’ll be just below the section of the railroad that crosses Stony Creek. I know that’s a common shot used in tourist brochures.
This is the Google Plus code for the location of the car park at the beginning of the Weir Track - 5RM74MF8+VX
This is roughly where the weir is - 5RM74MC5+QM
You should be able to get some nice shots along the Weir Track. I used to take a lot of photos along there a few years ago. It was not well known at the time and the further up the track you go, the fewer the people. At least that was my experience prior to 2013.
2. The Douglas Track. I’m not sure if this is still open, but you will find the start of the track just after the first river crossing on the Weir Track. It’s an old Aboriginal track that will take you up over Glacier rock and, eventually to Kuranda. You should get some good flying spots along this track.
3. Barron Gorge Power Station. (5RM74JXW+8W) As you cross over the Barron River, on your left, you’ll see a waterfall. There used to be an old track that would take you up to the railway line above the Power Station.
4. There is also Barron Falls Road, and Wrights Lookout (5RM75J7R+8X). Both are accessible via Kuranda. I don’t remember what Wrights Lookout is like, but I think there are several viewing platforms along a boardwalk at the end of Barron Falls Road. If the falls are flowing, and you are game enough, you could fly out and get some nice shots of the falls and the train from there. I also think you can see the Cable Cars, as they cross the Barron River, from there as well.
5. Although probably not suitable for filming the train, you can walk along the Barron River, from the Power Station Bridge, all they way up to the bottom of the falls. Be very, very careful, if you are going to do that though as they can release water without warning and you’ll be lucky not to get drowned. You have to climb over huge boulders, and the edge of the river is very steep. Be very, very careful.
And, be careful of crocodiles. There are saltwater crocodiles in the Barron River. The Weir Track should be safe enough, but don’t trust the Barron or any other rivers in the area.
Just a funny story about getting soaked in the Barron Gorge: I was doing some audio recording between the Power Station and the Falls one day. I had wedged myself between two large boulders - both feet on one side, and back on the other. I was holding my recording equipment in one hand and an expensive mic in the other. As I was recording, it started raining. I thought it would just be a light shower, but it got heavier and heavier. Water began flowing down the boulders making them very slippery. As I shifted my weight, to climb out, my feet slipped and I fell into the water. It was only a few feet deep but I fell backside first into it!! Thankfully my equipment survived but I lost a good patch lead and wind protector. It’s been over 4 years now but, if you find them ...
I hope you have fun in Cairns.
