Flying from cliffs, what to be aware of?

digiteye · Oct 3, 2018

A very scenic and quite common shooting situation is when you are standing high on a cliff, the ocean is beneath and you fly over the water to record that scenery.
You want to lower the altitude to get closer to the waves so the drone will be actually much lower than your home position.
What happens? Would the drone "know" its negative altitude vs home position? How would it consider the altitude from the sea level? What should be the RTH altitude (not to crash it against the cliffs if the RTH is measured from sea level)?

Any other considerations?

Thank you for your insight if you have encountered this situation. I'm going to fly on such an environment and worried a bit.

tcope · Oct 3, 2018

digiteye said:
What happens? Would the drone "know" its negative altitude vs home position?

Yes

digiteye said:
How would it consider the altitude from the sea level?

it knows nothing about sea level nor does it need to.

digiteye said:
What should be the RTH altitude (not to crash it against the cliffs if the RTH is measured from sea level)?RTH altitude if above your homepoint (take off point) only.

Forget everything about "sea level". You don't need to know anything about it.

Meta4 · Oct 3, 2018

digiteye said:
You want to lower the altitude to get closer to the waves so the drone will be actually much lower than your home position.
What happens? Would the drone "know" its negative altitude vs home position?

Thank you for your insight if you have encountered this situation. I'm going to fly on such an environment and worried a bit.

You're flying a plane and launch from Denver (alt 5430 ft) to fly to Los Angeles (alt 125 ft)
Should you be worried?

You are designing a drone and you realise that people might launch from a high point and fly lower.
How would you program it?

digiteye said:
How would it consider the altitude from the sea level? What should be the RTH altitude (not to crash it against the cliffs if the RTH is measured from sea level)?

Your drone doesn't know where sea level is.
The only height it understands is Home = zero

Freeman727 · Oct 3, 2018

Check this YouTube video about a guy who lost his drone flying off a cliff. Fun video with a couple of follow up videos:

Crunch · Oct 3, 2018

When you fly downward it just records a negative altitude so you fly along at say -15m. It might help to go to a comfortable height above the water (for a sea cliff) while you can see your drone and note that altitude so that when your further away you have an idea of your altitude above the waves. In a RTH situation it will go the set altitude. so if you are at -15m from you current position (15m below you) and your RTH is 50m then your drone will rise 65m to 50m (above you) for RTH. I've flown off cliffs often and not experienced any cliff specific problems apart from rising/turbulent wind near the cliff face.

Meta4 · Oct 3, 2018

Freeman727 said:
Check this YouTube video about a guy who lost his drone flying off a cliff. Fun video with a couple of follow up videos:

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Total waste of 30 minutes listening to this turkey who has no idea about anything drone-related.
Three minutes of looking at his recorded flight data would show what happened

AeroJ · Oct 3, 2018

Be aware of the sometimes powerful up-drafts and turbulent winds you sometimes get along cliff tops, most noticeable when you first drop off the edge of them. If you fly from the bottom of cliffs this can be a problem when you are trying to descend in a hurry towards the end of a battery pack. Turbulent winds can sometimes push you into the rock face so leave a nice wide margin.

Also some cliffs have nesting birds in them, the parents of which may feel the need to vigorously defend their nest sites from marauding drones. Gulls for example (alone or in groups) can easily take down a Mavic if so minded, so best to avoid them if you can...

Some general advice about cliffs and sea - if you are flying close to the waves, I'd do it from the beach, not the cliff above it. You will be able to see how close your UAV is to the water much better from the lower vantage point.

Gaz Mc · Oct 4, 2018

they found it in a later video....but its all click bait as everyone seems to put mavic 2 pro in there titles lately

Freeman727 said:
Check this YouTube video about a guy who lost his drone flying off a cliff. Fun video with a couple of follow up videos:

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For more detailed information, see our cookies page.

[/QUOTE

Freeman727 · Oct 4, 2018

Gaz Mc said:
they found it in a later video....but its all click bait as everyone seems to put mavic 2 pro in there titles lately

Yes, I fast forwarded to the 5 minutes he spent talking about losing his drone. He does offer some pointers on photography.

Ian in London · Oct 23, 2018

digiteye said:
A very scenic and quite common shooting situation is when you are standing high on a cliff, the ocean is beneath and you fly over the water to record that scenery.
You want to lower the altitude to get closer to the waves so the drone will be actually much lower than your home position.
What happens? Would the drone "know" its negative altitude vs home position? How would it consider the altitude from the sea level? What should be the RTH altitude (not to crash it against the cliffs if the RTH is measured from sea level)?

Any other considerations?

Thank you for your insight if you have encountered this situation. I'm going to fly on such an environment and worried a bit.

Well, having lost mine 20 months ago over the White Cliffs of Dover, I can say there are indeed a few considerations....

As others mentioned, your altitude will indeed show negative, and it all works fine, but keep an eye on:
1. Gauging the height of trees or water when looking down from above; VLOS won't help you stay above ground based obstacles if you're observing from above as it's hard to gauge the different heights
2. Accessibility of where you're flying. If you do hit something, or run out of battery, it helps if you can at least get down to retrieve it

3. RTH altitude: Be aware that your RTH altitude will stay relative to your take off height, which means if you're running low on battery and flying 100 metres below your take off height, any RTH will not only start rising 100 metres up to your take off height, but then also to the pre-programmed RTH altitude which defaults to 30m. So that's a mighty altitiude to rise up when you're on low battery
4 Wind: If the wind is blowing from behind you, then be aware the wind above the cliffs will be much stronger than below the cliffs. Again, it can make things hard when you're trying to use RTH to head back and have it rise up way above the height of the cliffs....

Cheers
Ian in London