RTH height when flying uphill?

[SurprisingEdge]

Hey folks,

Before I try something, I wanted to check in, to try to minimize chances of a crash.

There's somewhere I'd like to go fly my Mavic Pro, but it involves flying from down in a valley, to the top of a ridge. I'll be in LOS the whole time, so I'm not _too_ worried about connection problems, but, IF they were to happen... I'm not 100% clear on how RTH height and maximum height are going to interact.

I have maximum height set to 90m, as that's the legal limit here in Canada. The ridge is more than 90m high, but that limit is from the ground, so presumably that means 90m from the top of the ridge. Cool.

But what happens if I set my RTH height to 90m (presumably it wouldn't work to set it higher because of the max height setting?) and the drone is up top of a 200m ridge? Is it going to _descend_ to 90m above the home point (which would be below the top of the ridge ) and crash? Ideally I'd like it to stay ~90m from the _ground_, but I'm not sure how it would know how far away the ground is. I don't believe it has topo maps, or any way of ranging that far.

What do you think? Is there any way to protect against loss of connection for this kind of flight? Do I just need to remove my max height limit, keep within the legal limit myself, and risk going outside it on RTH by setting RTH height to 500m or something? Does RTH height honour the max height even?

 

[dirkclod]

It will not descend from higher than your set RTH home but come back at however high it is. It only will rise to that limit if you are below it .
Make sense ?
And welcome to the forum .

 

[SurprisingEdge]

It will not descend from higher than your set RTH home but come back at however high it is. It only will rise to that limit if you are below it .
Make sense ?
And welcome to the forum .

Yes, I think that makes sense, thanks. RTH height is a minimum, so if it's already higher, it'll stay there.

I also just realized, after posting, that since the mavic (probably?) can't tell it's AGL, the max height setting is probably relative to the home position anyway? So to fly up a 200m ridge, I'd have to raise the max height anyway.

 

[53-63-6f-74-74]

Remove your 90m height limit. If that is your AGL altitude limit you obviously won't make it very far uphill. You'll have to estimate as you go. If RTH activates it will not lower altitude before returning to home. If you are within your 90m AGL as you ascend up the ridge, you will probably be above it if RTH is activated and the aircraft flies away from the ridge. I would suppose that you will have to take a chance on regaining control before you get too much AGL. All heights are measured from the home point.

 

[msinger]

the max height setting is probably relative to the home position anyway?

You got it. The current altitude displayed in DJI GO is always the altitude above (or below) the takeoff point.

 

[4wd]

Since it won't go up any further, in the event of RTH you need to be 100% sure that the direct route back doesn't have higher ridge or tall trees in the way.

 

[SurprisingEdge]

Since it won't go up any further, in the event of RTH you need to be 100% sure that the direct route back doesn't have higher ridge or tall trees in the way.

That's a really good point! Thanks! With the route I plan to fly, that should be ok, but I'll double check, now that that's been pointed out.

 

[DanMan32]

It does have RTH obstacle avoidance, so it should go over obstacles. However would that be limited by the max limit?

 

[SurprisingEdge]

It does have RTH obstacle avoidance, so it should go over obstacles. However would that be limited by the max limit?

I prefer to never ever rely on the obstacle avoidance. Does the RTH obstacle avoidance do it by going up, or by trying to go around? I've never had it trigger.

 

[DanMan32]

I haven't empirically tested it, but sales info shows it going up, over, then back down.
I agree, I wouldn't rely on it, especially for trees that can have small undetected branches sticking out, but at least it's there. I'm not sure if it will even come back down to 'cruising altitude' once it has gone up.
If it uses the same algorithm as APAS, it will go up or around, depending on what seems easier.

 

[John235]

Like you, I live on a mountain. Suppose I fly out over the valley, 600 ft below me. Does that put me in violation of the 400ft limit? That would mean basically that I should fly mostly at my level or uphill. If I have my Max height set to 400 ft and fly out over the valley, I could fly as high as 1000 ft AGL. Would that put me in violation? Am understanding correctly?

 

[DanMan32]

If you fly past 400 from the mountain into the valley, and the ground below the AC at that point is more than 400ft below the AC, then yes, legally you are in violation.

Technically, the Mavic will fly as low as you want, assuming you have signal. The height limitation is applied relative to and above the launch point.

 

[John235]

If you fly past 400 from the mountain into the valley, and the ground below the AC at that point is more than 400ft below the AC, then yes, legally you are in violation.

Technically, the Mavic will fly as low as you want, assuming you have signal. The height limitation is applied relative to and above the launch point.

Thank you, Danman32.
Essentially, regs refer to AGL. It would mean I have to be careful if I set Max height to 400 while flying around these hills. Solution: set my Max height to some lower, safe value, and watch my display while flying toward the downside. I have already discovered that the height drops fast while flying toward the upside.