If I fly 1000' below home point will RTH still work if connection lost?

[68charger440]

I want to start my takeoff point at 11,000' altitude at ground level in the Colorado Rocky mountains, then fly roughly 1,000' down a cliff, and then back up taking stills and video along the way. If I have RTH altitude set at 45 meters and I lose contact with the P4 will it climb up the 1000' plus the 45 meter RTH altitude, and then land at the RTH point, or will being so far below ground level confuse it? Also, it might lose GPS when at the bottom.
Thx

 

[alokbhargava]

I see issue with GPS in such mountains and RTH can’t work without GPS.

 

[N017RW]

I want to start my takeoff point at 11,000' altitude at ground level in the Colorado Rocky mountains, then fly roughly 1,000' down a cliff, and then back up taking stills and video along the way. If I have RTH altitude set at 45 meters and I lose contact with the P4 will it climb up the 1000' plus the 45 meter RTH altitude, and then land at the RTH point, or will being so far below ground level confuse it? Also, it might lose GPS when at the bottom.
Thx

The answer is yes... it will rise to the RTH altitude set-point no matter what altitude it is at unless it is already above that point at signal loss.

Loss of signal can be an issue as the design of the antenna systems assumes the aircraft is above the controller. Otherwise the aircraft can 'shadow' it's antennas.

As stated above it needs GPS and adequate battery reserve to complete the maneuver so be mindful of those conditions.

 

[68charger440]

Thanks guys... Are the GPS sats in the southern sky or are they all over the sky? The cliff is a north face so I will have the southern sky blocked, but a good portion of the North, East, and Western sky will be visable at the bottom.

 

[msinger]

If I have RTH altitude set at 45 meters and I lose contact with the P4 will it climb up the 1000' plus the 45 meter RTH altitude, and then land at the RTH point, or will being so far below ground level confuse it?

When RTH is initiated, your Phantom will climb to the set RTH altitude before it starts flying back to the home point. That means it'll look at the current altitude displayed in DJI GO and ascend until that altitude matches the RTH altitude.

In your scenario above, the current altitude displayed in DJI GO would be a negative value if RTH is initiated after flying below the takeoff point. Assuming your Phantom has a good GPS connection, it would ascend up to 0 feet and then up to your RTH altitude before returning to the home point.

 

[rvrrat14]

Suggest you look at satellite predictor sites/apps. This will give you an idea of bird locations in your area at any given time and a better understanding of satellite coverage. Sats are directly overhead, low on horizon, and mid level but will vary throughout the day/night. The predictor may give you an idea of when the ‘best’ time is. Sometimes you may only have coverage directly overhead or only low on the horizon.
Please report back on your progress.

 

[N017RW]

Thanks guys... Are the GPS sats in the southern sky or are they all over the sky? The cliff is a north face so I will have the southern sky blocked, but a good portion of the North, East, and Western sky will be visable at the bottom.

The GPS satellites are constantly moving, not geostationary (as many are). You can Google this for animation that shows how they are moving.

 

[68charger440]

I must say it surprises me that the default action upon loss of GPS is not more customizable. Since in most cases greater altitude will both restore GPS and RC connectivity simply flying straight up would prevent autolanding at the bottom of the cliff leaving me no reasonable way to retrieve it.

 

[68charger440]

Suggest you look at satellite predictor sites/apps. This will give you an idea of bird locations in your area at any given time and a better understanding of satellite coverage. Sats are directly overhead, low on horizon, and mid level but will vary throughout the day/night. The predictor may give you an idea of when the ‘best’ time is. Sometimes you may only have coverage directly overhead or only low on the horizon.
Please report back on your progress.

Will do.
Thanks

 

[N017RW]

I must say it surprises me that the default action upon loss of GPS is not more customizable. Since in most cases greater altitude will both restore GPS and RC connectivity simply flying straight up would prevent autolanding at the bottom of the cliff leaving me no reasonable way to retrieve it.

Unfortunately most folks cannot fly without it. Especially BVLOS. Once it’s lost your captured by wind or air currents.
Up - is no guarantee of reconnection.

What options would you propose?

 

[68charger440]

Unfortunately most folks cannot fly without it. Especially BVLOS. Once it’s lost your captured by wind or air currents.
Up - is no guarantee of reconnection.

What options would you propose?

While "Up - is no guarantee of reconnection" it by far the best chance of reconnecting GPS, the RC, or both. If only GPS reconnects then RTH will take over and bring you home safely. If only RC reconnects then you can fly it back home even without GPS providing you are a good enough pilot. If they both reconnect then you can resume flying any way you wish.
So while drift, thermals etc. are valid concerns, autolanding in an unreachable location is a guaranteed loss of the bird. I would propose giving you the ability to fly at a predefined direction, speed and duration to a desired altitude based on compass, and barometric readings. In this particular scenario I would be able to fly due west for 50 miles with no obstructions, so a predefined full power up and 1/4 power due West for 1 minute would most likely keep me away from the cliff face while quickly returning me to a place where I would regain some or all control of the bird.

 

[Meta4]

Here's your GPS sat animation

A GPS predictor site won't kelp much as it would only show how many sats are visible with an unobstructed horizon and what you are planning would in effect block the view of half of the sky.
But it's a simple matter to watch the sat numbers on your app as you descend and if you lose enough to be close to dropping out of P-GPS mode, it would be a simple matter to climb higher if you wanted to maintain GPS.

I must say it surprises me that the default action upon loss of GPS is not more customizable. Since in most cases greater altitude will both restore GPS and RC connectivity simply flying straight up would prevent autolanding at the bottom of the cliff leaving me no reasonable way to retrieve it.

There is no default option for loss of GPS because there's not much you can do about it.
You lose GPS and your Phantom is now in atti mode. That's about all there is to it.
In post #11 you talk like you anticipate losing control signal and GPS together but that is unlikely.
They are two different systems and not related.

It's good that RTH is simple because too many options would just confuse matters

 

[With The Birds]

I must say it surprises me that the default action upon loss of GPS is not more customizable. Since in most cases greater altitude will both restore GPS and RC connectivity simply flying straight up would prevent autolanding at the bottom of the cliff leaving me no reasonable way to retrieve it.

Autoland is likely the preferred option with GPS loss and no control connection. The last thing you might want from a safety perspective is increasing altitude while drifting uncontrollably.

 

[rvrrat14]

GPS predictors are a planning tool, to be used preflight. It gives you a ‘prediction’ of the constellation before you launch. Knowing your location and geography of your flight, compared to the constellations, will give you an idea of when you may be lacking in coverage. Its up to you to understand your altitude vs obstructions, just as any pilot would. In mountainous regions, sats low on the horizon may not be your best bet.

 

[68charger440]

A GPS predictor site won't kelp much as it would only show how many sats are visible with an unobstructed horizon and what you are planning would in effect block the view of half of the sky.
But it's a simple matter to watch the sat numbers on your app as you descend and if you lose enough to be close to dropping out of P-GPS mode, it would be a simple matter to climb higher if you wanted to maintain GPS.
There is no default option for loss of GPS because there's not much you can do about it.
You lose GPS and your Phantom is now in atti mode. That's about all there is to it.
In post #11 you talk like you anticipate losing control signal and GPS together but that is unlikely.
They are two different systems and not related.
It's good that RTH is simple because too many options would just confuse matters

I agree the GPS animation will probably not be of much help when descending close to the cliff face.
When you say "you talk like you anticipate losing control signal and GPS together", you are misinterpreting my expectations during my flight. Being a very conservative pilot, I am simply trying to anticipate the possible problems I might run into and what I will do in those situations. I absolutely do plan on watching the sats and RC connections, and aborting if I see a problem arise with either. However, flying down a sheer cliff I may go from full connectivity to none in a few seconds.

Now when you say... "There is no default option for loss of GPS because there's not much you can do about it. You lose GPS and your Phantom is now in atti mode. That's about all there is to it."
That is where my suggested changes would IMHO be very helpful. You could indeed do a great deal about it if my suggestions were implemented. You would go from "there's not much you can do about it." to having a world of options.
I think we would agree that most fly aways and crashes can be traced to pilot error, so if we proceed with this discussion assuming that there is nothing wrong with the P4 itself then as I stated earlier increasing altitude would most likely regain sat connectivity and initiate a safe RTH. No lost drone and a happy ending!
If flying over water on a small lake surrounded by trees that caused the loss of sat connections for example, I can see no argument where autolanding is a better option then increasing altitude to regain sat connection. Just because you are higher does not increase your chances of hitting something before regaining control any more than drifting as the bird auto lands whow knows where would. I would posit that increasing altitude would be safer since in all but the very extreme circumstances the increased altitude would clear the obstructed view of the sats and RTH. The autolanding with uncontrolled drift would be more of a roll of the dice. As for the increased complexity of the additional options, I believe most people would never touch them, but for those more capable pilots it would be a lifesaver. I don't believe in dumbing down the bird for those who are not competent to use these advanced features.

 

[Meta4]

so if we proceed with this discussion assuming that there is nothing wrong with the P4 itself then as I stated earlier increasing altitude would most likely regain sat connectivity and initiate a safe RTH.

In normal flying, you aren't going to lose GPS unless you fly into an area where you lose enough of your sky view to cause loss of satellites.
That might be because you've flown into a canyon or down a cliff or under tree canopy etc that blocks the sky.
If you want to fly into one of those non-standard constricted situations, you need to have your wits about you because you are no longer out in the open and there are additional risks.
If you lost GPS because you flew under a bridge or tree canopy, going up is the last thing you want to do.

It would only be an uncommon and specialised situation where you would:
a. Lose GPS
b. Want the Phantom to automatically climb

 

[68charger440]

In normal flying, you aren't going to lose GPS unless you fly into an area where you lose enough of your sky view to cause loss of satellites.
That might be because you've flown into a canyon or down a cliff or under tree canopy etc that blocks the sky.
If you want to fly into one of those non-standard constricted situations, you need to have your wits about you because you are no longer out in the open and there are additional risks.
If you lost GPS because you flew under a bridge or tree canopy, going up is the last thing you want to do.
It would only be an uncommon and specialised situation where you would:
a. Lose GPS
b. Want the Phantom to automatically climb

My suggested changes would allow you to program it to fly out from under an obstruction and then in whatever direction you chose. It would just be a step in the preflight planning process that could be turned off completely if desired. I agree that these are not very common situations, but I do believe they are the situations that provide the most interest for serious enthusiasts, and I think they happen more often than you may think. People want those unique close up pics or videos that will by nescessity block good portions of the sky when getting close enough to get the shot.

 

[OOO]

I frequently fly with negative altitude (launching over a cliff or top of a canyon and flying in the canyon). Almost in every flight the drone goes into ATTI mode when I fly in a narrow canyon. Raising the drone usually works for me but it is very difficult to control the drone in such situation even in the absence of too much wind. I crashed my first drone (MP) in one of these flights. In addition, sometimes I see compass error messages while flying close to the big rocks or walls of the canyons and these messages usually disappear when I move away from the walls.

 

[68charger440]

I frequently fly with negative altitude (launching over a cliff or top of a canyon and flying in the canyon). Almost in every flight the drone goes into ATTI mode when I fly in a narrow canyon. Raising the drone usually works for me but it is very difficult to control the drone in such situation even in the absence of too much wind. I crashed my first drone (MP) in one of these flights. In addition, sometimes I see compass error messages while flying close to the big rocks or walls of the canyons and these messages usually disappear when I move away from the walls.

It sounds like you like the same type of flying as me. I make a point of flying in atti mode on a regular basis because it is not something you can learn quickly and especially so in a high pressure situation such as we are discussing in this thread.

 

[normr]

The GPS satellites are constantly moving, not geostationary (as many are). You can Google this for animation that shows how they are moving.

Here is a great YouTube video explaining GPS satellites and their orbits