RTH Altitude Clarification

[Fletch911]

There are a few threads on the RTH & Altitude, and I wanted to confirm a couple of important points with documented answers that were not opinions.
I think this is an important point that should be clarified. The FAA uses MSL as a baseline, but obstructions are posted as AGL. For UAV Pilots, the small scale of our operations makes this a very relevant question.

QUESTION 1:
Is the RTH Altitude calculated based on the Home position altitude as the base?
Example:

Home point is 1000 ft ASL
Flight area is 1200 ft ASL
RTH Altitude is set to 100 ft

What altitude will the bird RTH? If RTH is set based on the Home point, the bird would DESCEND and return.

QUESTION 2:
I read a thread that stated that if the bird is above 30M, it will return to home at it's current altitude.

Again, is the 'above 30M' calculated based on current AGL or Home Point AGL?

 

[GreggC]

There are a few threads on the RTH & Altitude, and I wanted to confirm a couple of important points with documented answers that were not opinions.
I think this is an important point that should be clarified. The FAA uses MSL as a baseline, but obstructions are posted as AGL. For UAV Pilots, the small scale of our operations makes this a very relevant question.

QUESTION 1:
Is the RTH Altitude calculated based on the Home position altitude as the base?
Example:

Home point is 1000 ft ASL
Flight area is 1200 ft ASL
RTH Altitude is set to 100 ft

What altitude will the bird RTH? If RTH is set based on the Home point, the bird would DESCEND and return.

QUESTION 2:
I read a thread that stated that if the bird is above 30M, it will return to home at it's current altitude.

Again, is the 'above 30M' calculated based on current AGL or Home Point AGL?

RTH is based on the home point altitude,
If your RTH altitude is set at 30 meters and your flying above 30 meters and activate RTH it will not descend to 30 meters, it will fly home at the altitude its at when RTH is activated.
If you are below 30 meters it will ascend to 30 meters and fly home.

 

[Fletch911]

Very nice, and logical. So suggested verbiage for the DJI manual would be to say that:

RETURN TO HOME ALTITUDE
"Return to Home (RTH) altitude is the minimum altitude, based on the altitude as measured at the Home point."

That sums it up very nicely. Thanks!

 

[jaywils]

So the altitude as indicated on GO app is relative to the home point, and not the height above the ground during flight, right?
A good point to remember if there are hills around that are higher than your launch point...which is never a good idea anyway.

 

[GreggC]

Yes,
RTH altitude will be "XX" above the exact spot on this planet where you take off.
And if you have hills, trees, buildings...etc in the area your RTH altitude should be 20 / 30 meters above the highest object.

 

[Dirby]

set your rth altitude to 100 meters and you should be fine.
100 m is 320 feet

 

[GreggC]

II would not recommend that,
If you have a "critical low battery" RTH the Phantom has to climb to 100 meters,
That's a lot of altitude, that's going to use a lot of battery, maybe too much to get home. Could fall out of the sky.
Just my opinion.

 

[ViperNuke]

Critical low battery rtl will land the phantom immediately I think..

 

[ParsnipHysorter]

So the altitude as indicated on GO app is relative to the home point, and not the height above the ground during flight, right?
A good point to remember if there are hills around that are higher than your launch point...which is never a good idea anyway.

Right. One way to think about it is the P3 has no idea how high above the ground it is, only height relative to the home point. Plan accordingly.

One potential way around this would be to use the GPS-calculated altitude above mean sea level in conjunction with a detailed digital topographic model of the area so it could terrain-fly, but this would have limitations and is currently not available in the P3... maybe some day?

 

[MichaelR]

Yes, I been thinking about this too.
I think that a smart feature for the Phantom 4 would be real-time altitude reading. I.e. Altitude above the ground at all times.... as well as maintaining the existing altitude reletive to Home Point of course.

I also think other cool features for future models might include an emergency built in back-up battery feature, which could save the bird in these sudden critical battery situations. Kind of like a 'limp home feature' you see in cars etc.

An emergency-only built-in parachute system, again for when there is a critical issue and it starts freefalling out of the sky for whatever reason.

None of these critical type issues have happened to me yet (touch wood), about 75 flights in, but reading some of these posts here, you never know!

Any thoughts..?

 

[Meta4]

Any thoughts..?

Weight

 

[John Locke]

Cost. Very little ROI

 

[JFHughes08088]

I like the parachute idea. Could be triggered by a drop fatter then x feet per second

 

[Erroll]

I like the parachute idea. Could be triggered by a drop fatter then x feet per second

Surely that would require a fast on-board barometer?

I seem to recall that Hubsan were working on a parachute which will trigger based on the attitude or orientation of the quad.

 

[tcope]

I always feel the need to throw my _opinion_ on on these threads.... my _recommendation_ (means, YMMV) is that people not rely on RTH just to fly the P3 back home. It should only be used when manual flight back is not possible. Again, this is just my opinion. I just don't think it's wise to give up control when you don't need to. It creates a door for issues. Not saying that there is anything wrong with RTH, I just don't see the need to create that door to something perhaps going wrong.