RTL Altitude idea - or does it already exist?

ArduPlane Plane 4.2
1

I understand RTL altitude setting and thus if you are flying at any other alt and engage RTL (or have it engaged through failsafe etc) then the plane will fly to that configured Alt and fly home at that height (of above terrain if that is enabled etc). My suggestion/ask is this - is it possible to configure AP such that if the plane is flying under the configured RTL Alt, then it will climb to that level before heading home, but…and this is the bit I am looking for… if the plane is flying above that level and RTL is engaged, then it stays at the current alt all the way home?

My impetus for this requirement is that I fly over a windfarm regularly and have my RTL alt set at legal max alt of 120m, but I often climb to much higher altitudes than this to clear the turbine blades then drop to below the 120m legal ceiling once back on the home side of the turbines over clear land, but I fear that if RTL was engaged whilst amongst turbines (where I asm maybe flying at 170m alt), the plane would drop down to the 120m set altitude and potentially hit a spinning turbine on its way home.

2

The normal behaviors is to raise if below but continue at current altitude if triggered above.

I was wrong - see below.

3

Unfortunately that is correct for copter, but in plane RTL will descend to the RTL altitude if triggered from above. From the wiki:

The target altitude for RTL mode is set using the ALT_HOLD_RTL parameter in centimeters. When initiated below ALT_HOLD_RTL, Plane will immediately climb at maximum allowable rate to reach that altitude, if above, it will descend in a linear manner versus distance to home, reaching that altitude at the home loiter point.

@pauljatherton You should consider setting up multiple rally points and your own lost link route over the wind farm. Multiple rally points can be set up so if you’re already on the “home” side the plane won’t fly away. Rally Points — Plane documentation

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4

Noted - thanks for the correction.

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5

Thanks for the info Allister. Any idea if there are plans to include this feature in the Plane code? Seems strange its in copter only.

6

That’s a question for the Devs. I don’t know. I agree, I like the logic in the copter RTL.

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7

The current behaviour (linearly sloping down to end up at target altitude when reaching the home point) is arguably the most efficient since depending on the airframe it may be able to glide for some of the way. If RTL is triggered due to low battery, this makes sense as a way to maximize efficiency on the way home.

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8

Hi, can we use custom scripting for this feature, as we know the parameter which controls the RTL height so by applying a simple logic, whenever RTL triggered check the current alt if it is greater than ALT_HOLD_RTL parameter then replace it with current altitude value.

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