Big alt lose when switch into RTL

Hello,everyone!
My plane 's firmware is Arduplane 3.7.1.When I fly it with FBWA where “the alt=100m,airspeed=20m/s”,my plane’s cruise speed is set 15m/s ,“ALT_HOLD_RTL” is set 75m,that is to say ,if switch to RTL mode ,my plane should fly to alt 75m,but the real phenomenon is big alt lose ,my plane keep falling . When alt is 30m,I switch to Manual to pull up my plane until safe landing.

Can you upload the dataflash log of this flight?

This is dataflash log, https://drive.google.com/open?id=0B8Meh7paj0moVVE5MWY1RzhTN3c.

I notice two strange things.

  1. The MSG message suggests the firmware is “Radius v1.7.1 (22b5c415)” Why is this not ArduPlane?
  2. The POS RelAlt message shows 0 for the entire flight, despite POS Alt showing values from 125[m] to 230[m]. Why would RelAlt be 0? If the firmware is not actually ArduPilot (as the MSG suggests) then could that be related?

Can anyone coment?

Best,
-Hunter

Thanks for your review!My plane’s firmware is Arduplane 3.7.1. The “Radius 1.7.1” is used to distinguish my plane from others.I give it a name “Radius 1.7.1”.
So why "The POS RelAlt message shows 0 for the entire flight, despite POS Alt showing values from 125[m] to 230[m].“I strongly think it is not related to the name"Radius”,maybe other reasons,I also wander why.

Sorry, I don’t know what would cause POS.RelAlt = 0 for the whole flight, while POS.Alt is non-zero, and BARO.Alt is also non-zero. This might be a good thing to figure out, though.

Can someone else help?

Got same problem too