Maiden flight with APM 2.76 - Multiple issues

Hi all,

Finally managed to get a maiden flight with my X8 yesterday.

The aircraft flies well in manual mode, the CoG is correct and everything works as it should. It is appropriately powered with a thrust to weight ratio of about 0.8.

In manual it requires about 30% more elevon throw than one would expect with a flying wing, but I have found no cause for this and it may well be airframe specific.

Issue 1: Both the flash and the telemetry logs show exaggerated attitude values. As a visual estimate, I would say that the aircraft never exceeded +- 45-50deg in the roll and +-30deg in pitch. The values shown in the logs do not diverge from reality in a linear way. The indicated attitude seems to be roughly correct until about 20deg and then starts diverging as roll increases. I can guarantee the aircraft never reached the 80deg roll maximum that is indicated.

Other logged data also seems suspect, but it is difficult for me to say, as observing other aspects of flight may not be as accurate as an observation of attitude.

I was not aware of any of this behavior until I reviewed the logs.

Issue 2:

When attempting to tune FBWA, the aircraft was completely unresponsive to roll inputs at the baseline RLL2SRV_P value of 0.4. This was raised in increments of 0.1 at first with minimal changes observed. Increasing by increments of 0.2 brought observable results and the aircraft was responding in a satisfactory way at a RLL2SRV_P value of 1.6, Both D and I values were left at the baseline of 0 for the time being.

Pitch tuning was not successful. I got up to a  PTCH2SRV_P of 1.4 with only a very small observed response to input and decided not to go any higher until I have advice on this.

I guess my questions are as follows:

What are the possible causes and remedies of issue 1?

Is it possible that issue 1 is related to the consistently high GPS HDOP values during the flight (cca 2.0)

Is it possible that issue 2 is related to issue 1?

What are the maximum "healthy" values for RLL2SRV_P and PTCH2SRV_P?

If my P values are too high already, is there some sort of scaling parameter that can be applied?

P.S. Please note that the actual flight only starts around line 105800 of the flash log.

Flash log

Many thanks,


2013-11-23 14-37-32.tlog

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  • You should do some testing on the ground and see what graphs you get. 

    GPS shouldn't set attitude, it's the job of the accelerometer to do that. 

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