@sanderux thanks for the reply.
You are right, that motor config was not powerful enough to keep the airspeed at 15 m/s.
I've been experimenting with the original Volantex motor and a T-Motor MN4012 480KV. The log you looked at was with the 480 kv, 6s lipo, Hobbywing Skywalker 80a esc, and the 10" prop that came with the plane. As you say it struggles to maintain 15 m/s.
When I test with the original 1100 kv (?) motor and 6s, it cruises easily at 15 m/s and 50%-60% throttle but draws about 15a. So I would like to get my quadranger running with the more efficient 480 kv motor.
Here's another test with the 480 kv motor and an 11" prop, angled up a bit so it gets about 2mm clearance from the fuselage: http://review.px4.io/plot_app?log=7e2a79cf-317f-4db0-a6c7-c47b69cd9834 . I also added a bit of upward trim to the elevator hoping to prevent the drop during the transition.
Now the plane takes about 20s to complete the transition to 13 m/s and cruises at 15 m/s at 80%-90% throttle drawing only 8-9a. I like that, so I didn't try cutting the cruise speed to 13 yet.
I am still confused about the transition logic, though. Visually, I saw that after reaching 13 m/s, the pusher motor stopped for almost 1s. Without any thrust, the plane glided with a bit of upwards pitch. Then it made a pitch adjustment and restarted the motor, resulting in a drop of about 5 m then some compensation then went on about the mission very well.
I'm fine with that if it's the expected transition behavior, but wouldn't it make more sense to keep the throttle up until the desired cruise speed is reached, or maybe first cut the throttle to the FW_THROTTLE_CRUISE level rather than 0?
Just trying to understand what PX4 is doing here. Any other comments about the config welcome. I'm also planning to try the same motor with a modified motor mount and 12" prop.