Had it out again yesterday.
I had:
* CA glued the tail boom grip to stop the tail slipping.
* CA glued the tail boom support grip....
* CA glued the tail servo mount to stop it rotating under torque.
This had the effect of making the tail much more stable for the first battery.
On the second battery the tail vibrated a little and somehow managed to pop out the night head bars (tail stabilizer bars) that run from the base of the frame to half way along the tail. How in hell it popped them out I have no idea, they were under compression with the glued tail grips holding them fast. Neither tail boom nor the fin they go between had moved or unglued.
Bizarrely when one fell out the tail vibrated more until the other fell out, then the heli chilled out and fly stable again.
I have CA glued them back in!
This heli airframe was the first I built and I already have a replacement being built, a HK450 V2 with an upgraded metal head and tail. The screws are better as there are hardly any self tappers now in the V2, mostly metal->metal machine screws though a little soft still you can get them to torgue up better. So when the V1 gets damaged anymore and glue won't fix it, it's for the bin. Loss of a massive $24.99!