[QC102]

I have been trying to sort this out for a while now.. been up and down the settings in increments of 5 then 2's and 3's.
Then by leaving one setting and doing the same with the other two. Snag is there are more variations than a winning lottery number.
I have  scoured youTube, scoured forums but it all seems to beat me hands down.
It seems I can get it to hover in "clean air" at around 6feet its obviously has a little drift. If I correct ie left /right  Ail movements.. it tilts to move and  drops level when I center the stick. These are quick flick movements. 
It seems OK  but if I try to use Yaw - it drops - not a fast dive - and  comes under control  given  a flip of throttle.
getting to wonder if  I am expecting too much..

I have  more than double checked the motors, ESC (no brake on - it squeals at about 50%- 60% power if I have them activated Bheli needed??)

The frame is a 500 "Alien" off eBay.
Motors are 2212 920KV Mars motors
ESC are Emax SimonK 30A
FC  is CC3D
I use DJI Phantom Props
Lipos vary 2200KvH 3 cell 25-35c Turnigy  and 4000KvH 3 cell10c   Turnigy

I have  attached  a .UAF export.
If anybody has time and patience to check it out - I am hoping you can  help.

TIA

[TheOtherCliff]

I fly that exact setup eBay Alien with a2212 920kv (some sell these as 1000kv) and it works fine with default PIDs on 3s with 10x4.5 props.  The phantom 9.4 inch props should be perfect too.

If you are using 16.09 (RC) you can try AutoTune, but really the default settings work well.
AutoTune will make the PIDs a bit tighter, so Attitude mode will hold better in fast forward flight.
https://librepilot.atlassian.net/wiki/display/LPDOC/AutoTune

[TheOtherCliff]

Also, the stock flight mode does not change the throttle when you change the bank angle, so when you are banked, some of the thrust goes sideways and less goes down, so it will drop a little.  CruiseControl and/or AltitudeVario (thrust modes) will correct for that if you enable them.

First rule of quadcopters (OK, maybe not first...) don't touch the transmitter trims.  Set them all back where they were when you did the transmitter wizard, then use Attitude -> Settings -> RotateVirtual to make it hover without drift.  If you don't know where they were, center them and re-run the tx wizard.  I usually get down to about 0.2 degree increments on rotate virtual.  If it is drifting forward you subtract from pitch.  If it is drifting left you subtract from roll.  Etc.

BLHeli is generally good (use PWMSync in GCS setup, not OneShot) and you should not hear anything different with light damping enabled.

[QC102]

It was that sudden dip which I did not understand - your explanation clears that up now.
I will try what you suggested an see how it improves.

I wanted this particular build to be as  stable as possible - as advised when  fitting GPS - which is my next move NEO M8N.
I have 16.09 and just testing the GPS - its picking up 11 sats indoors - which is almost  what My Phantom 3 Pro does.

Thanks for that advice, much appreciated.