Yes, we can help you.
Read and follow How to methodically tune (almost) any multicopter using ArduCopter 4.4.x
The bigger the vehicle the more you need to follow every step of that Blog post.
Your vehicle is very big, so you need to follow it extra carefully.
https://discuss.ardupilot.org/uploads/short-url/nv3HjLOPlOb66fc3ethXruci2TX.zip is an example of another vehicle