So I was wondering if someone could tell me when you have to get rid of the wings to land a bullseye everytime. Probably a gauged camera angle would be great (lets say top bottom view).
The Blastenheimer Bullseye achievement may take a few attempts, but essentially you want to lose your wings just after passing over the pier:
Keep in mind that you can be fired out of the cannon even without the quest, although if you have the quest then getting a bullseye will give you all 5 required cannon target points to complete the quest.
I have heard that the latest version of Deadly Boss Mods as of WoW patch 4.3.2 supports a warning telling you when to release from your wings, however I do not use DBM myself so cannot confirm this.
This comment on WoW Head also indicates that it is possible to create a temporary addon that will help with this achievement if you're struggling, although I have also never used this myself either.