Thanks for the feedback. Yeah, the gameplay loop is definitely lacking still. I'm working on improving that!
As far as parts/currency - they are currently just used for upgrades. I was trying to think of items that would be considered valuable and those were the first 3 I thought of. Though I just had the thought of "water" as I was typing this. I considered having ammo as an consumable but decided against it - can't entirely think of why at this moment.
The conveyance issues are always tricky, especially as I keep adding more "flair" to what's going on - some of it intentionally to distract. As far as the hits landing, there should be a "hit splash" as well as a sound effect. I'll see if I can work on the visibility/readability of the hit splash. But in answer to the question, yes you are hitting the helicopter. I think what hurts is you aren't really supposed to be encountering them in the early (weak) state. The helicopter has 25 HP and the starting bullets only deal 1 point of damage initially. Once you increase that damage and add things like "rapid fire" or "double shot" the choppers go down really easily. This in turn helps in conveying they're being hit! Otherwise it just feels like you're hopelessly spamming bullets to no end.
Sorry for the long reply. Thanks for giving it a play! Since they've recently extended the submission deadline a week, I plan to really work on the game loop and hope to have something a little more memorable by the end.