It'll never fly
it will never fly
There's no chance that something will work or be successful. He wants to work from home full time, but it will never fly with the bosses. It's an interesting concept, but it would never fly with ordinary consumers.
It'll never fly.
Fig. It will never work!; It will never be approved! (Refers originally to an evaluation of an unlikely-looking aircraft of some type.) l have read your report and studied your proposal. It'll never fly. Your design for a new electric automobile is interesting, but it'll never fly!