I keyframed the propeller so that, every 5 frames, it spins around the local x 360º. However, when I play the animation, nothing moves at all. I'm starting at frame 0, so I'm not sure why it isn't working.
Before I parented the propeller to the fuselage, the propeller would spin, but on the global axis instead of the local axis. I read that the problem could be solved by simply parenting the prop to the fuselage, so that's exactly what I did.
EDIT: I figured out that it wasn't moving since it just thinks it has to get to the point at which it has revolved completely, so it just doesn't move. This creates another question: how do I make it so that the object does exactly what it's supposed to between keyframes, instead of just aiming for the end result?