Hi! Yes, I know that faster-than-light travel is impossible. But please stay with me for a while to help me understand this. Let's imagine we take some unobtainium and build a 12-km-radius propeller, attached to an engine able to accelerate it up to 250,000 rpm (like a turbocharger, or not a few large industrial motors and turbines.) Then we plug this engine to the nearest sun or whatever and smoothly accelerate the thing. According to my (classical) calculations, the tips of the propeller would reach a linear velocity of c slightly under 239,000 rpm, and we'd still have over 11,000 remaining rpm's to (classically) accelerate them above c. To keep the thing stable, we maybe could add another counter-rotating propeller, as in Kamov-style helicopters. I know Relativity totally forbids this. But... what would happen as we approach the 239,000 rpm mark to make it impossible, please?