Why aren’t there airplane sized helicopters? Helicopters seem better in terms of no long runway needed, and the ease of moving in any direction.
In: Engineering
Physically, the big reason is the speed of sound.
Typically, you don’t want the tips of helicopter blades to go past the speed of sound, as it causes instability and less lift from the blades. So if you make the blades longer, they have to turn slower to keep their speed below the speed of sound. If you make the blades wider for more lift, it makes the rotating mass much heavier, which domino’s to make the whole drivetrain much heavier. That’s why ‘heavy lift’ helicopters have two main sets of blades. Additionally, say your blades rotate150mph below the speed of sound. It means that you can only move at 150mph horizontally before the blades go past the speed of sound as they rotate from the back to the front of the aircraft. So you can only easily make helicopters so big and so fast; planes have much higher limits on both of those factors.
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