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Propellers work by creating an area of low pressure in front of the propeller, allowing the higher pressure air behind the propeller to push the propeller forward. If a propeller with long blades and a propeller with small blades were spinning at the same speed, then the propeller with long blades would provide more thrust. However, propellers with long blades require more force to spin, so a more powerful engine would be needed. Adding a propeller with long blades to an airplane could increase thrust, but the plane would need a heavier engine.