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Propellers have a fundamental speed limit on them, the tips can not exceed the speed of sound or else shock waves form which cause the efficiency to drop off sharply, as well as creating massive noise pollution from the sonic boom constantly coming off the propeller. Todays commercial "jet" engines are actually closer related to propeller planes than pure jets, turbofans provide the majority of their thrust from the ducted fan rather than the jet exhaust coming out the back.



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