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I know the q400 is one of few airliners that has a turboprop engines. I know that some military airplanes use turboprop engines so why don't many airliners use them?

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    $\begingroup$ I believe this could answer your question: aviation.stackexchange.com/a/1817/9907 $\endgroup$ – 1101 Aug 21 '15 at 21:59
  • $\begingroup$ Most military airplanes are jets, not turboprops. $\endgroup$ – cpast Aug 21 '15 at 22:48
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    $\begingroup$ The question shows little or no prior research. A search returns the typical answer "Because propellers become less efficient as the speed of the aircraft increases, turboprops are used only for low speed aircraft like cargo planes. High speed transports usually use high bypass turbofans because of the high fuel efficiency and high speed capability of turbofans." (source). Some have speculated the fuel price increase may lead to widen the use of turboprop. $\endgroup$ – mins Aug 22 '15 at 10:28
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Turboprop engines are used in ATR aircraft too. The main reason the airlines are not using turboprop engines are,

  1. They are not as efficient as jet engines for high altitude long distance flights. This is why all the turboprop aircraft are used of short haul flights.
  2. Their efficiency decreases as the speed increases above Mach 0.6~0.7.In comparison, Boeing 747-8 cruises at around Mach 0.85.(Their efficient (cruise) speed is less compared to jet aircraft(~700-750 kmph versus ~880-840 kmph). This adds quite a bit of travel time to long haul flights.
  3. The cabin (and outside) is significantly quieter in case of turbofan engines when compared turboprop engines. This is an important issue in case of civil aircraft where the noise (and vibrations) affect passenger comfort.
  4. The turbofan engines produce a lot more thrust compared to turboprop engines, for a given size(the turboprop engine output is measured in shaft power though). This makes them unsuitable for large aircraft.
  5. The huge propellers in the large turboprop aircraft require long landing gears which increase the weight and complicate the maintenance.

The largest (and fastest) turboprop powered civil aircraft, flew slower and lower than jet aircraft from comparable era. It wasn't known for its comfort either.

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    $\begingroup$ Point 1 and 4 are utterly wrong. $\endgroup$ – Peter Kämpf Aug 22 '15 at 7:26
  • $\begingroup$ @Peter Is point 1 wrong even given point 2 (which seems to say that a turboprop will take longer to fly a certain distance at efficient speeds)? $\endgroup$ – cpast Aug 22 '15 at 16:00
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    $\begingroup$ @cpast: That depends on how you define efficiency (see the answer about the efficiency of the Concorde engines). But if we take the fuel per seat-mile (no speed involved), the turboprop clearly comes out ahead. If we take transport performance (lowest cost for seat-miles per hour), the competition is closer, but still in favor of turboprop $\endgroup$ – Peter Kämpf Aug 22 '15 at 17:58

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