Why would a turboprop rev down just before going full throttle during takeoff?

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The only turbprop I've travelled is the ATR 72. I've noticed that the props' rev go down (for like a second, the sound also goes down) just before engaging full throttle in order to takeoff. I've included a video (video is not mine), this thing happens at 1:40. Why the RPM drops for a sec? Or is this just the sound?










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    The only turbprop I've travelled is the ATR 72. I've noticed that the props' rev go down (for like a second, the sound also goes down) just before engaging full throttle in order to takeoff. I've included a video (video is not mine), this thing happens at 1:40. Why the RPM drops for a sec? Or is this just the sound?










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    New contributor




    Abrar Borno is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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      up vote
      3
      down vote

      favorite









      up vote
      3
      down vote

      favorite











      The only turbprop I've travelled is the ATR 72. I've noticed that the props' rev go down (for like a second, the sound also goes down) just before engaging full throttle in order to takeoff. I've included a video (video is not mine), this thing happens at 1:40. Why the RPM drops for a sec? Or is this just the sound?










      share|improve this question









      New contributor




      Abrar Borno is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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      The only turbprop I've travelled is the ATR 72. I've noticed that the props' rev go down (for like a second, the sound also goes down) just before engaging full throttle in order to takeoff. I've included a video (video is not mine), this thing happens at 1:40. Why the RPM drops for a sec? Or is this just the sound?







      takeoff propeller turboprop throttle sound






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      edited 4 hours ago









      ymb1

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      asked 6 hours ago









      Abrar Borno

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          2 Answers
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          Most likely this is happening after the pilot advances the power lever -- but the power lever controls both throttle (fuel flow, in a turbine), and propeller pitch.



          The propeller can change pitch pretty quickly, while the turbine takes longer to increase power (increased fuel flow must produce hotter combuster air, which must then spin up both the turbine-compressor section, and the independent shaft power turbine connected to the gear box and propeller). Usually, the engine's rotating parts will change RPM faster than the ones that spin the (relatively large) propeller, so you may hear the "whine" or "whistle" of the primary shaft spooling up before the propeller noise starts to rise, possibly even while the propeller is still slowing down from the pitch increase.






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            Because the pilot is taxiing the airplane with the props in the beta range (turboprops turn into landsharks if you don’t do this and you end up really riding the brakes to keep the speed down), then on takeoff, the propellers move into a maximum power setting, the engine snarls and slows a bit under the increased workload.






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              2 Answers
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              active

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              2 Answers
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              active

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              active

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              up vote
              5
              down vote













              Most likely this is happening after the pilot advances the power lever -- but the power lever controls both throttle (fuel flow, in a turbine), and propeller pitch.



              The propeller can change pitch pretty quickly, while the turbine takes longer to increase power (increased fuel flow must produce hotter combuster air, which must then spin up both the turbine-compressor section, and the independent shaft power turbine connected to the gear box and propeller). Usually, the engine's rotating parts will change RPM faster than the ones that spin the (relatively large) propeller, so you may hear the "whine" or "whistle" of the primary shaft spooling up before the propeller noise starts to rise, possibly even while the propeller is still slowing down from the pitch increase.






              share|improve this answer


























                up vote
                5
                down vote













                Most likely this is happening after the pilot advances the power lever -- but the power lever controls both throttle (fuel flow, in a turbine), and propeller pitch.



                The propeller can change pitch pretty quickly, while the turbine takes longer to increase power (increased fuel flow must produce hotter combuster air, which must then spin up both the turbine-compressor section, and the independent shaft power turbine connected to the gear box and propeller). Usually, the engine's rotating parts will change RPM faster than the ones that spin the (relatively large) propeller, so you may hear the "whine" or "whistle" of the primary shaft spooling up before the propeller noise starts to rise, possibly even while the propeller is still slowing down from the pitch increase.






                share|improve this answer
























                  up vote
                  5
                  down vote










                  up vote
                  5
                  down vote









                  Most likely this is happening after the pilot advances the power lever -- but the power lever controls both throttle (fuel flow, in a turbine), and propeller pitch.



                  The propeller can change pitch pretty quickly, while the turbine takes longer to increase power (increased fuel flow must produce hotter combuster air, which must then spin up both the turbine-compressor section, and the independent shaft power turbine connected to the gear box and propeller). Usually, the engine's rotating parts will change RPM faster than the ones that spin the (relatively large) propeller, so you may hear the "whine" or "whistle" of the primary shaft spooling up before the propeller noise starts to rise, possibly even while the propeller is still slowing down from the pitch increase.






                  share|improve this answer














                  Most likely this is happening after the pilot advances the power lever -- but the power lever controls both throttle (fuel flow, in a turbine), and propeller pitch.



                  The propeller can change pitch pretty quickly, while the turbine takes longer to increase power (increased fuel flow must produce hotter combuster air, which must then spin up both the turbine-compressor section, and the independent shaft power turbine connected to the gear box and propeller). Usually, the engine's rotating parts will change RPM faster than the ones that spin the (relatively large) propeller, so you may hear the "whine" or "whistle" of the primary shaft spooling up before the propeller noise starts to rise, possibly even while the propeller is still slowing down from the pitch increase.







                  share|improve this answer














                  share|improve this answer



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                  edited 3 hours ago

























                  answered 5 hours ago









                  Zeiss Ikon

                  1,1039




                  1,1039




















                      up vote
                      1
                      down vote













                      Because the pilot is taxiing the airplane with the props in the beta range (turboprops turn into landsharks if you don’t do this and you end up really riding the brakes to keep the speed down), then on takeoff, the propellers move into a maximum power setting, the engine snarls and slows a bit under the increased workload.






                      share|improve this answer
























                        up vote
                        1
                        down vote













                        Because the pilot is taxiing the airplane with the props in the beta range (turboprops turn into landsharks if you don’t do this and you end up really riding the brakes to keep the speed down), then on takeoff, the propellers move into a maximum power setting, the engine snarls and slows a bit under the increased workload.






                        share|improve this answer






















                          up vote
                          1
                          down vote










                          up vote
                          1
                          down vote









                          Because the pilot is taxiing the airplane with the props in the beta range (turboprops turn into landsharks if you don’t do this and you end up really riding the brakes to keep the speed down), then on takeoff, the propellers move into a maximum power setting, the engine snarls and slows a bit under the increased workload.






                          share|improve this answer












                          Because the pilot is taxiing the airplane with the props in the beta range (turboprops turn into landsharks if you don’t do this and you end up really riding the brakes to keep the speed down), then on takeoff, the propellers move into a maximum power setting, the engine snarls and slows a bit under the increased workload.







                          share|improve this answer












                          share|improve this answer



                          share|improve this answer










                          answered 1 hour ago









                          Carlo Felicione

                          35k263133




                          35k263133




















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