What's the difference between a “runaway prop” and a “feathered prop”?












22














My father was a P-51 fighter pilot in WWII. Another P-51 flown by a buddy of his suffered a "runaway prop", and as a result of that, the plane could not maintain its normal high speed, and in the end, the engine overheated and the plane exploded over the English Channel. Luckily, the pilot, Major Foy of the 357th FG, had noted excessively high engine temperatures, and bailed out just before it exploded. What would cause a "runaway prop" of the variable prop to create a loss of thrust and a high engine temperature?










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    22














    My father was a P-51 fighter pilot in WWII. Another P-51 flown by a buddy of his suffered a "runaway prop", and as a result of that, the plane could not maintain its normal high speed, and in the end, the engine overheated and the plane exploded over the English Channel. Luckily, the pilot, Major Foy of the 357th FG, had noted excessively high engine temperatures, and bailed out just before it exploded. What would cause a "runaway prop" of the variable prop to create a loss of thrust and a high engine temperature?










    share|improve this question







    New contributor




    Judd Peterson is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
    Check out our Code of Conduct.























      22












      22








      22


      1





      My father was a P-51 fighter pilot in WWII. Another P-51 flown by a buddy of his suffered a "runaway prop", and as a result of that, the plane could not maintain its normal high speed, and in the end, the engine overheated and the plane exploded over the English Channel. Luckily, the pilot, Major Foy of the 357th FG, had noted excessively high engine temperatures, and bailed out just before it exploded. What would cause a "runaway prop" of the variable prop to create a loss of thrust and a high engine temperature?










      share|improve this question







      New contributor




      Judd Peterson is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.











      My father was a P-51 fighter pilot in WWII. Another P-51 flown by a buddy of his suffered a "runaway prop", and as a result of that, the plane could not maintain its normal high speed, and in the end, the engine overheated and the plane exploded over the English Channel. Luckily, the pilot, Major Foy of the 357th FG, had noted excessively high engine temperatures, and bailed out just before it exploded. What would cause a "runaway prop" of the variable prop to create a loss of thrust and a high engine temperature?







      propeller






      share|improve this question







      New contributor




      Judd Peterson is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.











      share|improve this question







      New contributor




      Judd Peterson is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.









      share|improve this question




      share|improve this question






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      Judd Peterson is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.









      asked Dec 19 at 4:48









      Judd Peterson

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      Judd Peterson is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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          2 Answers
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          37














          A "run away prop" is caused by a failure of the pitch control mechanism of a constant speed propeller. Feathering turns the prop blade as close to 90 degrees to the wind as possible, minimizing the effects of the airstream. This obviously reduces drag and is used when an engine is shut down.



          A run away condition is created when the propeller malfunction causes the blade to move to the "fine" setting, which is used at slower air speeds. It is the opposite of being feathered in that now the prop blades are much more angled to the wind as in a windmill. The force of the airstream literally now turns the engine to excessive rpm. The prop is at the wrong pitch for its airspeed, much like a truck dropping into low gear at highway speed. The engine rpm redlines and causes overheating, while the drag of the improperly set prop slows the plane down.



          Thankfully, the pilot was aware of the danger and was able to get away.






          share|improve this answer

















          • 1




            If the effect of this is an overheating/exploding engine, how do you survive this in an aircraft where you can't easily bail out?
            – Phillip Copley
            Dec 19 at 14:53






          • 4




            Related incident: Atlantic Southeast Airlines Flight 2311
            – Ferrybig
            Dec 19 at 15:41






          • 1




            To target the question, the difference between the two prop settings is something approaching 90 degrees.
            – Criggie
            Dec 19 at 18:58






          • 2




            @FreeMan He asked "how do you survive this in an aircraft where you can't easily bail out". Modern constant-speed prop GA and commercial planes don't have ejection seats, and it's not standard practice to pack parachutes for all on board. This applies to more than WWII-era military aircraft.
            – Roy Tinker
            Dec 19 at 20:27








          • 3




            @PhillipCopley: You don't.
            – Sean
            Dec 19 at 22:04



















          13














          The prop regulates engine rpm using a flyweight governor (functionally similar to the ones on steam engines) which drive propeller pitch coarse or fine as required to keep rpm constant, regardless of throttle setting. The governor either controls an electric signal (curtiss electric) or engine oil pressure (hydramatic propellers) to provide the driving force to rotate the blades.



          The aerodynamic loads on the blades are always trying to drive them to full fine pitch and the servo forces varied by the governor push against that. If the governor fails or the oil supply to the prop hub fails such that the governor is not able to vary the blades against air loads, the blades will naturally relax to the full fine position, which unloads the engine and allows it to overspeed; how badly depends on the throttle setting.



          So if a prop runs away, you'll be cruising along minding your own business and suddenly the RPM will surge past the redline until you yank the throttle back. It's not that different from pushing in the clutch on a car while you've got the pedal down. You'd better let off on the gas post haste if you don't want to destroy the engine.



          Overheating is something else. A runaway happens very quickly, whereas an overheating engine is more of a long term problem. Not sure if the overheating was directly related to the prop problems. If you'd had a runaway but were able to reduce the throttle enough to keep the engine at or below redline rpm, I'm not sure why you'd get overheating with the power cut way back. It's possible that to avoid descending, he kept enough throttle on to maintain altitude but in doing so the rpm remained well above redline and the extended overspeed operation overheated the engine (Mostly from the excess heat generated by the too fast piston movement).






          share|improve this answer





















          • the frictional heating created by an engine being forced to spin in overspeed is enough to wreck the engine and start it on fire even if the engine itself is shut down (mags off) while windmilling.
            – niels nielsen
            Dec 20 at 4:59











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          2 Answers
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          2 Answers
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          active

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          37














          A "run away prop" is caused by a failure of the pitch control mechanism of a constant speed propeller. Feathering turns the prop blade as close to 90 degrees to the wind as possible, minimizing the effects of the airstream. This obviously reduces drag and is used when an engine is shut down.



          A run away condition is created when the propeller malfunction causes the blade to move to the "fine" setting, which is used at slower air speeds. It is the opposite of being feathered in that now the prop blades are much more angled to the wind as in a windmill. The force of the airstream literally now turns the engine to excessive rpm. The prop is at the wrong pitch for its airspeed, much like a truck dropping into low gear at highway speed. The engine rpm redlines and causes overheating, while the drag of the improperly set prop slows the plane down.



          Thankfully, the pilot was aware of the danger and was able to get away.






          share|improve this answer

















          • 1




            If the effect of this is an overheating/exploding engine, how do you survive this in an aircraft where you can't easily bail out?
            – Phillip Copley
            Dec 19 at 14:53






          • 4




            Related incident: Atlantic Southeast Airlines Flight 2311
            – Ferrybig
            Dec 19 at 15:41






          • 1




            To target the question, the difference between the two prop settings is something approaching 90 degrees.
            – Criggie
            Dec 19 at 18:58






          • 2




            @FreeMan He asked "how do you survive this in an aircraft where you can't easily bail out". Modern constant-speed prop GA and commercial planes don't have ejection seats, and it's not standard practice to pack parachutes for all on board. This applies to more than WWII-era military aircraft.
            – Roy Tinker
            Dec 19 at 20:27








          • 3




            @PhillipCopley: You don't.
            – Sean
            Dec 19 at 22:04
















          37














          A "run away prop" is caused by a failure of the pitch control mechanism of a constant speed propeller. Feathering turns the prop blade as close to 90 degrees to the wind as possible, minimizing the effects of the airstream. This obviously reduces drag and is used when an engine is shut down.



          A run away condition is created when the propeller malfunction causes the blade to move to the "fine" setting, which is used at slower air speeds. It is the opposite of being feathered in that now the prop blades are much more angled to the wind as in a windmill. The force of the airstream literally now turns the engine to excessive rpm. The prop is at the wrong pitch for its airspeed, much like a truck dropping into low gear at highway speed. The engine rpm redlines and causes overheating, while the drag of the improperly set prop slows the plane down.



          Thankfully, the pilot was aware of the danger and was able to get away.






          share|improve this answer

















          • 1




            If the effect of this is an overheating/exploding engine, how do you survive this in an aircraft where you can't easily bail out?
            – Phillip Copley
            Dec 19 at 14:53






          • 4




            Related incident: Atlantic Southeast Airlines Flight 2311
            – Ferrybig
            Dec 19 at 15:41






          • 1




            To target the question, the difference between the two prop settings is something approaching 90 degrees.
            – Criggie
            Dec 19 at 18:58






          • 2




            @FreeMan He asked "how do you survive this in an aircraft where you can't easily bail out". Modern constant-speed prop GA and commercial planes don't have ejection seats, and it's not standard practice to pack parachutes for all on board. This applies to more than WWII-era military aircraft.
            – Roy Tinker
            Dec 19 at 20:27








          • 3




            @PhillipCopley: You don't.
            – Sean
            Dec 19 at 22:04














          37












          37








          37






          A "run away prop" is caused by a failure of the pitch control mechanism of a constant speed propeller. Feathering turns the prop blade as close to 90 degrees to the wind as possible, minimizing the effects of the airstream. This obviously reduces drag and is used when an engine is shut down.



          A run away condition is created when the propeller malfunction causes the blade to move to the "fine" setting, which is used at slower air speeds. It is the opposite of being feathered in that now the prop blades are much more angled to the wind as in a windmill. The force of the airstream literally now turns the engine to excessive rpm. The prop is at the wrong pitch for its airspeed, much like a truck dropping into low gear at highway speed. The engine rpm redlines and causes overheating, while the drag of the improperly set prop slows the plane down.



          Thankfully, the pilot was aware of the danger and was able to get away.






          share|improve this answer












          A "run away prop" is caused by a failure of the pitch control mechanism of a constant speed propeller. Feathering turns the prop blade as close to 90 degrees to the wind as possible, minimizing the effects of the airstream. This obviously reduces drag and is used when an engine is shut down.



          A run away condition is created when the propeller malfunction causes the blade to move to the "fine" setting, which is used at slower air speeds. It is the opposite of being feathered in that now the prop blades are much more angled to the wind as in a windmill. The force of the airstream literally now turns the engine to excessive rpm. The prop is at the wrong pitch for its airspeed, much like a truck dropping into low gear at highway speed. The engine rpm redlines and causes overheating, while the drag of the improperly set prop slows the plane down.



          Thankfully, the pilot was aware of the danger and was able to get away.







          share|improve this answer












          share|improve this answer



          share|improve this answer










          answered Dec 19 at 5:30









          Robert DiGiovanni

          1,4251315




          1,4251315








          • 1




            If the effect of this is an overheating/exploding engine, how do you survive this in an aircraft where you can't easily bail out?
            – Phillip Copley
            Dec 19 at 14:53






          • 4




            Related incident: Atlantic Southeast Airlines Flight 2311
            – Ferrybig
            Dec 19 at 15:41






          • 1




            To target the question, the difference between the two prop settings is something approaching 90 degrees.
            – Criggie
            Dec 19 at 18:58






          • 2




            @FreeMan He asked "how do you survive this in an aircraft where you can't easily bail out". Modern constant-speed prop GA and commercial planes don't have ejection seats, and it's not standard practice to pack parachutes for all on board. This applies to more than WWII-era military aircraft.
            – Roy Tinker
            Dec 19 at 20:27








          • 3




            @PhillipCopley: You don't.
            – Sean
            Dec 19 at 22:04














          • 1




            If the effect of this is an overheating/exploding engine, how do you survive this in an aircraft where you can't easily bail out?
            – Phillip Copley
            Dec 19 at 14:53






          • 4




            Related incident: Atlantic Southeast Airlines Flight 2311
            – Ferrybig
            Dec 19 at 15:41






          • 1




            To target the question, the difference between the two prop settings is something approaching 90 degrees.
            – Criggie
            Dec 19 at 18:58






          • 2




            @FreeMan He asked "how do you survive this in an aircraft where you can't easily bail out". Modern constant-speed prop GA and commercial planes don't have ejection seats, and it's not standard practice to pack parachutes for all on board. This applies to more than WWII-era military aircraft.
            – Roy Tinker
            Dec 19 at 20:27








          • 3




            @PhillipCopley: You don't.
            – Sean
            Dec 19 at 22:04








          1




          1




          If the effect of this is an overheating/exploding engine, how do you survive this in an aircraft where you can't easily bail out?
          – Phillip Copley
          Dec 19 at 14:53




          If the effect of this is an overheating/exploding engine, how do you survive this in an aircraft where you can't easily bail out?
          – Phillip Copley
          Dec 19 at 14:53




          4




          4




          Related incident: Atlantic Southeast Airlines Flight 2311
          – Ferrybig
          Dec 19 at 15:41




          Related incident: Atlantic Southeast Airlines Flight 2311
          – Ferrybig
          Dec 19 at 15:41




          1




          1




          To target the question, the difference between the two prop settings is something approaching 90 degrees.
          – Criggie
          Dec 19 at 18:58




          To target the question, the difference between the two prop settings is something approaching 90 degrees.
          – Criggie
          Dec 19 at 18:58




          2




          2




          @FreeMan He asked "how do you survive this in an aircraft where you can't easily bail out". Modern constant-speed prop GA and commercial planes don't have ejection seats, and it's not standard practice to pack parachutes for all on board. This applies to more than WWII-era military aircraft.
          – Roy Tinker
          Dec 19 at 20:27






          @FreeMan He asked "how do you survive this in an aircraft where you can't easily bail out". Modern constant-speed prop GA and commercial planes don't have ejection seats, and it's not standard practice to pack parachutes for all on board. This applies to more than WWII-era military aircraft.
          – Roy Tinker
          Dec 19 at 20:27






          3




          3




          @PhillipCopley: You don't.
          – Sean
          Dec 19 at 22:04




          @PhillipCopley: You don't.
          – Sean
          Dec 19 at 22:04











          13














          The prop regulates engine rpm using a flyweight governor (functionally similar to the ones on steam engines) which drive propeller pitch coarse or fine as required to keep rpm constant, regardless of throttle setting. The governor either controls an electric signal (curtiss electric) or engine oil pressure (hydramatic propellers) to provide the driving force to rotate the blades.



          The aerodynamic loads on the blades are always trying to drive them to full fine pitch and the servo forces varied by the governor push against that. If the governor fails or the oil supply to the prop hub fails such that the governor is not able to vary the blades against air loads, the blades will naturally relax to the full fine position, which unloads the engine and allows it to overspeed; how badly depends on the throttle setting.



          So if a prop runs away, you'll be cruising along minding your own business and suddenly the RPM will surge past the redline until you yank the throttle back. It's not that different from pushing in the clutch on a car while you've got the pedal down. You'd better let off on the gas post haste if you don't want to destroy the engine.



          Overheating is something else. A runaway happens very quickly, whereas an overheating engine is more of a long term problem. Not sure if the overheating was directly related to the prop problems. If you'd had a runaway but were able to reduce the throttle enough to keep the engine at or below redline rpm, I'm not sure why you'd get overheating with the power cut way back. It's possible that to avoid descending, he kept enough throttle on to maintain altitude but in doing so the rpm remained well above redline and the extended overspeed operation overheated the engine (Mostly from the excess heat generated by the too fast piston movement).






          share|improve this answer





















          • the frictional heating created by an engine being forced to spin in overspeed is enough to wreck the engine and start it on fire even if the engine itself is shut down (mags off) while windmilling.
            – niels nielsen
            Dec 20 at 4:59
















          13














          The prop regulates engine rpm using a flyweight governor (functionally similar to the ones on steam engines) which drive propeller pitch coarse or fine as required to keep rpm constant, regardless of throttle setting. The governor either controls an electric signal (curtiss electric) or engine oil pressure (hydramatic propellers) to provide the driving force to rotate the blades.



          The aerodynamic loads on the blades are always trying to drive them to full fine pitch and the servo forces varied by the governor push against that. If the governor fails or the oil supply to the prop hub fails such that the governor is not able to vary the blades against air loads, the blades will naturally relax to the full fine position, which unloads the engine and allows it to overspeed; how badly depends on the throttle setting.



          So if a prop runs away, you'll be cruising along minding your own business and suddenly the RPM will surge past the redline until you yank the throttle back. It's not that different from pushing in the clutch on a car while you've got the pedal down. You'd better let off on the gas post haste if you don't want to destroy the engine.



          Overheating is something else. A runaway happens very quickly, whereas an overheating engine is more of a long term problem. Not sure if the overheating was directly related to the prop problems. If you'd had a runaway but were able to reduce the throttle enough to keep the engine at or below redline rpm, I'm not sure why you'd get overheating with the power cut way back. It's possible that to avoid descending, he kept enough throttle on to maintain altitude but in doing so the rpm remained well above redline and the extended overspeed operation overheated the engine (Mostly from the excess heat generated by the too fast piston movement).






          share|improve this answer





















          • the frictional heating created by an engine being forced to spin in overspeed is enough to wreck the engine and start it on fire even if the engine itself is shut down (mags off) while windmilling.
            – niels nielsen
            Dec 20 at 4:59














          13












          13








          13






          The prop regulates engine rpm using a flyweight governor (functionally similar to the ones on steam engines) which drive propeller pitch coarse or fine as required to keep rpm constant, regardless of throttle setting. The governor either controls an electric signal (curtiss electric) or engine oil pressure (hydramatic propellers) to provide the driving force to rotate the blades.



          The aerodynamic loads on the blades are always trying to drive them to full fine pitch and the servo forces varied by the governor push against that. If the governor fails or the oil supply to the prop hub fails such that the governor is not able to vary the blades against air loads, the blades will naturally relax to the full fine position, which unloads the engine and allows it to overspeed; how badly depends on the throttle setting.



          So if a prop runs away, you'll be cruising along minding your own business and suddenly the RPM will surge past the redline until you yank the throttle back. It's not that different from pushing in the clutch on a car while you've got the pedal down. You'd better let off on the gas post haste if you don't want to destroy the engine.



          Overheating is something else. A runaway happens very quickly, whereas an overheating engine is more of a long term problem. Not sure if the overheating was directly related to the prop problems. If you'd had a runaway but were able to reduce the throttle enough to keep the engine at or below redline rpm, I'm not sure why you'd get overheating with the power cut way back. It's possible that to avoid descending, he kept enough throttle on to maintain altitude but in doing so the rpm remained well above redline and the extended overspeed operation overheated the engine (Mostly from the excess heat generated by the too fast piston movement).






          share|improve this answer












          The prop regulates engine rpm using a flyweight governor (functionally similar to the ones on steam engines) which drive propeller pitch coarse or fine as required to keep rpm constant, regardless of throttle setting. The governor either controls an electric signal (curtiss electric) or engine oil pressure (hydramatic propellers) to provide the driving force to rotate the blades.



          The aerodynamic loads on the blades are always trying to drive them to full fine pitch and the servo forces varied by the governor push against that. If the governor fails or the oil supply to the prop hub fails such that the governor is not able to vary the blades against air loads, the blades will naturally relax to the full fine position, which unloads the engine and allows it to overspeed; how badly depends on the throttle setting.



          So if a prop runs away, you'll be cruising along minding your own business and suddenly the RPM will surge past the redline until you yank the throttle back. It's not that different from pushing in the clutch on a car while you've got the pedal down. You'd better let off on the gas post haste if you don't want to destroy the engine.



          Overheating is something else. A runaway happens very quickly, whereas an overheating engine is more of a long term problem. Not sure if the overheating was directly related to the prop problems. If you'd had a runaway but were able to reduce the throttle enough to keep the engine at or below redline rpm, I'm not sure why you'd get overheating with the power cut way back. It's possible that to avoid descending, he kept enough throttle on to maintain altitude but in doing so the rpm remained well above redline and the extended overspeed operation overheated the engine (Mostly from the excess heat generated by the too fast piston movement).







          share|improve this answer












          share|improve this answer



          share|improve this answer










          answered Dec 19 at 5:21









          John K

          13.6k11442




          13.6k11442












          • the frictional heating created by an engine being forced to spin in overspeed is enough to wreck the engine and start it on fire even if the engine itself is shut down (mags off) while windmilling.
            – niels nielsen
            Dec 20 at 4:59


















          • the frictional heating created by an engine being forced to spin in overspeed is enough to wreck the engine and start it on fire even if the engine itself is shut down (mags off) while windmilling.
            – niels nielsen
            Dec 20 at 4:59
















          the frictional heating created by an engine being forced to spin in overspeed is enough to wreck the engine and start it on fire even if the engine itself is shut down (mags off) while windmilling.
          – niels nielsen
          Dec 20 at 4:59




          the frictional heating created by an engine being forced to spin in overspeed is enough to wreck the engine and start it on fire even if the engine itself is shut down (mags off) while windmilling.
          – niels nielsen
          Dec 20 at 4:59










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