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  • #46
    I have had wing tanks not properly feed before. I always dump the wing tank after 90 min of flight if I going somewhere.

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    • #47
      I seem to remember during my primary training, an instructor telling me that a windmilling prop is much like a solid disk of the same diameter. Not true???

      Mike Wood
      Montgomery, TX
      '46 BC12D
      N44085 #9885

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      • #48
        A windmilling prop would tend to be not stalled which means the airfoil generates "lift" which in this case causes rotation of the engine. I takes energy to overcome the friction and compression of the engine. That energy needs to come from somewhere and in this case it comes at the expense of the aircraft's movement through the air (drag) which is dependent on gravity.

        A stationary prop is most likely stalled (certainly all but the root portions) so while there is some energy used in creating some turbulence behind the blades, there is no energy taken by the engine (which of course is not rotating).

        So stationary/stalled blade takes less energy= lower drag.

        May seem counter intuitive but there you go. If there was no friction or compression in the engine that's a different story (but also a fictitious one).
        Scott
        CF-CLR Blog: http://c-fclr.blogspot.ca/

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        • #49
          If you do the match there is probably very little difference between a windmilling propeller and a stationary one. They are both induced drag if it not spinning at an rpm to equal pitch advancement or creating lift through excess rpm. The only way a stationary blade in less drag is if it is possible for you to feather it like in most twins. There is a reason twins have that ability.

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          • #50
            I'm not completely clear on what you mean Tom. Induced drag is a component of lift (but only if the lift is contributing to overcoming gravity). Lift created by the H stabilizer for example is actually drag as it's effectively adding to the weight of the airplane.

            The rotating prop has induced drag (sort of), but the stationary prop is all parasitic drag.

            Now in addition to the induced drag of the spinning prop, there is lift, which in this case is also drag (from the perspective of the airframe) because the lift is only turning the dead engine, not contributing to counteracting gravity. You basically have a wind turbine that extracts energy from the airflow, which comes from the aircraft's kinetic energy. Extracting kinetic energy means the aircraft slows or descends.

            The rotating prop converts the aircraft's kinetic energy into rotation of the engine which in turn generates heat, mostly through compressing and moving air through the combustion chambers. The heat will be dissipated through the engine's cooling fins. For the sake of argument, if you assume a broken crankshaft that allows the prop to spin without moving the pistons, maybe the prop spins up fast enough that the effective angle of attack on the blades minimizes drag to the point where there's less drag than the stationary prop. But that's not the scenario here.

            Stationary prop creates parasitic drag and nothing else. Drag increases at the square of speed, but this applies to both the spinning and stationary states.

            We all know it takes a fair amount of energy to swing a prop. Takes a lot more to turn it at a few hundred RPM.

            S
            Scott
            CF-CLR Blog: http://c-fclr.blogspot.ca/

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            • #51
              Originally posted by Scott View Post
              I'm not completely clear on what you mean Tom. S
              ??? I'm not sure that should have been directed at me.

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              • #52
                Originally posted by Scott View Post
                I'm not completely clear on what you mean Tom. Induced drag is a component of lift (but only if the lift is contributing to overcoming gravity). Lift created by the H stabilizer for example is actually drag as it's effectively adding to the weight of the airplane.

                The rotating prop has induced drag (sort of), but the stationary prop is all parasitic drag.

                Now in addition to the induced drag of the spinning prop, there is lift, which in this case is also drag (from the perspective of the airframe) because the lift is only turning the dead engine, not contributing to counteracting gravity. You basically have a wind turbine that extracts energy from the airflow, which comes from the aircraft's kinetic energy. Extracting kinetic energy means the aircraft slows or descends.

                The rotating prop converts the aircraft's kinetic energy into rotation of the engine which in turn generates heat, mostly through compressing and moving air through the combustion chambers. The heat will be dissipated through the engine's cooling fins. For the sake of argument, if you assume a broken crankshaft that allows the prop to spin without moving the pistons, maybe the prop spins up fast enough that the effective angle of attack on the blades minimizes drag to the point where there's less drag than the stationary prop. But that's not the scenario here.

                Stationary prop creates parasitic drag and nothing else. Drag increases at the square of speed, but this applies to both the spinning and stationary states.

                We all know it takes a fair amount of energy to swing a prop. Takes a lot more to turn it at a few hundred RPM.

                S
                I think it was meant for me, and should have said parasite drag, not induced.

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                • #53
                  whoops, My BAD, sorry getting nicknames mixed up. I guess we use nicknames for a reason and I shouldn't try to shortcut same. my apologies.
                  Scott
                  CF-CLR Blog: http://c-fclr.blogspot.ca/

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