"P" factor question

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  • #16
    Originally posted by Larry sreyoB View Post
    You can adjust your browser's zoom-level with <CTRL><+> and <CTRL><->. <CTRL><0> takes you back to 100%.

    Chuckle, you always speak in Greek??????

    best, randy

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    • #17
      Originally posted by Tom Charlton View Post
      Hi Tom T.
      . . . I’d postulate that: The –mass- of the rotating parts, non-accelerating, constant RPM, is irrelevant. The resistance to turning the propeller against air molecules is everything.

      Regards,
      Tom Charlton
      Possibly, but an image and sound of a P-51 rolling inverted and crashing directly in front of me at OSH upon jamming on the throttle to do a go-around after a botched formation landing is indelibly etched in my mind. I was not thinking in a detached manner and had neglected to factor in the weight of the prop.

      I will have to go think about this some more.

      I must ask those with experience in both types (in-line/"V" vs Radial) if one type or the other has more of a tendency to bite when jamming on the throttle.

      - TT
      Tom Tyson-A&P

      Pilots without Mechanics are just Pedestrians with fancy watches . . .
      ( . . . and Mechanics without Pilots are Unemployed.)

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      • #18
        So how does that work if the aircraft is on a treadmill?

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        • #19
          Tom, I'd expect the inlines to react worse because they had higher rpm limits than radials: larger change in angular momentum with a sudden application.

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          • #20
            Originally posted by Tom Tyson View Post
            Possibly, but an image and sound of a P-51 rolling inverted and crashing directly in front of me at OSH upon jamming on the throttle to do a go-around . . .
            Hi Tom T,
            Ya-but, but . . . note my “non-accelerating” mention.
            non-accelerating, constant RPM
            Likely incorporated into my sentence in a confusing manor.

            I will have to go think about this some more.
            Ha, don’t we all! Sometimes I even think with less than inconsequential inconsistencies! (now what’n the sam-heck does he mean with that) (Hmm . . . nice word salad)

            Regards,
            Tom Charlton (likely good that he’s confined his self to fly’n a Cub now-a-days)<g>
            "The aeroplane has unveiled for us the true face of the earth." - Antoine de Saint-Exupery

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            • #21
              Originally posted by Mase Taylor View Post
              So how does that work if the aircraft is on a treadmill?
              Sorry Mase, I beat ya to it in my post# 5 of this thread:<g>
              Hidden within the word salad of my post you’ll find:
              You could do an experiment with an airplane on a giant treadmill.<GD&R>
              But . . . your contributions are always appreciated and looked forward to with great anticipation.

              BTW, Got your tickets for Duluth?

              Regards,
              Tom Charlton (who doesn’t recall ever having been on an actual treadmill<g>)

              Last edited by Tom Charlton; 07-09-2018, 13:38.
              "The aeroplane has unveiled for us the true face of the earth." - Antoine de Saint-Exupery

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              • #22
                Originally posted by Larry sreyoB View Post
                You can adjust your browser's zoom-level with <CTRL><+> and <CTRL><->. <CTRL><0> takes you back to 100%.

                Larry….that was wayyy too easy, Thanks.

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                • #23
                  Originally posted by Randy Sohn View Post

                  Chuckle, you always speak in Greek??????

                  best, randy
                  Not Greek... He speaks GEEK...

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                  • #24
                    Originally posted by Jeff Hartmann View Post

                    Not Greek... He speaks GEEK...
                    Chuckle, nah, I just meant that the advice you'd offered was "Greek to me".

                    best , randy (who is severely technical/computer challenged, "sorry 'bout that")

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                    • #25
                      There are actually two reactions.

                      Torque is free space thing ,based on mass and acceleration.

                      But in air, with a prop, you have a different, but similar consequencies factor, of the "bite" of the prop.

                      Two identical engines with flat blade props (no twist, no airfoil). One is set with the blades in full flat pitch, the other with the blades set to full feather pitch.

                      At idle, slam the throttle forward, which one is going to produce the most amount of rolling motion?

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                      • #26
                        Terry--
                        Remember that an instant before the power application, the blade drag is contributing some torque reaction, which is being taken up by aileron trim. When you slam the throttle, the torque the crank delivers to the prop jumps up, and by Newton's 3rd, the same torque increase is delivered to the airframe, and you get roll motion.

                        As the prop accelerates, the blade drag goes up as the inertia reaction tapers off. Eventually, you reach a steady state where the torque reaction is increased by a comparatively small amount, and you adjust the aileron trim to take it up. The consequence of a prop being in flat pitch is not so much increasing the roll reaction as extending it for a longer time.

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                        • #27
                          Hmm, I will have to think about that a bit.

                          In flat pitch, the prop's contribution would be the mass being accelerated. With feather pitch, there would be the drag part of it.

                          Another point of view, once accelerated, and at steady state RPM, a flat pitch prop would have little torque reaction. But a feather pitch prop would have a torque reaction from the drag.

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                          • #28
                            Originally posted by Terry Carraway View Post
                            Hmm, I will have to think about that a bit.

                            In flat pitch, the prop's contribution would be the mass being accelerated. With feather pitch, there would be the drag part of it.

                            Another point of view, once accelerated, and at steady state RPM, a flat pitch prop would have little torque reaction. But a feather pitch prop would have a torque reaction from the drag.
                            Hi Terry,

                            Yup that’s what I’m think’n there’s torque from accelerating the inertia of the prop. A separate consideration is steady state RPM wherein torque is just a function of how hard does the power plant need to work to keep’er spinning.

                            Seems I read something in the past saying with a typical General Aviation aircraft the torque was about equivalent to moving from the right seat to the left seat. In effect . . . inconsequential.

                            Regards,
                            Tom Charlton




                            "The aeroplane has unveiled for us the true face of the earth." - Antoine de Saint-Exupery

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                            • #29
                              Originally posted by Terry Carraway View Post
                              In flat pitch, the prop's contribution would be the mass being accelerated. With feather pitch, there would be the drag part of it.

                              Another point of view, once accelerated, and at steady state RPM, a flat pitch prop would have little torque reaction. But a feather pitch prop would have a torque reaction from the drag.
                              Another point of view - the entire "ground return" of the engine's output goes into the airframe. That is, everything the engine produces that isn't lost in friction torques the aircraft. A high-performance engine mounted on the centerline in a light aircraft - that's going to get ugly.

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                              • #30
                                Originally posted by Russell Holton View Post
                                "ground return"
                                Excellent metaphor!

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