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Centre Of Pressure

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  • Centre Of Pressure

    Hi all,Is there anyone out there that knows how i could find the centre of pressure of a gyroplane? Does the centre of pressure have much effect on the centre of gravity say if centre of gravity was on the thrustline and the centre of pressure was say i dunno 300 to 450mm (foot to foot and half) from CLT, Could you still have the symptoms of a high thrustline machine at high speed?CheersTrent

  • #2
    Trent,If I understand your question correctly, then I would say YES.I think, If the vertical center of gravity VCG is on the thrustline...true CLT and if the frontal center of pressure was well below the thrustline, (18") then your center of drag is 18" below the thrustline, then yes I would think the craft could behave like a HTL unless you have a neg incidence stab countering, the low drag or lower center of pressure. Finding the center of pressure either frontal or side view can be approximated with a picture of the gyro and pilot insitu.Carefully Cut out the pictured pilot and gyro, then like a weather vane ****, you can find the pivot point, where it will spin in either direction, ie: balanced.Take the pivot point forward of the center of pressure and the gyro will now turn towards you when you blow on it, ie; the gyro will turn into the relative airflow. This is in the proper direction, stable.It does so because you have more plate surface area rear of the pivot point.You can take a picture of the front of the gyro with pilot instu and roughly estimate the center of drag/pressure by approximating the frontal surface area. If the gyro is CLT and you have a lot of surface area down low, ie, large cabin with long sloping windscreen etc, then at speed this is going to cause your gyro"s nose to lower.


    • #3
      Hi Mitch,thanks for taking your time to reply, the other Paul abbott book is the gyroplane flight manual. my first books i brought about gyro"s. Just thought there might have been some mathmatical way. Been doing some looking around on the forums and understand that rotor drag less"ns as speed increases (yes?????) and airframe drag increases naturally, there for making it worse again.... so i guess the only way to make a as close to stable machine is to have to centre of pressure and centre of gravity on the same line. Well i"ll try the cut out method on my rebuilt machine compared to old machine and see how much difference there is. Test flying is getting close just gotta dot the i"s and cross the t"s so hopefully in the next coupl"a weeks. yay


      • #4
        Anytime Trent.Mate, one of my favourite statements about CLT is this......The best setup is achieved by making the vertical C of D and C of G, coaxial (or nearly so) with the line of thrust.Even if the gyro is CLT or slightly low thrust line, a little neg incidence on the HS is still preferable and often built in to ensure the COG is held forward of the RTV.