Announcement

Collapse
No announcement yet.

Main Gear distance back from CG?

Collapse
X
  • Filter
  • Time
  • Show
Clear All
new posts

  • Main Gear distance back from CG?

    When looking in top view, is there a generally accepted distance that the main gear be from the craft's CG? Most single-place gyros rock back on their tails without pilot, others like the Sport Copter do not. When watching someone balance on the mains during takeoff it might be assumed that the gear should be located directly under the CG, but as with many things gyro related appearances may be deceiving.

    Regards,
    Brian Jackson

  • #2
    A general rule is with the gyro at a 10 degree nose up attitude the mains should be located directly under the rotor head.

    Comment


    • #3
      A round about way of answering your question Brian.

      When beginning the takeoff roll once some reasonable rotor rpm is achieved and I move the cyclic fully aft the rotor thrust vector (right angle to the center of the rotor disk) is pointed at the front wheel.

      As rotor rpm increases and lift increases the nose lifts and I begin to move the cyclic forward to balance on the mains and my rotor thrust vector moves aft. This is a gyroplanes way of telling the pilot when she is ready to lift off.

      At some point the rotor thrust vector will get close enough to the center of gravity and the gyroplane will lift off. If I have too much aft cyclic or the mains are too far forward I will lift off at less than the target airspeed with the nose high. If the mains are too far aft I may lift off at higher than my target air speed.

      A heavy person in a single seater likely need the mains further forward and a light person may need the mins further aft because the pilot is well ahead of the center of gravity. In a single seater the pilot is a larger percentage of the all up weight than a tandem.

      Part of the reason for the hang test is to find out where the rotor head needs to be.

      In this picture of The Predator the horizontal center of gravity is about eight inches ahead of the rear black fuel tank strap and the mains are about two feet behind that center of gravity.

      If I have the nose tire about an inch above the ground on my takeoff roll she will lift off at just about 50kts. With a heavy passenger and full fuel she will lift off closer to 60kts because the center of gravity has moved forward in relation to the mains.
      Regards, Vance Breese Gyroplane CFI http://www.breeseaircraft.com/

      Comment


      • #4
        Using Alanís method of measurement The Predator has the rotor head over the mains at six degrees.

        This is the same picture rotated six degrees.
        Regards, Vance Breese Gyroplane CFI http://www.breeseaircraft.com/

        Comment


        • #5
          Brian you could have the mains under the tail if you wanted to,with the wheels back that far when the rotor develops lift the gyro would take off

          at a level attitude.I watched a video of a Chinese guy with the wheels at the very rear and he got off just fine.

          On my RAF I moved the gear aft 6" to help keep the nose wheel on the ground during the take off run,it made things more manageable for me

          and it shortened my distance by quite a lot,by allowing me to achieve a better angle of attack on the rotor,rotor RPM was achieved faster.
          Best Regards,
          Eddie Sigman,Polvadera,nm
          (575) 835-4921

          Comment


          • #6
            With a non-castering NW, moving the RAF main gear back would seem to make the takeoff roll a bit more "darty".
            Perhaps eddie or others can comment on that.
            I don't know, however, because I've yet to modify mine, though I'm considering it.

            Regards, Kolibri
            PP - ASEL complex (Piper 180, C206, RV-7A), SP - Gyro (Calidus, RAF, SC2), soloed in gliders; checkride soon

            Wasn't happy with my RAF's pitch instability, so I installed a Boyer H-Stab to my great satisfaction!

            "
            When an honest but mistaken man learns of his error, he either ceases to be mistaken -- or he ceases to be honest."

            Comment


            • #7
              Brian I would comment further on this subject as I have more than 600 hrs with my mains moved back,however if I do the Kolibri is lurking around

              waiting for my comments so he can jump on the safety band wagon and tell everyone that I am surely going to kill myself because I have

              moved my mains back, because the placement of the gear is causing excessive forces on my rodends

              Best Regards,
              Eddie Sigman,Polvadera,nm
              (575) 835-4921

              Comment


              • #8
                eddie, it was a sincere question, with no ulterior motive. Geez.
                PP - ASEL complex (Piper 180, C206, RV-7A), SP - Gyro (Calidus, RAF, SC2), soloed in gliders; checkride soon

                Wasn't happy with my RAF's pitch instability, so I installed a Boyer H-Stab to my great satisfaction!

                "
                When an honest but mistaken man learns of his error, he either ceases to be mistaken -- or he ceases to be honest."

                Comment


                • #9
                  Alright guys let's cool this animosity. Thank you all for the great info as I continue to learn and expand my understanding of why things are done the way they are. Regardless of personal opinions, preference or argument styles, good information still finds itself here.

                  Comment


                  • #10
                    Somewhere I heard(or read) you should have 15% of the all up flying weight on the nose wheel when pilot is in the seat. Moving the rear gear would determine how much weight is distributed between the two points.
                    Could the gyro elders confirm this?
                    Bobby Munroe
                    Private Pilot (SEL)
                    PRA Chapter 62 #42748
                    EAA #1160523

                    Comment


                    • #11
                      Although RAF takeoff roll procedure (when solo) is to balance the mains, with a passenger I was taught to lightly keep the NW on the runway.
                      When I do so, I notice the "dartiness" of my non-castering NW controlled by the rudder pedals. I do not care for it, and consider it a bad design.

                      My question merely asked if this dartiness increases once the mains are moved back 5-6".
                      Personally, I'd like to move back my mains.

                      Regards, Kolibri

                      PP - ASEL complex (Piper 180, C206, RV-7A), SP - Gyro (Calidus, RAF, SC2), soloed in gliders; checkride soon

                      Wasn't happy with my RAF's pitch instability, so I installed a Boyer H-Stab to my great satisfaction!

                      "
                      When an honest but mistaken man learns of his error, he either ceases to be mistaken -- or he ceases to be honest."

                      Comment


                      • #12
                        Originally posted by Kolibri View Post
                        Although RAF takeoff roll procedure (when solo) is to balance the mains, with a passenger I was taught to lightly keep the NW on the runway.
                        When I do so, I notice the "dartiness" of my non-castering NW controlled by the rudder pedals. I do not care for it, and consider it a bad design.

                        My question merely asked if this dartiness increases once the mains are moved back 5-6".
                        Personally, I'd like to move back my mains.

                        Regards, Kolibri
                        In my opinion until you learn to take off properly in an RAF your takeoffs will be afflicted with "dartiness".

                        I strongly suggest that you find a competent RAF flight instructor and take a few hours of dual instruction.

                        The RAFs, Groen Brothers Modified RAFs and SparrowHawks I have flown were stable in takeoff when the correct procedures were followed.

                        There are more than a few of the above that have been tipped over from poor takeoff and landing procedure and destroyed.

                        Flight instruction is much cheaper and safer than destroying the aircraft.
                        Regards, Vance Breese Gyroplane CFI http://www.breeseaircraft.com/

                        Comment


                        • #13
                          Click image for larger version

Name:	RAF2000 dual takeoff procedure.png
Views:	1
Size:	236.0 KB
ID:	1131494


                          Vance, as much as you'd like to believe otherwise, there's nothing faulty about my RAF takeoffs.
                          However, having flown two Sport Copter gyros with free-castering NW, I notice the difference.
                          I'll stick by my term for the RAF as "darty".

                          That aside, if I were a newly minted gyro CFI, with -- what, three? -- former students who subsequently damaged their machines,
                          I'd spend more time contemplating the quality and efficacy of my instruction vs. opining about somebody else with likely more
                          RAF experience who has never had a takeoff or landing incident, much less damaged or destroyed his gyro.

                          But that's just me.



                          PP - ASEL complex (Piper 180, C206, RV-7A), SP - Gyro (Calidus, RAF, SC2), soloed in gliders; checkride soon

                          Wasn't happy with my RAF's pitch instability, so I installed a Boyer H-Stab to my great satisfaction!

                          "
                          When an honest but mistaken man learns of his error, he either ceases to be mistaken -- or he ceases to be honest."

                          Comment


                          • #14
                            Originally posted by Kolibri View Post
                            Click image for larger version

Name:	RAF2000 dual takeoff procedure.png
Views:	1
Size:	236.0 KB
ID:	1131494


                            Vance, as much as you'd like to believe otherwise, there's nothing faulty about my RAF takeoffs.
                            However, having flown two Sport Copter gyros with free-castering NW, I notice the difference.
                            I'll stick by my term for the RAF as "darty".

                            That aside, if I were a newly minted gyro CFI, with -- what, three? -- former students who subsequently damaged their machines,
                            I'd spend more time contemplating the quality and efficacy of my instruction vs. opining about somebody else with likely more
                            RAF experience who has never had a takeoff or landing incident, much less damaged or destroyed his gyro.

                            But that's just me.

                            Exactly the response I expected.

                            In my opinion based on my experience if the procedure is followed an RAF is not "darty".

                            I prefer a free castering nose wheel for most gyroplane operations; that is not what this thread or your inquiry is about.


                            Regards, Vance Breese Gyroplane CFI http://www.breeseaircraft.com/

                            Comment


                            • #15
                              I quoted the procedure from the RAF Manual, and that is what I use.
                              If you believe that RAF's procedure is somehow improper, then go take it up with RAFSA.

                              With mains moved back, I presume that the NW will be on the runway for even solo takeoffs.
                              My question was about the sensation of that. Your non-dartiness opinion is noted.
                              PP - ASEL complex (Piper 180, C206, RV-7A), SP - Gyro (Calidus, RAF, SC2), soloed in gliders; checkride soon

                              Wasn't happy with my RAF's pitch instability, so I installed a Boyer H-Stab to my great satisfaction!

                              "
                              When an honest but mistaken man learns of his error, he either ceases to be mistaken -- or he ceases to be honest."

                              Comment

                              Working...
                              X