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Tandem TRex with 3 Rotor Blades

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    Tandem TRex with 3 Rotor Blades

    Hi all

    Look what long holiday did to my Tandem TRex. Always lazy/bored of flying alone outdoor and this holiday do not have any funfly in Yishun so decided to change my Tandem TRex to 3 rotor blades instead. Took me a while to make those head and the swash plate driver/follower.

    After a few short hovering at living room, feels like it fly better on much lower RPM. Maybe due to 3 rotor blades per head?

    Anyway, it is not for the fainted heart.

    SH


    #2
    nice man you running on 1 or 2 motors. must bring to bishan funfly

    Comment


      #3
      Thanks. It is running at 2 motors. It can fly with only one motor BUT the belt suffers from alot of tension. Using 2 motors, the belt run much better.

      SH

      Comment


        #4
        Looks much better with 3 blades. I notice that you are not using o-rings like your 4 bladed heli. Is there much different in performance? How much more weight can it lift with an additional blade.

        Especially for your other 4 bladed heli, if can lift 1.5~1.7kg heli weight would be great for me.....you know my situation.

        Thanks for the photo SH. At least they are bigger and can see more detail. If you have step by step photo of how you made the rotor head it will be really great to see.
        Heli
        Honey Bee CP2 : Sold (Maiden:17 Dec 05)
        Trex 450XL (CDE) : MM450TH, Quark 33A, GY401, JR RS10DS (Maiden : Align Frame - 1 Jul 06; SuperFrame - 29 Aug 06)

        Plane
        Estarter : Align 450s, Align 25A, Electron 6 (Maiden :16 Sep 06)

        PT-17w : Sold
        Buggy
        Acme NB 16 : Half 8 Nitro (Maiden :23 Dec 06)


        Transmtter : JR PCM 9X II, Aggressor SRX
        Charger : Tahmazo T15
        Balancer : TP205
        Battery :Thunder Power, FullRiver, Warbird


        Comment


          #5
          Hi w_kby

          If u see closely, I still using O Ring for the articulated damper. Instead of 3 or 4 O rings, now only using 1 O ring per blade grip.

          The reason I change from 3 to 1 is because for 3 blades and above, if the articulated (especially lead/lag) damper is weak, the lead/lag blade motion (during spinning..especially high speed) will cause the whole head to shake/wobble alot (See below). If the wobble getting to much and it turn to very high resonance that will cause whole heli to fail.

          By using 1 O Ring, the damping is much stronger/stiffer. That mean I can run the head in much higher RPM (or close to normal 2 bladed TRex speed). The drawback maybe stability might loose out a bit.

          Note: In real heli with fully articulated head, there is a situation whereby the lead/lag blades will cause one side to off balance than the other causing the whole head to wobble. When wobble too much, it will break the whole head into pieces. It is called "Ground Resonance"





          SH

          Comment


            #6
            Thanks SH for the explaination and links.

            Just recovered from a bad day. Crashed both my heli and estarter (total loss) in one day.

            After watching those link.... again.

            So you mean it is better then to use 1 o-ring like your 3 blades design if I go 4 baldes? Please advise thanks.
            Heli
            Honey Bee CP2 : Sold (Maiden:17 Dec 05)
            Trex 450XL (CDE) : MM450TH, Quark 33A, GY401, JR RS10DS (Maiden : Align Frame - 1 Jul 06; SuperFrame - 29 Aug 06)

            Plane
            Estarter : Align 450s, Align 25A, Electron 6 (Maiden :16 Sep 06)

            PT-17w : Sold
            Buggy
            Acme NB 16 : Half 8 Nitro (Maiden :23 Dec 06)


            Transmtter : JR PCM 9X II, Aggressor SRX
            Charger : Tahmazo T15
            Balancer : TP205
            Battery :Thunder Power, FullRiver, Warbird


            Comment


              #7
              What have you done? Trying new stunts or not pilot fault? Sorry to hear the lost.

              Well, this is what I learn from my experiments:

              Advantage of weak damper:
              -------------------------
              Blades can flap up and creating a conning shape. With conning shape, heli appears to be more stable.

              If heli do not have cyclic gyro, the cyclic response are slower or like normal flybarred type.

              Noise is lower.

              Disadvantage of weak damper:
              --------------------------
              When spin up in higher RPM or using heavier blades, it is very easy to go resonance stage. Therefore, u are restricted to very low RPM and if blades are heavier, it can go resonance much easier.

              U can only run at low RPM thus not that efficient for motor and your heli eat more current than normal. (Unless u can find very low KV motor and using low teeth count pinion)

              Since RPM is lower, u need to increase more pitch. More pitch also mean more friction and thus more current.

              If rotor mass is high and low RPM, tail rotor authority drop. Therefore, u need bigger tail rotor. If u do not have elevated tail, u can't go any bigger tail rotor without increasing the tail height.

              Having higher pitch may cause pitch up more obvious when forward fly fast (cannot confirm on this)

              Advantage of using stronger damper:
              ----------------------------------
              Very low chance of encounter resonance (resonance may still happen if using very heavy blades and spin at very high RPM though)

              Can spin at higher RPM and thus motor more efficient and lower current.

              No need to go high pitch. If lift power it not you looking for, therefore, low pitch is suffient. If lifting power is require, u can have high RPM + high pitch (provided motor, ESC and battery can handle it), the lifting power can be very high.

              Less pitch meaning lesser obvious on pitch up during forward fly.

              Not restricted to the type of blades to use.

              Tail can use normal TRex tail blades.

              Disadvantage of using stronger damper:
              -------------------------------------
              less/small conning effect (can be no conning is produce..also depend on the heli weight) meaning lesser stability

              Without cyclic gyro, the cyclic response can be very fast

              SH

              Comment


                #8
                My heli crash by my son while trying to avoid a butterfly during his landing and take off practice from bench table....hit the bench lor.

                I flew the estarter, no excuse, just me....only 5 second flight and crash nose down. total loss

                Back to Multiblade:

                So if I need to lift heavy scale heli using Trex, it should be better to go for higher headspeed with less damper or perhaps even the rigid head?

                In which case, I must add 2 gyro for the cyclic? Will this arrangement be good?

                Having watch these video, I am think ground resonance cannot ignore.

                Please advise. Thanks

                Originally posted by Super-Hornet
                What have you done? Trying new stunts or not pilot fault? Sorry to hear the lost.

                Well, this is what I learn from my experiments:

                Advantage of weak damper:
                -------------------------
                Blades can flap up and creating a conning shape. With conning shape, heli appears to be more stable.

                If heli do not have cyclic gyro, the cyclic response are slower or like normal flybarred type.

                Noise is lower.

                Disadvantage of weak damper:
                --------------------------
                When spin up in higher RPM or using heavier blades, it is very easy to go resonance stage. Therefore, u are restricted to very low RPM and if blades are heavier, it can go resonance much easier.

                U can only run at low RPM thus not that efficient for motor and your heli eat more current than normal. (Unless u can find very low KV motor and using low teeth count pinion)

                Since RPM is lower, u need to increase more pitch. More pitch also mean more friction and thus more current.

                If rotor mass is high and low RPM, tail rotor authority drop. Therefore, u need bigger tail rotor. If u do not have elevated tail, u can't go any bigger tail rotor without increasing the tail height.

                Having higher pitch may cause pitch up more obvious when forward fly fast (cannot confirm on this)

                Advantage of using stronger damper:
                ----------------------------------
                Very low chance of encounter resonance (resonance may still happen if using very heavy blades and spin at very high RPM though)

                Can spin at higher RPM and thus motor more efficient and lower current.

                No need to go high pitch. If lift power it not you looking for, therefore, low pitch is suffient. If lifting power is require, u can have high RPM + high pitch (provided motor, ESC and battery can handle it), the lifting power can be very high.

                Less pitch meaning lesser obvious on pitch up during forward fly.

                Not restricted to the type of blades to use.

                Tail can use normal TRex tail blades.

                Disadvantage of using stronger damper:
                -------------------------------------
                less/small conning effect (can be no conning is produce..also depend on the heli weight) meaning lesser stability

                Without cyclic gyro, the cyclic response can be very fast

                SH
                Heli
                Honey Bee CP2 : Sold (Maiden:17 Dec 05)
                Trex 450XL (CDE) : MM450TH, Quark 33A, GY401, JR RS10DS (Maiden : Align Frame - 1 Jul 06; SuperFrame - 29 Aug 06)

                Plane
                Estarter : Align 450s, Align 25A, Electron 6 (Maiden :16 Sep 06)

                PT-17w : Sold
                Buggy
                Acme NB 16 : Half 8 Nitro (Maiden :23 Dec 06)


                Transmtter : JR PCM 9X II, Aggressor SRX
                Charger : Tahmazo T15
                Balancer : TP205
                Battery :Thunder Power, FullRiver, Warbird


                Comment


                  #9
                  Well, I tried rigid head before going to articulated. For rigid head, unless u have very very soft and flexible blades (like in real heli), the cyclics behave kinda weird or not used to. When u push cyclics to an axis (either elevator or aileron), the rotor disc try to tilt to that axis but since the rotor head is rigid, the whole heli will try to tilt instead (that is why the cyclics feels very fast) and if the heli is restricted or the body take time to turn, the rotor disc tend to go from one axis (axis u want to turn to 90Degree of the other axis)

                  Since we can't find a very flexible blades (unless u DIY the blades), we have no choice but to go articulated head....unless u do not mind the behavior of the rigid head with our Align blades.

                  SH

                  Comment


                    #10
                    BTW, I tried 3 and 4 bladed head without gyro and it can fly. 2 bladed flybarless u definately need gyro or weigted tip blades, For 4 bladed even thought u can fly it without gyro, I still prefer fly it with cyclic gyro.

                    Right now my 4 bladed TRex I also installed 2 cyclics gyro. The good thing about cyclic gyro is that, it actually make the cyclic response slower especially during higher RPM than without (therefore, more predictable) and the Elevator gyro should assist in (or assist in reducing) the sudden pitch up problem when going forward flight.

                    SH

                    Comment


                      #11
                      Well SH,

                      You certainly have tried everything under the Sun.

                      Will copy your ideas and do some experimentation once I bulid a spare heli. Will certainly need more of your help in future.

                      Thanks alot

                      Originally posted by Super-Hornet
                      Well, I tried rigid head before going to articulated. For rigid head, unless u have very very soft and flexible blades (like in real heli), the cyclics behave kinda weird or not used to. When u push cyclics to an axis (either elevator or aileron), the rotor disc try to tilt to that axis but since the rotor head is rigid, the whole heli will try to tilt instead (that is why the cyclics feels very fast) and if the heli is restricted or the body take time to turn, the rotor disc tend to go from one axis (axis u want to turn to 90Degree of the other axis)

                      Since we can't find a very flexible blades (unless u DIY the blades), we have no choice but to go articulated head....unless u do not mind the behavior of the rigid head with our Align blades.

                      SH
                      Heli
                      Honey Bee CP2 : Sold (Maiden:17 Dec 05)
                      Trex 450XL (CDE) : MM450TH, Quark 33A, GY401, JR RS10DS (Maiden : Align Frame - 1 Jul 06; SuperFrame - 29 Aug 06)

                      Plane
                      Estarter : Align 450s, Align 25A, Electron 6 (Maiden :16 Sep 06)

                      PT-17w : Sold
                      Buggy
                      Acme NB 16 : Half 8 Nitro (Maiden :23 Dec 06)


                      Transmtter : JR PCM 9X II, Aggressor SRX
                      Charger : Tahmazo T15
                      Balancer : TP205
                      Battery :Thunder Power, FullRiver, Warbird


                      Comment

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