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Arrow-copter. This is my dream-gyro

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  • #31
    Xavier
    Thank you for the link. A friend, who understands German, told me about it and when he tried to show me couldn't find the thread. I tried to get on to their forum but it keeps telling me (in English) I haven't finished registering but the instructions are in German!!!.
    Nice to see the photos, that's me up the ladder. Helmut and Norbert were very welcoming, Helmut's trailer for the Arrowcopter is unbelievable.
    The most frustrating thing was that they are just inside the German border so having driven through France and Belgium with their speed limits, I only had a few kilometers on the autobahn at 180 k/h. I will run the thread through Google translator to see what they say.
    ​​​​​​
    I know I sound like a dripping tap (faucet) but get a frequency analyser on your gyro it's the simplest way to reduce the number of potential causes. It's a real pity you're not nearer I'm sure a decent analysis would help.
    Mike G

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    • #32
      A rotor like Arrowcopter produces strong 2/rev vibrations, due to high load and high forward speed. In tip plane as well as axially.
      Unfortunately, even perfect balancing can not do anything against 2/rev vibrations.

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      • #33
        JC
        You are (as usual) right to say that the 2/rev vibration cannot be reduced by balancing (or tracking come to that), I've said it so often here that people have stopped listening, but the 2/rev vibration measured at the top of the mast (so due to the rotor) on the Arrowcopter I measured recently in Germany was reasonable compared to other well known gyros. It comes out on the lower end of the typical Eurogyro rotor 2/rev vibration. To be fair to the others, there wasn't a suitable accelerometer fixing point on the rotor head so we were measuring on the mast rather than next to the bearing.

        I think that the very strong/rigid carbon fiber monocoque cockpit/mast tends to transmit more vibration into the cockpit than on some others (not all) but I always say if I'm going to crash I want to be in an Arrowcopter, it's built like a formula 1 racing car.

        How do you like my new Avatar? When balancing rotors I often feel like Don Quichotte trying to fight windmills.

        Mike





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        • #34
          Mike,
          To check my spreadsheet, do you measure the vertical vibration on the mast of the Arrowcopter with the corresponding environment: Mass in flight, rpm, forward speed? Thank you

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          • #35
            JC
            I gave up measuring vertical vibration at the mast when I realised it tends to follow the Y axis (avant/arrière) very closely, so for balancing I didn't need that third axis. I do measure vertical and horizontal axis in the cockpit now as standard if I can find somewhere to fit the second accelerometer. Vertical in the cockpit (the most disturbing for the pilot I think) tends to follow the Y axis at the mast but at a reduced level.

            Mike

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            • #36
              Did I understand you correctly, Mike ? You put both accelerometers in the cockpit, pointing left/right and up/down and none on the mast?

              -- Chris.

              P.S.: I love your Don Quixote allusion :)
              Last edited by ckurz7000; 09-19-2017, 11:59 PM.
              Read about my trip across the USA in an MT03 gyro here.

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              • #37
                Mike,
                Mu of Arrowcopter is higher that much others. Vertical force vibration 2/rev transmitted on the mast tip increases.

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                • #38
                  Chris
                  the PB4 has two connections for accelerometers. The Smart Avionics accelerometer probes are dual, there are two accelerometers in each probe at 90° to each other. So when balancing I capture 4 accelerometers at the same time. At the mast I have one probe with one accelerometer pointing left/right (X) and one fore/aft (Y). In the cockpit I have the other probe with one accelerometer horizontal left/right (the same direction as X) called X2 and the other pointing vertical called Y2.

                  The PB4 gives you a polar chart and you can select which pair of accelerometers you want to look at at any one time. In theory you can end up juggling 2 charts with 12 move lines (6 on each) at the same time but the technique I use simplifies things a bit (but not always). PB4 training now available

                  JC what makes the Arrowcopter have a higher mu? I thought it had a standard Averso rotor diameter so even if it flies a bit faster the rotor is probably at a higher rpm due to the weight.

                  Mike

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                  • #39
                    Originally posted by Jean - Claude View Post
                    Mike,
                    Mu of Arrowcopter is higher that much others. Vertical force vibration 2/rev transmitted on the mast tip increases.
                    Solo I cruise at around 175 km/h at a rrpm of about 360. Two up it is more like 160 km/h and 400 rrpm. If I didn't mistype on my calculator, that's a mu between 0.25-0.3 depending on the condition.

                    -- Chris.
                    Last edited by ckurz7000; 09-20-2017, 11:36 PM.
                    Read about my trip across the USA in an MT03 gyro here.

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                    • #40
                      Mike
                      It seems to me diameter is 8.6 meters and chord 0.25 meters. Also, the wing reduces a bit the rotor load, and slows down rpm.
                      Then the better streamline allows a higher forward speed.
                      So, solo, Chris shows mu = 0.3

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                      • #41
                        JC

                        Are you sure the chord is 0.25? I thought the Arrowcopter rotor used Averso blades and I think Averso are 0.2 chord.
                        Chris can you clarify what chord you have.

                        I hadn't thought about the effect of the wing, good point.

                        So what is the mechanism that causes high mu to increase 2/rev? I understand that link between airspeed and 2/rev?

                        Mike

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                        • #42
                          Higher rpm cause higher coriolis forces at higher flapping angles. And the drag difference between blades fore/aft and sideways is bigger. Both contribute to 2/rev.

                          -- Chris.

                          P.S.: I think the cord is 20 cm.
                          Read about my trip across the USA in an MT03 gyro here.

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                          • #43
                            Mike,
                            Chord of Averso's blades is 0.216 m (or 21,6 cm). Arrowcopter' chord is still a mystery

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                            • #44
                              Chris
                              I knew that increasing airspeed cause an increased 2/rev due to "drag difference", JC calls it "rotating drag"I think I'd prefer "alternating drag" but I digress.

                              I'm not sure I understand you Coriolis argument, you'll have to explain to me (and others??) in a more simplified text how that works. I'm collecting "causes of 2/rev" and I'd like to understand this one before I add it to my list.

                              My interest was more in JC's use of the term mu and any direct link there could be between mu and 2/rev other than "your arrowcopter flies faster so there's more 2/rev". It's clear that by flying faster the airspeed part of the mu equation gets bigger but then so does the rpm part. OK the rpm increase might not be as great as the airspeed increase so yes mu has increases but for me that's incidental.

                              Is the real cause of the 2/rev increase for the Arrowcopter "drag difference" plus Coriolis (perhaps) ?

                              JC
                              When I finally get my pre rotator sorted out what data do you need to compliment your spreadsheet? I can run some tests but mass will be using my bathroom scales under each wheel, rotor rpm will be accurate (thanks to PB4) but airspeed is hopelessly inaccurate. I find most of these open tandems have very optimistic ASIs. I can measure vibration in any direction you want.

                              Mike G

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                              • #45
                                Originally posted by Mike G View Post
                                My interest was more in JC's use of the term mu and any direct link there could be between mu and 2/rev other than "your arrowcopter flies faster so there's more 2/rev". It's clear that by flying faster the airspeed part of the mu equation gets bigger but then so does the rpm part. OK the rpm increase might not be as great as the airspeed increase so yes mu has increases but for me that's incidental.
                                Mu characterizes a more general state of operation. It allows useful comparisons despite the change in diameter, chord, blade pitch, etc.
                                But if the geometrys are the same, then yes, you can consider the only increase in forward speed.

                                When I finally get my pre rotator sorted out what data do you need to compliment your spreadsheet?
                                Can you give to me your measure results of the vertical and fore/aft vibrations 2/rev at the top of the mast, during a fast flight in level? There is no need for bath room scales. Just total mass, rrpm, forward speed evalued. Thank you, Mike






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