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Official Freewing MiG-29 Fulcrum Twin 80mm Thread

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  • I didn't say you made conclusions, I said the video itself is not 'conclusive' (With regards to the structural problem, it is assumed).

    Throttle doesn't equal speed. And when speed is up, the camera picks it up as noise. When the jet goes slow, it is much more silent. At the times of your flaps deployment you were not going particularly fast. You hear this too when flying inside a sailplane, the faster you go, the more noisy it gets, and when you let speed drop, it gets silent ;)

    From your own video, at 1:55 your were going pretty fast. Then you pulled up and turned, bleeding energy and speed in particular. THEN you deploy flaps at 2:05 when it's already much more silent. Notice as you pull up and bleed speed even further the mic goes super silent.

    Then you retract flaps and speed up again... by 2:25 it gets noisy again just as it is to be expected.

    Comment


    • Originally posted by Airguardian View Post
      I didn't say you made conclusions, I said the video itself is not 'conclusive' (With regards to the structural problem, it is assumed).

      Throttle doesn't equal speed. And when speed is up, the camera picks it up as noise. When the jet goes slow, it is much more silent. At the times of your flaps deployment you were not going particularly fast. You hear this too when flying inside a sailplane, the faster you go, the more noisy it gets, and when you let speed drop, it gets silent ;)

      From your own video, at 1:55 your were going pretty fast. Then you pulled up and turned, bleeding energy and speed in particular. THEN you deploy flaps at 2:05 when it's already much more silent. Notice as you pull up and bleed speed even further the mic goes super silent.

      Then you retract flaps and speed up again... by 2:25 it gets noisy again just as it is to be expected.
      It is what it is. I did the video to show something for me and for others to see. If you can draw a conclusion, fine. If you can't, also fine. I didn't do it for that. It does show that flaps didn't appear to affect elevator authority in my flight. In some of the crashes, the Mig wasn't going all that fast either. I'll have no qualms about flying this plane under the conditions that I fly it.

      Comment


      • Xviper....just curious / What mods have you implemented on your MiG?

        Thanks

        Comment


        • Originally posted by GliderGuy View Post
          Xviper....just curious / What mods have you implemented on your MiG?

          Thanks
          MotionRC supplied upgrade elevator servos and extensions. I stiffened up the elevator servos with a piece of CF rod, epoxied to the the stock ends (clevis?), making the whole rod unbendable, RF choke, VT nozzles, HobbyEagle gyro, by-passed BB with elevator, AIL and flaps, Assan steering gyro.
          The video above was without choke, VT and steering gyro.

          Comment


          • Originally posted by 4qr1hu9n7 View Post

            I mentioned the "low voltage" issue weeks ago. Unfortunately it fell on deaf ears. I sent an email to "Motion" regarding this issue. It too fell on deaf ears. Oh well. They know what's best for the customer.
            On deaf ears? Where do you get that idea from?

            Voltage drop issues have been discussed and relatively accepted here since the crashes started becoming known.

            Just because some, myself included, am pretty sure the mechanical issues are a way more dominant factor in these problems, does not mean we reject the possibility of low voltage due to long/thin cables also being part of the equation. It is possible to think more than one thought at a time.
            Freewing A-10 turbine conversion: http://fb.me/FreewingA10TurbineConversion

            Comment


            • Originally posted by radfordc View Post
              If the stabs are being bent down severely I don't think any servo will save the plane.
              Precisely. The mechanical issues are so severe that servo power at the time is really not very relevant at all.

              What we have documented on video several times by now are elevators bent totally out of position, which is a mechanical issue, and not a matter of a servo not holding up.

              Sure, we can ALSO assume the servos being extremely marginal, as is their power supply/delivery, and upgrading those makes a lot of sense, but in the end of the day it doesn't matter much unless also upgrading the tail stiffness (or never making mistakes)
              Freewing A-10 turbine conversion: http://fb.me/FreewingA10TurbineConversion

              Comment


              • Don't blame it on the servos
                Don't blame it on the wiring
                Don't blame it on the flaps down
                Blame it on the boogie.

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                • Hi all,

                  Tell me I’m wrong if you like, but just throwing it out there.

                  Is it possible that with the flaps down, at certain speeds and angles of attack, air is deflected from under the rear of the flaps up under the leading edge of the elevator, forcing the leading edge down and causing the aircraft to pitch down violently?

                  Click image for larger version

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                  • Wind tunnel Image...and one must disregard any assumed ground effects because folks don't typically crash MiGs while on the ground roll out...unless they hit something.

                    More likely the downward "waterfall" of the air from the top surface of the wing and loading the top of the FFSs is involved. A picture is worth a thousand words.

                    -GG

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                    • Fair enough 😂

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                      • Originally posted by The43rdHammer View Post
                        Hi all,

                        Tell me I’m wrong if you like, but just throwing it out there.

                        Is it possible that with the flaps down, at certain speeds and angles of attack, air is deflected from under the rear of the flaps up under the leading edge of the elevator, forcing the leading edge down and causing the aircraft to pitch down violently?
                        If air was deflected under the LE of the elevator, the LE would be pushed up, not down. I'm thinking that's what you meant.

                        Anyway.... that is not what would happen if the air was pushing up under the LE of the elevator - because under that load the servo would prevent any movement from happening, as long as the servos are working. (and as long as the load is within the capacity of the servo to fight against)

                        We can argue whether the aerodynamic pressure from the flap puts pressure on the stab it in either direction. Yes its quite likely that is happening, you can see the surface of the stab deflecting. But that isn't the point - because you see in either case (up or down pressure) the result is an increased load to the servo - which could (possibly) cause a voltage drop. THEN if the servo stopped working the LE of the stab would deflect upwards, leading to a pitch down.

                        We have seen here in many examples that when the elevators stop working, the plane tends to pitch down.
                        The important thing is, why do both stabilizer servos stop working?
                        IMO... I am on the side of those who say its voltage drop, caused by the servos working too hard for any number of reasons.
                        Marc flies FW & FL: AL37, MiG-29, T45,F4, A4, A10, F104 70 and 90, P38, Dauntless SBD, Corsair, B17, B24, B26 & P61, Lipp.P19, ME262, Komets, Vampire, SeaVixen, FMS Tigercat, FOX Glider & Radian XL.

                        Rabid Models foamies, including my 8' B17 & 9' B36... and my Mud Ducks! www.rabidmodels.com

                        Comment


                        • The LE would go up and the trailing edge would go down, pitching the aircraft down. I may not be a PHD in aerodynamics but I do know up from down 😜

                          There was an interesting article in RCME a few years back about why the fluid dynamics of full sized aircraft doesn’t apply to scale aircraft.

                          Cheers

                          Andy

                          Comment


                          • Originally posted by The43rdHammer View Post
                            Tell me I’m wrong if you like, but just throwing it out there.

                            Is it possible that with the flaps down, at certain speeds and angles of attack, air is deflected from under the rear of the flaps up under the leading edge of the elevator, forcing the leading edge down and causing the aircraft to pitch down violently?
                            Air doesn't quite work like that.
                            I talked about this pretty extensively early in the thread. Deflecting the flap deflects the wing wake further down. The immediate effect of this is that the stabs see a more negative AoA of the incoming air. This causes them to be under heavier aerodynamic force, causing increased bending moment and torsion on the stabs, which is transmitted to the aircraft through the stab shaft and the servo linkage.

                            In subsonic speeds, the air takes particular 'paths' around an object (according to its shape) even before the object gets there, so thinking of the air as being 'thrown' down as if it were small elastic balls doesn't quite totally work out.


                            In any case, the down-wake deflection by the flaps will certainly cause a pitch up moment on the stabs, not so much by lifting the leading edge but because the center of pressure of the stab is aft of the shaft/hinge, so when throwing air over it, it will try to align with the incoming air. This is LE up, TE down, and the servo is the one resisting that change, so yes, if the servo doesn't cope, the stab will not keep the nose of the plane up.

                            Originally posted by The43rdHammer View Post
                            There was an interesting article in RCME a few years back about why the fluid dynamics of full sized aircraft doesn’t apply to scale aircraft.
                            I have seen this argument very often, typically wielded by people that don't have a deep grasp of the subject... usually to try and further the point that they are nothing alike (which would be wrong).

                            There are differences of course, but most fail to point that there also are many similitudes.
                            Models are very often used to predict the behavior of bigger (more expensive) stuff before being built... long story short, if you want to calculate how fluids will behave around an object of a certain shape at a different scale you take care of things like the 'Reynolds number' which gives you an idea of which kind of forces (viscous or inertial) are more predominant/relevant internally in the fluid for the case at hand. One can use scaling factors with this in mind or trick the 'simulation' by changing the speed, size, or parameters of the fluid being used so that the reynolds of the model match more closely the ones expected for the fullscale stuff.

                            But the underlying physics are the same and most of what applies to the big stuff applies too to the small stuff. The equations used would be pretty much the same, etc.
                            With this I mean that quoting scientific research on the differences between models and full-size stuff as if trying to defend that they are nothing alike is a moot point. :)

                            Comment


                            • Originally posted by Airguardian View Post


                              I have seen this argument very often, typically wielded by people that don't have a deep grasp of the subject... usually to try and further the point
                              Er .... it was the late Professor David R Burton of Liverpool John Moores University 🙃

                              Comment


                              • A misunderstanding, I was not questioning the validity of his or other articles, but implying that using them as 'proof' that fullscale and models are like 'sheep' and 'fish' would be an error! ;)

                                Reading these without deeper understanding of the subject could lead to wrong conclussions, all I'm trying to say!

                                Comment


                                • Originally posted by Airguardian View Post
                                  A misunderstanding, I was not questioning the validity of his or other articles, but implying that using them as 'proof' that fullscale and models are like 'sheep' and 'fish' would be an error! ;)

                                  Reading these without deeper understanding of the subject could lead to wrong conclussions, all I'm trying to say!
                                  😂😂🤣 don’t worry mate, the professor might be wrong and you might be right ... who am I to say!

                                  Andy

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                                  • Originally posted by janmb View Post

                                    On deaf ears? Where do you get that idea from?

                                    Voltage drop issues have been discussed and relatively accepted here since the crashes started becoming known.

                                    Just because some, myself included, am pretty sure the mechanical issues are a way more dominant factor in these problems, does not mean we reject the possibility of low voltage due to long/thin cables also being part of the equation. It is possible to think more than one thought at a time.
                                    How about just admitting "pilot error".? It's never the error of the pilot when a crash occurs. No. It has to be something else. Is this comment to your satisfaction ??
                                    4QR1HU9N7

                                    Comment


                                    • For those interested in doing more research on the topic, I leave this here:

                                      Comment


                                      • And this topic goes on an on once again.....................The mysterious MIG that crashes and no one knows why, pilot error, don't fly fast with the flaps down, is it a servo issue, is it a voltage drop, did I lose signal....... I didn't buy one but it sure has been intertaining reading this thread, I feel sorry for those that did crash and lost all that money, I wouldn't be to happy thats for sure, makes you wonder what the next EDF Jet will be like..........

                                        Comment


                                        • Originally posted by DCORSAIR View Post
                                          And this topic goes on an on once again.....................The mysterious MIG that crashes and no one knows why, pilot error, don't fly fast with the flaps down, is it a servo issue, is it a voltage drop, did I lose signal....... I didn't buy one but it sure has been intertaining reading this thread, I feel sorry for those that did crash and lost all that money, I wouldn't be to happy thats for sure, makes you wonder what the next EDF Jet will be like..........
                                          For those who have crashed...me too. But, don't forget positive consideration for all the MiG pilots who haven't crashed and who are enjoying the heck out of this awesome EDF. I would buy another as soon as I decided to spend the money... if I were to crash mine...even if no Version 2 changes were done.

                                          If a Version 2 of the MiG is released (who knows), it will be interesting to see what mods are done.

                                          -GG

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