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Official Freewing MiG-29 Fulcrum Twin 80mm Thread

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  • Originally posted by Airguardian View Post
    Hard to tell since you don't mention names but, FWIW, I never said stabs were meant to be balanced on the CP.

    .
    Neither did anyone else. I don't know where he got that idea.

    Originally posted by Airguardian View Post
    This said, installing a stab so that the pivot line is very far from CP will obviously cause a lot of innecessary torque that the servo, servo linkage and servo assembly will have to deal with.
    And the supporting structure.

    Comment


    • Originally posted by Airguardian View Post
      Hard to tell since you don't mention names but, FWIW, I never said stabs were meant to be balanced on the CP.

      This said, installing a stab so that the pivot line is very far from CP will obviously cause a lot of innecessary torque that the servo, servo linkage and servo assembly will have to deal with.
      Hi,

      Very true. Again, this is why I wish they'd apply some good science when they'd design these birds. Where that pivot is in relation to the CP (which is largely a function of airfoil/planform design) can be optimized (for least amount of work for the servo) for a given speed. Until then, a good linkage train and a good servo will have to do that trick. My main point was that the idea that balancing a FF stab on the pivot (without any requisite information on the design variables) is 'always necessary' or even 'always beneficial' isn't always true.

      For those of you who converted to turbine, how much fuel are you carrying? What kind of flight times?

      Comment


      • Over at the Aviation Stack Exchange, 1/4 of the mean chord seems to be a "magic number".

        https://aviation.stackexchange.com/q...al-stabilizers

        https://aviation.stackexchange.com/q...es/67069#67069

        Comment


        • Hi

          Well, maiden done! Man, you guys weren't kidding about this CG being too far forward. Didn't help that my wheels weigh a ton, either. Gonna try again tomorrow with a relaxed CG.

          Comment


          • Originally posted by Shaun Evans View Post
            Hi

            Well, maiden done! Man, you guys weren't kidding about this CG being too far forward. Didn't help that my wheels weigh a ton, either. Gonna try again tomorrow with a relaxed CG.
            Perhaps you now believe my comment in post #4451.

            Comment


            • Originally posted by fredmdbud View Post
              Over at the Aviation Stack Exchange, 1/4 of the mean chord seems to be a "magic number".

              https://aviation.stackexchange.com/q...al-stabilizers

              https://aviation.stackexchange.com/q...es/67069#67069
              I believe someone mentioned that in this thread last November.

              https://www.hobbysquawk.com/forum/rc...967#post283967

              Comment


              • Originally posted by kallend View Post

                Perhaps you now believe my comment in post #4451.
                Hi,

                Little shade in there? I didn't disbelieve your post, lol. 😁 I just ask questions and collect as many data points and information as possible--and never in a disrespectful or unfriendly spirit. I hope it didn't come off otherwise. I did read your (and others') comments regarding the CG being too far forward, so I arranged my components such that I could rearrange them easily after I had a chance to maiden it. So thank you.

                Comment


                • Originally posted by Airguardian View Post
                  Hard to tell since you don't mention names but, FWIW, I never said stabs were meant to be balanced on the CP.

                  This said, installing a stab so that the pivot line is very far from CP will obviously cause a lot of innecessary torque that the servo, servo linkage and servo assembly will have to deal with.
                  The E-Flite SU-30 has weights in their stabilizers.
                  4QR1HU9N7

                  Comment


                  • Originally posted by 4qr1hu9n7 View Post

                    The E-Flite SU-30 has weights in their stabilizers.
                    I have the SU-30 and even with those weights, I don't believe those stabs are "balanced". They may help but they aren't balanced at the pivot point. If you remove the rods, the stabs will fall to one side.

                    Comment


                    • Originally posted by 4qr1hu9n7 View Post

                      The E-Flite SU-30 has weights in their stabilizers.
                      I think we need to be more careful distinguishing static balance from aerodynamic balance.

                      Comment


                      • Has anybody used the Top Design struts, wheels, and brakes that are supposed to be a drop in replacement on the Mig-29?

                        Comment


                        • Originally posted by 4qr1hu9n7 View Post

                          The E-Flite SU-30 has weights in their stabilizers.
                          As Kallend pointed out, I was talking about aerodynamic balance, not mass-balance.

                          Comment


                          • Originally posted by kallend View Post

                            I believe someone mentioned that in this thread last November.

                            https://www.hobbysquawk.com/forum/rc...967#post283967
                            The 2nd Stack Exchange answer quite a nice job using more conceptual and understandable English :)

                            Comment


                            • That was close....

                              I've GOT to find a a lighter wheel/brake combo. Relaxing the CG seems a huge improvement (as discovered and advised by many of you) but with wheels/brakes this heavy, it's almost moot since the gear-down CG and the gear-up CG are so significantly far apart :(

                              Luckily, I arranged stuff in there such that I had room to move stuff around some more. After a near-crash, I got two more decent flights. I'm getting 6 minute flights without having to carry external fuel, so that's good.
                              Last edited by Shaun Evans; Apr 26, 2021, 07:27 AM. Reason: Re-read my original post and decided it was dumb.

                              Comment


                              • Forgive an old fool but if the pivot isn't at the aerodynamic balance point wouldn't a change in air velocity change the force needed to move the stab? Even if you balance it as in your example when you increase throttle (air flow) it would change the force (thumb and forefinger) to move it?

                                In our case with the pivot being so far forward is it possible to get it reasonably balanced?

                                Comment


                                • Originally posted by Shaun Evans View Post

                                  ....... the actual engineer who designed the stabs on my jet applied some tried-and-true formulas/calculations and a specific airfoil to the design. . . . .

                                  .
                                  I think you assume too much.

                                  Comment


                                  • Originally posted by Evan D View Post
                                    Forgive an old fool but if the pivot isn't at the aerodynamic balance point wouldn't a change in air velocity change the force needed to move the stab? Even if you balance it as in your example when you increase throttle (air flow) it would change the force (thumb and forefinger) to move it?

                                    In our case with the pivot being so far forward is it possible to get it reasonably balanced?
                                    Haha,

                                    For some reason I get the impression that you're no 'old fool', but you're absolutely correct. The way I understand it, these full-flying stabs (in full-scale aircraft) are designed to be most stable (requiring the least effort to move them) at a specific speed. Normally, that speed is some calculation of the 'average' speed the airplane will fly at during normal flight. Obviously, there probably aren't too many RC jet makers who incorporate all this, so it's mostly academic, I suppose.

                                    Comment


                                    • And not too many RC jets use hydraulics to move control surfaces.

                                      Comment


                                      • Originally posted by kallend View Post

                                        I think you assume too much.
                                        Do tell?

                                        If you mean with regard to this MiG, I'm not assuming anything. My first post was asking about what calculations went into the stab design. After reading all the posts on this (and other posts on other birds by people in here whose comments interested me) it doesn't seem like the designer did much in that regard. If you're referring to the stabs on the jet in my story, then no, I'm not assuming anything at all--I'm stating facts straight from the designer.

                                        After re-reading my own posts, I see that I'm coming off as a know-it-all. That paired with being the last on the scene isn't a good look. You can't always infer tone on the net, so let me say that I'm not nearly as smug and condescending as it reads!

                                        Comment


                                        • Not related to RC planes....BUT....interesting.

                                          Many of the FFS in full size aircraft (example Piper) incorporate “anti-servo” tabs on the trailing edge of the FFS to provide “resistance” to the control movement. This is done so the pilot gets “feel” feedback and thus avoids over stressing the airframe by deflecting the FFS too much.

                                          As the trailing edge of the FFS moves up, the anti-servo tab’s trailing edge also moves up. Thus....fighting the movement of the FFS. Same on the reverse movement. Downward FFS trailing edge is accompanied by the trailing edge of the anti-servo tab moving down.

                                          Bottom line, the general population of pilots needs to feel resistance to control movement.

                                          Aside - A lot of work goes into the design of hydraulic assisted systems on big aircraft to provide simulated control force feedback to the pilot for this very same reason. FFS or otherwise.

                                          For sailplanes, not wanting the drag of an anti-servo tab....engineers put springs on the FFS systems that the pilot must fight against.

                                          General population pilots might separate wings from aircraft by over Ging the airframe without pitch control pressure feel feedback.

                                          -GG
                                          Click image for larger version  Name:	0F59F41A-EA00-4D5C-88D9-3B143EA94808.jpeg Views:	0 Size:	39.7 KB ID:	310266

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