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Official Freewing JAS 39 Gripen 80mm EDF Jet

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  • Originally posted by janmb View Post

    Forcing an aircraft to yaw means the inner wing flying slightly slower than the outer wing, which in turn means the inner wing generating less lift than the outer one. Which in turn means that the yaw you commanded also causes roll in the same direction.
    The effect you describe is not the primary reason that yaw/roll coupling occurs...in fact it's nearly negligible. The reason a plane rolls when yawed is almost all due to dihedral effect. An aircraft with positive dihedral will roll in the same direction that the rudder is moved. An aircraft with negative dihedral (anhedral) will roll opposite the direction that the rudder is moved. Zero effective dihedral often results in no roll coupling at all (as Kallend pointed out with finely tuned pattern ships).

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    • That is not so.

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      • That is so.

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        • Are doing som small maintenance on my Gripen. So I fly the Mirage. Almost as good as the Gripen in hige alpha ;-)

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          • Originally posted by Evan D View Post
            When I stated that yaw really effects roll in my earlier post I want to clarify that I meant during high alpha or very low/ zero airspeed Using the yaw TV really effects roll. And not necessarily in a bad way, you can do some neat things with it.

            I also said way back after my first TV flights with the Gripen to be careful using a lot of yaw TV input because the plane will do a quick corkscrew and end up pointed straight down and to play with it at altitude.
            All of those aspects are 100% as one should expect.

            Slamming in a lot of yaw from vectoring at slow speed/high thrust does do exactly that. Not unique for the Gripen in the slightest.

            Freewing A-10 turbine conversion: http://fb.me/FreewingA10TurbineConversion

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            • Originally posted by radfordc View Post

              The effect you describe is not the primary reason that yaw/roll coupling occurs...in fact it's nearly negligible. The reason a plane rolls when yawed is almost all due to dihedral effect. An aircraft with positive dihedral will roll in the same direction that the rudder is moved. An aircraft with negative dihedral (anhedral) will roll opposite the direction that the rudder is moved. Zero effective dihedral often results in no roll coupling at all (as Kallend pointed out with finely tuned pattern ships).
              Not the case at all.

              I've flown planes ranging from high anhendral to high dihedral, obviously including straight wings, and they all have positive yaw to roll coupling.

              What on the other hand does affect this a lot is the angle of the rudder, both sideways tilt in the case of twin rudders, as well as hinge line.
              Freewing A-10 turbine conversion: http://fb.me/FreewingA10TurbineConversion

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              • Precisely.

                And vertical placement of the rudder affects that too.

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                • Got asked about my Gripen programming... didn't measure throws in mm (leaving that for another day), but, FWIW, this is what I have set up on the transmitter and gyro (Taranis X9D+ / S8R):

                  Radio: Taranis X9D+

                  INPUTS PAGE (Sticks; Low-Medium-High rates)
                  ROLL THROWS 60-70-90
                  ROLL EXPO 70-70-70

                  PITCH THROWS 60-70-100
                  PITCH EXPO 55-55-55

                  RUDDER THROWS 45-55-100
                  RUDDER EXPO 40-45-55

                  MIXES PAGE
                  ALL WEIGHTS TO 100%

                  SERVO OUTPUTS PAGE

                  LEFT ELEVON 150%
                  RIGHT ELEVON 150%
                  RUDDER 150%
                  CANARD 100% (Remember this one goes through an external gyro on my JAS, and it didn't seem to appreciate the extra Tx range)

                  S8R SETTINGS

                  Master gain 70-90 (On a dial, I typically have it around those values)

                  Config Settings
                  Delta Horz
                  S8R enable
                  Quick mode disable
                  Ch5 ail2 (Not relevant for elevon setup)
                  Ch6 ele2 (Not relevant for elevon setup)
                  Ail reverse
                  Ele reverse
                  Rud reverse
                  Ail2 normal (Not relevant for elevon setup)
                  Ele2 normal (Not relevant for elevon setup)
                  Ail stab gain 42
                  Ele stab gain 80
                  Rud stab gain 50

                  All else: default (not used)

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                  • Originally posted by rms View Post
                    Are doing som small maintenance on my Gripen. So I fly the Mirage. Almost as good as the Gripen in hige alpha ;-)
                    That looked like on of my flights after the landing. "Hey, I've got 14 seconds of battery left, time for another quick flight!". Way to get that battery down to 3.8 volts... 😎

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                    • Think Motion RC seem to have an issue with there stock. The Gripen has been out if stock now for 3 months!!!!! Never mind the Rafale is due in a week Thursday πŸ‘

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                      • Must be an EU thing. MotionRC.com and RC Castle has had stock during that time period.

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                        • Be interesting to see how the Rafale compares with the Gripen. One thing I have notice is it looks like the Rafale canard only work in pitch, unlike the Gripen which work in both pitch and roll.. Also the Rafale comes with a built in gyro. Will the Gripen be back in stock in Europe before the Rafale is released??????
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                          • Originally posted by Captain Moron View Post
                            Be interesting to see how the Rafale compares with the Gripen. One thing I have notice is it looks like the Rafale canard only work in pitch, unlike the Gripen which work in both pitch and roll.. Also the Rafale comes with a built in gyro. Will the Gripen be back in stock in Europe before the Rafale is released??????
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                            It's likely that the canards on the Rafale can be wired to work in pitch and roll, if so desired. Evan D has indicated that roll mixing on the Gripen canards have limited effectiveness, so I suspect it will be no different for the Rafale. The control box on the Rafale takes all the inputs and does the mixing for you. Nothing says you can't unplug the two leads for the canards and do your own mixing in the RX. Horizon Hobby distributes the Rafale in N. America and it won't come with the Reflex. You can see the recent videos (on the other forum) of the first couple of flights of the Rafale. It appears to be more sluggish due to it being a heavier plane and those twin exhausts reducing the thrust somewhat. Even with Reflex, it still waddles like a fat duck walking. I think with the use of a different gyro, most of this can be dialed out.
                            Have you tried sending a message to MotionEU and asking them for an ETA?

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                            • I have contacted Motion RC and I do not think they really know
                              I was told it would be early January and then I was told it would be early this week but I surpose it is on a container from China and it will be here when it arrives, not much Motion RC can do. All I can do is do what I am not good at and that is be just wait, it will get here at some time. Funny you should say it is sluggish I thought that when I watch the video
                              Thanks for your reply

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                              • I was told "I haven't a clue" when I called and asked when the TVs are coming. I understand delays but would think if they wanted to know they could find out exactly what ship the container is on and when it will dock. If it's docked they should have some idea when it'll be released, etc...

                                In the case of the TVs at least remove the expected late 2020 from the web site.

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                                • Originally posted by Captain Moron View Post
                                  Be interesting to see how the Rafale compares with the Gripen. One thing I have notice is it looks like the Rafale canard only work in pitch, unlike the Gripen which work in both pitch and roll.. Also the Rafale comes with a built in gyro. Will the Gripen be back in stock in Europe before the Rafale is released??????
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                                  Many of us have disabled (or not enabled) the roll input to the Gripen's canards. It is not scale, it is aerodynamically undesirable, and unnecessary to achieve a high roll rate anyway.

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                                  • That is interesting ,so you do not use the roll rate on your canards just use the pitch movement and have the roll rate on your canard disabled

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                                    • Yes.
                                      And even better if you use a gyro on canards (pitch only).

                                      This is the way.

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                                      • Originally posted by Captain Moron View Post
                                        That is interesting ,so you do not use the roll rate on your canards just use the pitch movement and have the roll rate on your canard disabled
                                        Correct. The canards are too close to the centerline to produce much rolling moment unless they have a lot of deflection, which will also produce a lot of drag and produce asymmetric .airflow over the wing. The elevons, being farther out, have a much greater effect.

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                                        • Originally posted by Captain Moron View Post
                                          Be interesting to see how the Rafale compares with the Gripen. One thing I have notice is it looks like the Rafale canard only work in pitch, unlike the Gripen which work in both pitch and roll.. Also the Rafale comes with a built in gyro. Will the Gripen be back in stock in Europe before the Rafale is released??????
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                                          Neither of the two should have canards operate in roll anyway.

                                          Not only is it completely meaningless in terms of providing roll authority. These aircraft roll like drill bits at the merest hint of elevon control input anyway.

                                          And more importantly, it acts against the canards' primary purpose of shaping the on-coming air onto the main wing. Huge roll deflections on the canards messes that up completely, and gives one wing completely different alpha than the other.
                                          Freewing A-10 turbine conversion: http://fb.me/FreewingA10TurbineConversion

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