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Official Freewing 90mm F-4 Phantom II Thread

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  • Apologies for a post that is likely answered elsewhere in this thread but I’m posting from an iPhone and the search features don’t work too well in this format.

    I direct my question to those with the 8S high performance version of the F-4. I have purchased all of the recommended components and batteries from Motion R/C.

    According to the manual, the recommended center of gravity is 190mm or 7.5”. No matter how hard I try to shove things further back, I am still coming out nose heavy and the F-4 is balancing at 7.0” to 7.125”. I absolutely do not want to add more weight to this already heavy model unless it is absolutely necessary for successful flight. Obviously I’m worried about being able to flare for the landing.

    Thoughts and recommendations or point me to the post(s) that address this issue. Please and thank-you.
    Attached Files

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    • Two things I did... I cut the foam block behind the batteries back about an inch. I repositioned the mixing board back too. Second, I added the 3D printed tail cones. They look great and add a little tail weight. While the F-4 feels heavy picking it up, it has a lot of surface area and doesn't fly heavy.

      My 6+2 batteries fit side by side no problem. If yours don't maybe laying one atop the other?

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      • For what its worth, I put enough lead under the rear compartment where the elevator servo is, to balance as shown. About 1.7" ahead of the gear well. That is behind the recommended cg. The plane take offs and landings can be done at slower speeds with this setup. Click image for larger version

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        Landings here: https://www.youtube.com/watch?v=RtlmjuSVczA&t=99s
        ​​​​​​​

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        • Originally posted by Robbie9859901 View Post
          For what its worth, I put enough lead under the rear compartment where the elevator servo is, to balance as shown. About 1.7" ahead of the gear well. That is behind the recommended cg. The plane take offs and landings can be done at slower speeds with this setup. Click image for larger version

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          Landings here: https://www.youtube.com/watch?v=RtlmjuSVczA&t=99s
          So, it would seem that you feel it is pretty important to hit that recommended CG mark, even if additional weight is needed?

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          • The weight that needs to be added to move the balance point aft isn't much percentage wise to the total weight of the a/c. You won't notice much difference in rate of climb with an additional 3-4 oz. of total weight. On a 3D plane this will make a difference, but not on normal jet maneuvers. There is a limit, but the farther back the CG is the less work the elevator had to do. The cg is closer to the main gear and the elevator will have to do less work to get the nose up on takeoff. You will be able to rotate for take off at slower speeds. The same thing happens on landings, Your landings will be slower as the elevator is more affective at slower speeds. After touch down you can hold the weight off the nose wheel better and not break the nose gear axle. I believe that freewing has the recommended CG where they are to protect the customer from taking off too soon with out enough airspeed. I have 5 different freewing jets and they all are balanced 3/8" to 1/2" behind the recommended CG. I use a CG balancer, not just fingers. Anyway, that's my theory.

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            • Originally posted by Robbie9859901 View Post
              The weight that needs to be added to move the balance point aft isn't much percentage wise to the total weight of the a/c. You won't notice much difference in rate of climb with an additional 3-4 oz. of total weight…I have 5 different freewing jets and they all are balanced 3/8" to 1/2" behind the recommended CG. I use a CG balancer, not just fingers. Anyway, that's my theory.
              Thanks, I agree and always use a balancer in the shop, I’ll double-check at the field with fingers, but I like precision. Guess we’ll be adding weight. Thanks. 🙂

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              • Originally posted by Robbie9859901 View Post
                When you're taxi'g back, was the elevator in a 'neutral' position? If so, it looked like you have a ton of up elevator. Is that correct?

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                • Originally posted by jasmith41 View Post

                  When you're taxi'g back, was the elevator in a 'neutral' position? If so, it looked like you have a ton of up elevator. Is that correct?
                  Click image for larger version

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                  This is takeoff setting about .8" below the line

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                  • Click image for larger version

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                    This is cruise setting with about 75% power. The plane will climb at full power with this setting. about .5" below the line

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                    • Click image for larger version

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                      This is landing with full flaps. about 1" below the line

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                      • I have the 8s version f4 fantom i'm having a problem with batteries that they said you can use to make 8s.I;m wanting to run a 6s 5000mah 50c and a 2s 5000mah 50c 7.4v as stated in the directions but when i plug in one or the other to the double connector it will literally want to fry the connector , but i can plug in two 6s 5000mah or any of the same mah packs and nothing happens no welding flash nothing. Also the joiner plug was not plugged into the plane for the fear of frying the electronics. Any thoughts?

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                        • You are using a parallel adapter. You need a series adapter.

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                          • Originally posted by Evan D View Post
                            You are using a parallel adapter. You need a series adapter.
                            now that im looking at it you are correct i'll order the one from motion, Thank you sir

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                            • The manual recommends a CG of 190mm from leading edge. For those of you who are flying this F4 did you find 190 to be the correct CG or are you using something else?

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                              • Originally posted by paulsnapp View Post
                                The manual recommends a CG of 190mm from leading edge. For those of you who are flying this F4 did you find 190 to be the correct CG or are you using something else?
                                recommended CG and initial elevator position worked out fine as a starting point.

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                                • Originally posted by paulsnapp View Post
                                  The manual recommends a CG of 190mm from leading edge. For those of you who are flying this F4 did you find 190 to be the correct CG or are you using something else?
                                  Couple of things…
                                  1) I agree…Manual CG is an OK starting point.
                                  2) Order more nose gear connector pins. You’ll need them while learning to land. They break.
                                  3) Embed some carbon or metal into the bottom of the nose radome to avoid sanding off the radome when the nose connector pin breaks.

                                  With practice, this goes away.

                                  -GG

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                                  • Also…..Use this technique!!!

                                    https://m.youtube.com/watch?v=5ioZTAJttGU

                                    Align FFS = how to

                                    You’ll need to do the adjustments with the set screws on each FFS since there is only one servo.

                                    It’s a sure-fire way get things aligned.

                                    -GG

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