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1/20 Scale U-2R (3D Printed)

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  • #21
    Originally posted by Dirty Dee View Post
    Lead time on some 1mm piano wire and printer issues slowed me down a bit. But still moving along. I was curious about how the glide slope would be, so I made a downsized 1/50 scale chuck glider at 88g balanced to 25% MAC

    Did some thrust tests and found that the long intakes and exhaust create 25% thrust losses.

    FSA: 1,338 mm^2
    Tail Exhaust Area: 1,306mm^2
    97.6% FSA

    Baseline:
    With the EDF mounted in the single section
    Grams of Thrust: 500g
    Max Amps: 26.4A
    Max Watts: 297.5W

    Full Exhaust:
    Full tail section
    Grams of Thrust: 440g
    Max Amps: 25A
    Max Watts: 283W

    12% losses

    Complete Intake and Exhaust:
    Full inlet and exhaust
    Grams of Thrust: 375g
    Max Amps: 25.3A
    Max Watts: 288W

    25% losses
    That settles it, in putting cheater holes in my hobby people U-2.

    Comment


    • #22
      Thanks Alpha.

      Im having some trouble visualizing this arrangement. Is there an example of another design doing this, or a napkin sketch?

      The wings are removable and mimic the designs of the 70mm F16 and YAK130 with attachment. The failure happened at the interface of the wing to the fuselage, so the wings im thinking might be ok seeing how little flex happened during the test. I did however retest with wrapped carbon spars, and the failure then moved into the fuselage where the 6mm spar slips in. I'll be needing to beef that area up with more wall thickness.

      Comment


      • #23
        Originally posted by Phantom View Post

        That settles it, in putting cheater holes in my hobby people U-2.
        Take a look at some videos online, doesn't seem the plane suffers from lack of thrust and departs a hand toss fairly nicely. But, regaining 10-15% thrust would be a good bonus to flight time and performance.

        Comment


        • #24
          Originally posted by Dirty Dee View Post

          Take a look at some videos online, doesn't seem the plane suffers from lack of thrust and departs a hand toss fairly nicely. But, regaining 10-15% thrust would be a good bonus to flight time and performance.

          True, but their U-2 isn't modified with 3 extra servos, flaps and rudder, and two centerline wheels. I've been trying to find something to stuff in her to get some more static thrust. I just installed a 70mm FW 6s setup in my FA-50 but I can't do anything like that with my U-2 because there is no room for any bigger batteries than stock.

          Comment


          • #25
            Originally posted by Phantom View Post

            True, but their U-2 isn't modified with 3 extra servos, flaps and rudder, and two centerline wheels.
            One guy with flaps, retracts, and rudder. 35 oz AUW.
            https://www.rcgroups.com/forums/show...&postcount=443



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            • #26
              Yep listening to his bird, is the same thing I'm dealing with wide open throttle just to maintain flight. 2/3 to 3/4 throttle is a poorly powered edf, even for a glider like the U-2, but I'm at full throttle unless I want to lose altitude. An edf adequately powered can maintain level flight at 50% throttle, obviously a better power to weight ratio is gravy. But the phase 3 U-2, is very under powered.

              Comment


              • #27
                Gotcha, I forgot yours is already flying. Yea putting in a cheater at the top should help a bit. Do you still have the original power system? Maybe upgrading to a changesun 64mm might help with more thrust. A 70mm might get choked out.

                Comment


                • #28
                  Originally posted by Dirty Dee View Post
                  Gotcha, I forgot yours is already flying. Yea putting in a cheater at the top should help a bit. Do you still have the original power system? Maybe upgrading to a changesun 64mm might help with more thrust. A 70mm might get choked out.
                  Yep still the original power system, honestly I don't think I can fit a 70mm in her. But the cheater holes are going in, and the next step would be a better 64mm setup.

                  Comment


                  • #29
                    Some follow-up thrust testing. Using the obsolete fuselage, I did an acetone coat on the inside intake and exhaust surfacing to give them a bit of vapor smoothing. There was no difference in thrust post acetone smoothing as I still saw 375g of thrust like the original test. It seems that the 0.15mm layer height is smooth enough as-is.


                    Moving on to the cheater intake, 2 thrust runs were used with separate batteries and values averaged. The cheater only added 0.5g of material to the airframe.


                    Baseline:
                    With the EDF mounted in the single section
                    Grams of Thrust: 500g
                    Max Amps: 26.4A
                    Max Watts: 297.5W

                    Complete Intake and Exhaust (No cheater):
                    Grams of Thrust: 375g
                    Max Amps: 25.3A
                    Max Watts: 288W

                    25% losses

                    Complete Intake and Exhaust (With Cheater):
                    Grams of Thrust: 395g
                    Max Amps: 26.4A
                    Max Watts: 304W

                    21% losses


                    I had some design revisions to use 3/32" piano wire for the flap and elevator linkages so many pieces got updated and reprinted. I am working on finishing assembling and wiring the next 3 days and hoping for a maiden this upcoming Sunday.

                    Comment


                    • #30
                      Minor tasks to complete, but maiden Sunday should be a go. Planning to fly without superpods to shave off 90 grams from AUW, but they may prove helpful on the belly landing.

                      Tossing a mobius camera onto the airframe for footage capture.

                      Comment


                      • #31
                        Pretty slick.

                        Mike
                        \"When Inverted Down Is Up And Up Is Expensive\"

                        Comment


                        • #32
                          All rigged up and wired up. Just need to set low/mid/high rates and double check CG balance with the 1800mAH packs. I will be mounting a Mobius camera for some in-flight footage so I'll need to take that into account as well.

                          Final weights with everything now is 1147g AUW without the super pods. With the super pods added, it is 1228g (81g more)

                          Holding this is my hand to get a feel for a hand toss, I am very much considering a dolly for the maiden. 1.1kg doesnt sound like much, but it definitely has some heft when it is held in one hand.

                          Comment


                          • #33
                            Chris, Best of luck on your check flight. I'll "throw a nickel on the grass" for ya. Best, Steve
                            Captain: Got any ideas?
                            F/O: Actually not.
                            — Captain Chesley B 'Sully' Sullenberger III and F/O Jeff Skiles—

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                            • #34
                              Wow that is SO cool Chris! Like Elbee says, best of luck on the maiden!
                              My YouTube RC videos:
                              https://www.youtube.com/channel/UCDZ..._bdGEJBmtV7YUw

                              Comment


                              • #35
                                Thanks guys!

                                Not wanting to have a bad toss ruin my day (and be a waste of a 2 hour round-trip drive) I built a launch dolly so it with ROG from the runway.

                                Comment


                                • #36
                                  So today was a bit of a struggle with a maiden. The dolly kept veering off course before there was enough speed for the rudder to be effective. I may have made a mistake with not having enough angle on the fuselage in addition to placing the dolly with the center of gravity between the 2 formers.

                                  After several dolly attempts, I added half flaps, and then finally full flaps. The flight with the full flaps actually departed and started to pull away. But, it needed full up elevator to even remain level, so I brought it down into the grass.

                                  Next we shifted the center of gravity back a bit, and attempted a hand-launch into the wind. First launch with no flaps didnt have enough lift and gently went into the grass. The next flight had half-flaps and seemed like it was going to make it, but then it tipped over and crashed. The damage was fairly minor, but enough that I couldn't do a field repair. I did get it back together in about 5 minutes when I did get home, so its ready for the next go.

                                  With only 0.35 TWR, I am thinking it might be weak for a hand-toss, so I ordered some 4S 1300mAH 45C packs. Doing a quick test with a 4S battery I own at 50% capacity, I was able to get 590g of thrust. Hoping to get those packs before next weekend and try again.


                                  Here is the flight footage from the only 2 launches that sustained flight for a few seconds.

                                  Phantom do you have any thrust or watt numbers of your U2? curious how those compare to mine.

                                  Comment


                                  • #37
                                    You might be able to put a small battery and an Rx and a steering servo tied to your radio frequency to keep the dolly on course. Just a thought.

                                    Comment


                                    • #38
                                      Originally posted by Dirty Dee View Post
                                      So today was a bit of a struggle with a maiden. The dolly kept veering off course before there was enough speed for the rudder to be effective. I may have made a mistake with not having enough angle on the fuselage in addition to placing the dolly with the center of gravity between the 2 formers.

                                      After several dolly attempts, I added half flaps, and then finally full flaps. The flight with the full flaps actually departed and started to pull away. But, it needed full up elevator to even remain level, so I brought it down into the grass.

                                      Next we shifted the center of gravity back a bit, and attempted a hand-launch into the wind. First launch with no flaps didnt have enough lift and gently went into the grass. The next flight had half-flaps and seemed like it was going to make it, but then it tipped over and crashed. The damage was fairly minor, but enough that I couldn't do a field repair. I did get it back together in about 5 minutes when I did get home, so its ready for the next go.

                                      With only 0.35 TWR, I am thinking it might be weak for a hand-toss, so I ordered some 4S 1300mAH 45C packs. Doing a quick test with a 4S battery I own at 50% capacity, I was able to get 590g of thrust. Hoping to get those packs before next weekend and try again.


                                      Here is the flight footage from the only 2 launches that sustained flight for a few seconds.

                                      Phantom do you have any thrust or watt numbers of your U2? curious how those compare to mine.

                                      I will do some thrust/watts/amotests for you today my friend. As I have yet to do the cheater hole mods and my U-2 is still with the stock power system, I will do pre and post cheater hole mods power checks. I'm also going to look up the ESC and motor specs and see if they can support 4s, if so I will conduct both 3s and 4s tests. My personal opinion on EDF's a minimum od 0.50 TWR is an absolute must, and more is always better.

                                      Comment


                                      • #39
                                        Originally posted by Dirty Dee View Post
                                        So today was a bit of a struggle with a maiden. The dolly kept veering off course before there was enough speed for the rudder to be effective. I may have made a mistake with not having enough angle on the fuselage in addition to placing the dolly with the center of gravity between the 2 formers.

                                        After several dolly attempts, I added half flaps, and then finally full flaps. The flight with the full flaps actually departed and started to pull away. But, it needed full up elevator to even remain level, so I brought it down into the grass.

                                        Next we shifted the center of gravity back a bit, and attempted a hand-launch into the wind. First launch with no flaps didnt have enough lift and gently went into the grass. The next flight had half-flaps and seemed like it was going to make it, but then it tipped over and crashed. The damage was fairly minor, but enough that I couldn't do a field repair. I did get it back together in about 5 minutes when I did get home, so its ready for the next go.

                                        With only 0.35 TWR, I am thinking it might be weak for a hand-toss, so I ordered some 4S 1300mAH 45C packs. Doing a quick test with a 4S battery I own at 50% capacity, I was able to get 590g of thrust. Hoping to get those packs before next weekend and try again.


                                        Here is the flight footage from the only 2 launches that sustained flight for a few seconds.

                                        Phantom do you have any thrust or watt numbers of your U2? curious how those compare to mine.

                                        Ok DD,

                                        Here's the specs, it has a 40amp ESC and a 480 sized 960kv motor with a 64mm 6 bladed fan, all stock setup.

                                        Freshly charge battery for both tests 12.6v CHNL 3S 2200MAH 40C 80C Burst

                                        No cheater holes=33.94amps, voltage sag under load 11.38v 387.5w, 0.024ah use. So the stock setup still makes more power than your setup.

                                        With cheater holes =39.52amps, voltage sag under load 11.37v 455.6w 0.032ah used

                                        So cheater holes? Heck yeah! I don't have any thrust numbers but 68 more watts!

                                        I don't remember how far back your fan is mounted in your fuselage, mine is mounted just behind my wings. So I actually don't have as far from the intakes and I thought, and still gained 68watts with the cheater holes.

                                        39.52 amps maxes out the ESC on 3s so 4s is out of the question without upgrading the power system.

                                        Hope this helps, attaching pictures of the wheel mod and the newly cut cheater holes.
                                        Attached Files

                                        Comment


                                        • #40
                                          Do you have this design for sale at all anywhere, it really is a fantastic looking plane that you have obviously put a lot of time into!

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