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SZD-22 Mucha 1/4

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  • #16
    The leading edge has been added to the wings. Some work with the wood plane to get the basic shaping down to the wing sheeting. I need to make some templates for final shaping. There is still some work around the servo mounting area. Time to put in mounting frames for the servos and also reduce the size of the servo cover especially for the spoiler servo. There is this big opening for a tiny servo. The wings are around 1250g at this point.


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    A few more pieces of balsa to finish closing up the top of the fuselage There is still a "fin" to add in front of the stab mount area. And the stab mount needs some filler to get the stab shimmed at the correct angle. The white piece is a fiberglass fairing that gets attached over the stab opening. It will be a pain since it needs to be removable. Since the wing and stab are built, I can get things assembled to make sure the wing joiner tubing is all aligned. Glue that tubing in and then build the root fairings. The bottom of the fuselage is still open at this point. It needs two stringers, and the wheel mounts glued in before finishing up the bottom sheeting.

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    • #17
      Time for alignment and wing tube gluing.... Everything assembled with a few reference points and distances selected. Distanced checked from the front as well as from the top. And check the angles of the two wings.

      Finally break out the good epoxy to glue the tubes in the fuselage.

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      • #18
        Looking great Mike. What do you use "bad" epoxy for?
        Steve K

        Kremer Aerotowing Team

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        • #19
          Originally posted by stevekremer View Post
          Looking great Mike. What do you use "bad" epoxy for?
          I don't use "bad" aka 5 minute epoxy for anything I want to stay together. I would use the bad epoxy to glue something on that you want to be able to easily remove.

          Regular epoxy I use when I want to know how long it takes to cure or I just want to add some kind of filler to the glue joint. Like the 2 hour stuff. The "good" stuff usually takes 8 hours or more where you want to keep things clamped or bagged.

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          • stevekremer
            stevekremer commented
            Editing a comment
            Thanks Mike, Makes sense.

        • #20
          Fiddling with the motor mounting. I verified the angle of the front bulkhead is good to mount the motor without any angled shims. The front bulkhead is 3mm 3-ply. It will also get a nice 30mm hole cut in the middle for the removable prop hardware. There was an internal ply piece that was intended for the tow release servo and keeps the front end aligned when putting together all the ply parts. I did not glue that in since I knew I was going to put a motor in there. I still might use part of it to strengthen the front end near the front of the canopy.

          It's a Hacker A40 so more power than I should need. FES Ex-Uni6 for the prop hub. After some test fitting, a 6mm ply mount mounted to the back of the bulkhead places the motor in the correct location for the nose cone. I'll added another 2mm ply in front of the bulkhead for holding the blind nuts. The nose cone was machined in layers on the CNC with the center hole cut for the front bearing support. At this point is is just held in with a few bolts to check how it all fits.
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          I will add some extra parts internally to get the 6mm mount glued to the fuselage sides and a box back to the second former. It will get fiberglassed outside once I finish the sheeting.

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          • #21
            Some more testing on the motor installation. Can I install and remove it once the sheeting is completed? I needed to trim the front formers a little. They were intended to hold a ply plate that also held the tow release servo and helped align the front of the fuselage formers at the initial glue-up. I didn't glue it in since I expected to remove it. I trimmed some of the former pieces that had tabs for that plate. This gives good clearance for a hex driver for all four bolts on the motor mount. I also had to trim the top of the former a little for the hex driver access. This view is from the bottom.

            When installing the motor, I can use some masking tape to hold all four bolts in place in the motor mount plate. Slide the motor into place and then use a hex driver to screw things in. Finally pull off the masking tape that remains on the motor case. The ESC will get installed on the top in front of the canopy. This is under the instrument panel. I also have to fit a tow release and servo up front. I can fit a two-cell 18650 or 20700 battery pack at the top of the fuselage above the motor.

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            • #22
              Time for a better fuselage rack. CNC router to cut some 3/4 ply to the shape of the fuselage. Glue on some EPE foam sheet with clear Gorilla glue. Screw to a 3 ft board. Stand done except for cutting in a slot for the front skid.


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              • Steve P
                Steve P commented
                Editing a comment
                Nice Rackā€¦

              • mlachow
                mlachow commented
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                Fits like a glove.

            • #23
              Time to work on the wheel mount a little. The ply box was already drilled for some aluminum wheel mounts. I cut some balsa with a nice 52mm radius to fit into the box. Then glued some 1/32 ply to the balsa to finish the bottom. Add a little epoxy/microlight fillet and that should keep the grass out of the fuselage. I need a better wheel. That plastic hub thing probably won't survive. Some spacers will also be needed.

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              • #24
                The wing LE still needed some shaping. Fired up the copy of devWing and generated enough LE templates to do the standing to the HQ 2.5/12 airfoil shape. This is one of the older OldGliders kits so it has a HQ airfoil. Some of the newer designs use Selig and HQ/W airfoils. I had some scrap 3mm 3-ply from model packing. Perfect price for material. Two planes, one for heavier cuts, one for finer cuts. And a nice long T-bar sander gets the job done quickly. EPE foam on the bench to protect the balsa.
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                • #25
                  I finished up adding the last of the sheeting to the rear of the fuselage. On the bottom of the fuselage I glued the sheeting on one side. Then I beveled the bottom sheeting at the center so that the other sheet could just be overlapped instead of fitting the last sheet to on both edges.

                  After that I did another check to make sure the fin is still vertical.

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                  • #26
                    What make and model laser are you using?

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                  • #27
                    Getting the bottom of the nose ready for sheeting. The last bottom stringers were laminated from two thinner strips since the front end curves way more than spruce likes to bend.
                    I also glued some balsa filler pieces along the front skid. The skid will be three layers laminated. But the extra balsa glued to the center piece will provide a nice glue area for the sheeting. I also added some extra gluing pieces around the landing gear box.

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                    Finally I finished mounting the landing gear and made up some spacers for the wheel. Sheeting was added from the rear of the skid to the wheel area. I also have to build the wing fairings and fin piece in front of the stab. And add in a towline release.

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                    • #28
                      I started sheeting the wing fairings. Something to do while waiting for other things. The rear part goes back quite a way. Instead of just balsa sheeting on the rear, I first put down some 0.4mm ply so there is a good centerline for sanding things to shape. The top and bottom need to be sheeted.
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                      • #29
                        Another while something else is drying project is the canopy frame. It is laminated from two layers of 3-ply. First I glued the base and front frame. After that was done, I used some thin ply spacers to allow for covering and finishing and aligned the rear part of the frame. FInally a little fillet front and back.

                        The instrument panel still needs to be built and glued to the canopy frame in the front.

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                        I do have one other decision to make. Just do the standard removable canopy. Or put in a rear hinge like the real one. Maybe a brass barrel hinge can be mounted in the rear to get the movement. The only funny looking thing is the instrument panel gets attached to the frame on the model.

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                        • #30
                          The nosecone is progressing. A mount needed to be glued near the front of the nosecone for the front bearing on the UNI-FES6. The nosecone is made up of layers all of which have the same inside diameter to align them when gluing. The bearing mount is glued to the piece closest to the front. Then there is a layer of 1.5mm ply for more support. I used some thin dowels and drilled holes all the way back to the ply motor mount. Two final front layers just big enough for the shaft to pass through cap the front end. I was able to finish gluing all that up and doing a little more shaping.

                          The next trick was to see if I could remove the motor and reinstall the motor. It worked. The motor wasn't glued in. There is visibility to the top two motor mount screws. The bottom two will be hidden unless I make some small holes in the front sheeting near those bolt heads.

                          It really isn't that hard to get the bolts in there. The trick is to tape the bolts to the motor case with some masking tape and have the ends just stick through a small amount. The front bearing actually helps to make the alignment pretty easy. Even doing the bottom ones blind.
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