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Jan 18, 2020, 08:00 PM
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Build Log

Carl Golberg Super Chipmunk


My very first RC airplane was a Super chipmunk ARF. I remember having save money and walked into a Hobby shop in long meadow MA in 1989. I was a young kid, had no idea what I needed and unfortunately the shop was happy to load me up and send me on my way. Obviously it was not a good first plane and I had no chance in hell of being successful. About the most I ever got to do with it was taxi around the high school football fields. Fortunately for me A member of Hamden County Radio Control club of South Hadley Ma found me and helped me get on the right track. So I built a PT40 (I did a horrible job but it flew) gutted the chipmunk and learned to fly. The chipmunk got put in the rafters. I started out in life and it and just it disappeared over time never to be flown.

Fast forward to December 2019. I was telling my wife about the plane I never flew and always wanted to. During the discussion I said it may be cool to find a Carl Goldberg Super Chipmunk Kit because well, I have a bit more experience now . How cool would it to be able to get a Chipmunk and fly it right. I also said they are getting harder and harder to find now that they were no longer in production. Well the little turd, she got with a buddy of mine and found one. I knew she was hunting but I thought she was unsuccessful. She gave it to me for a Christmas gift.

The kit was complete and in super shape. The kit it was Die Cut and I have some of the forms dating to 1989. I checked with the AMA historian and found that Carl Goldberg Inc. released this kit late 1989. It was not in the pricing catalog for that year but had AMA forms dated 10/89. One interesting thing on this kit is the elevator tips did not have holes like in the plans but were elongated to lighten them up. I don't know when this change was made but I could date the kit I am sure by that feature. My best guess is the kit was made between 1989 and 1995. Right about when I started flying. My wife wins Christmas!

I will be powering it with a Saito FA 100 and I would like to add smoke. I am not sure if I will however as it seems a bit expensive. I will play it by ear for now. I plan to use two aileron servos instead of one. I will also be adding flaps. I like the look of the fixed gear but I hear they break. The Kit allows for optional retracts. I may build them in and go with a fully loaded version (since I have power).


Anyway here we go.


As always, I make lots of mistakes. I do my best not to but I like to share them when I do. If you see something please feel free to comment.

things I am currently looking for are ways to beef up the Landing gear. I have an idea or two so perhaps I will be able to make them work out.
Last edited by Taxus812; Jan 18, 2020 at 09:44 PM.
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Jan 18, 2020, 09:00 PM
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First up is the powerplant. Initially I planned to use an Enya 90-4c I have on the shelf. I decided on a Saito FA 100 instead. More power , smaller size and lighter (about 200g lighter). I got one used here on RCgroups in very good shape. I did a good lookover and it is very clean. Just had some rusty looking castor on the main bearings that cleaned right up. I reset the carb to factory and adjusted the valves. (Not horrible but in need of adjustment). I will be running a 14x8 prop. I’ll will run it and do an initial tune in the morning. I plan to mount the engine sideways and possibly get a slimline muffler with smoke jet.


Update: I started the motor and adjusted the high speed needle. She ran fantastic. I got about 9700rpm and in backed it down to about 9400. She got good smoke (I use 30% heli fuel). I backed it down and adjusted the low speed needle. Very little adjustment needed. I got clean transiti9n from low to high and a clean idol at 2300rpm.
Last edited by Taxus812; Jan 19, 2020 at 10:45 PM.
Jan 18, 2020, 09:20 PM
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Start of build !


I need to spread this build out so I will be breaking it up.

Today I started with the stabs, elevators and rudder.
The instructions have you build a few shaping tools first.

Then they have you laminate the elevators tips, rudder and center blocks (installed later). The stabs are not laminated but are sheated instead. They use CA, I tried it but the stink bothers my lungs. I instead uses sig bond. The risk there is warping and you need to press it between glass. If you escape warps it is softer to sand.


One thing I forgot. The 3/16x 1/2 wood was crowned pretty bad. A lot of it was usable and I straightened it by wetting it with windex and using pins. It was nice and straight when dry. The real bad stuff I cut out. If this was not going g to be laminated I probably would not have used any of it.
Last edited by Taxus812; Jan 18, 2020 at 10:46 PM.
Jan 18, 2020, 09:38 PM
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Almost forgot.


I decided I dont want to use the plastic wingtips that came with the kit. I put some feelers out on the best way to do it. I got some good advice and got an idea of how I will do it.

Last night I built new wing tips. I decided to try to carve them out of 1x2 solid block.

The plan was to hollow them out but I weighed the original tips . They were 7g and there is a rib that is glued in so I expect I will be about 9g total. The rough tips are only 12g and they are not shaped yet (still a lot of wood left to remove). I expect they will end up around 9 or 10g. Not enough weight difference to hollow them out

I may do the final shaping with them installed.
Last edited by Taxus812; Jan 18, 2020 at 10:36 PM.
Jan 19, 2020, 09:24 AM
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Here’s a wing tip, tip for ya. Take some 1/32 ply and make it in the shape of the wing tip and cutout what you’d like to hollow out from the tip. Cut the tip in half on the centerline and glue the ply in between the half’s. You now have your outline to sand too on the inside and outside. You also get the advantage of having a dent resistant T/E.

R
Jan 19, 2020, 09:39 AM
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Quote:
Originally Posted by imodel
Heres a wing tip, tip for ya. Take some 1/32 ply and make it in the shape of the wing tip and cutout what youd like to hollow out from the tip. Cut the tip in half on the centerline and glue the ply in between the halfs. You now have your outline to sand too on the inside and outside. You also get the advantage of having a dent resistant T/E.

R
Nice tip I was picturing tape as a guide. Your tip is a lot better. I could have save $$ as well with 1 square stock.

Unfortunately I dont think I can cut the tips I made in half straight enough now they are shaped. Any idea on how to do that accurately?
Jan 19, 2020, 11:14 AM
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Unless you have a scroll or band saw that can handle the the height, you’d have to start over and laminate the tip from several layers.

R
Jan 19, 2020, 08:50 PM
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I do have a scroll saw and a band saw but as you can see from the Top picture, I cut like a blind driver. I will have to look at the wingtips it again when I get to that part.
Jan 19, 2020, 09:18 PM
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Tail complete.


Today I worked on completing the tail.
First thing they have you do is drill the hinges. I used my robet tool then a harry higgly tool to cut hinge slot. I love that tool. Once the centerline is marked you lay the tool flat on the table surface and press it into the part. Perfectly straight hinge slot. You temporally install the rudder and elevator then tape them so you can shape the edges. I had to sand the outside edges round using the tool I assembled at the beginning. One thing to note is the sandpaper will stretch eventually and you will be digging the edge of the wood tool into you nice round edge. I was to do it again I would mostly finish using my sanding bar then final shape using the tool

One thing I am noticing is this wood is DRY. I found a small warp in the horizontal stabilizer. It wasn't horrible but it was in there. I was able to straiten it using Windex then hit it with heat. the Windex softens the wood then the heat sets the shape. The heat also softens the glue a bit. So for small warps this worked. Also the bow was on only one of the 5/16x1/2 LE and it warped about 1/6" (visible). I also found some of the sheeting cracked not due to pressure just contracted and cracked. I presses some Sig Bond into the crack. Not much else I could do. Perhaps this wood being so old has something to do with it.

The hardest part is that elevator joiner. Note you must mark and cut them with the elevators in place to get it correctly positioned. I realized that just before I made a big mistake. I always mess these up because I can never get them straight. I always get one that looks great and one that is an abomination under god. This was no different. I even used my Robarts hinge tool as a drill guide and still went in at a slight angle. Mind you a small angle seem like a mile. I then spent the better part of an hour twisting that thing until everything was flat and lined up properly.

Then you add nylon to reinforce the part. It is then coated in CA. I really hate this but I thought I would try it. Do it again epoxy . Anyway in my tradition I screwed up that one side when the tape moved and glued in place. it doesn't affect anything but I know its there. At least it is on the bottom. Oh I almost forgot. I tried to make the top of the wire (connecting the elevators) at the same height as the center of the hinges. I was thinking it mattered but realized later that as long as it is forward of that point the connection will be actually better. Now one other note. When you use CA (never again) you have to push that sucker in quick or it will not go as far in as your want. Aske me how I know.

Overall it worked out and everything moves freely and is tight.

I set up for the wing tomorrow. One last tip go to staples and make a copy of the plan. You can then cut it up as needed.
Last edited by Taxus812; Jan 19, 2020 at 09:39 PM.
Jan 20, 2020, 03:54 PM
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Good luck with this project!

I had one sitting in my garage for years that I finally built last fall with my daughter. I set it up for electric and am having a wonderful time with it - i did a very short build post in glow-to-electric conversions.

What a great flying airplane.

I'd highly recommend the canopy and cowl from Fiberglass specialties, if you haven't ordered them already.
Jan 20, 2020, 03:55 PM
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Im didnt knock out a ton today. I dont really want to dig into the wings until next week.

I instead, fixed a hinge I was not happy with, worked on the wingtips and made a engine test stand.

I decided I like imodels suggestion. So I set out to figure a way I could cut them straight. Hey nothing ventured nothing gained. I realized I could tack glue them to another piece of balsa and setup a rip fence on my bandsaw. It worked
Last edited by Taxus812; Jan 22, 2020 at 11:00 AM.
Jan 20, 2020, 03:55 PM
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Quote:
Originally Posted by cdavis11
Good luck with this project!

I had one sitting in my garage for years that I finally built last fall with my daughter. I set it up for electric and am having a wonderful time with it - i did a very short build post in glow-to-electric conversions.

What a great flying airplane.

I'd highly recommend the canopy and cowl from Fiberglass specialties, if you haven't ordered them already.

Thanks Im looking forward to it.
Jan 25, 2020, 08:50 PM
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Starting the wings


I got started on the wings today. I plan to take my time.
Last edited by Taxus812; Jan 26, 2020 at 12:20 AM.
Jan 26, 2020, 07:14 PM
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Servo bays complete ! I played around and figured how to get them to fit. It’s tight they sit right up against the ribs. Because if that I had to offset one screw but it structurally won’t have any affect.

If you are wondering why I made the bottoms of the servo covers angled it was not for appearance. I measured up from the TE 80mm to mark the location of the support so it is parallel to the TE. This allowed me to make the servo perpendicular to that edged and thus perpendicular to the TE.
Last edited by Taxus812; Jan 27, 2020 at 05:25 PM.
Jan 27, 2020, 09:13 AM
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What the heck! (Cant use the other word but that is what I am thinking)


I was looking at the plane while was having coffee (I Work at home and my office is across from my shop). I have to be careful to NOT get sucked into my hobby. It’s easy to do but I manage.

Anyway, I started to look at the landing gear blocks again. I was reading about breakouts but I feel like the reinforcement should hold. If they are to strong I really see something else giving an that could be worse.

I did find a very old blurb about a different failure. The holes elongated because of using plywood (And the fact the kit used massively thick wire) . Solid wood blocks were the solution. Now I’m rethinking it. I used epoxy so using my heat gun (for covering) I can easily remove the blocks. Not something I WANT to do but will before it is closed up.

Well I decided to see how the gear would fit. I figured that would help me decide. Not even close! Now I have to rethink the whole thing.

One other thing I found when looking (not critical) was the stringer across rib 2 is not straight. It appears the the notch in rib 3 was aft a bit and 2 was forward a bit from where it should be. Fortunately it only moves the stringer a small amount forward of where it needs to be. I may fix I may not. I wish I caught that before I sheeted. I will say in my defense that you can’t see the alignment great when its on the top. It doesn’t stand out at you .


Repair underway
Last edited by Taxus812; Jan 27, 2020 at 05:29 PM.


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