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Rotor Build Part 4: Internal Bits
Posted by J.S. Decker on May 9, 2008, 19:26
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In this part, fabrication and installation of the internal parts is demonstrated. The internal parts include the ballast tube, crush blocks, servo trays, canopy formers, and other parts that you can’t see from the outside of the plane.
Since I started building TWF planes a few years ago I have fallen into using scrap materials that I have on hand to fabricate the internal parts. So, what you see me doing here might not make sense when view from the context of usual materials and parts you see kits. The material that is used for most parts is the cheap 1/4-inch thick plywood that you can get from a DIY store. In my case, I got a few pieces that added up to more than a full 4x8 sheet for one dollar when my local Home Depot wanted to get rid of a bunch of scrap that had accumulated in their lumber department. So, while it wasn’t free, it was close to it. Initially, I use this material for little projects around the house, building stuff for the kid’s school projects, and then I got the geeky idea to start building “battery charger caddies”… now, it seems that I try to use this material when ever need some the harder than balsawood, because I have it, it is easy to shape with my tools, and it is inexpensive.
With that back drop, here is how I built and install the internal parts for this Rotor.
- Fabricate and Trial Fit First: Fabricate and trial fit all of the glued in place fuselage components described before starting to glue them in place. By doing so, you can assure that everything fits and works together as desired before being permanently glued in place.
- Ballast Tube: The ballast tube shown fits under the mono-block. Three lead bars that have a combined weight of 22 ounces. With an expected AUW, unballasted, somewhere around 45 oz, the wing loading will be around 21 oz per sq ft. With an additional 22 ounces of ballast, the wing load will be a nearly ballistic 32 oz per sq ft.
A here are couple notes on the ballast tube installation. The ballast is secured with a screw through the bottom of the fuse. The front of the ballast tube is secured to the bottom of the fuse with a mixture of resin, milled FG, and microballoons. This mixture of goo is used to fill the void between the bottom of the flat ballast tube and round bottom of the fuse, which prevents distorting the ballast tube when tightening the retaining bolt. The ballast tube is also glued to the fuse with Goop/Liquid Nails adhesive near the middle and opposite end of the ballast tube.
A couple notes this ballast tube, this was the first ballast tube I built. It looks like fecal material, so it was not used in the F3J plane I was building at the time. But, I kept for someday when I build some slope plane. Well, someday came for this ballast tube.
"Someday" in future, look for an article on fabrication of ballast tubes and lead bars in the techniques section.
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| Balast tube and the 22 oz of lead bars that go into it. |
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| Trial fit of the ballast after installing the servo trays. Easy enough to get in and out of the plane. |
- Canopy Hook: A cup hook in installed in the fuse to attach the rubber band that holds the canopy in place. For slopers with canopies, I prefer rubber band hold downs. So, I cut a little wood block, screw a cup hook to the block, and glue the assembly into the fuse, which in case was the top of the ballast tube. Goop/Liquid Nails adhesive was used.
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| Completed canopy. Not the small block on the left side, the small block fits into the flange of the fuse as hold the front of the canopy into the fuse. The small wood block with the cup hook was glued into the fuse retains the canopy hold down rubber band. |
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| Everything installed in the fuse. The cup hook that the rubber bands are attached to is between the mono-block and the servo tray on the right, which is the rear servo tray. |
- Crush Blocks: Crush blocks are pieces of plywood installed between the sides of the fuse about a half-inch behind the LE and in front of the TE. They are glued in place with Goop/Liquid Nails adhesive. The purpose of the blocks is to prevent the LE or TE edges of the wing from puncturing the fuse during hard landings, cartwheels, and ground loops. Even with the stainless steel tubes and hardened joiner rod in the Winch Doctor hardware and a stout composite fuselage, you need to install crush blocks.
Note the crush blocks are not visible in any of the photos. The front crush block is under the front servo tray and the rear crush block is behind the canopy opening. Trust me they are there and they are important.
- Servo Trays: The servo trays are cut from 1/4-inch plywood fit and then reinforced with scrap CF. The reinforcement was two layer of 5.7 oz bidirectional CF on each side of the servo trays. The CF on each side consisted of one layer 0-90 and one layer on 45 degree bias. The servo trays are glued into the fuse with Goop/Liquid Nails adhesive.
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| 1/4-inch plywood servo trays about to have CF laminated to both side and sucked down in a vacuum bag. |
- Canopy Formers: The canopy formers are cut from 1/4-inch plywood, the edges are beveled to make fitting them easier, and glued in place with Goop/Liquid Nails adhesive. The formers are installed close to the ends. A small block of wood is glued to the front former to secure the front of the canopy in the lip of the fuselage.
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| The canopy formers and hold down loop just prior to being glued in. The black marks on the fuse locate the LE and TE of the wing to help located the crush blocks. |
- Canopy Hold Down Loop: The canopy hold down loop is cut from 1/4-inch plywood and glued in place with Goop/Liquid Nails adhesive. The loop needs to be big enough that it is easy to push a rubber band through the hole. The inside radius of the loop is rounded and smoothed with sandpaper so that the retaining rubber band is not abraded. The loop is located directly over the cup hook that was installed in the fuse.
This is one of those parts that could be done a thousand different ways. I did it once this way, it works well, is robust, and I have continued to use it.
- Stinger: The stinger is glued in place by shaping a half-inch long balsawood plug to fit into the tailcone, placing the plug half way inside the tailcone, gluing the balsawood plug in place with CA or 5 minute epoxy, fitting the plug into the stinger, and gluing the stinger in place with CA or 5 minute epoxy. The joint is then sanded, FG is placed over the joint, the FG is wet with resin, and allowed to cure.
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| Balsa plug glued into the tailcone. The plugs was drilled out after being glued in place so that it was hollow. |
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| Stinger glued in place with a mixture of 5 minute epoxy and microballoons. The joint was sanded, FG was applied, and resin was applied. |
The fuse and canopy are ready for finish.
Rotor Build Part 1: Preassembly and Component Weights
Rotor Build Part 2: Pitcheron/Wingeron Hardware Installation
Rotor Build Part 3: Fin and Stab Installation
Rotor Build Part 4: Internal Bits
Rotor Build Part 5: Conclusion
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