RCU Forums - View Single Post - Top Flite B-25 - Wingspan Models Add-ons Build Thread
Old 07-26-2008, 01:37 AM
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RCKen
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Default RE: Top Flite B-25 - Wingspan Models Add-ons Build Thread

With the fuselage opened up for the bomb bay the first thing I wanted to do was mount the air tank for the retracts that we removed when installing the top turret. Have you ever had that sinking feeling in the pit of your stomach when you realize that you screwed up? Looking in to the fuselage that feeling was rapidly setting on me. Because of the spacing of the cross braces on the fuselage formers there was no way for me to get the tank inserted into the area above the wing tubes, And because of the former braces that were installed when the top turret was put in there was no way to slide the tank in from the front of the fuselage either. This one was tougher to solve than a Rubik’s Cube. I spent an entire evening trying different methods of trying to get the air tank where I wanted it to go, with absolutely no luck. My initial intentions were to install the tank so that I could get to in the event it needed to be removed for any maintenance. It was rapidly looking like that wasn’t going to be the case here. Finally I came to the realization that I was going to need to disassemble part of the fuselage to get the tank in. Doing some dry fitting with the tank and evaluating the inside of the fuselage I decided that the best way to accomplish this was to remove the rear wing tube and cut the former that was located immediately forward of that. I wasn’t worried too much about the way I removed the former cross section because I could easily rebuild that member, but the wing tube was another story. Since the tube was made out of fiberglass I really wanted to get it out without destroying it if possible.

Looking at the fiberglass tube it looked like it was installed with simple epoxy. So, this was a good thing. About the only thing that will “undo” set epoxy is heat, so I pulled out my covering heat gun. Using the heat gun I worked the area on the end of each wing tube to soften the epoxy. As the epoxy was softened a hobby knife was used to remove the epoxy from the tube and the side of the fuselage. It really came off a lot quicker than I first thought it would. But with all the epoxy off of the tube inside the fuselage the wing tube still was not free so that I could remove it. Apparently epoxy was in the area where the tube was in contact with the fuselage. There really wasn’t any easy way to use a hobby knife to cut the tube loose, the tube is really pretty thin and a sharp knife would cut through it if a mistake were made. So, a custom cutting tool was needed. For this I turned to a bag of brass tubing I keep to find a brass tube that was just bigger than the wing tube that needed to be cut out. As a side note, if anybody lives near a Hobby Lobby (I am referring to the craft stores and not the hobby shops) you need buy a bag of tubing there. They sell a bag of various sized tubing for about $15, and it’s worth every penny. No matter what size tubing I need I always seem to find it in that bag of goodies, so get one for your shop!! Trust me!!!! Anyway, back to the job at hand. I found a piece of tubing that had an inside diameter that was just a hair bigger than the outside diameter of the wing tube, so this was perfect. I first used a hobby knife to shave down the inside edge of the tubing to sharpen it up. Then I used a rotary tool with a cutting disk to cut teeth into the tube. The last step was to wrap some tape around the other end so my hand wouldn’t get cut up as I used the tool. I was now ready to finish up getting the wing tube out. The brass tube cutter I made was perfect for the job. It made small work of cutting the epoxy loose around the outside of the wing tube. With it cut loose the tube slid right out. It needed just a little work to finish cleaning off the rest of the epoxy on the outside of it, which was accomplished with a heat gun and a hobby knife. The last step was to cut through the cross member on the fuselage former. Using a razor saw this was easy to do.

With the fuselage opened up I now reused the mounting rings I removed when preparing to install the top turret. Medium CA was used to glue the rings in place to hold the air tank. The airline was extended back to reach this new install location and the tank was then secured in the ring mounts. A little bit if thick CA was used to secure the tank to the mounting rings.

Before moving on to the next step let me make this comments. I would have much rather have avoided having to do these steps, but I honestly thought this wouldn’t be so difficult. So if anybody is planning on doing these add-ons I hope that they can benefit from my mistakes. If I was to redo this installation I would have removed the air tank, cut open the bomb bay section, and then installed the air tank in the new location BEFORE installing the top turret. By doing this the tank can easily be slid backwards through the fuselage in to it’s new location. Oh well, lesson learned and I hope that I help some others out there.

Pictures
1. With the fuselage open the cross members prevented installing the air tank in the fuselage
2. Using a heat gun to soften up the epoxy on the wing tube.
3. With the epoxy soft use a hobby knife to remove the epoxy.
4. Making a circular cutter from bass tube.
5. Using the cutter to cut away the fiberglass wing tube.
6. The fiberglass wing tube removed intact.
7. Use a razor saw to cut away the cross member.
8. Install the tank mounting rings.
9. Install the rear ring.
10. Extend the air tube back to the new tank location.
11. Place the tank in position and secured with thick CA

Until next time

Ken
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