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RBC Kits A-4

Old 02-21-2012, 04:32 AM
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Default RBC Kits A-4

I did a search for this kit and found a build thread from 2003, but the author never finished the build. I'm going to build this kit and install a ChangeSun 10 blade 70mm fan. The kit is old but a simple build. I fly off of a grass field so this will be bungee launch project. The kit has all the balsa parts and sheeting required to finish the plane. It uses lite ply throughout, I'll use aircraft grade plywood where I think it needs it. It is built in modules which makes things easier for the builder. I'll following the instructions...so will begin with the wing.

Keith
Old 02-21-2012, 06:56 AM
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Default RE: RBC Kits A-4

The wing isn't pinned down in the early stages...it is held until the top sheeting is applied. I drew the locations of the spars and ribs onto the lower sheeting but found out the balsa parts are a bit different. Not a big deal but it does show how much the plans will distort because of moisture. The parts fit well. And the wing is small...not much to it. The servos will be on the top surface because there is no LG. I like the kit so far....excellent plans, directions, and wood.

Keith
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Old 02-22-2012, 04:28 AM
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Default RE: RBC Kits A-4

Still adding internal wing bits and pieces. The directions have you gluing the ribs and spars to one half at a time and then gluing the center seem last. I joined the bottom sheeting first and then added the ribs and spars...I think it was much easier. I won't be able to do that with the top sheeting.. so will glue one side at a time. The wing is already fairly stiff. The entire structure (sheeting, ribs and spars) is 1/16 sheet balsa. Did I mention how small this wing is....that is the GP mini F-86 sitting on top of the A4 wing.

Keith
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Old 02-22-2012, 01:56 PM
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Default RE: RBC Kits A-4

You may have screwed yourself the way you did it.
I don't see where you used the tapered washout jig. It won't fly very well without the required washout.
Old 02-22-2012, 11:23 PM
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Default RE: RBC Kits A-4

The washout is locked in when the top sheeting in applied...so no problems yet.

Keith
Old 02-23-2012, 12:18 PM
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Default RE: RBC Kits A-4

I glued all the nose section pieces of the fuselage, there are 13 pieces. I added a piece of scrap balsa to the bottom forward edge of the sides so that the bottom edge would be flat. There is a slight up turn on the bottom....that would made it a compound curve...curving in and up at the nose. I thought it would be easier to make it flat so I only had to content with the one curve. I can sand back the up turn after all the pieces have been glued. I also will change the lite ply bungee hook with a lamination of two 1/16 aircraft ply pieces..it will be much stronger and last the life time of the model.

Keith
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Old 02-27-2012, 03:59 AM
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Default RE: RBC Kits A-4

Began shaping the nose section and started assembling the mid section. The wing is required for the mid section so I'll need to finish the wing now. The MF5 (mid section side pieces) parts need some careful attention to mate them to the front former. The ChangeSun fan arrived, looks pretty good. There is a thread (F-86 and Mig 15) describing the difference between a four blade unit and the ChangeSun ten blade fan.

Keith
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Old 03-05-2012, 11:25 AM
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Default RE: RBC Kits A-4

I was working on the mid fuselage section and discovered some missing pieces. The parts sheet for the duct pieces for the mid section is missing...I emailed RBC and they mailed the missing pieces that day. While I'm waiting for those pieces I started gluing on the top wing skin. I used the technique used on the RBC F-100 kit by using tape on the work board and on the bottom TE. I glued the wash out template to the board and then glued the wing TE to the template. With that done I applied yellow glue to the structure and put everything I had that would fit on top of the wing to hold it down. The final picture shows the wash out at the wing tip. Should be able to do the other side tomorrow. Then the LE and tips can be glued on.

Keith
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Old 03-06-2012, 08:33 AM
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Default RE: RBC Kits A-4

The left top skin is now drying. I had some trouble with the TE curling up. There is almost no structure on the TE piece and the grain runs lengthwise. I had to weight it down so there is a downward curl so the wing will fit the fuselage wing saddle. The right side mid wing area is good...it does fit the wing saddle. The tip however now curls downward. I'll use the wing tip block to straigthen the curl at the tip.

I'll add photos later, the program isn't allowing me to attach photos at this time.

Keith
Old 03-07-2012, 12:19 AM
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Default RE: RBC Kits A-4

the photos..........
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Old 03-14-2012, 12:39 AM
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Default RE: RBC Kits A-4

Was not happy with the wing TE. It was curled downward, almost like having flaps. I cut off the TE and will add some more wood and sand it to shape. Still haven't received the missing pieces from RBC. I can work on the tail section, just can't glue the vertical on.

Keith
Old 03-15-2012, 08:35 AM
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Default RE: RBC Kits A-4

I removed about one inch of the TE. After sanding the edge straight, I glued on a piece of TE stock I had. The TE stock was 1 1/4" wide so removed 1/4". I used a 1/4 X 1 1/2" stick to hold the wing to the board, careful not to crush the wing. There is a 1/32" difference between the TE stock and the wing. I'll sand that down after the glue dries. I'm happy with the left side, the TE is now straight with no curl. Also, the wing tips can now be added...with the curl the tip blocks were not thick enough. Will add the tips tomorrow and then finish off the center LE area to match the fuselage former.

Keith
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Old 03-16-2012, 09:08 AM
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Default RE: RBC Kits A-4

The wing is now rough sanded. I will do the final sanding just before covering. I'm happy with the new TE, it is straight and the airfoil matches the wing. Next will be to finish the LE center section to match the fuselage former. I'll start assembling the tail section. The previous A4 thread showed a photo of the tail section. The vertical fin didn't fit on the tail section, there was a large gap between the vertical and the tail section. Will never know how that was fixed...but the horizontal stab incidence was affected. I think I'll assemble the vertical fin while it is sitting on top of the tail section...less likely to repeat the same problem.

Keith
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Old 03-17-2012, 11:39 AM
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Default RE: RBC Kits A-4

The tail section is fairly straight forward. It is recommended to fit the fan shroud during assembly. I added some plywood pads for the mounting screws, much better than just the lite ply. This area will not be accessible after assembly. I noticed the top stringer is not straight, has a slight bow. I'll be sure to assemble the vertical fin with the tail and mid fuselage sections screwed together and the fin bottom rib laying on top. That way there will be no gaps between the fin and fuselage.

Still waiting for the missing parts. I can sheet the tail section now. The mid section can be sheeted after I mount the wing.

Keith
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Old 03-18-2012, 04:23 AM
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Default RE: RBC Kits A-4

The wing is mounted to the mid section. I added a plywood pad for the mount screw...much stronger than a single piece of 3/32 lite ply. I can now finish the wing LE center section. The inlet ducting pieces are the ones that are missing so have to wait to finish the mid section. Also installed the screws that hold the mid and tail sections together...can now sheet the tail section

Still had trouble fitting the wing to the saddle...the TE is too wide and thin at the center. I decided to cut a notch in the TE instead of sanding. The wing now sits in the saddle perfectly. All the ribs were positioned and glued per the plans, as was the wing sheeting...not sure why al the trouble.

Keith
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