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Part 3: R.C 3D Depron air-plane. MK2 R.A.F Bulldog
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Feb 26 2011 by FaTe
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Part 3! Re-enforcements, load bearing tricks and starting to install electrical equipment. We are going to use more of the carbon fibre rod and carbon fibre strip.

Also you will need a drill with 2MM, 4MM and 5MM WOOD bits.

View part 1 View part 2 View part 4

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Continuing from part 1 I used the same process as on the main wing by cutting a V groove in the center of the tail. Using the UHU polystyrene glue apply a bead in the groove and after 10 minutes push the 3MM carbon fibre rod into place.
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Using a ruler or similar means you can use clamps or pegs to keep pressure on the rod while the glue dries without leaving marks. The result is a flush rod embedded in the tail.
build imageWith the main wing inserted mark out an area on the side shock pieces that lines up with the carbon fibre rod on the wind.

This will act as 1 half of a clamp to secure the wing in place. All you need do is push a piece of carbon fibre strip against the main fuselage so it leaves an imprint, then cut a slit with your knife in the position. You'll then be able to push the strip all the way through, now you can glue it in position using the UHU glue.















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To add extra support on the middle of the main wing I added an extra strip of Depron on each side. These two pieces increase the middle area against the wing from 6MM to 18MM which is much better and almost no extra weight at all. With the wings in place even without clamps or anything additional it stays quite solid in place. This is encouraging as the clamp I have planned will ensure it's solid at all times.




Time for our first 2 electrical components to be given a home. The easiest is the battery slot, I just lined up the battery at the very front against the carbon fibre strip and cut the hole slightly too small. This means the battery is held in snug.


The servo hole requires a cut in the right shock section against the lateral carbon fibre strip. You will also need to cut out an area for the servo head to freely move for hooking up push rods later.
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Now to complete the other side of the wing clamp. Cut a 80MM length of carbon fibre strip, ONE half of it needs attached too the wing against the pipe already there. Glue the strip into place with 40MM extending out, clamp the piece into place while it dries. (use a cut off piece of Depron on the other side to prevent unwanted imprints.) Now when the wing opens it creates a full panel, later we'll be drilling this to create a clamp. Here you can see how the battery slots into place. I shook the fuselage around and it didn't budge at all although you can always use a bit of velcro extra if your worried.













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In part 2 we added the shock pieces which give the top of the tail a big contact surface but now the bottom needs something similar. Cut two 40MM pieces of Depron out and glue them into place one on each side flush with the cut out area.

I glued them slightly angled upwards so they have a natural press against the tail, also note I cut out a little groove where the rod on the bottom of the tail is so nothing catches.
Now the two pieces need re-enforcing, again the carbon fibre strip comes in handy. Cut out a length the same width as the blocks and cut out a slit in the fuselage for it to push through. Apply glue, wait 10 minutes then clamp it into place while it dries fully.


Now both the main wing and the tail have carbon fibre strips on each side which can be drilled and using plastic bolts create solid clamps.













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Now to re-enforce the bottom of the fuselage for 2 reasons:
1) If the landing gear ever fails it'll act as a skid pad.

2) Taking the wing in and out will cause stress, this carbon fibre strip refuses to bend sideways so this resolves that problem.
First sand down the bottom of the fuselage with a super fine grit in and over the 1000 range. Now apply UHU glue too the area and on the strip, leave for 10 minutes and place in position.

Because the profile of the bottom is not straight it will need to help to keep in place. You can't use clamps here but Scotch tape works wonders instead. Give it an hour to dry and not the usual 20 minutes to make sure it's fully dry.

















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On to being able to fix our wings in place for flight!

I bought 5MM*13MM Plastic bolts with aluminium lock nuts (they have spikes which keep it in place). So using a drill I drilled through pilot holes using a 2MM drill bit first, directly through the middle of the carbon fibre piece and through the other side.
As you can see I wasn't quite careful enough on 1 side although it is fixable. (as you will see later)

Notice I flatted the grab spikes as I thought drilling holes in carbon fibre that small is too risky, instead glue them in place!
Exact same procedure for the main wing, you will need the wing in position to mark on the top of the wing where your hole needs to go. Once u have the tops drilled and 2 markings on the wing, take the wing back out and now you can easily drill the rest. Note how the bolt on the left sits next too the servo position, in turn this is attached too the main fuselage. All the pressure is directed into the the carbon rods, out through the fuselage.

















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Here you can see I repeated flatting the spikes out, glueing them in place instead. Also note I placed a 2nd strip the same way I applied the first just on the opposite of the rod. It's not needed for indoor flight but I'd add it regardless. Now the wings are able to be secured in place, the tail bolts need trimmed but I'm saving all that for end with decoration. Both wings are very solid in place, however if your unsure on the strength you can always add a small piece of pipe in the wing where the bolt can run through. Glue the pieces of pipe in place so it acts as a guide for the bolt and stops damage too the Depron. A top of view of the finished "flight ready" construction, taking the bolts out then the wings takes about a minute. The wings fold up and the entire aircraft is reduced too a length of 42cm making it super compact for transport. I wanted to mock up the aileron servo, battery and motor + prop in place to get a glimpse of a finished product. I'm waiting to place the remaining 2 servos and receiver until I need to balance Centre of Gravity (COG).



In part 4:

  • Fixing the broken carbon fibre strip from drilling.

  • Sanding techniques (Didn't think I was going to leave it shoddy did you?!)

  • Running control lines to ailerons, rudder and elevator.

  • Making control horns for the control lines.

  • First steps in decoration.

  • Installing the last 2 servos while setting our COG.

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