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Part 4: R.C 3D Depron air-plane. MK2 R.A.F Bulldog - Final build part
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Published
Mar 20 2011 by FaTe
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The BullDog is finally taking shape, in this part we will see some simple paint tricks and techniques that help bring the Depron alive. Also we'll be installing the rest of the radio gear and control lines!

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View part 2
View part 3
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Before we start I want to show you how I fixed the split carbon fibre strip. Although I started with a pilot hole and worked my way up through drill bit sizes and kept a good steady pace it split anyway.

To fix the split I used 2 pieces of the same carbon fibre strip across the strip (Notice the grain is side on to the original).
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I first used a bit of epoxy to attach the two pieces, 1 on the very end and 1 at the fold edge of the wing. Once dried I give a layer of the UHU glue over the top to make sure no epoxy is exposed to Depron.

Now the two crossing grains of fibre are bonded it's very strong.


Now the Depron is ready for sanding (profiling) the edges. Basically I keep edges rounded using a small fine sanding thin block and a file set for big chunks of area that need brought down in size.
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Lots of my cuts around the larger Depron pieces where slightly angled due to cutting on my desk, this is a perfect time to tidy all those area's up and give everything a smoother shape.
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You can see how all the edges are nicely rounded with no more knife marks or scuffs, keeping a general round edge and not making it complex means if you have a little accident it's easier to repair and profile back into shape.
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For the following you will need:
  1. Acrylic Red and Black paint.
  2. X-20 Thinner.
  3. Paint brushes in various sizes.
  4. Red TrimLine (Self Adhesive coach line)
  5. Decal sheet containing Blue/White/Red circles and same colour for tail stripes.
The original plans has markings for where to mark off lines for painting. I generally paint in the area's as close to the borders as possible knowing I have trim line. The rear tail is the easiest being all red it's straight forward, the wings are the same case as the tail section of the fuselage painting close to edge as you can.

When your happy with the result cut approximate lengths of TrimLine to size for the rear fuselage, run the TrimLine along the edges of your paint to create a really nice edge. The hardest area to decorate is the canopy, using the black Acrylic paint create the general shape. When it's fully dried use a ruler against the paint line and using a black Disk writing pen colour the edges into a perfect line.
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I went as far as to paint the black walk strip on the wing centre which also hides the tape hinge.
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Also using some of the TrimLine I created the "Do not walk" icons.
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Remember some may disappear as we need to mount 2 servos yet.
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Since beginning the build I've noticed the wing holes for bolts are becoming damaged. To stop further damage I'm using aluminium pipe with a 5MM inside diameter.
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Cutting pieces to 5MM thick then coating with UHU glue as well as the holes. After 10 minutes insert the collars into place and leave them for a few hours too fully harden.

No more damage!
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Making control horns is not difficult. I'm using a piece of plastic from a container which I've cut into the shape you see in the photo. Once you have the shape use a knife to score cross marks into the area that will slot into the flap, this will provide a good bonding surface for glue.

To create the holes for the control line I used a lighter to heat up the end of a spare piece of rod. Once it was red glowing hot I poked holes through the plastic and trimmed off excess with the knife.
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Electronic configuration will vary a fair bit depending on what radio gear you have, however the basic layout is nearly always the same. Remember to run a control test your electrical equipment before moving onto installing it!
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Here you can see the elevator control line guide pipe in place flush with the rear of the stab.
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I installed the final 2 servos by reverse mounting one so that the weight between them is balanced equally.
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There is a small hole I cut below the stab which all the wiring from this side of the fuselage runs through.
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The black receiver is UHU glued in place directly under the stab out of the way and you can see all the wiring running too it carefully tucked into the space between the wing contact surface and the stab piece.
So now all the electronics are installed, the carbon fibre rod that runs down the main wing is approximately 1/3 into the wing which is where our Centre Of Gravity (COG) should be. Before you glue all components into place do some balance tests too see if you need to move components slightly around to balance out.



Now we need to glue in our control horns and test how much movement we get from the control surfaces. Remember if you don't get lots of movement as you want on a control surface then simply making a hole wider out on the control horn will result in more movement (throw).
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To fix the mistake I made running the control lines on a bend in the wing I decided to pattern the tops.
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I simply used the blue and red TrimLine, to create equal spacing I used a piece of the backing as a guide when laying the strips down.
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This serves other purposes like being able to see the orientation of the plane (White wings meaning the plane is facing away from me / Crossed pattern means facing towards me).
Finally the Bulldog is ready for it's maiden flight.
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