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Tuesday, October 02, 2007

Making knuckle joints for your F3B Wings.

Fig 1

Having seen Evan making and helping him to make the knuckle joints on his Shongololo prompted me to capture this on camera and document it for future reference to all our club members and other viewers on the BERG Blog that might want to do the same.

The first thing that you must do is to make sure that your hinging on you ailerons and or flaps are already done and working freely and correctly.

Make sure that there will be a cavity in the wing were the knuckle can hide in when completed. Now take 25mm wide colored Sellotape (available from Waltons in SA. (The glue side is white.)) and tape on to the top (opposite side of hinge) of the aileron/flap 10 mm overhanging. See Fig 1 and Fig 2 ( I suppose other tapes could be used, but Evan suggests that this Sellotape from Waltons is the best for the job, as it is quite stiff and the glue is not affected by the resin)

Now fold the flap/aileron so that the aileron/flap is just about underneath the wing and just about level. See Fig 2. below.

Fig 2

Fig 3

Make a very runny past of epoxy resin and micro balloons (Tomato Sauce consistency) and add pigment (if required) coloring to match your wing color. Poor this mix into a piggy-bag (plastic coin bag) and cut the corner off. Now squeeze the mixture on to the junction of tape and aileron/flap and continue to the full length of the wing. See Fig 3. above. The mix must be able to flow across the tape and wing skin junction, so it must not be thick.

Fig 4

Now get your helper to fold the wing over on the hinge while keeping the aileron/flap as close to level as possible, use an old credit card and from underneath guide the Sellotape into the cavity. You will end up with the wing in an upside down position.
See Fig 4.

Fig 5

Fig 6 Carefully jig the flap/aileron with masking tape and rig it up on blankets as seen in fig 5 and let dry over night. See Fig 6.

The angle between the wing and control surface must be enough to cause the tape to form a curve into which the mixture can flow.

Once dry you can remove the tape and admire your handy work. If you have used the coloured Selotape as described above you will find that there is no glue residue and the knuckle will be nice and smooth. Requiring only a light sanding along the front edge to get it nice and straight.

Evan has created a file containing a step by step drawing "Making Knuckels.pdf 05-Oct-2007 20:51 21K "and can be found in the BERG vault to download.

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