Tag Archives: Scarf Joint

Building Aero 3D Day 38: Trailing Edge

Servo Wire Hole Drilled

Wednesday, Peter came over and we made some more progress. Could only do a little bit as the trailing edge is required to continue.

First, using a forstner drill bit, I drilled a hole into the top center of the wing. Peter held a piece of ply behind to help prevent the balsa sheeting from splintering while I drilled. This hole is where the servo leads (likely a Y extension) will come up through and into the fuselage to connect with the receiver.

Once that was done we determined the length of the trailing edge, which needs to be made out of two pieces, insuring some excess. Allowing for 3 inches of overlap I cut the excess off of one piece to make it more manageable to work with and then:

  • Marked 3 inches from each end of the scarf
  • Drew a line along the diagonal of the wider side of one
  • Marked side to be sanded
  • Determined how the diagonal line needed to be drawn on the other and which side marked to
  • Ensure pieces would fit together, one on top of the other
  • Sanded down to the line testing the fit along the way
  • Using 30 minute epoxy I glued the two pieces together
  • Placed a pin in each end and clamped to dry

You can see the final scarf joint clamped together and left to dry in the image below.

Due to Covid-19 and social distancing I’m not sure when our next session is going to be.

Building Aero 3D Day 21: Ribs Glued & Scarf Joints

Today started by reinforcing the scarf joints, seen in the featured image above, using gussets which in this case is made out of wood (filler I believe). The pieces are cut to the width of the sides they are going on (1/4” in this case) and a length that goes a bit past the scarf joint on each end. You can see the glued pieces, using medium CA in the featured image above. In the image at the bottom you can see where weights were left on the spars to keep them flat.

Once that was done we moved on to the wing. Using the big ruler to help keep a straight edge we propped up the trailing edge along it… we started with the ruler at the end closest to us in the picture below (right) and pinned some blocks to support it from the other side.

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Building Aero 3D Day 20: Scarf Joints

Scarf Joint Marked

Yesterday I learned how to make a scarf joint and then proceeded to make four of them. For this model the wing is one piece; however, the spars are not long enough in a single piece so need to make them out of two pieces. Since need one for top and bottom need two of each. The main spars are made out of 1/2” x 1/4” balsa and the other two out of 1/4” x 1/4” balsa.

The rule of thumb (apparently with full scall aircraft too) is a ratio of 12:1. That is for every 1 unit of thickness you need 12 units of overlapping length. I may not have explained that well so here are the numbers for my pieces.

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