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After breaking the carbon tube spar in the flying stab of my Revolto, I decided to make the repair stronger than the original. The stock 4mm carbon tube has a thin wall and easily fractures under a twisting load, which makes it a poor choice for a flying stab spar. Everyone I know who has a Revolto has broken this tube, with only one exception. Plus there are more reports of breaking the carbon tube spar on the internet forums.
The repair starts off with a 4mm carbon tube, but with a thicker wall. The original 4mm carbon tube had a .116" hole. The replacement 4mm carbon tube has a .078" hole, so the tubing wall is considerably thicker, which should increase the overall strength.
The center section of the carbon spar gets sleeved with 5" long piece of 3/16" brass tubing. The brass tube transmits 100% of the torque force to the flying stab halves, which should eliminate any torsion fracturing of the carbon tube.
The inner tubing guides of each stab half, plus the fuselage rod bearings will need to be drilled to clear the 3/16" brass tubing. The goal for the bearings is zero friction with zero slop.
With the beefed up flying stab spar, the next weakest point was the flimsy plastic control horn. Although mine hasn't broken (yet), I've heard of several that have broken, so it's getting an upgrade. A new control horn was made from an unused part of the fiberglass hardware that's included in the Value Hobbies epp foamies. This fiberglass sheet is 1mm thick, and way stronger than the original plastic control horn. The control horn was sandwiched on both sides with a couple of prop hub adapters that fit the 3/16" brass tubing just loose enough to allow thin CA glue to wick in there. This gives plenty of surface area for the CA glue to securely bond the control horn and the prop hub adapters to the brass tubing. This area of the brass tubing was roughed up with sandpaper to further strengthen the bond.
The original method of gluing the flying stab halves to the carbon tube calls for using CA glue. This requires extreme caution to make sure the CA doesn't accidentally wick into the rod bearing and turn the flying stab into a fixed position flying stab.
This time the carbon tube was inserted into one of the flying stab halves, then a thick bead of Foam Tac was laid on top of the exposed carbon and brass tubing. Then the carbon/brass tube was spun around about a dozen times, which pulled the Foam Tac down into the slot and spread it out. Once it was dry, this stab half was inserted into the fuselage bearings, along with the new control horn and the prop hub adapters. The control horn and hub adapters were then glued with thin CA onto the brass tubing in the proper position. Finally the other stab half was slid onto the carbon tube, a thick bead of Foam Tac was laid down on the exposed carbon/brass tubing, and the stab was spun around about a dozen times to spread the glue into the slot. The stab halves were carefully aligned and jigged into place, and the Foam Tac was allowed to fully dry.
The result is a flying stab with zero torsion slop, and a much stronger spar. Plus I'm really super excited to have my Revolto flying again! :drink:
The repair starts off with a 4mm carbon tube, but with a thicker wall. The original 4mm carbon tube had a .116" hole. The replacement 4mm carbon tube has a .078" hole, so the tubing wall is considerably thicker, which should increase the overall strength.
The center section of the carbon spar gets sleeved with 5" long piece of 3/16" brass tubing. The brass tube transmits 100% of the torque force to the flying stab halves, which should eliminate any torsion fracturing of the carbon tube.
The inner tubing guides of each stab half, plus the fuselage rod bearings will need to be drilled to clear the 3/16" brass tubing. The goal for the bearings is zero friction with zero slop.
With the beefed up flying stab spar, the next weakest point was the flimsy plastic control horn. Although mine hasn't broken (yet), I've heard of several that have broken, so it's getting an upgrade. A new control horn was made from an unused part of the fiberglass hardware that's included in the Value Hobbies epp foamies. This fiberglass sheet is 1mm thick, and way stronger than the original plastic control horn. The control horn was sandwiched on both sides with a couple of prop hub adapters that fit the 3/16" brass tubing just loose enough to allow thin CA glue to wick in there. This gives plenty of surface area for the CA glue to securely bond the control horn and the prop hub adapters to the brass tubing. This area of the brass tubing was roughed up with sandpaper to further strengthen the bond.
The original method of gluing the flying stab halves to the carbon tube calls for using CA glue. This requires extreme caution to make sure the CA doesn't accidentally wick into the rod bearing and turn the flying stab into a fixed position flying stab.
This time the carbon tube was inserted into one of the flying stab halves, then a thick bead of Foam Tac was laid on top of the exposed carbon and brass tubing. Then the carbon/brass tube was spun around about a dozen times, which pulled the Foam Tac down into the slot and spread it out. Once it was dry, this stab half was inserted into the fuselage bearings, along with the new control horn and the prop hub adapters. The control horn and hub adapters were then glued with thin CA onto the brass tubing in the proper position. Finally the other stab half was slid onto the carbon tube, a thick bead of Foam Tac was laid down on the exposed carbon/brass tubing, and the stab was spun around about a dozen times to spread the glue into the slot. The stab halves were carefully aligned and jigged into place, and the Foam Tac was allowed to fully dry.
The result is a flying stab with zero torsion slop, and a much stronger spar. Plus I'm really super excited to have my Revolto flying again! :drink:
