Where can I cut weight from a balsa bridge?
The places a balsa bridge usually carries wasted weight: glue, oversized members near the supports, extra bracing and heavy sticks in low-force spots.
Updated · 1 min read
Short answer: glue first, then members that carry little force, then extra bracing. Don't thin a member that bows or breaks in tests.
In order of ease
- Glue. Use a few milligrams per joint, wipe off squeeze-out and never coat a surface. A coach's rule of thumb is that glue should be under 5% of the bridge's mass. See gluing joints.
- Stick selection. Weigh the sticks, and use the lightest ones for tension members and low-force positions. See choosing sticks.
- Members near the supports. The forces are often smaller there than at mid-span, so these can be smaller sections.
- Extra bracing and gussets. Remove any that testing shows aren't doing anything.
- Overlong sticks. Trim to exact length, since overhangs add weight.
What not to cut
- Compression members that bowed in a test.
- A joint that opened or pulled apart.
- Sideways bracing that stops the bridge twisting.
Cut one thing per version, so you can tell what the change did. See practice bridges and efficiency.