Catapult Design Experiment

This is the catapult.
I’m using 2x4s for the catapult frame. The frame is made of two side walls connected at the bottom with stringers. The side walls are made of an 8 foot 2×4 at the base, and a shorter 2×4 attached in the middle as an upright. Because there would be a lot of toque applied to this upright, I use the remainder of that piece as a 45 degree cross brace.
To hold the tensioned arm down before launch, I used some barrel latches. These were mounted at the rear of the base and could catch the arm using a small bracket. I used two latches to hold the arm evenly and tied the two together using paracord. A longer line was tied to the joined latches and would back as the pull-cord used to release the catapult.

To power the catapult, I decided to use surgical tubing. It is amazingly stretchy, quite durable, and comes in large rolls. I screwed in some eyelets at the top of the uprights and secured the tubing to them using zip-ties. I ran the tubing through the uprights and around the arm. Not knowing how tight to pull the tubing, we did a small shop test to see how far I could launch a roll of tape. I purposely left one side of the tubing disconnected so I could make on-the-fly adjustments.
After testing larger projectiles, I decided to double up the tubing and shortened it to a semi-scary tension.
Supplies:
2X4s
Aluminum Channel
Surgical Tubing
Latches
Construction Ties (Lumber Connectors)
Paracord
Dust Pan
Lag Eyebolts
Zip-Ties