CATAPULT SAMPLE:Return to the Sunrise Klondike Archive
Notations
1.  The lashing at the bottom is optional for strength
2.  This is tied only to show the arm in the up position, it obviously would not work this way.
3.  There will be a skillet up here to throw the projectile.
There is no pulling rope attached in this picture, but one may be used.
Also, I do not advocate using this device inside a building as it may be problematic with your sponsor. (it also slips alot on this type of floor)

                
Ari Klein