So as you say, the release angle is the angle your projectile should travel along relative to horizontal. Generally 35-40 degrees are the angles you want to shoot for, though there are differing schools of thought on that one. 33 degrees sounds a tad low but it can indeed work better depending on the configuration.
To get your machine to release at such an angle is really only something that can be found via trial-and-error. Video footage shot directly from the side is extremely helpful. For a hinged counterweight trebuchet (HCW - sounds like this is what you have), you ideally want the arm and hanger to both "stall" in the vertical position. Stall is seen only via video, and will show as several frames in a row where the object in mind does not move (much at least). As long as your arm isn't too heavy relative to your counterweight and projectile (sounds like you are OK on the last 2 at least, assuming this is a ~10-pound projectile we are talking about), a HCW arm will tend to stall fairly close to vertical. There are things that affect this, but it ought to be close.
Your sling wants to release at the arm stall, and be
roughly 35-45 degrees behind the arm/above horizontal at that time (as a general rule of thumb). Tweaking your release pin angle will tweak the final trajectory but typically has only a minimal effect on the sling location at that time. To get your sling length right for the release timing: short slings will get into position earlier, long slings will take longer to get there. A sling roughly 80% of the length of the long arm (10'6" in your case I think?) is a good starting point, it sounds like you might be too long at 10' though without a video it can be hard to tell. Pin angle should start at 45 degrees (measured as the angle between the axis of the arm and the axis of the pin), and be adjusted accordingly per above.
Hopefully that helps some? Feel free to ask for clarification if something seems confusing! And feel free to post pictures/video (or links to such) as it can help give some better guidance (the above are general rules of thumb).
- Roughly ideal tuning position. In reality the arm and counterweight tend to not perfectly align in this way.
- Ideal tuning position.png (13.89 KiB) Viewed 23311 times