Aerodynamic question

[Airpi]

Alright, me and a friend of mine have been wondering what is more important for accuracy and distance in projectiles:a uniform surface, or a sleeker (if irregular) surface. Specifically, a water balloon vs a waterballoon in some kind a catridge, in this case two paper cups taped together. I thought the more regular surface of the cup would give it better range, as a water balloon is flexible and would flatten out as it moved agaisnt the resistance of the air. The other side is that the paper cups would either be flat and wind resistant or pointy and dangerous. Any input? If this is a debated subject, I thought we could put it to the test and see which is superior once we finish our launchers.

[Silence]

For the theoretical side of your question, I am probably relatively naive compared to Drenchenator and the like. However, I will suggest that it is better for a projectile to have a uniform cross-section shape throughout, while the actual cross-section does not need to be uniform. This is because fluid air resistance is generally experienced along the lines of the trajectory, rather than perpendicular to the trajectory.

In this situation, I doubt a cup method would work very well. The actual water balloons are durable and resiliant enough to travel without rupturing, and their elasticity would pull them back to some extent as they expand perpendicular to the trajectory. In contrast, it is almost a given that a dual-cup shell would spin, twist, and move in very random and irregular patterns, and because the shape is only uniform during rotations of the water balloons, your shell would not have good performance. Also, a shell would require more work and reduce the splash of the balloon, and if it is tight, then it might even prevent the rupturing of the balloon upon impact.

[Lightbulb41]

I Use the paper cup method on one side as I fire them out of the Cannon. It protects the balloon from the impact of the highpressure on the cannon. It works well. Once I get the balloon a out of the barrel It falls away causing the balloon to be farily acurate.

[Airpi]

Yeah, we were planning on finding some cheap cups to act as a sabot for the balloons. The two-cup thing was really just a theoretical thing that we were considering using if it improved accuracy significantly enough to be worth all the mess.

[Silence]

The single paper cup is, I believe, also known as a sabot. It's used as wadding like Lightbulb41 said to protect the balloon, and is absolutely necessary--if not to prevent rupturing the balloon, then to establish a strong seal to maximize performance. Duxburian says the Ridgewood Militia (RM) uses Pringles cans as their Douchenator sabots, and in the absence of those, they use tennis ball cans (usually holding three or four tennis balls). In addition, many people (including me) use tennis ball cans to store balloons during transportation, though you could also use Pringles cans instead. If I ever build a water balloon launcher (or even an APWL), I'll try to create a design that uses a plunger as a built-in sabot for convenience.

EDIT: Didn't see Airpi's post...

[Lightbulb41]

Unfotuneatly a 6 inch barrel on mine causes sabot problems... I can't seem to find anything big enough to work unless i build a reusable wadding that after x amout of feet gets yanked back and able to be retrived...