Ping Pong Parachute B/C

[andrewwski]

Well, a FAQ has been posted about the maximum pressure.

What's the maximum psi?

Due to the variation in the sites where the ping pong parachutes will be held, there can not be one max psi that is published.

Teams will be placed in Tier 3 per rule 5.g. if any part of their rocket or parachute hits the ceiling or any part connected to the ceiling.

This seems to be lacking safety considerations. It does not address the safety concern of overpressurizing the bottle, or it (shortsightedly) assumes that designing to not hit the ceiling will self-limit the pressures that teams elect to fly with. I see two issues here:

1. In the case of very high ceilings, teams will want to go for higher pressures. For example, the competition I am supervising will have an approximately 50 foot tall ceiling - about twice the height of a standard gym. It is not unfathomable that some tournament locations will have even higher ceilings (e.g. fieldhouses, atriums, etc).

2. The rules place no limit on the maximum mass of the rocket. Thus, teams may design heavier rockets, which will require higher pressures to reach the target altitude.

Has the rules committee concluded that even a combination of the above should not result in a dangerous pressure? Even if that is the case, there is nothing to prevent teams from testing at higher pressures - and if my years of experience with SO tells me anything, it's that eventually some team will try anything. I worry that some team will try 120+ psi, because they can.

The response to this FAQ does not follow logically, either. The assertion that "there can not be one max psi that is published" does not follow logically from "the variation in sites where the ping pong parachutes will be held." Publishing a maximum pressure, determined only from safety limits, does not compel a team to launch at that higher pressure. They may choose to launch at a lower pressure, there is only a maximum that they cannot exceed out of safety concerns.

Am I missing something here? I'm really scratching my head over this.

I'm running this event at an invitational and regional, and am going to set a tournament-level rule on the maximum pressure. I'm not sure what that will be yet, but I'm thinking of building a blast chamber and buying a bunch of 1L bottles and pressurizing them until failure, then taking the 3-sigma or 6-sigma value.

[klastyioer]

Hi there!
What resources, links, or videos were very helpful for you all that did it last year?

this wasnt an event last year or ever, its based off indoor bottle rockets and a ping pong parachute trial event

[Vortexx2]

what types of material would be good to make the fins out of?

[klastyioer]

how do you test max psi without exploding a bottle?

[Unome]

Well, a FAQ has been posted about the maximum pressure.

What's the maximum psi?

Due to the variation in the sites where the ping pong parachutes will be held, there can not be one max psi that is published.

Teams will be placed in Tier 3 per rule 5.g. if any part of their rocket or parachute hits the ceiling or any part connected to the ceiling.

This seems to be lacking safety considerations. It does not address the safety concern of overpressurizing the bottle, or it (shortsightedly) assumes that designing to not hit the ceiling will self-limit the pressures that teams elect to fly with. I see two issues here:

1. In the case of very high ceilings, teams will want to go for higher pressures. For example, the competition I am supervising will have an approximately 50 foot tall ceiling - about twice the height of a standard gym. It is not unfathomable that some tournament locations will have even higher ceilings (e.g. fieldhouses, atriums, etc).

2. The rules place no limit on the maximum mass of the rocket. Thus, teams may design heavier rockets, which will require higher pressures to reach the target altitude.

Has the rules committee concluded that even a combination of the above should not result in a dangerous pressure? Even if that is the case, there is nothing to prevent teams from testing at higher pressures - and if my years of experience with SO tells me anything, it's that eventually some team will try anything. I worry that some team will try 120+ psi, because they can.

The response to this FAQ does not follow logically, either. The assertion that "there can not be one max psi that is published" does not follow logically from "the variation in sites where the ping pong parachutes will be held." Publishing a maximum pressure, determined only from safety limits, does not compel a team to launch at that higher pressure. They may choose to launch at a lower pressure, there is only a maximum that they cannot exceed out of safety concerns.

Am I missing something here? I'm really scratching my head over this.

I'm running this event at an invitational and regional, and am going to set a tournament-level rule on the maximum pressure. I'm not sure what that will be yet, but I'm thinking of building a blast chamber and buying a bunch of 1L bottles and pressurizing them until failure, then taking the 3-sigma or 6-sigma value.

I think there was a max psi in the draft rules for exactly that reason, I'm not sure why they removed it.

[Airco2020]

I'm running this event at an invitational and regional, and am going to set a tournament-level rule on the maximum pressure. I'm not sure what that will be yet, but I'm thinking of building a blast chamber and buying a bunch of 1L bottles and pressurizing them until failure, then taking the 3-sigma or 6-sigma value.

I'm curious to see the results of this test!

I see pressures as high as 150psi quoted for 2L bottles...not sure what that means for 1L. I think the connection for filling the bottle will leak long before you can ever get to those high pressures but also not sure what the launcher will be. We built one from PVC and it has trouble keeping any pressures above 40psi or so but it's also not built that well!

[sciolyperson1]

I'm running this event at an invitational and regional, and am going to set a tournament-level rule on the maximum pressure. I'm not sure what that will be yet, but I'm thinking of building a blast chamber and buying a bunch of 1L bottles and pressurizing them until failure, then taking the 3-sigma or 6-sigma value.

I'm curious to see the results of this test!

I see pressures as high as 150psi quoted for 2L bottles...not sure what that means for 1L. I think the connection for filling the bottle will leak long before you can ever get to those high pressures but also not sure what the launcher will be. We built one from PVC and it has trouble keeping any pressures above 40psi or so but it's also not built that well!

At summer camp (we taught bottle), the max we could pump it to was 80psi, after that it would start leaking. 80psi (with water though), went really high, although I personally don't think exsessive psi is an issue.

"The Event Supervisor will check the gauge on the pump to ensure the rocket is pressurized to the psi chosen and justified by the team's data." (5.c.)

[eagerlearner102]

How different is the structure of the rocket in bottle rocket compared to the rocket in ping pong parachute? Obviously, there are different objectives.

[goodcheer]

d.The nose of the rocket must be rounded or blunt at the tip and designed such that when a standard bottle cap (~3.1 cm
diameter x 1.25 cm tall) is placed on top of the nose, no portion of the nose touches the inside top of the bottle cap (see
Figure 1).

To satisfy this rule, can the ping pong ball be the top-most rounded portion of the rocket but then detach? Otherwise, if the top of the rocket is blunt, how does one attach the ping pong ball?

But based on rule 5c:

c. When called to launch, teams will load their rocket onto the launcher. Once the rocket is loaded, but
NOT pressurized, teams will place the parachute payload system on or in the rocket. After the payload
parachute system is loaded it cannot be manipulated.

So it seems like the ping pong ball is separate from the rocket in which case it seems like the rocket itself needs a blunt nose apart from the ping pong ball?

I don't see any problem with making the ping pong ball the top-most portion of the rocket. Regardless of what the nose looks like before launch, it could be different after the parachute deploys. If the ping pong ball is at the tip, it will deploy and the rocket will come down without the ping pong ball as the tip and if the rocket has a different tip, the entire nose could separate from the rocket to deploy the parachute and ping pong ball. Probably need to make sure everything considered to be a tip is properly blunt both before and after deployment. Just my opinion.

[goodcheer]

[/quote]

I'm curious to see the results of this test!

I see pressures as high as 150psi quoted for 2L bottles...not sure what that means for 1L. I think the connection for filling the bottle will leak long before you can ever get to those high pressures but also not sure what the launcher will be. We built one from PVC and it has trouble keeping any pressures above 40psi or so but it's also not built that well!
[/quote]

At summer camp (we taught bottle), the max we could pump it to was 80psi, after that it would start leaking. 80psi (with water though), went really high, although I personally don't think exsessive psi is an issue.

"The Event Supervisor will check the gauge on the pump to ensure the rocket is pressurized to the psi chosen and justified by the team's data." (5.c.)
[/quote]

I agree higher pressures shouldn't cause extreme safety concerns. Although concern for safety is always important, there are some safety risks in nearly all the events. In this event, the main protection would be to keep everyone a safe distance from the bottle when it is being pressurized. Then, make sure it is constructed according to the rules. I appreciate the Event Supervisors who actually check these issues out before the event. It seems they would have some leeway in setting some limits depending on their site and if they examine a rocket and determine it should not be pressurized beyond a certain limit, then it seems they would be able to do that too. My opinions. Happy launching and deploying!