Bottle Rocket B

[SOCoach]

I think I found it . . . going from the tip of the nosecone back (to the bottom of the bottle), the CG needs to come before the CP in order to backslide. Is that correct?

[Toms_42]

Yep. Sorta.
I can't speak for OpenRocket but RockSim even calculates the weight of the rocket fairly accurately given the materials you select for the various sections of the rocket. Once you've done that you have to select an engine. Even though "water at 60PSI" isn't an option, it doesn't really matter. I am primarily concerned with how changes affected the flight so I would select an engine and stick with it. Then I would make changes, simulate a launch and see how it compared to the previous launches. It even simulated the fall down to earth realistically, complete with backslide if designed correctly.
I can't remember which engine I selected, but it was one that took the rocket to "water rocket" heights (around 120m).

I'm not sure how accurate RockSim is for bottle rockets. I've used it for solid fuel rockets, but never for water. If you're trying to get an accurate idea of launch height, using a solid fuel engine in the sim will be very different, as water rockets tend to be one quick burst vs solid fuel is more prolonged at lower thrust.

EDIT: tip for rocksim: ALWAYS put moderate wind in. without it, rockets that are overstable (Cg too far ahead of cp) will perform just as well as a properly balanced rocket.

[SOCoach]

I am looking to buy a new rocket launcher. Has anyone purchased the Bigfoot Water Launchers? Any good? Any other brands any would recommend?

[Toms_42]

I am looking to buy a new rocket launcher. Has anyone purchased the Bigfoot Water Launchers? Any good? Any other brands any would recommend?

I have a friend who bought the bigfoot launcher and thought it was great. Back in 2012, we used this:
http://www.pitsco.com/Aquaport_II_Water_Rocket_Launcher
It's expensive, but it worked well. Of course, you can easily make a water rocket launcher yourself, with a guide such as this one:
http://www.uswaterrockets.com/construct ... torial.htm
The money for an aquaport would probably be more useful if spent on an air compressor, as pumping the bottle rockets can be very tedious especially if you have a lot.

[SOCoach]

Our team competed at an invitational this weekend and one of the rockets had a long nosecone of clear plastic material . . . but had no cap on the end. The nose was open approximately an inch at the end of the rocket. I assumed when it was launched air would rush down the nosecone and knock it down, not so. The rocket got great height and backslid beautifully. Has anyone seen or had any success with an open ended nosecone?

[dragonzord0130]

Our team competed at an invitational this weekend and one of the rockets had a long nosecone of clear plastic material . . . but had no cap on the end. The nose was open approximately an inch at the end of the rocket. I assumed when it was launched air would rush down the nosecone and knock it down, not so. The rocket got great height and backslid beautifully. Has anyone seen or had any success with an open ended nosecone?

My team uses the same material for our rockets, but it is not open-ended.

[SOCoach]

What kind of rocket weights have teams been getting . . . we can't seem to get ours much under 140ish - 10-12 second flight times.

[ecolson]

I am confused by the rules. Are parachutes allowed this year

No, not that I'm aware of.

Parachutes are not allowed in division B 2015. Here is a quote from the rulebook: "Rockets must not change shape or deploy any type of recovery system. "

[mineturtle314]

Our team competed at an invitational this weekend and one of the rockets had a long nosecone of clear plastic material . . . but had no cap on the end. The nose was open approximately an inch at the end of the rocket. I assumed when it was launched air would rush down the nosecone and knock it down, not so. The rocket got great height and backslid beautifully. Has anyone seen or had any success with an open ended nosecone?

I have never seen that before at any of my competitions. However, if you could find a way for the cone to catch some air in it then it may come down more gradual.

[jgrischow1]

Rule 3 c. says "The structural integrity of the pressure vessel must not be altered. This includes, but is not limited to: physical, thermal, or chemical damage"

If we use acetone to dissolve the glue that held the labels to the bottle, would that be a chemical or physical alteration? If so, any idea how to remove the glue without altering the bottle, or is its presence negligible?