2L rocket testflights

[arjan]

Here's a video from the first testflights of my 2L rocket built from four 0.5L bottles.
Launch pressure was 60 psi because i wanted to make sure that the recovery system worked.
As you can see the onboard camera is al over the payloadbay because it came loose.
[youtube][/youtube]
Here's a onboard video of the last flight. I was planning to launch it at 100 psi but at 80 psi there was a leak at the nozzle, because it was getting dark and there was no time to fix it, i decided to quickly launch the rocket therefor there's no ground footage of this launch.

[youtube][/youtube]

-Arjan

[U.S. Water Rockets1]

Nice work! The loose camera was entertaining but the flight where it worked was really sweet! Hopefully, you can fix the leak and fly even higher next time!

[arjan]

Here some pictures of the rocket.

connection of 2 bottles. I put the neck of 1 bottle through a hole in the bottom of another bottle, a rubber washer around the neck and then placed the cap on. Don't know how much pressure it will hold. Does anyone have experience with this type of connection?

2011-07-31 10.11.30.jpg (184.32 KiB) Viewed 143 times

[Tim Chen]

I was wondering if I understand your explanation of the joint correctly. If I am interpreting you right then you said that you made a hole in the bottom of each bottle and then put the next bottle through the hole and put a rubber washer and a cap on to hold them together?

I can see how that should work very well because the pressure trying to stretch the rocket lengthwise will pull the washers tighter and tighter against the caps and the bottoms and seal it stronger and stronger. It sounds like a neat idea.

The only part I cannot understand is how you got the caps inside the bottles and even if I could do that I wouldn't be able to screw them on the neck inside.

Is there a trick to that (like building a ship in a bottle)?

[arjan]

I was wondering if I understand your explanation of the joint correctly. If I am interpreting you right then you said that you made a hole in the bottom of each bottle and then put the next bottle through the hole and put a rubber washer and a cap on to hold them together?

The only part I cannot understand is how you got the caps inside the bottles and even if I could do that I wouldn't be able to screw them on the neck inside.

Is there a trick to that (like building a ship in a bottle)?

That was exactly what i was trying to say (sorry for my bad english)

I cut a hole in the caps and then squeeze them through the hole in the bottom of the bottle. Then put the neck of the other bottle through the hole. then i got 2 sticks from an old kite, put them through the neck of the first bottle and got the washer and the cap on the other bottle. It takes a little practise but it's doable.

I can see how that should work very well because the pressure trying to stretch the rocket lengthwise will pull the washers tighter and tighter against the caps and the bottoms and seal it stronger and stronger. It sounds like a neat idea.

Infact there are some small leaks on the joints when i begin to pressurise the rocket but when the pressure comes above 20 psi they disapear!

Hasn't anyone tried this before?

-Arjan

[Team Seneca]

Hasn't anyone tried this before?

I know I have seen people join bottles from the neck to the bottom but I recall the focus was on trying to glue them together. You may have to look around and do some googling to see if the idea has ever come up before but you may have invented a brand new type of splice. If the idea has not been published before then you get to name the technique!

Just be sure to carefully search around for prior use. There's a few people running around looking at obscure forums or webpages showing new ideas they can swipe for their own self promotion. They then publish videos or articles about stuff they "invented" and taking credit for themselves, or failing to credit the original author leaving the viewer the mistaken impression that nobody thought of it already.

Sometimes duplicated ideas are just coincidence and that is accidental, but some teams make it a habit.

[Brian]

I've experimented with this idea but I tried it on bottles with the lumpy base. The idea was that the shape of the bottom would stop the lid twisting when I removed a bottle from it, but because of the shape, it didn't seal. Even though they've leaked I've tested them to 100psi without breaking (havn't tested them higher).
If you can make a removable one of these, they'd be a better alternative to current couplings.

[U.S. Water Rockets2]

I've experimented with this idea but I tried it on bottles with the lumpy base. The idea was that the shape of the bottom would stop the lid twisting when I removed a bottle from it, but because of the shape, it didn't seal. Even though they've leaked I've tested them to 100psi without breaking (havn't tested them higher).
If you can make a removable one of these, they'd be a better alternative to current couplings.

Here's a suggestion:
Are regular tornado tubes made of a plastic that glue will stick to? What if you cut a tornado tube in half and used that in place of the bottle cap but you put it all together and then put a little glue around the base inside the bottle so that it would be held there and you could screw in and out the second bottle without reaching inside the first to hold the cap?

[arjan]

Hasn't anyone tried this before?

I know I have seen people join bottles from the neck to the bottom but I recall the focus was on trying to glue them together. You may have to look around and do some googling to see if the idea has ever come up before but you may have invented a brand new type of splice. If the idea has not been published before then you get to name the technique!

When i first saw a video of a multi bottle rocket i thought they where spliced like this, so i googled a lot to see how they did it, but i never found someone who spliced the bottles like this so i tried it myself. If this realy is a new technique i would probably call it a "karman splice" since my lastname is Karman.

[arjan]

I've experimented with this idea but I tried it on bottles with the lumpy base. The idea was that the shape of the bottom would stop the lid twisting when I removed a bottle from it, but because of the shape, it didn't seal. Even though they've leaked I've tested them to 100psi without breaking (havn't tested them higher).
If you can make a removable one of these, they'd be a better alternative to current couplings.

What do you mean with "stop the lid twisting"?

Haven't tried to remove a bottle yet but i don't see why it wouldn't be removable.

-Arjan

[arjan]

Here's a suggestion:
Are regular tornado tubes made of a plastic that glue will stick to? What if you cut a tornado tube in half and used that in place of the bottle cap but you put it all together and then put a little glue around the base inside the bottle so that it would be held there and you could screw in and out the second bottle without reaching inside the first to hold the cap?

The tornado tubes i've seen where made of hard plastic and thus not bendable, you have to bend the cap a little to make it fit through the hole.

-Arjan

[Brian]

What do you mean with "stop the lid twisting"?

When I tried screwing a bottle in or out, the lid would spin with the bottle instead of screwing on, I'll post a picture of my attempt.

The tornado tubes i've seen where made of hard plastic and thus not bendable, you have to bend the cap a little to make it fit through the hole.

The way I put the lid in was by cutting open a bottle, putting in a bottle then splicing the bottle together.

[arjan]

I tried to remove one of the bottles yesterday, the cap came of easy but couldn't get the bottle out because it's a very tight fit, i was afraid to damage the bottle so i put the cap back on.
Today i decided to launch the rocket again, no leaks this time but at 90 psi... CATO.

[youtube][/youtube]

The lower bottle was still on the launcher.
I think i damaged the bottle when i tried to remove it, there where 2 cracks in the bottom of the lower bottle.

-Arjan

[Brian]

Here was my attempt

The lid has the same shape as the bottle's bottom cut out so it does't twist when adding or removing another bottle, but this made it hard to seal.

coupling (1).JPG (150.03 KiB) Viewed 99 times

CATO

A shame about the rocket. How did removing the bottle form the cracks?
Good to here no leaks though!

[arjan]

The thread of the bottle was stuck inside, so i pulled and twisted making a cracking noise so i decided to leave it in. The rocket will be ok soon, i'll try to fix it this weekend.