Cluster Booster holder

[teper]

So, I working on creating a booster system as follows.
There is a lower plate that the three boosters screw into.

The Bottom Mount From Above

Rocket Cluster Booster Mount.png (14.83 KiB) Viewed 48 times

Their heads go through the plate, and are clamped to the plate by caps. These caps have holes in them to allow water to come out, and to fit a 1/2 inch guide tube.There is a large hole in the center of this piece, as shown in the picture, to allow the center booster neck to go through without becoming caught on the plate. The center nozzle sits slightly below the booster nozzles

There is also an upper plate. The center of the upper plate is clamped inside the Robinson coupling on the main booster. Unlike the lower plate, the hole in the center of the upper just fits the Robinson coupling shaft. On either side of the plate there are o-rings that seal the coupling (I've tried this, it works). Like the lower plate, the upper has 3 arms that extend outside the rocket body, and these hold the upper parts of the three boosters. The upper part of each booster slides into a hole in the arm that fits the cap, but not the plastic ring below the cap. Those three rings are what transfer the thrust of the auxiliary boosters to the main booster. When the boosters burnout, (hopefully all three at the same time) all three auxiliary boosters, and the lower plate which connects them slide off the main booster. As they fall, a pin is pulled on one of them, which releases their parachute. The main booster, which is still providing thrust, continues upward.

I have 3 questions

1) what material should the upper and lower plates be made out of (I'm thinking acrylic for the lower, and 6061 aluminum for the upper)

2) Will the upper plate exhibit too much drag on the rocket

3) Any other problems you see with this design

[Blenderite]

Air Command did something very similar to this.
Here is a very good description and photos of how he did it: http://www.aircommandrockets.com/day77.htm
And this too: http://www.aircommandrockets.com/day76.htm

There are a few posts on this blog as well: http://www.fisk.me.uk/blog/page/2/

I recommend you take a look at them.

[WRA2]

So, I working on creating a booster system as follows.
There is a lower plate that the three boosters screw into.

Rocket Cluster Booster Mount.png

Their heads go through the plate, and are clamped to the plate by caps. These caps have holes in them to allow water to come out, and to fit a 1/2 inch guide tube.There is a large hole in the center of this piece, as shown in the picture, to allow the center booster neck to go through without becoming caught on the plate. The center nozzle sits slightly below the booster nozzles

There is also an upper plate. The center of the upper plate is clamped inside the Robinson coupling on the main booster. Unlike the lower plate, the hole in the center of the upper just fits the Robinson coupling shaft. On either side of the plate there are o-rings that seal the coupling (I've tried this, it works). Like the lower plate, the upper has 3 arms that extend outside the rocket body, and these hold the upper parts of the three boosters. The upper part of each booster slides into a hole in the arm that fits the cap, but not the plastic ring below the cap. Those three rings are what transfer the thrust of the auxiliary boosters to the main booster. When the booster burnout, (hopefully all three at the same time) all three auxiliary boosters, and the lower plate which connects them slide off the main booster. As they fall, a pin is pulled on one of them, which releases their parachute. The main booster, which is still providing thrust, continues upward.

I have 3 questions

1) what material should the upper and lower plates be made out of (I'm thinking acrylic for the lower, and 6061 aluminum for the upper)

2) Will the upper plate exhibit too much drag on the rocket

3) Any other problems you see with this design

I would not recommend using aluminum for the top plate. You might be able to accomplish the same thing (with less drag) if you made the top plate instead from a lattice made of wood dowels. Metal parts like that are not recommended for any rocket. Also with the aluminum, the rocket would not be eligible to compete for a world record.

[teper]

The boosters produce a lot of thrust. The reason I was thinking aluminum was that it is light and strong. I don't know if wood would be able to hold all of the force of the boosters, without bending more than a centimeter upwards, and still be lighter than the aluminum. Once the holder bends more than a centimeter, the boosters can come free of their o-rings at the base, and pressure would start forcing the water out. Also, how would the would dowels attach to the robinson coupling?

This Is slightly different than Air command's rocket. The boosters fall away because they stop producing thrust before the main booster. Then that booster continues upwards, and when It burns out, an upper sustainer is launched.

I tried the Idea of air commands separate drop away boosters, and found that the boosters lifted themselves off the orings. Ultimately, I like the individual drop away boosters better, but don't see how I could do them.

[WRA2]

The boosters produce a lot of thrust. The reason I was thinking aluminum was that it is light and strong. I don't know if wood would be able to hold all of the force of the boosters, without bending more than a centimeter upwards, and still be lighter than the aluminum. Once the holder bends more than a centimeter, the boosters can come free of their o-rings at the base, and pressure would start forcing the water out. Also, how would the would dowels attach to the robinson coupling?

This Is slightly different than Air command's rocket. The boosters fall away because they stop producing thrust before the main booster. Then that booster continues upwards, and when It burns out, an upper sustainer is launched.

I tried the Idea of air commands separate drop away boosters, and found that the boosters lifted themselves off the orings. Ultimately, I like the individual drop away boosters better, but don't see how I could do them.

I think I understand what you are trying to do. The flat upper plate will be squeezed between the bottles coupled together by the Robinson coupling? This provides the "holding" for the tops of the boosters so that they don't fly away themselves. The aluminum plate will probably flex just as much unless it was thick (which would add more weight and drag). Might be good to try the concept using a wood or acrylic plate anyways (easier to build) to see if the concept works. The drag and extra weight at the bottom of the sustainer may cause stability issues though.

[teper]

Yes, that is how I hope the system will work

The extra weight at the bottom is there is air command's design, and when you look from the top, the profile of the bottom plate is barely visible. It might still affect the stability, but only testing will determine that.

I was planning on making both of the plates out of acrylic first to try, just like you said. Do you have any Ideas on how to eliminate the flexing? Maybe a right angle piece on the top? Any ideas?

[Blenderite]

Assuming you don't use it excessively, I would think that the alumininum would be more rigid, maybe even weight less. If you used sheet aluminum and carefully bend it to form the necessary shapes. I would think acrylic would be too heavy, but I am not very familiar with it.

[U.S. Water Rockets1]

The bracket on the sustainer looks like it would have most of the drag of the boosters, because it is so big and flat.

[Nick B]

Air Command did something very similar to this.
Here is a very good description and photos of how he did it: http://www.aircommandrockets.com/day77.htm
And this too: http://www.aircommandrockets.com/day76.htm

There are a few posts on this blog as well: http://www.fisk.me.uk/blog/page/2/

I recommend you take a look at them.

I think if george re-did those projects with smaller but more multiple staging, he'd be eating up sum serious realestate.