Static Test of Four Stage Rack Rocket

[tdesmarais]

https://www.youtube.com/watch?v=ovhTtvgyV4E

Cliff Sojourner posted this high speed video of a 4 stage rack rocket I tested at the last LUNAR launch. The second stage hung up (I was also testing having a streamer on each engine, which I believe caused the hangup), causing the deflected thrust to mostly burn through the rails.

I think the streamers will work fine, with a little practive on my part.

I used 1/16" balsa for the fins, and they took major damage, so I'm going back to 1/16" bass wood for the fins.

I used scotch tape to bind the engines together, I still need to go back to the video to try to see how much side thrust spilled at staging, as well as the delay in startup at staging.

-Tom

 

[lessgravity]

That's a great static test video. I'm in the process of building a 18mm Rack rocket currently myself. I totally don't expect to get it back but it would be nice.
Couple of questions.
What motors did you use? By the looks of the sustainer motor they were Quest.
How long is your body tube beyond the rack? It's hard to tell from the video.
Is the nose weighted?

 

[tdesmarais]

For the static test, I used all Quest motors, B6-0, B6-0, B6-0, to B6-2.

The body tube is 8".

There isn't a nose for the static test. I have a simple platform that I use for static tests and piston launches. It is made of a 16"x16"x3/4" piece of plywood with two 4" 2x4s screwed to it. Then attached to one of the 2x4s are two hose clamps that I use to hold the body tube, motors, or piston launchers in place.

The nice thing about rack rockets is that they usually don't need any extra nose weight. With all of those motors above the fins, the CG is usually fine, unlike standard staging.

 

[Gillard]

nice video, i've never seen a rack rocket before - looks like an interesting take on staging.

 

[AHansom]

Very cool idea. Do you think gravity had any effect on seperation? Can it was tested pointing up?

 

[lessgravity]

i've never seen a rack rocket before - looks like an interesting take on staging.

Dick Stafford had a great write up on rack rockets on his blog 3 years ago:
Here's the link

 

[Rocketjunkie]

Dick Stafford had a great write up on rack rockets on his blog 3 years ago:
Here's the link

This is the rocket I flew that is described in the blog.

 

[georgegassaway]

Looks like when the 2nd engine burned out, to ignite the 3rd engine, it ‘popped” apart too easily, and the 3rd engine took awhile to ignite. Perhaps you needed to use some more tape to hold the engines together? I can think of an accident I had years back when engines field to stage at all, because the one wrap of Scotch tape I normally used was not enough, allowing the engines to pop apart before the upper engine lit. Since then, I have either used two full wraps of Scotch tape, or for Chad-staging have used Masking tape.

This way, the tape does not let go until after the upper engine has ignited, and causes so much back-pressure inside the empty lower casing that it forces the tape to blow apart and melt.

- George Gassaway

 

[tdesmarais]

Interesting.

We have an ongoing debate about whether it is better to use masking tape or scotch tape. I have almost always used masking tape, but I decided to try scotch tape for this test. My rack rockets with wood racks usually don't survive very long and I was wondering if the masking tape was causing more flames sideways at staging.

I'll have to try it again with masking tape.

I was hoping for more detail at the staging time. If Cliff lets me use his camera again, I'll need to zoom in closer.