Cluster on a two-stage rocket?

[cptcommache]

Good morning, new user here and have a question before I do something I regret!

I've been designing my own low-powered rockets this year and my next launch was planned to be a two-stage rocket with a 3-engine cluster on the first stage. I've already built the entire thing and literally have it ready to fly this weekend, but a thought occurred to me this morning that I need to verify.

The booster stage of the rocket is a 3-engine C6-0 cluster arranged in a tight triangle configuration (this will be my second cluster launch with the first being a success earlier this year), and the upper stage is a single C6-5 centered between the 3 booster engines.

I've realized that I am completely relying on the second stage to ignite from those C6-0's. My concern stems from the fact that the engines are not in direct line with each other. Most likely one ejection charge will fire a split second before the others, which will separate the booster stage, but if this ejection charge isn't directly in line with the booster engine, do I risk it not igniting? The upper stage recovery relies on the C6-5 ejection charge which would not deploy if the engine doesn't ignite. (Also for reference, the distance between the C6-0 cluster and the C6-5 is approximately 3cm)

I have a huge field to launch in but I still don't want a rocket falling ballistic out of the sky. Plus I have an onboard camera and altimeter that I am putting at risk. Any thoughts?

 

[watheyak]

I’ve done this exact thing, at about twice the distance (probably 6cm). Worked every time!

The amount of burning particles in the gap must be pretty dense and energetic. That rocket was eventually retired due to heat/fire damage inside the coupler from the C6-0s.

 

[cptcommache]

Wow great! Last thing I want to do is chuck a rocket in the sky and not have a parachute deploy. I appreciate the input.

Do you think my shorter distance would be better/worse concerning the chances of the upper stage lighting?

 

[stealth6]

Here's something "similar" I did a ways back. Launches on a 4-way cluster, then three of those motors each gap-stage to what I called "parasites" which were in effect three individual second stage rockets. All BP, no timers or any fancy electronics.

thread about it here: Multi rocket second stage | The Rocketry Forum

s6

 

[BABAR]

Where is booster venting?

so long as flow can go up from booster motors around the base of the sustainer you should be great. To achieve this you may need the vents to be in the sustainer just below the lower sustainer motor mount centering ring.

pics would help.

gaps aren’t a problem if you vent correctly.

hope you get 4 straight trails!

you may want to test it once BEFORE you commit to adding altimeter and camera. Add a dummy load and if external a rough dummy camera before you commit expensive equipment to an unproven rocket IMO.

 

[BABAR]

Here's something "similar" I did a ways back. Launches on a 4-way cluster, then three of those motors each gap-stage to what I called "parasites" which were in effect three individual second stage rockets. All BP, no timers or any fancy electronics.

thread about it here: Multi rocket second stage | The Rocketry Forum

s6

Cool rocket but very different risk.

Yours, essentially zero risk if a sustainer doesn’t light, it will likely ride down still connected to booster.

For @cptcommache rocket it is gonna be a really ugly inbound return if sustainer fails to ignite.