Considering a step up to hobbyist - Arizona

[5thDay]

Greetings my name is Jeremy and my 4 year old son and I enjoy loosing model rockets.

Oops I meant flying!

I have always enjoyed rocketry but hadn't designed or built my own until recently. Given nice weather, running to a craft store for some B motors to put into a ready to fly rocket was a lot of fun for my son and the rest of the family and neighbors who all wanted to see a launch.

We call it "up in the air day" and we get out the foam stomp rockets, our drones, even paper airplanes a few times! It makes it fun for him and I have a ton of fun myself. Lately, I've had a bit more of the hobby bug as I see a lot of avenues my previous experience with related hobbies (electronics, circuit design, mod building, scientific knowledge and understanding of physics) as well as my work experience in aerospace (advanced composites, ablative materials, etc.).

The reason I say I am considering making this a hobby is that do more of the things I enjoy I face much higher cost investments to do those things. If I go all-in I would want NAR membership, certification attempts, reloadable hardware and in general larger rockets to house electronics. For now, it is still a lot of fun for me and I located some mid power single use motors to see what I am capable of and how much I might enjoy doing sanctioned launches and being responsible for the higher impulse.

Long introduction, sorry I am just being a little more upfront than most as I won't turn down good advice from others who have been at this point. I do have a specific question about a Soyuz cluster I am building that I can't figure out. I will put it into the appropriate area but it is the reason I ultimately registered as a member. In short, (yes I am doing a 20 motor cluster with hot staging) I am reluctant to fly beyond booster separation because with those off the rocket I don't understand how I will not be instantly unstable...

A couple quick photos attached. That is not the rod I will use for this Soyuz! I took that photo so I can caption it "time to build a new launch rod!"

 

[neil_w]

In general, I would say:
1) Designing and/or building rockets is fun. I recommend it.
2) You don't need to jump all the way in at once. In fact, I would *not* recommend it. Work your way up. I hope you have done some builds in between RTFs and the Soyuz, which is a almost impossibly large jump in complexity.
3) If you're gonna drop the boosters on the Soyuz, then whatever remains must be stable on its own. If that means adding fins to it (maybe clear fins) then that's what you need to do. There have been some very impressive Soyuz builds on this forum in the past, e.g.: https://www.rocketryforum.com/threads/soyuz.160900/. I don't know how that particular build handled stability of the core. On this one (https://www.rocketryforum.com/threads/soyuz-1-25-why-not.156583/) you can definitely see the fins that were added to the core.

 

[5thDay]

Thanks for the reply Neil. I agree 100% with your phrasing about stability "that's what you need to do." I am all in on safety and the impression my flights make on the entire hobby.
If I can't figure out stability on the core then I will end the flight at the Korlev Cross and bring out the drogue before I can start flipping or pitching over.

Something I have considered is when the boosters hinge down to be released that they could pull folded fins with them. That is something I can sim where I can't sim the booster stage due to cant limitations in OpenRocket.

 

[Jerry F.]

Have you looked at the Booster Pods/hardware available at Apogee Components? They are a little smaller than what you have, but the hardware might work for you...

 

[David Schwantz]

Hello, and who ever says,"take it slow" is dead wrong. Jump in with both feet!! Love the Soyuz idea. Don't know if you 3D print, but if you go the Thingiverse and search Soyuz, you will find a lot of files. One of them has a printed core fin can. Fin fit between boosters. They also have hooks and locks for the boosters. I am just by chance doing one as we speak also. Added pic. Water bottle for size reference. As far as your cluster goes. Search "flash pan". I have never done it, but should work with BP motors. good luck and more pics")

 

[5thDay]

Built it and did a first test flight. I wasn't happy with the options for stable flight after separation so for first flight I secured the boosters and third stage and used a single F72-10 in Blok A with a small A booster for the capsule section at apogee. It went to just under 1,000 feet and landed 2 yards over intact.
What I learned from the flight was I need a LOT more mass (my dry weight was 504g) and will be starting over with a build at least twice this size.

 

[5thDay]

A few things I do different with my flights and launches, and why I mentioned that I needed the larger 4" frame for electronics.

My launch is treated like an air start. My launch controller is just a switch that triggers an input on the flight controller. This helps in a few ways: I am not that worried about everything lighting at the exact same time (before the clips get yanked out) and I can do creative staging within each booster's cluster to either extend burns or ensure I stay in peak acceleration.
I fly without an IMU also to save complexity. I don't need to detect launch because my Arduino gets the launch signal directly in order to switch case to ascent mode. While I loose the ability to detect if I pitch over, I do abort ascent mode when my altimeter detects my altitude is less than the previous reading. I've had some near horizontal firings but never a firing that pointed to ground level.
My launch rod is special in that it neutralizes rocket weight. This makes OpenRocket sims unreliable but does allow me to do some fun things with lift off speed and underpowered motors. Basically it is a series of springs and washers that progressively compress depending on the weight of the rocket. Effectively a rocket weighs 0 and even something as little as blowing upwards on the rocket will lift it on the springs. I designed this when considering how much of my thrustcurve was being wasted getting a rocket to start moving. It also gives me better control over takeoff speed as long as I have good data about when a motor starts to produce enough thrust to overcome gravity.