Twin tube fin rocket

[Lamp]

I had been thinking about stability and decided to make a rocket with 2 tube fins.
First I designed, built and flew a scaled down LPR version.


This is the LPR version flying on an A8-3

After this flight (which went well), I designed a HPR version with a 2.6" body, 38mm motor mount with two 4" tube fins mounted through the wall. I modeled the rocket in Rocksim which let me check radial stability which was surprisingly uniform. Although I could not figure out how model it with the fins TTW, I designed it to be overstable and figured the difference would not be big enough to invalidate the design. The rocket has so far had two flights and performs well.


This is the launch shot of the second flight on an H268R.



A shot in flight


Recovery...


A shot of the landed rocket after its first flight showing the TTW fins.

 

[Scott_650]

Some details on your build would be appreciated - looks very interesting!

 

[Lamp]

What would you like to know...

It is a pretty standard dual deploy build.. the only real difference is the fins. I would post the Rocksim file if I could figure out how to do it.

The only real thing that is different is the fins and how I mounted them TTW. Sorry, but I don't have any photos of this.

I wrapped the bottom of the body tube with a sheet of A4 paper to accurately measure the circumference by marking where the paper started to wrap around itself. I cut measured lengths from a 4" FG tube and evened them up. I assembled the top and middle centering ring on the motor mount, spacing the middle centering ring to match the location where the top of the fins would be. I did not attach the rear centering ring.

When the epoxy was hard, I partially slid the MMT into the body tube, put a fin on the MMT next to the base of the body tube. I marked each side of where the fin intersected the body tube on the paper which I left wraped around the tube. Using this I could measure and accurately mark a fresh sheet of A4 with the center point of each fin and where each fin would go through the body tube. I transferred the marks up the body tube using some angled aluminium. I then glued in the MMT.

I measured and marked 1/2" up from the base of the body tube and the length of the fin. I used a dremel with a plastic cutting disk to cut the fin slots. I also used a dremel to make a vertical cut through each fin and a mini flat file to widen each slot. By distorting the fin tube, I could get one side of the cut into one of the slots and work/roll it around towards the other slot. I could then get the other side of the cut into the other slot. I worked the fin back so the cut was lined up and even onto the MMT. I used a strip of fiberglass to join the fin tube back together inside the body and then epoxied in the rear centering ring.

I drilled small holes into the body tube and injected epoxy using a syringe to form the internal fillets.

Everything else was pretty standard.

 

[Lamp]

Oh, it looks like the Rocksim file did attach.

 

[Hobie1dog]

thanks or the pictures

 

[Cape Byron]

Nice and different. Good work!