Experimental: Tri-Magnum

Here is an idea that I pulled out of my Rocketry Journal from a few years ago. I was able to fool Rocksim into making the thing so I could at least test the idea before building this design. This design idea consist of three rear ejection parachutes using sort of a ring fin as a motor mount instead of using centering rings to center the motor mount. The void area between the three-ring fin pylon is used as a parachute storage area.

With Rocksim I was able to make a stable sim that flies on a both 1/2A3T-2 and A10T-3 with good deployment velocities.

This will be my first actual build thread so please bare with me.

Thanks and Enjoy, JP

James Pierson
NAR# 77907

Attached Thumbnails

 

Attached Files

Tri Magnum 13 MM.rkt (57.3 KB, 125 views)

Photo: Tri Magnum #1
In this photo I am showing the motor mount tube with ring fins/spacers and rear fins attached to MM tube. I ran the ring fin material long to be cut to proper length later. Also in this photo is the ejection bulkhead and upper centering ring attached to the BT-5 tube and its landing nosecone. I used a PNC because in theory this thing lands on its nose cone first. Also showing is the BT-60 outer BT cut to length.

Attached Thumbnails

 

Photo: Tri Magnum Piston #2
In this photo I have changed the design. Originally I had planned on gluing this assembly into the BT-60 BT and rely on the ejection charge to blow out the three parachutes equally. The change here is that I attached an upper piston bulkhead to the MM ringfin/spacer assembly. This change will allow the entire assembly to be blown out of the BT-60 and release the parachutes. This change will also keep the parachutes pot of the hot ejection gases. The problem is how to keep the MM ringfin/spacer assembly connected to the main BT-60 and its nose cone???

James Pierson
NAR# 77907

Attached Thumbnails

 

Photo: Tri magnum Shock Cord #3
The problem is how to keep the MM ringfin/spacer assembly connected to the main BT-60 and its nose cone???
Problem solved! I decided on an interior shock cord assembly and towards the base of the BT-60 to cut three 1/2" round ejection gas escape holes not shown in this photo. The upper bulkhead with nose cone is to be glued into the BT-60 and not the MM ringfin/spacer assembly. This ringfin/spacer assembly now has became an ejection piston thingy. Sweet!

James Pierson
NAR# 77907

Attached Thumbnails

 

Photo: Tri Magnum Piston Test Fit #4
Just a little bit of careful sanding and the ejection piston assembly slides nicely the outer BT-60 tube. I am going to opt not to paint this assembly later for fear of paint sticking.


James Pierson
NAR #77907

Attached Thumbnails

 

Photo: Tri Magnum Pre Assembly #5
I decided to attach the three rear 1/8"shock cords before I glued the upper bulkhead/ nose cone into place. FYI the upper shock cord is 1/4" braided elastic. I should have used a kevlar cord but I have none on hand at this time. The length of this cord was adjusted several times before I glued the upper bulkhead into place. Judged the length on how powerful I thought the 13mm ejection charges where. In other words I guessed.

James Pierson
NAR# 77907

Attached Thumbnails

 

Photo: Tri Magnum Before Chutes #6
A rear view of this design to show the chute placement area.

JP

Attached Thumbnails

 

Photo: Tri Magnum 3 Chutes Loaded #7
I had planned on using 8" parachute however after seeing the Semroc 12" chutes I ordered I could not bring myself to chop the 12" chutes down to 8". Rocksim said 12" parachutes were a good design change anyway.

James Pierson
NAR# 77097

Attached Thumbnails

 

Photo: Tri Magnum Almost Done #8
Fully loaded and TRF. Chutes seem to fit quite well so I decided to pull the motor and give a test blow to see if the piston and chutes would come out as planned and it worked good. Sweet!!

James Pierson
NAR #77907

Attached Thumbnails

 

Photo: Test Flight #1
Here is the first launch using a 1/2A3T-2. All seems well with the flight except the predicted altitude in Rocksim was a bit off. Rocksim predicted an altitude of 80 feet and it was more like 60 feet actually.

James Pierson
NAR# 77907

Attached Thumbnails