Retrofitting a Leader Secured to the MMT Behind the Rocket

[jqavins]

When I build my Estes Red Nova, I followed the instructions and attached the elastic to the body tube with the classic Estes tri-fold. Recently, the elastic broke during a launch mishap, and today I sat down to repair the rocket. I've decided, in the interim, not to use the tri-fold anymore. So here's what I did.

Years ago, I read a method to install a replaceable Kevlar leader in a new build. I think it was by a Michaelson. You make little notches in the centering rings next to the MMT, and install a very small tube alongside the motor tube, through which you run the Kevlar. Tie a loop in the end of the Kevlar at the aft end of the motor mount and put it around the aft end of the MMT. If When the leader needs replacing, you can use the old one to draw a new one in. Which is great, but how do you do that as a retrofit?

Here's what I did:
Somewhere in the partially unpacked garage, I have a set of long drills, which I think go down small enough, but I don't know where they are. So instead, I cut a wire hanger and then filed one end so it has both a point and a straightish sharp edge. That makes it more or less a zero flutes drill. It's not a great drill, but these are cardboard centering rings, so it'll do.

Drill through both centering rings.

I'd like the holes bigger, because the best thing I have on hand to pull the leader (coming soon) is not enough smaller than the hanger wire. Fortunately, because these are still cardboard CRs, I can force the holes open further with a bamboo skewer.

Then push a rod through both holes that is smaller than the holes and longer than the rocket. I used a 1/8" launch rod. (Had I a 1/16" rod, I would not have needed to open the holes with the skewer.)

Put a little CA accelerator on the rod, and a drop of CA on the end of the leader, bring them together, then draw the leader through the rocket. (The hole needs to be bigger than the rod because it needs to pass the rod and Kevlar together.) Which way? Doesn't matter! You just need the leader to be longer than that rocket so it's sticking out both ends. (I didn't snap a picture here, but just imagine that the shiny rod above is dull, yellow, and floppy. )

Make a loop at the aft end using the knot of your choice (I used a half hitch on a bite) and drop it over the end of the MMT.


Note that I did not install a tube to run the leader through, as is done in the article I read those years ago. This means that there is some risk of the the leader biting into the CRs when it is yanked taught during deployment. That's a risk I can live with.

 

[bjphoenix]

I've done the same thing but I did have some long drill bits. I didn't think about using a sharpened piece of wire but I can imagine that it would work well enough for cardboard centering rings.

 

[Back_at_it]

If you used the paper centering rings, your method will work great.

I've had shock cord on some older rockets that had plywood upper rings fail and my solution was to use another tri-fold mount but attach Kevlar to the tri-fold.

Surprisingly the tri-fold is pretty strong if you use quality paper. What I don't like about it is the bulk it takes up inside the bodytube

 

[jqavins]

My "drill" should even work for balsa rings, but the skewer hole expander shouldn't. Then I'd have to look harder for a thinner rod, or fuss and fiddle to fish a piece of piano wire through.