Shock cord repair and replacement

[billdz]

On its last flight my fiberglass Darkstar Jr had a premature deployment that dirtied the inside of the airframe and the kevlar shock cord. Also noticed a small fray on the cord. This got me wondering how it will be possible to maintain and eventually replace a shock cord like this one, which is attached to the motor mount and is inaccessible. What's the trick?

 

[K'Tesh]

Can you glue in a baffle? If you can you could attach a new shock cord to that.

 

[Paradox_2112]

You could always cut the cord where it is frayed, and sew it back over itself to form an attachment point up high in the booster.
Just a thought.

 

[markkoelsch]

Dirty not so much an issue.

I usually put a few layers of tape over the cord around the area the Kevlar intersects with the tube.

 

[billdz]

@Mark - Good idea, I've put on some tape.
@Paradox - I don't know how to sew but guess I'll have to find someone if need be.
@K'Tesh - Guess I could put a new cord on a new baffle or bulkhead although it would be difficult to mount so deep in the airframe.

Oh, I hope the existing cord lasts for a while longer.

 

[K'Tesh]

@K'Tesh - Guess I could put a new cord on a new baffle or bulkhead although it would be difficult to mount so deep in the airframe.

Why does it have to be deep in the airframe? The further forward, the longer motor you can put in the rocket, it'd improve stability for a larger motor, and prevent the parachute from falling backwards into the airframe.

 

[K'Tesh]

Why does it have to be deep in the airframe? The further forward, the longer motor you can put in the rocket, it'd improve stability for a larger motor, and prevent the parachute from falling backwards into the airframe.

You could always cut the cord where it is frayed, and sew it back over itself to form an attachment point up high in the booster.
Just a thought.

IINM, the Darkstar Jr is a 3" rocket. Sewing inside the tube would likely be difficult at best.

 

[billdz]

"IINM, the Darkstar Jr is a 3" rocket. Sewing inside the tube would likely be difficult at best."
Yes, that's for sure. The rocket has only a diameter of 2.2".

"Why does it have to be deep in the airframe?"
Well, at least deep enough to be below the chute, shock cord, and the shoulder of the coupler. Guess I could swab some glue far enough down the tube by taping a Q-tip to a long rod.

 

[mccordmw]

I've fixed crunchy old nylon shock cords in the past by drilling a new hole in the forward centering ring and sticking in a forged eye bolt with a butterfly anchor (toggle bolt) through it. Use some epoxy to make sure it doesn't wiggle loose. Works perfectly fine.

 

[billdz]

"I've fixed crunchy old nylon shock cords in the past by drilling a new hole in the forward centering ring..."
How do you drill a hole into a centering ring that is 3 feet deep in the airframe?

 

[Glasspack]

With a long drill bit............... then make a slotted pipe to turn the eye bolt down in the tube