Alternative shock cord mounting technique

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matthewdlaudato

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Probably not new. My D-Region Tomahawk needed its 3rd new cord, and I've had enough with teabags. Here's the interior after cleaning out the old tea bags:
ImageUploadedByRocketry Forum1483807641.828538.jpg
 

matthewdlaudato

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I decided to use a 2" section of 1/4" launch lug (Loc part #LL-25), and just thread the new cord through it.

ImageUploadedByRocketry Forum1483807761.616129.jpg

That's the rough idea. I am not overly concerned with the chute catching on the lug - it's a big enough body tube, but I'll certainly pay attention to that when folding and packing.
 

matthewdlaudato

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Here's the lug, mounted with some Loctite 5min epoxy. Top of the lug is 2 1/2" down, enough clearance for the 2" nose shoulder.

ImageUploadedByRocketry Forum1483807919.969501.jpg
 

TangoJuliet

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A thought: Drill through the bottom of the MMT Centering Rings, between MMT and BT, then run Kevlar Cord through the hole. Pull through to NC end of BT, then tie a loop into it. To the loop, tie a length of Bungee Cord between it and the NC. With that in place, pull the Kevlar Cord back to a length just short of the BT (to prevent a zipper), the cut the cord, tie a knot in the end and sufficiently glue it to the outside of the rear centering ring.
 

matthewdlaudato

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Then I threaded the cord through and tied an overhand knot. Pretty sure the lug won't separate - appears bonded well, plus I used an extra long cord (around 6 feet of 3/8" sewing elastic).

The finished product:

ImageUploadedByRocketry Forum1483808197.038862.jpg

That's one less rocket on the winter fix pile!
 
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matthewdlaudato

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A thought: Drill through the bottom of the MMT Centering Rings, between MMT and BT, then run Kevlar Cord through the hole. Pull through to NC end of BT, then tie a loop into it. To the loop, tie a length of Bungee Cord between it and the NC. With that in place, pull the Kevlar Cord back to a length just short of the BT (to prevent a zipper), the cut the cord, tie a knot in the end and sufficiently glue it to the outside of the rear centering ring.
This particular rocket makes that impractical, plastic fin can and a challenge to get to the innards. But interesting idea for another bird for sure.
 

Micromeister

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I've been retro-fitting ShockCords in many of my older Fleet.
I've never liked the old Estes teabag or adding anything to the inside of the tube that might fowl the recovery system or catch the shockline on the way out. Instead I use a section of Tube coupler or thick Centering ring, sanded down to slip easily into the interior of the model being retro-fitted. Along one side a line is filed to accept 70-100lb Kevlar or Stainless Steel Aircraft Cable Shock cord anchor. To the anchor which is generally no more then 8-12in long with an overhand loop or crimp sleeve loop 70-100lb kevlar is attached with 2 or3 half hitches. Our Kevlar is only long enough to reach to about 1/2" inside the forward end of the model body tube. To this end 1/8" or 1/4" Oval elastic is attached again with 2 or 3 half hitches. Overall I've found the 36-42" of elastic is enough to prevent the dreaded ESTES DENT for models up to BT-55 or BT-60. For larger models BT-60 and Up the 1/4" elastic is usually 48-72" long.

Once the Shockcord assembly is ready to be installed in the model the interior is gently sanded with 360 grit to remove any build up of ejection soot and such.
Test the tube fit with the sanded coupler or thick centering ring to ensure it can be lowered all the way to the forward motor mount centering without binding. Using a long 3/16" dia. dowel with a cotton ball attached as a swab, apply 5minute epoxy to the interior body tube at the forward centering ring. Using a pusher tube or large dowel lower the shockcord anchor coupler or ring into the epoxy. If desired additional epoxy can be applyed to the interior of the coupling or ring to add longevity to this mount.

Since changing over to this type Shockcord retro-fit method, I haven't lost a single shockcord to burnoff or breakage. Takes a little more time to get everything sliding smoothly but once done I have logged more the 20 flights on these retro-fitted models. One of my favorite flyers (Goblin) has 68 flights on the new shockcord.

PS: I strongly suggest the use of Stainless Steel fishing leaders or .024" dia 7x19 70lb Cable for smaller Model rockets or .031" 1x19 - 185lb aircraft cable for MPR models up to 3.3lbs. Used with their plier crimp sleeves these Shockcord anchors are all but indestructable. The number of strands in the cable contrubute to the flexability of the cable, Generally the more strands the softer and easier to flex the cable is. For Micro models from T2+ to BT-5 I'm using Beldon Beading Stainless Steel Wire .018" x 49 strand. Amazingly flexable.

Below are a couple photos of the process for a BT-50 size Body. I've used this method on models all the way down to Micro-Maxx T2+ size tubes so any broken shock cord can fairly easily be repaired with this method.

Shock-Cord Mount-h2_Retro mount 6pic pg2of2_09-28-06.jpg


473p02a_BT-50h-Bt70 MMT & Shock Anchor_01-15-08.JPG


473p02b_Shockcord anchor-100lb Kevlar_01-15-08.JPG


Shock-Cord Mount-h1_Retro mount 8pic pg1of2_09-28-06.jpg


451e8_30in MB-Shockline 7pic pg_10-06-06.jpg
 
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