Quantcast

Opinion on shock cord - Wildman Punisher Sport

The Rocketry Forum

Help Support The Rocketry Forum:

Mendal

Well-Known Member
Joined
Feb 5, 2016
Messages
242
Reaction score
15
Looking to start to build my Punisher from Wildman, This will be my first fiberglass build, I have 1/8" kevlar, and I'm thinking of using it but I'm not sure its enough, do I need to go 1/4"? I plan to epoxy to the MMT I was thinking one side as aligning 2 sides with the TTW fins can be a pain.

But the biggest question is, is a 1/8" cord enough or do I need to go up to 1/4".

thanks in advance
 

rharshberger

Well-Known Member
Joined
Oct 13, 2014
Messages
9,703
Reaction score
1,682
Location
Pasco, WA
Do you know the actual strength/ working load limit of your 1/8" kevlar?

Actually epoxying to opposite sides of the MMT is fairly easy as long as you mark the fin locations on the MMT and additional marks where you want the Kevlar to go, but you can also do just one side (IMO two sides is better though).

The 1/8" inch depending on its strength and length should be strong enough (Top Flight Recoveries 1/8" kevlar is rated at 1,200lbs, and Giant Leap Rocketry states theirs is good for 3-4" rockets). Wildmans 1/4" Kevlar is rated at 3600lbs and is more than enough for a 54mm FG rocket. Make the shock cords as long as you can since kevlar has near zero elasticity, I like 20-25 feet long. Obviously the smaller diameter kevlar will pack better in a smaller airframe.
 
Last edited:

Onebadhawk

Sponsor
TRF Sponsor
Joined
Jan 11, 2013
Messages
6,058
Reaction score
362
Every mill's 1/4" Tubular Kevlar isn't the same. ...
I've seen some that's super small, thin, and light
that would be more appropriate for a 38 mm or 54 mm rocket....
Wildman ' s is quite large, strong .....
I'm not saying it's all wonderful, , it is what it is,, it perfect for a 3" or 4" rocket...
What's much more important is the length. ...
It should be long enough to allow the kinetic energy of separation to dissipate
before the two sections come to the end of the Kevlar. ....

Teddy
 

blackjack2564

Crazy Jim's Gone Banana's
TRF Supporter
Joined
Jan 18, 2009
Messages
9,061
Reaction score
1,163
Location
Savannah Ga
What size/diameter Punisher?

If the Kevlar is from me....it's rated at 750 lbs. Made in USA.

If your Punisher is a 38mm airframe . Yes
54mm airframe I would use a couple feet of 1/4 in. for Y-harness to motor mount, just enough to clear top of airframe. Then use the 1/8 for shock cord. The 1/4 in will provide protection from zipper in airframe. Both sides of "Y" hit edge of tube, increasing footprint against side of tubing.

3in Punisher NO. Use 1/4in.

You don't want thin Kevlar going to motor mount on larger rockets. It may be strong enough, but can cut through an airframe like butter causing a zipper should things go sideways during recovery.

That's how I do it anyhow.
 

Mendal

Well-Known Member
Joined
Feb 5, 2016
Messages
242
Reaction score
15
What size/diameter Punisher?

If the Kevlar is from me....it's rated at 750 lbs. Made in USA.

If your Punisher is a 38mm airframe . Yes
54mm airframe I would use a couple feet of 1/4 in. for Y-harness to motor mount, just enough to clear top of airframe. Then use the 1/8 for shock cord. The 1/4 in will provide protection from zipper in airframe. Both sides of "Y" hit edge of tube, increasing footprint against side of tubing.

3in Punisher NO. Use 1/4in.

You don't want thin Kevlar going to motor mount on larger rockets. It may be strong enough, but can cut through an airframe like butter causing a zipper should things go sideways during recovery.

That's how I do it anyhow.
Thanks all for the replys, Yes jim the 1/8" is from you. The Punisher is the 54mm FG flavor.

What if I were to Y-Harness with the 1/8" then run 20 of so feet of shock cord (1/8") out to the nose?
 

ksaves2

Lifetime Supporter
TRF Lifetime Supporter
Joined
Nov 25, 2009
Messages
5,981
Reaction score
294
Do the Y harness/bridle like everyone suggests. I prepared mine with an end-loop with a barrel swivel that is sized so it's "just" below the open end of the sustainer. I can attach the length of harness I want to use and if it wears from scraping the open end of the tube after several flights, I can replace it easily.
The end of the bridle/barrel swivel is and inch or so below the open end of the sustainer so I can easily get at it.

Kurt
 

blackjack2564

Crazy Jim's Gone Banana's
TRF Supporter
Joined
Jan 18, 2009
Messages
9,061
Reaction score
1,163
Location
Savannah Ga
Thanks all for the replys, Yes jim the 1/8" is from you. The Punisher is the 54mm FG flavor.

What if I were to Y-Harness with the 1/8" then run 20 of so feet of shock cord (1/8") out to the nose?
Ok....but I would wrap tape around whatever hits the edge of airframe or after several flights you will find the Kevlar beginning to "fray".

20ft is more than enough.... 12-15 is plenty for this version Punisher.
 

Onebadhawk

Sponsor
TRF Sponsor
Joined
Jan 11, 2013
Messages
6,058
Reaction score
362
Ok....but I would wrap tape around whatever hits the edge of airframe or after several flights you will find the Kevlar beginning to "fray".

20ft is more than enough.... 12-15 is plenty for this version Punisher.
+1...
lol...

Teddy
 

Mendal

Well-Known Member
Joined
Feb 5, 2016
Messages
242
Reaction score
15
I did order some 1/4" today so I'll probably wait and do what Kurt suggested we will see how impatient I get :)
 

ksaves2

Lifetime Supporter
TRF Lifetime Supporter
Joined
Nov 25, 2009
Messages
5,981
Reaction score
294
I did order some 1/4" today so I'll probably wait and do what Kurt suggested we will see how impatient I get :)
Yeah, the tape trick that Jim and Teddy seconded is good to milk as much life out of the Kevlar as you can. Using a barrel swivel or a quick link to the bridle allows for replacement of the bulk of the harness if necessary in the future.
If using a 29/240 or 360 casing, the bridle can be stuffed down between the casing and inside wall of the bodytube so it's behind the ejection charge blast and the replaceable harness (with a protector maybe) takes the brunt of the blast.

The Punisher Sport can take the I200 and I'm going to try to doctor a delay grain so I can get a second or two longer delay to fly it. The Nosecone can take an EggFinder GPS tracker and can unfurl the main with a Jolly Logic Chute Release.
Kurt
 

Mendal

Well-Known Member
Joined
Feb 5, 2016
Messages
242
Reaction score
15
I'm planning a chute release, I was thinking of building an AV bay in the nose. How do you vent the nose? I went as far as thinking of ordering a longer coupler and a switch band and venting there. Or do you just drill the body and coupler and align the vent holes?

i have the LDRS special, with the red tube and black nose and fins I'm tempted not to paint it, and just be careful and just rough what I need to. But if I do, should it be clear coated?

sorry for all the questions but thank you all for the great feedback!
 

ksaves2

Lifetime Supporter
TRF Lifetime Supporter
Joined
Nov 25, 2009
Messages
5,981
Reaction score
294
Here are some bridle shots of a Punisher Sport 54 for 29mm motors:
19370001.jpg Top view looking down. I decided to foam the fincan.
The pink string is so I can grab the barrel swivel with the quicklink attached. It stays below the lip. If anything needs to be replaced, I can detach from the bridle and replace the the harness.

20160617_190019.jpg20160617_190037.jpg20160617_190120.jpg Internal shots with a cheap ebay endoscope for an Android device. I paid for the MScopes Pro app. I don't like to "sock in" my kevlar where the CR exits are located because I feel epoxy impregnated kevlar becomes brittle. As long as it's not allowed to go from "side to side" it should be O.K. Now I put masking tape on the other side to
plug the gap but the foam I elected to use busted through. Why foam? 'Cause I've never done it before and simply wanted to try it! :smile: There is a fillet on the other side of the CR though. One can see the wellnut for the launch button in the upper right of the last picture. I used the endoscope to examine the single shockcord that occurred with a burn through with the Formula 54 below.
21000002.jpg The repaired Formula 54 is on the left of the Punisher.
The fisheye of the sport camera distorts the shot.
20160617_185333.jpg20160617_185539.jpg One can see the coupler used for the internal repair/stenting off to the left and the cord looks a bit ratty but I've yanked on it pretty hard and I believe there is competency left in it.
pic2.jpgpic1.jpgpic3.jpg These are three shots of the removed Dino cord protector. That grotey stuff peeled off is borate soaked (flame retardant) cardboard I had
duct taped to the cord protector on the end closest to the motor. The protector is reusable
but I'll duct tape two new pieces of the flame retardant cardboard to it.
These cheap endoscopes are not 720P but give one enough resolution for gross observation of internal stuff. I did add an external light source though in the form of a hand held light to
give more illumination of the internals. Kurt
 

blackjack2564

Crazy Jim's Gone Banana's
TRF Supporter
Joined
Jan 18, 2009
Messages
9,061
Reaction score
1,163
Location
Savannah Ga
I'm planning a chute release, I was thinking of building an AV bay in the nose. How do you vent the nose? I went as far as thinking of ordering a longer coupler and a switch band and venting there. Or do you just drill the body and coupler and align the vent holes?

Punisher sport build thread here: http://www.rocketryforum.com/showthread.php?133618-CJ-s-LDRS-35-Punisher-Sport-Drag-Race-35-00-build

You put a small pressure relief vent in airframe [right in middle] & in NC 3inches above the coupler/shoulder . I used a 7/64 drill bit. Same one used for mounting holes for altimeter.

If making an av-bay in NC coupler , 3 vent holes [or sampling ports] for altimeter in vent band...5/32th's bit.
It's all in build thread.
 
Top