Big Bertha Parachute, Shock Cord

[ArthurAstroCam]

I had read somewhere that a builder put his parachute lines around his shock cord. I do not know if this is an accepted best practice, so in building Big Bertha, I used a 15" nylon parachute. And decided to put the lines around the shock cord. Was this a good idea?

 

[BigMacDaddy]

I believe that you are asking if you should attach the parachute to the shock cord or to the nosecone?

Many people tie a loop in the shock cord and use a fishing swivel leader to attach and detach parachutes (you tie the parachute lines to the small hole in swivel leader and use the snap clip to clip to the loop you made in shock cord). If you attach your parachute a away from the nose cone it is less likely to get tangled (nose cone does not snake through the lines and swivel leader lets parachute / rocket independently twist). However, keep in mind that the nose cone basically pulls the parachute from the tube so do not attach parachute too close to body (basically attach close to middle of shock cord). This also lets you detach parachute and store flat and separately from rocket (it gets less squashed and opens more easily) or swap parachute to other rockets.

 

[Rob Campbell]

Just be sure to place the loop in the shock cord about 2/3 of the way up between the body tube and the nose cone. This is to keep the nose cone from hitting the body tube and fins while under the chute.

 

[ArthurAstroCam]

I believe that you are asking if you should attach the parachute to the shock cord or to the nosecone?

Many people tie a loop in the shock cord and use a fishing swivel leader to attach and detach parachutes (you tie the parachute lines to the small hole in swivel leader and use the snap clip to clip to the loop you made in shock cord). If you attach your parachute a away from the nose cone it is less likely to get tangled (nose cone does not snake through the lines and swivel leader lets parachute / rocket independently twist). However, keep in mind that the nose cone basically pulls the parachute from the tube so do not attach parachute too close to body (basically attach close to middle of shock cord). This also lets you detach parachute and store flat and separately from rocket (it gets less squashed and opens more easily) or swap parachute to other rockets.

View attachment 502916

I did the swivel pount on my AstroCam, but decided on a different approach on this rocket. The strings are loose in a simple single knot, so I may use a couple of small pieces of masking tape to either side of the string, along on the shock cord, to bring it up to the nose cone end of the shock cord.

 

[JonathanOtt]

You mean when wrapping and packing the 'chute into the tube for flight?

 

[neil_w]

I did the swivel pount on my AstroCam, but decided on a different approach on this rocket. The strings are loose in a simple single knot, so I may use a couple of small pieces of masking tape to either side of the string, along on the shock cord, to bring it up to the nose cone end of the shock cord.

Are you saying that the chute is not securely anchored to one location on the shock cord? Don't do this.

You can anchor the shock cord to the nose cone (traditional) or to a location further down on the shock cord away from the nose cone... but anchor it.

 

[ArthurAstroCam]

Are you saying that the chute is not securely anchored to one location on the shock cord? Don't do this.

You can anchor the shock cord to the nose cone (traditional) or to a location further down on the shock cord away from the nose cone... but anchor it.

Anchor it how? So you are saying it should be on the opposite end of the shock cord, away from the nose cone?

 

[ArthurAstroCam]

You mean when wrapping and packing the 'chute into the tube for flight?

No, in the build process.

 

[JonathanOtt]

View attachment 502921

 

[ArthurAstroCam]

View attachment 502921

So you think I should attach it not around the shock cord, but to the nose cone? Others have said around the shock cord.

 

[JonathanOtt]

 

[JonathanOtt]

So you think I should attach it not around the shock cord, but to the nose cone? Others have said around the shock cord.

Arthur,

Just follow the instructions.

 

[ArthurAstroCam]

Arthur,

Just follow the instructions.

Which, I have done. But as I mentioned here, others have said that around the shock cord was a better option than at the nose cone.

 

[ArthurAstroCam]

View attachment 502922

See my response.

 

[JonathanOtt]

In the grand scheme of things, it doesn't really matter. The way it is in the instructions is just fine.

 

[ArthurAstroCam]

In the grand scheme of things, it doesn't really matter. The way it is in the instructions is just fine.

Well, I do have swivel hooks in my range box, and it is very easy to undo the lines off the shock cord. So maybe I will move it.

 

[neil_w]

 

[David_Stack]

Good Morning Arthur;

Some modelers have experienced failure of the plastic 'loop' molded into the base of the nose cone. If that attachment point should break then at least one part of the model is no longer attached during recovery. For that reason many will attach the chute to the shock cord, at a point about 1/3 of the distance between the nose cone and the body tube (closer to the nose cone). Doing so means that the only load applied to that molded loop on the nose cone is the weight of the nose cone itself (there is no 'jerk' experienced when the chute opens).

If you decide to attach the chute to the shock cord and want to be able to easily remove the chute from the airframe for storage (or to use it on another rocket), then terminating the shroud lines at a swivel, and attaching THAT to a loop in the shock cord is a viable option.

Give this a read (and there are numerous other posts here in the forum as well): https://www.rocketryforum.com/threads/snap-swivels-and-lpr-parachute-attachment.165867/

r/
Dave

 

[ArthurAstroCam]

View attachment 502923

What is "loop"? An additional piece of string?

 

[neil_w]

Some modelers have experienced failure of the plastic 'loop' molded into the base of the nose cone. If that attachment point should break then at least one part of the model is no longer attached during recovery. For that reason many will attach the chute to the shock cord, at a point about 1/3 of the distance between the nose cone and the body tube (closer to the nose cone). Doing so means that the only load applied to that molded loop on the nose cone is the weight of the nose cone itself (there is no 'jerk' experienced when the chute opens).

I believe the other theory is that keeping the nose cone a bit separated from the parachute will reduce the chance of it getting tangled in the shroud lines. I don't know how big an issue this is, but I've taken to tying the parachute not 1/3 of the way down, but just around 8" or something like that (I don't measure).

 

[Antares JS]

In the grand scheme of things, it doesn't really matter. The way it is in the instructions is just fine.

Agreed. OP, between this and some of the other questions you've asked, I think you're overthinking things a bit here. For what it's worth, I'm coming up on 25 years of building rockets, and I usually just secure parachutes to the nose per the instructions and they work just fine.

The only notable time I don't do this is in high power rockets with heavy parts when I don't want to have the whole rocket hanging off that little plastic loop on the nose. In that case I usually put the parachute on the end of the shock cord and hang the nose off of a loop 2/3 of the way down.

 

[neil_w]

What is "loop"? An additional piece of string?

It is the shock cord. Loop the shock cord over itself and tie a square knot. The loop just needs to be large enough to hook a snap swivel to (maybe 1/2" - 1").

Or just connect it to the nose cone and be done with it. This is a minor improvement we're talking about.

 

[ArthurAstroCam]

It is the shock cord. Loop the shock cord over itself and tie a square knot. The loop just needs to be large enough to hook a snap swivel to (maybe 1/2" - 1").

Or just connect it to the nose cone and be done with it. This is a minor improvement we're talking about.

Thank you, I think I will go with a swivel hook to the nose cone loop. And attach the chute lines to the swivel. Thats how I did it with the AstroCam.

 

[BigMacDaddy]

If you ever start scratch building or a shock cord breaks, this is a bit better than the rubber bands that come in the kits (not recommending you upgrade kits or anything but this is cheaper than buying replacement / new shock cords from Estes) -- https://www.walmart.com/ip/Dritz-1-4-Braided-Elastic-8-Yd/47437621?athbdg=L1100 (you can also go up to the next size - https://www.walmart.com/ip/Dritz-1-2-Braided-Elastic-4-5-Yd/163955515)

If you want to eventually use Kevlar (again not recommending that you upgrade kits but if you scratch build, move to heavier rockets, etc...) this is good for shock cords -- https://www.amazon.com/dp/B088PR8XZ9?psc=1&ref=ppx_yo2_dt_b_product_details (I bought 150# x 500').

 

[neil_w]

If you ever start scratch building or a shock cord breaks, this is a bit better than the rubber bands that come in the kits (not recommending you upgrade kits or anything but this is cheaper than buying replacement / new shock cords from Estes) -- https://www.walmart.com/ip/Dritz-1-4-Braided-Elastic-8-Yd/47437621?athbdg=L1100 (you can also go up to the next size - https://www.walmart.com/ip/Dritz-1-2-Braided-Elastic-4-5-Yd/163955515)

I use 1/8" or 1/4", depending on body tube size and/or motor mount size. *Usually* my 18mm models use 1/8" and my 24mm models use 1/4", but there are exceptions.

Important: make sure to use *braided* elastic (as correctly linked by @BigMacDaddy above). Once I bought knit elastic by mistake and basically chucked it out, it's useless for shock cords.

 

[user 35280]

86 the rubber band shock cords and upgrade to Kevlar and a elastic type of shock cord.

 

[ArthurAstroCam]

86 the rubber band shock cords and upgrade to Kevlar and a elastic type of shock cord.

I get that all the time. Rocket is built, I think the stock shock cord is fine for now.

 

[bjphoenix]

Which, I have done. But as I mentioned here, others have said that around the shock cord was a better option than at the nose cone.

I get that all the time. Rocket is built, I think the stock shock cord is fine for now.

I have a lot of old rockets and I've experienced broken shock cords and lost nose cones. With the short rubber bands I've had nose cones snap back into the front of the body tube, damaging the body tube and sometimes damaging a balsa nose cone. So recently I retrofitted all of my old rockets for kevlar. I've been using 10' kevlar for LPR, with a snap swivel on the end of the kevlar at the nose cone. My parachutes also have small snap swivels so I snap the shock cord to the nose cone and snap the parachute to the snap swivel on the shock cord. This is pretty robust but it can be a problem eliminating tangles from the shock cord.

I've had people recommend putting the snap swivel on the shock cord so it can slide up and down, then if the shock cord breaks the rocket pieces will fall to earth rather than have the nose cone drift off on the parachute.

 

[dr wogz]

We should point out:

• Tying a loop in the shock cord is best when you use a string (Not elastic) for the shock cords. Kevlar, spider line, a shoelace, etc.. The knot being a simple overhand knot in the cord. I put mine about 2-3" below the NC attachment.
• Tying a knot in the elastic (rubber band type) weakens it at this point (so I've been told & have personally experienced)

 

[neil_w]

We should point out:

• Tying a loop in the shock cord is best when you use a string (Not elastic) for the shock cords. Kevlar, spider line, a shoelace, etc.. The knot being a simple overhand knot in the cord. I put mine about 2-3" below the NC attachment.
• Tying a knot in the elastic (rubber band type) weakens it at this point (so I've been told & have personally experienced)

My knotted braided elastic cords have experienced no problems.