Is a shock cord protector absolutely necessary for high powered rockets?

[Five]

I have only flown low and mid powered rockets and never had the need for a shock cord protector. For low powered rockets I’ve always used recovery wadding. Sometimes the Estes parachutes got melted but that was expected from the plastic. Mid powered I used the dog barf or a fire resistant blanket in which both work great.
For my certification test I plan on using a 36” rip-stop chute and 12x12” loc precision fire resistant blanket in a 4” BT, no electronics.
Is a shock cord protector necessary with high powered motors(H or I)?

 

[Eljay]

Absolutely not but if you have a nylon shock cord that can get nailed by the ejection charge you may find it burns through after a few launches. A lot of people like to use a kevlar harness that ends around the top of the body tube and then clip on a nylon shock cord from there. Depending on the design etc. you may just be able to get enough dog barf on there to keep the shock cord from getting nailed. It's kind of a judgement call. But if you're not sure then getting some Nomex on the bottom of the shock cord is pretty darn cheap insurance especially on a cert flight.

 

[Five]

Absolutely not but if you have a nylon shock cord that can get nailed by the ejection charge you may find it burns through after a few launches. A lot of people like to use a kevlar harness that ends around the top of the body tube and then clip on a nylon shock cord from there. Depending on the design etc. you may just be able to get enough dog barf on there to keep the shock cord from getting nailed. It's kind of a judgement call. But if you're not sure then getting some Nomex on the bottom of the shock cord is pretty darn cheap insurance especially on a cert flight.

I think I’ll be fine without it. I will take your advice though with the Nomex. I have an extra 6x6 fire blanket that I’ll put in at the bottom of the shock cord.

 

[manixFan]

I've used both nylon strap and tubular nylon with no protection in rockets that have seen many flights, and neither has ever failed. But they are sufficiently large to have a lot of margin. The only rockets I used shock cord protectors on were large 6" (or larger) birds that had multi-gram ejection charges. I put a one of those sheaths over the part of the shock cord that was right over the ejection charge.

In several instances I have also done what Eljay suggests, using a Nomex sheet right over the ejection charge. For smaller rockets, I've also used the Quest style parachute wadding since it holds it shape better than the Estes stuff. But just be sure it does not interfere with a clean ejection of your chute, so test it several times before your flight. (Either use the breath puff test or the sharp swing test.)

Good luck on your cert flight.


Tony

 

[Five]

I've used both nylon strap and tubular nylon with no protection in rockets that have seen many flights, and neither has ever failed. But they are sufficiently large to have a lot of margin. The only rockets I used shock cord protectors on were large 6" (or larger) birds that had multi-gram ejection charges. I put a one of those sheaths over the part of the shock cord that was right over the ejection charge.


Tony

I wasn’t sure being that I’m new to HPR.
Thx

 

[Eljay]

It's good you're thinking this stuff through. As the rockets get larger you'll find there's often several ways of achieving a goal (and you may take some of those techniques back down to smaller rockets as well).

One nice thing about having a 4" BT is you can reach down in there and get to stuff later and there's enough room that you have some flexibility in general.

 

[Gramparocket]

Is your shock cord nylon? Then it's a good I idea to protect it. I roll my chute into a burrito with the blanket, place that in the rocket then accordion fold the nylon shock cord on top of that, I have had no cords burned yet,it will protect the cord pretty well. If you still want to do better, than put in a protector. I agree with a post above and prefer to use Kevlar cord.

 

[kalsow]

Duct tape is your friend. It's cheap, sturdy and replaceable. Cover the bottom foot or two of your shock cord and you're golden. Replace the tape when it's charred.

 

[Five]

Here’s a few pics from start to finish.


Thank all of you for the advice. It’s good to know that there are people out there that are willing to help another fellow rocketeer.

 

[OverTheTop]

A nylon harness can be punched through by a single charge if you are unlucky. I fly nylon a lot and have nearly had this happen. I now always use a protector. Kevlar will be less susceptible but is less stretchy and more inclined to snap if you don't allow for it.

A harness protector can be as simple as a layer or two of masking tape. It works surprisingly well.

 

[Handeman]

I've started wrapping the lower part of nylon cords with duct or electrical tape and then using the chute protector by just stuffing it down the tube before the rest of the nylon cord and chute go in. The protector works like dog barf or wadding would, but a lot less messy. Just remember to attach it to the shock cord.

 

[Five]

I had and exra

 

[Five]

I had an extra 6x6” fire blanket that I ran the shock cord through and put in the BT then I put the parachute with the main fire blanket wrapped around it.