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Will my swivel hold up?

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utahrc

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I'm going to be flying my L1 this weekend and the chute I'm using is an X-form from topflight. The packaging recommends a swivel and the 1000 lb swivels that I ordered won't be here in time. The largest I could find locally are 275lb Berkley brand ball bearing barrel swivels. Should these be sufficient for a 6 lb rocket?

I don't have any doubt that in a best-case, deploy-at-apogee situation, that they'll hold up fine. But they do look a little scrawny for less-than-ideal deployment situations.

So now I'm deciding - do I use the 275lb swivels that I have in hand, or go without?
 

DynaSoar

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Originally posted by utahrc
I'm going to be flying my L1 this weekend and I the chute I'm using is an X-form from topflight. The packaging recommends a swivel and the 1000 lb swivels that I ordered won't be here in time. The largest I could find locally are 275lb Berkley brand ball bearing barrel swivels. Should these be sufficient for a 6 lb rocket?

I don't have any doubt that in a best-case, deploy-at-apogee situation, that they'll hold up fine. But they do look a little scrawny for less-than-ideal deployment situations.

So now I'm deciding - do I use the 275lb swivels that I have in hand, or go without?
Are you sure the strength of all the rest of the recovery components are greater than 275 lbs?
 

utahrc

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The swivel is 275 lbs test, that means it FAILS at 275 lbs (or thereabouts). The quick links that I have (1/8") have a working load of 220 lbs, which means they fail somewhere much higher - maybe 400+ lbs. I have tubular nylon for the shock cord, which I believe can sustain very high momentary stress (because of its elasticity) and it attaches to some mean-looking u-bolts. I don't know much about what the shroud lines or the plywood bulkheads can take.
 

DynaSoar

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Originally posted by utahrc
The swivel is 275 lbs test, that means it FAILS at 275 lbs (or thereabouts). The quick links that I have (1/8") have a working load of 220 lbs, which means they fail somewhere much higher - maybe 400+ lbs. I have tubular nylon for the shock cord, which I believe can sustain very high momentary stress (because of its elasticity) and it attaches to some mean-looking u-bolts. I don't know much about what the shroud lines or the plywood bulkheads can take.
If you know your chute and can model it open at different speeds, you can get an idea of how much pull it give.

The bulkheads are probably fine. Glued to the body, if they start to flex they'll transfer momentum to the body. Good for not breaking, but can cause whiplash and Estes dents. Someone told me their Vulcanite drove its booster into the payload section and bashed it in. I doubt that was from elastic shock. Probably from the chute slowing the payload section in front of the booster still moving at high speed.

How much give is in your shock cord? Is it going to absorb much? I know it gives some, but it does it quick and then it's tight. The chute is going to pull according to airflow for as long as it takes to get it to terminal descent velocity.

Do a simple sim on the Rocket Simulator on EMRR
http://www.rocketreviews.com/tools.shtml
and do the full table. It'll give you the speed at each 0.1 sec. Check out the range of your delay around apogee and see what speed is predicted. If your delay is longer than apogee, use the equivalent pre-apogee speed; it's all ballistic.

Once you have the speed, if it's legal to do so, try tying it to the back of a car and testing it. If you can find a spring scale, like for weighing big fish, you can get the actual pull at various speeds. If your projected opening speed is too fast to test, get some measurements at lower speeds and extrapolate. There may be a fairly simple square-inch x speed calculator somewhere for doing this; I don't know.

Did the chute come with a max rating? I'd worry about it shredding or busting a shroud.

Frankly, I'd add a small loop of strong elastic material (not necessarily elastic itself, but something with give) to absorb some of the shock from the swivel. It can have more rating than the swivel, but beling elastic it'll start to give first and absorb some.
 

Stymye

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mabey skip the swivel if you think it might fail, one flight without a swivel won't hurt anything till you get the proper one.
 

jcsalem

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The smaller X-type 'chutes (24" and smaller) really require a swivel because they spin A LOT coming down. If you don't have a swivel the shock cords gets extremely twisted which can cause some failures and is also a pain to untwist later.

I have limited experience with larger X-types (30" and 36") -- less than 10 flights. From what I've seen so far, they don't spin as much as the smaller ones.

-- Jim
 

Stymye

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my L1 rocket does not have a swivel , it tends to twist up just a little bit during recovery but after 7 flights I have never had a anything near a failure happen.

I think a swivel is better to use,and most of my rockets use one.
I just never installed one in my L1 for whatever reason..so I'm just commenting on my only my experience.

results may vary.
 

North Star

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I use a 'Top Flite' 70" X form chute on my stretched PML Ptery Jnr. which weighs in about the same as your rocket.
I normally use a swivel but I have noticed that with these bigger chute sizes there is hardly any spin.
 

utahrc

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I've got 80" and 90" Top Flite X-Type's to choose from, so if 70" doesn't spin too bad, I should be OK. I think I've found someone to loan me a 1000 lb swivel though.
 

DynaSoar

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Originally posted by utahrc
I've got 80" and 90" Top Flite X-Type's to choose from, so if 70" doesn't spin too bad, I should be OK. I think I've found someone to loan me a 1000 lb swivel though.
I've flown a lot of X-forms, they're my favorite. If they spin coming down, it's no big deal. A swivel won't stop that, it'll just prevent the shrouds from tangling for next time.

I always use those "quick link" connectors that look like an oval/rectangular chain link, with a threaded tightener on one side that can open and close. After a flight, I remove it, the shrouds fall free and untangle, and on it goes again. The smallest, 1/8", has a 220 lbs rating. The zinc ones cost aboyt $1.50 at Lowe's, the 316L stainless steel about $4.00, but they're not stronger.

Lowe's has them up through 3/4". I didn't check the rating.

Here's a picture of one:
 
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