# Swivel strength for low to mid power model rockets

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#### BABAR

##### Builds Rockets for NASA
TRF Supporter
I got a 36” X chute from buyrocketmotors.com, figured might as well get it with the motors for my Interceptor E

On their site, didn’t say anything about swivels.

@neil_w showed me the thin mil version on another site, when I went there and looked up my size I got this

Which included this quote

manufacturer recommends the use of a Swivel with the X-Form Parachutes. Use SW-600 up to SW-1500 for the 36" size.

This seems a big step up from the fishing swivels I get from Wallyworld and use for my low power bird.

Do I need something that supports 600 to 1000 lbs?

TRF Supporter

#### HHaase

##### Siegecraft Electronics
I swear, one of these days I'm going to figure out how to attach my recovery gear to load cell and try to actually measure the shock loads during flight.

To answer the question in your 2nd post, the amazon link you have appears to be the exact same swivel as the SW-600
This link also shows some smaller sizes as well, down to 30lb rating according to the chart.

-Hans

#### jimzcatz

##### Boss, Carolina Rocket Mafia
why do you feel the need for a swivel?

#### crossfire

I got a 36” X chute from buyrocketmotors.com, figured might as well get it with the motors for my Interceptor E

On their site, didn’t say anything about swivels.

@neil_w showed me the thin mil version on another site, when I went there and looked up my size I got this

Which included this quote

manufacturer recommends the use of a Swivel with the X-Form Parachutes. Use SW-600 up to SW-1500 for the 36" size.

This seems a big step up from the fishing swivels I get from Wallyworld and use for my low power bird.

Do I need something that supports 600 to 1000 lbs?
Some times a larger swivel is recommend because of the eyelet size on the swivel. A larger eyelet is much easier to tie off or get through a quick link.

#### BABAR

##### Builds Rockets for NASA
TRF Supporter
why do you feel the need for a swivel?
This site

said swivels recommended for X chutes over 30 inches, and I have seen one deploy and then start spinning and turn into a streamer.

#### teepot

##### Well-Known Member
TRF Supporter
Without a swivel the x form chutes sometimes wrap themselves up because they spin. I get Dr. Fish swivels from Amazon. They have a large variety of strengths available. I put multiple swivels on my shock cord and at the chute attachment point.

#### Handeman

##### Well-Known Member
TRF Supporter
I've never uses swivels on chutes, except fishing snap swivels for plastic LPR chutes and that is for the snap part.

I have not had any luck with barrel swivels. They are much cheaper then ball bearing swivels, but they never seem to work when I try them. It's ball bearings only for me now.

##### Lonewolf.... No Club
Thought: You could always do a R&D test of whichever swivel you want to use.
(Actual weight of rocket at ejection) x (??) = ballast. (I'd use a multiplier of 3)
Attach the swivel to a fixed support, replicate the shock chord length used on the rocket, then drop the ballast.

#### teepot

##### Well-Known Member
TRF Supporter
I try to match all the parts of the shock cord set up to the same strengths. 1500 lb kevlar gets a 1300 lb swivel, rather than a 500 lb one, etc. I figure the weakest link is the bond of the motor mount to the body tube.

#### caveduck

##### semi old rocketeer
I also got a batch of Dr. Fish swivels in various of the larger sizes and a few smaller ones for LPR. If you read down in the reviews someone tested them and they were reasonably close to the rated breaking strength. Some other ones not so much. Spot on with sometimes wanting a physically bigger one just to have the eyes big enough for a quick link.

#### Mike Haberer

##### Well-Known Member
TRF Supporter
I got a 36” X chute from buyrocketmotors.com, figured might as well get it with the motors for my Interceptor E

On their site, didn’t say anything about swivels.

@neil_w showed me the thin mil version on another site, when I went there and looked up my size I got this

Which included this quote

manufacturer recommends the use of a Swivel with the X-Form Parachutes. Use SW-600 up to SW-1500 for the 36" size.

This seems a big step up from the fishing swivels I get from Wallyworld and use for my low power bird.

Do I need something that supports 600 to 1000 lbs?
You figure out the capacity of the connector required (swivel, shock cord, eyebolt, quicklink) based on the weight of the rocket multiplied by the max number of G's you expect the recovery system needs to handle. If you have a 10 Lb. rocket subjected to 50 G's, you need 500 Lb. Figuring out Max G's is a bit of a challenge - it's either terminal velocity when the chute opens or at ejection if your shock cord is too short. That's why most posts recommend a long shock cord, the longer the better, at least 3x the rocket length. I generally use 50 G's to size my connectors as I probably read that somewhere.

#### BABAR

##### Builds Rockets for NASA
TRF Supporter
You figure out the capacity of the connector required (swivel, shock cord, eyebolt, quicklink) based on the weight of the rocket multiplied by the max number of G's you expect the recovery system needs to handle. If you have a 10 Lb. rocket subjected to 50 G's, you need 500 Lb. Figuring out Max G's is a bit of a challenge - it's either terminal velocity when the chute opens or at ejection if your shock cord is too short. That's why most posts recommend a long shock cord, the longer the better, at least 3x the rocket length. I generally use 50 G's to size my connectors as I probably read that somewhere.

#### BABAR

##### Builds Rockets for NASA
TRF Supporter
Thought: You could always do a R&D test of whichever swivel you want to use.
(Actual weight of rocket at ejection) x (??) = ballast. (I'd use a multiplier of 3)
Attach the swivel to a fixed support, replicate the shock chord length used on the rocket, then drop the ballast.
I think (especially for non-electronic) staging this may underestimate the strength required. Ideally we’d all like to pop at apogee and have the maximum force essentially the weight of the rocket. Given possibility of early or late ejection, even with an elastic shock cord the force may be several times the weight of the rocket. I am thinking that the Wallyworld fishing swivels probably won’t hack it.

Curious if anyone has opinions of barrel vs ball bearing swivels. Seems like barrel swivels are generallly stronger and cheaper but don’t “twirl” as easily.

Oops, just saw @Handeman post. Thanks

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#### Mike Haberer

##### Well-Known Member
TRF Supporter
My last thought is that it isn't always easy to know how any particular part of the recovery system is rated. Some vendors provide max weight ratings for the products they sell, some don't. That true for Kevlar tubular and strap nylon as well. For metal connectors like quick links, it also depends on the metal being used (e.g., zinc coated vs. stainless steel) and can actually be different between like metals depending on alloy blends. I keep a spreadsheet of known ratings of connectors (by size and composition) that provide them so I can interpolate a value for those that don't.

##### Lonewolf.... No Club
Thought: You could always do a R&D test of whichever swivel you want to use.
(Actual weight of rocket at ejection) x (??) = ballast. (I'd use a multiplier of 3)
Attach the swivel to a fixed support, replicate the shock chord length used on the rocket, then drop the ballast.
I think (especially for non-electronic) staging this may underestimate the strength required. Ideally we’d all like to pop at apogee and have the maximum force essentially the weight of the rocket. Given possibility of early or late ejection, even with an elastic shock cord the force may be several times the weight of the rocket. ....
Exactly why I stated I'd use a multiplier of 3...

The 3x weight plus the solid fixed support should result in loadings higher than the swivel will ever see during flight.

Wow,
Nice swivels on Amazon and Wally World.. ( What the heck is Wally World ?? )..
It might be a better idea to give your business to a rocketry specific vendor..
What he has will be more likely to be appropriate for the rocketry application,
and you'd be supporting a vendor who supports launches..
I'm sure you enjoy having a vendor at your launches..

In the pics are a 500 lb ball bearing swivel ( $5 ) and a 1500 lb ball bearing Badhawk" swivel ($7 ) ..
The attachment hole in the Badhawk swivel is large enough to fit a 5/32" Quick Link through..

Also,
Rich is correct.
The spin will occur through the path of least resistance..
If it's physically easier to spin the material then to get your non ball bearing swivel to spin,
the material or chute will still spin up..

Teddy

#### tsmith1315

##### Well-Known Member
( What the heck is Wally World ?? )..
That's where the Griswold family was going on their Vacation.

Lol..

TRF Supporter
or Walmart

#### Joshua Smith

##### kernelsmith
TRF Supporter
I swear, one of these days I'm going to figure out how to attach my recovery gear to load cell and try to actually measure the shock loads during flight.

-Hans
This would be fun honestly. I've also always wanted to do it...well ever since I started thinking about what my shock cord/recovery harness min breaking strength should be. I imagine the really challenging part is finding a strong enough load cell that's also light enough to fly. Obviously the more the load cell weighs in proportion to the rocket's overall weight, the more you affect the recovery force itself. You increase the rocket's weight, increasing the potential load, but you also therefore affect the rocket's altitude and orientation at chute inflation etc. I would imagine someone has tried this, maybe a good NARCON or other presentation topic

#### Sooner Boomer

##### Well-Known Member
I swear, one of these days I'm going to figure out how to attach my recovery gear to load cell and try to actually measure the shock loads during flight.
Seems like it would be easier to test from the bed of a pickup. Wouldn't *exactly* duplicate flight environment, but would be easier to carry out, and would probably be close enough. Lots more room in the bed of a pickup than in the bodytube of (most) rockets.

#### Joshua Smith

##### kernelsmith
TRF Supporter
Seems like it would be easier to test from the bed of a pickup. Wouldn't *exactly* duplicate flight environment, but would be easier to carry out, and would probably be close enough. Lots more room in the bed of a pickup than in the bodytube of (most) rockets.
Oh for sure, but then the question would be how representative are the results, but of course to know that for sure, someone's got to get some operational data