Newb Question - Standard Dual Deploy

[Chris in Idaho]

Sorry if this has been beaten to death but my searches only found altimeter threads, shear pin threads, black powder threads, etc.

So, in standard dual deploy, where does the payload section containing the main chute separate?

Does it separate from the nose cone and stay connected to the av bay?

Does it separate from the av bay and stay connected to the nose cone?

Does it separate from both the av bay and nose cone and just slide freely on the kevlar?

Thanks in advance!

 

[Antares JS]

The nose comes off, the tube stays connected to the av bay.

 

[cerving]

Or you can separate it at the AV bay... I've done it both ways. It largely depends on the build. For example, I have a Wildman Punisher 3 that I've added a main chute bay to because I got tired of stuffing the chute into the nose cone (it's head-end deploy), so it was natural to have it separate at the AV bay like a head-end deploy rocket would.

 

[Titan II]

https://www.apogeerockets.com/Intro-to-Dual-Deployment
Pluse of bunch of information here...

https://www.google.com/search?q=DUA...BA8gBAOIDBBgAIEGIBgGQBgg&sclient=gws-wiz-serp

 

[Chris in Idaho]

The nose comes off, the tube stays connected to the av bay.

Thanks. You'd still need the payload tube to be removable from the Av bay, so is it shear pins at the nose cone and metal screws at the av bay?

Or you can separate it at the AV bay... I've done it both ways. It largely depends on the build. For example, I have a Wildman Punisher 3 that I've added a main chute bay to because I got tired of stuffing the chute into the nose cone (it's head-end deploy), so it was natural to have it separate at the AV bay like a head-end deploy rocket would.

That makes sense too. I imagine the nose cone now makes a good spot for an eggfinder?

 

[Scott_650]

John Coker may not be the most dynamic presenter but he does a great job of explaining things in a logical, succinct way http://www.jcrocket.com/howtolist.shtml

 

[Antares JS]

Thanks. You'd still need the payload tube to be removable from the Av bay, so is it shear pins at the nose cone and metal screws at the av bay?

Yes, though shear pins are not always necessary depending on the rocket.

 

[Raythain]

Yes, though shear pins are not always necessary depending on the rocket.

Not to hijack the thread, but are there rules of thumb about shear pins? Some combination of volume and material where they become necessary?

Or is it ground test and find out?

 

[Antares JS]

Not to hijack the thread, but are there rules of thumb about shear pins? Some combination of volume and material where they become necessary?

Or is it ground test and find out?

A post I made a while back on this topic:

Shear pins are not generally needed to prevent drag separation. In my mind, shear pins have up to three purposes:

-Holding break points together between smooth fiberglass parts or other materials that don't have much friction between them.

-Holding your second break point together in a dual-deploy rocket to ensure it doesn't open when the first event happens and everything is being jerked around. (Even then, friction fit is usually good enough for smaller rockets.)

-Greater consistency in the force required to separate two parts, since friction fit can be a bit subjective.

My few fiberglass rockets, my level 3 prototype, and my level 3 rocket are my only rockets that use shear pins.

 

[Titan II]

Yes, though shear pins are not always necessary depending on the rocket.

Then there are some, like me, who use shear pins on all separation points on all rockets. Both methods work if done properly. You will fine several threads here...

https://www.rocketryforum.com/search/518693/?q=shear+pin+size&o=relevance

 

[Handeman]

I started using shear pins with fiberglass rockets. I never use them with cardboard.
That's just me, but friction fit can work quite well. It just takes some practice.

 

[Rocketclar]

I try to make my stuff somewhat interchangeable. So I have put 54mm tubes in several 3 and 4" NCs. Then I can slide my Eggfinder GPS sled into any of them (pic of sled). I have to shear pin that since it will drag separate pulling out the main at apogee when the drogue fires. Most of the NC/GPS sled combinations weigh about 19 oz.
I have a couple of 4" PML kits that use 2 pistons. Then the rockets break at the fin can and NC (see picture.)

 

[Rocketclar]

BTW Chris, I use to live in Boise (worked for Micron) and flew at the Swan Falls and Soldier Mtn sites of the Tripoli Club.

 

[Dan Griffing]

Not to hijack the thread, but are there rules of thumb about shear pins? Some combination of volume and material where they become necessary?

Or is it ground test and find out?

On my 4” fiberglass rockets I use 3 black nylon 2/56 shear pins that have an 18lb spec sheer force. If the pins are aligned so that they sheer at the same time, it takes 54lb of total force to shear them. This means that the pressure difference only needs to be 4.3 psi to shear all 3 pins. However, if the pins are misaligned so that they shear one at a time, it only takes a pressure difference of 1.4 psi.