Dual deploy and payload bay length.

[DeltaVee]

I have a 4" diameter dual-deploy project for my L-2 certification... for the sake of argument I've got a nose cone with a 3" shoulder and an electronics bay that's 8" overall length, and a one inch switch ring, so that 3.5" of shoulder for e-bay will stick into the payload. All this shoulder material will occupy 6.5 total inches of the 4" diameter payload bay.

The current design is for an 18" payload bay tube, so if I want a 20' nylon shock cord in the payload bay along with a 36"-42" parachute, should the remaining amount of payload bay at 11.5" long x 4" dia. have enough real-estate for this?

This length is nearly the same as for a 3.1" dia d-d rocket I have (17" long - 5.5" of total shoulder). When I pack that it seems tight...

The tube I have for the payload is currently 25" in length and I was planning on cutting it down somewhat, since this is an upscale project and a precise upscale would have called for a 15" payload tube, rather than 18"!

Looking for opinions since a bit longer isn't a big deal. But I'd like to make this upscale at least a bit more "spot-on" as it were!

I guess after all that hot air above... what I'm asking is: Given a 4" diameter tube, what would be the minimum usable payload bay length for 20 feet of shock cord plus a 36-50 inch parachute in a D-D situation?

 

[RokitFlyr]

It's tight, but should work with careful packing. Put a bulkhead inside the nosecone at the top of the shoulder and you gain that 3" of space.

 

[cerving]

12" is about the minimum for a parachute/shock cord for a 3" or 4" diameter rocket, you should be fine. Be sure to wrap your chute tightly in the Nomex so it slides out easily, that will help.

 

[DeltaVee]

12" is about the minimum for a parachute/shock cord for a 3" or 4" diameter rocket, you should be fine. Be sure to wrap your chute tightly in the Nomex so it slides out easily, that will help.

This is a good R.O.T. to know! Thanks!

 

[DeltaVee]

@RokitFlyr
I already modded the nose cone... includes two 1/4-20 all thread, plus a 4" stainless eye-bolt.


You can see the 1/4 inch bulkhead neatly nestled into the shoulder... 3.89" in diameter, the cone had just enough flex to pass it through.



Lower 1" sawed off, plus the bulkhead with epoxied 1/4-20 nuts, and the end-cap designed to fit on the not-at-all circular back end!



fully assembled... that end plate is stepped btw. The inner bulkhead and all-thread are epoxied in. The end plate can be removed.

Was a bit of a pain, since I had to align the all thread rods while the epoxy was still fluid... but I wanted 3" of shoulder at least... which meant keeping part of the deep angle cut for the cheap plastic shock cord mount. Access to a precision laser cutter made the bulkheads a snap, though.

 

[mtnmanak]

The answer varies wildly with a couple variables: What is the diameter of the shock cord (nylon shock cords come in a lot of different sizes) and what is the brand of parachute?

On the "big" end of the equation, it would be tight if you are trying to shove a 1" wide nylon shock cord along with a bulky parachute like the ones from LOC or other lower Cd manufacturers.

On the other side of the equation, if you use thin Kevlar shocks cords with very high performance compact chutes like Fruity Chutes Iris chutes, you will have all kinds of room to spare.

Best way to figure it out is shove what you have in the tube and see how much room it takes up, then cut to that length.

For the nosecone, I would cut the entire beveled section off and get a bulkhead forward of the nosecone shoulder. John Coker has some great suggestions in this video:

 

[mtnmanak]

Another option for nosecones is to use these:

https://inverted-pursuits-lab.squar...true&sa=false&sbp=false&q=false&category_id=4

After you own a sled or two, you can just buy the internal sleeves for new nosecones and move the built out sleds around. Gives you space for head end dual deploy or to add trackers. I have been putting these in my plastic nosecones lately and love them.

 

[RokitFlyr]

@RokitFlyr
I already modded the nose cone... includes two 1/4-20 all thread, plus a 4" stainless eye-bolt.

View attachment 671153
You can see the 1/4 inch bulkhead neatly nestled into the shoulder... 3.89" in diameter, the cone had just enough flex to pass it through.

View attachment 671154

Lower 1" sawed off, plus the bulkhead with epoxied 1/4-20 nuts, and the end-cap designed to fit on the not-at-all circular back end!

View attachment 671155

fully assembled... that end plate is stepped btw. The inner bulkhead and all-thread are epoxied in. The end plate can be removed.

Was a bit of a pain, since I had to align the all thread rods while the epoxy was still fluid... but I wanted 3" of shoulder at least... which meant keeping part of the deep angle cut for the cheap plastic shock cord mount. Access to a precision laser cutter made the bulkheads a snap, though.

The end cap is not necessary and limits the space. Put an eye bolt in the bulkhead. The nosecone AV bays also don't give any more room.

 

[RokitFlyr]

Another option for nosecones is to use these:

https://inverted-pursuits-lab.squar...true&sa=false&sbp=false&q=false&category_id=4

After you own a sled or two, you can just buy the internal sleeves for new nosecones and move the built out sleds around. Gives you space for head end dual deploy or to add trackers. I have been putting these in my plastic nosecones lately and love them.

View attachment 671176

View attachment 671177

View attachment 671178

How does this give more room in the payload bay? That was the Op's question.

 

[RokitFlyr]

The answer varies wildly with a couple variables: What is the diameter of the shock cord (nylon shock cords come in a lot of different sizes) and what is the brand of parachute?

On the "big" end of the equation, it would be tight if you are trying to shove a 1" wide nylon shock cord along with a bulky parachute like the ones from LOC or other lower Cd manufacturers.

On the other side of the equation, if you are use thin Kevlar shocks cords with very high performance compact chutes like Fruity Chutes Iris chutes, you will have all kinds of room to spare.

Best way to figure it out is shove what you have in the tube and see how much room it takes up, then cut to that length.

For the nosecone, I would cut the entire beveled section off and get a bulkhead forward of the nosecone shoulder. John Coker has some great suggestions in this video:

Exactly.

 

[Ronz Rocketz]

Forgive me, how is this dual deploy? Is there a single charge or two?

FYI, a J270W is 356mm long. In Freedom Units, that’s 14in which gives me just enough space in my LOC Patriot for the laundry and shoulder, barely. Haven’t blown through the Nomex yet.

I’m planning to convert it to dual deploy with an Eggtimer Quantum using the LOC payload bay.

 

[cerving]

How does this give more room in the payload bay? That was the Op's question.

It works if you have a FG nose cone with a separate glue-in coupler/shoulder. The suggestion is to put a bulkplate ahead of the coupler, so you have the entire volume of the shoulder for the chute. That's typically about 1C.

This doesn't really work with a plastic nose cone, though... unless you glue the bulkplate in as far forward as you can get it to go, inside the molded shoulder. You need a really good epoxy fillet to keep it from pulling out, and if the nose cone is polyethylene (like the LOC nose cones), they do not glue well.

 

[Titan II]

I just epoxy a length of Kevlar shock cord to the inside of the cone. Same concept as attaching a shock cord to a motor mount. I have done this on several rockets. Simple, strong, light, and takes up negligible space.

 

[mtnmanak]

How does this give more room in the payload bay? That was the Op's question.

Should have been more clear - I was commenting on the nosecone work mentioned in post #5 - separate from the discussion about determining the length of the payload bay.

 

[RokitFlyr]

As with most posts, answers to questions not asked.

 

[DeltaVee]

Good stuff to consider here. My biggest concern was what could be considered the minimum length of payload bay for 4 inch diameter in a dual deploy situation. I don't think this project would warrant anything wider than 3/8" tubular nylon, perhaps around 20 feet or so. The nose cone is polystyrene, and the forward plate and hardware are already epoxied into place. Along with the epoxy fillets on the forward plate, Ive built up (using sheet polystyrene + plastruct) several tabs to help retain the forward bulkhead. I'm sort of committed to this as it stands

 

[mtnmanak]

As with most posts, answers to questions not asked.

It is a forum, some of the point is to have an open discussion and see where it leads us

 

[RokitFlyr]

Well, we might as well start talking about glue/epoxy.

 

[mtnmanak]

Every thread is a glue thread. This is known.

 

[Capt. Eric]

How does this give more room in the payload bay? That was the Op's question.

You could then leave the fwd end of the mid-body ebay, which no longer has any "e" in it, open and have another 7.5" of space.

 

[SolarYellow]

Good stuff to consider here. My biggest concern was what could be considered the minimum length of payload bay for 4 inch diameter in a dual deploy situation. I don't think this project would warrant anything wider than 3/8" tubular nylon, perhaps around 20 feet or so. The nose cone is polystyrene, and the forward plate and hardware are already epoxied into place. Along with the epoxy fillets on the forward plate, Ive built up (using sheet polystyrene + plastruct) several tabs to help retain the forward bulkhead. I'm sort of committed to this as it stands

Since it's polystyrene, you could have cut out the wedge and replaced it with sheet polystyrene formed to match the curve of the shoulder. Then you could have the full shoulder for its full length. I've done that on a few Estes nose cones. There's a how-to (at least one) on a Doorknob or Big Daddy thread around here somewhere. Then you could use the bulkplate you've epoxied in as the anchor and used the shoulder for payload bay volume.

 

[SolarYellow]

You could then leave the fwd end of the mid-body ebay, which no longer has any "e" in it, open and have another 7.5" of space.

Even as it is, it's unlikely the electronics in the ebay are going to need the full 8 inches of length. Could always inset the upper bulkhead a few inches to gain more payload.

 

[DeltaVee]

Since it's polystyrene, you could have cut out the wedge and replaced it with sheet polystyrene formed to match the curve of the shoulder. Then you could have the full shoulder for its full length. I've done that on a few Estes nose cones. There's a how-to (at least one) on a Doorknob or Big Daddy thread around here somewhere. Then you could use the bulkplate you've epoxied in as the anchor and used the shoulder for payload bay volume.

Had to do that on my Estes Sahara... I'll admit if I didn't have access to a laser cutter to cut funny shaped bulkheads, I probably would have gone that route. Getting things just right on the Sahara was a bit of a pain as well... In terms of issues I'd call at sixes. Next time I will probably do exactly what you are talking about... Because it's certainly easier to align additional reinforcing all thread with full circular symmetry