Dual-Deploy Chute Placement

[Heisenberg]

For a typical dual-deployment design where the avionics bay separates the rocket into a aft booster section and a forward payload section, it seems that the majority place the main chute in the payload section. What are the disadvantages in reversing that putting the chute in the booster section and the drogue in the payload section? I'm working on my first dual-deploy and it appears I may have a space issue in my payload section.

 

[WillMarchant]

I'd worry that the apogee event would end up separating the lower section as well and your mains would come out shortly after apogee.

 

[Handeman]

What Will mentions is a definate possiblility. The other consideration is that if you put the drogue on the payload, when it deployes, the full weight of the fincan will be pulling at the main body seperation point. You would probably have to use sheer pins with the main deployment.

On the other hand, popping only the nose cone with the drogue could result in a much more easily controlled decent

 

[Pantherjon]

How much of a 'space issue' is it? What diameter tube, length, etc? A parachute CAN be packed that will not take up a whole bunch of space..In my 3" Thor the payload tube has only like 10" of space(3" in diameter and 10" length after coupler and nosecone shoulder space) and I use a 48" main. It fits with some wiggle room..I could probably get a 60" in there if I tried..And the 48" chute is nylon..If I used my 48" silk chute there would be TONS of room- so that is another consideration- what size chute and material the chute is made of?

 

[Heisenberg]

Hey thanks for the replies. It looks like I will have about 4 inches between the Nose cone and the avionics bay. Its a 4 inch airframe. I'm still building the rocket so its not a big deal if I need to modify if I have to. I estimate it will weigh between 5.5 to 6 lbs when complete so I'm looking at a 42 to 48 inch chute.

 

[Pantherjon]

Hey thanks for the replies. It looks like I will have about 4 inches between the Nose cone and the avionics bay. Its a 4 inch airframe. I'm still building the rocket so its not a big deal if I need to modify if I have to. I estimate it will weigh between 5.5 to 6 lbs when complete so I'm looking at a 42 to 48 inch chute.

That is a bit tight, but doable, I believe, if the chute is folded right..What material is the chute, nylon or silk? And how long and what type shock cord will you be using?

 

[blackjack2564]

Cut the bottom of the nose cone off, and glue a bulkplate with a eyebolt pre-installed up in the top of shoulder of the NC. That should gain you another 3 1/2 to 4 1/2 inches. Plus the other 4in. in the payload = problem solved!

I did this on a few of mine. Easy way out. If you really want to gain some room, Forgo the Bulk Plate and just epoxy the shockcord to the side or tip of NC.

 

[Heisenberg]

The chute is 1.1 oz ripstop nylon, with about 3 feet of 5/8 inch tubular shock cord. I like the idea of cutting the bottom of the nose cone out. That would gain me an additional 4 inches.

 

[als57]

The chute is 1.1 oz ripstop nylon, with about 3 feet of 5/8 inch tubular shock cord. I like the idea of cutting the bottom of the nose cone out. That would gain me an additional 4 inches.

3 feet of shock cord seems rather short. Perhaps I missed something?:confused2:

Al

 

[MaxQ]

I like the idea of cutting the bottom of the nose cone out. That would gain me an additional 4 inches.

I've done that myself on several projects - but I had a problem getting a secure, permanent attachment between the glued - in bulkplate and the blow molded plastic nose cone shoulder (if that is indeed what the nose cone is made of).
Even scoring the inside of the nose cone shoulder didn't quite give a secure base for the epoxy..and there can be some sudden stress on that joint...
I didn't want the recovery harness pulling the bulkplate out of the nose cone.

I elected to bolt in some small L brackets on one project, and a threaded rod through the nose cone shoulder with flush mounted nuts and washers on each end - on another...just for an extra margin of security.

Three feet of shock cord does seem short to me as well.....

 

[Heisenberg]

Ok that raises another question. Most photos I see of a typical dual deploy rocket with the avionoics bay in the middle show a much shorter shock cord between the parachute and the avionics than what is used between the avionics and the booster. I've seen the rule of thumb of a shock cord being 3 to 5 times the length of the rocket which I assume pertains to the booster section. What's the rule of thumb for the payload section? Is it the same?

 

[blackjack2564]

What length is this rocket? There is another simple alternative to this scenario if you are still building.........simply use a longer payload section of tube.
THAT would be the easiest way around all this.

To the point...... around 10-15 ft should do it for this.

Got any pics or kit specs?

 

[Heisenberg]

The overall length of the rocket will be about 58 inches. The photo shows the avionics bay and nose cone in the foreground and the black payload section in the background. The space between is about what would be left for a chute in the present configuration - about 4 inches. At this point I'm leaning towards a longer payload section. I'll have to carbon it but that shouldnt be a big deal. I'm thinking what, another 4 inches?

 

[WillMarchant]

You could take some of the aft end of that nosecone off and put in a bulkhead. That would gain you an inch or two...

 

[ben_ullman]

The overall length of the rocket will be about 58 inches. The photo shows the avionics bay and nose cone in the foreground and the black payload section in the background. The space between is about what would be left for a chute in the present configuration - about 4 inches. At this point I'm leaning towards a longer payload section. I'll have to carbon it but that shouldnt be a big deal. I'm thinking what, another 4 inches?

I see your in VA. Where abouts are you? If I was doing that nosecone I could get another 4" out of it. The blowmolded NC's have a lip on the inside if you pull the bottom off. I foam the nosecones and as its expanding pop the bulkhead in and the foam pressure pushes it against the lip. I then put a thin layer of epoxy on there just to make it look nice and for easy cleanup.

Ben

 

[Heisenberg]

I'm halfway between Williamsburg and Richmond. What type of foam are you using?

 

[MaxQ]

I see your in VA. Where abouts are you? If I was doing that nosecone I could get another 4" out of it. The blowmolded NC's have a lip on the inside if you pull the bottom off. I foam the nosecones and as its expanding pop the bulkhead in and the foam pressure pushes it against the lip. I then put a thin layer of epoxy on there just to make it look nice and for easy cleanup.

Ben

<I foam the nosecones and as its expanding "pop" the bulkhead in>

If the lip holds it in, I guess you have to deform just enough to pop it in...?

Any chance it could "pop" out ,....the same way it pops in?

 

[ben_ullman]

<I foam the nosecones and as its expanding "pop" the bulkhead in>

If the lip holds it in, I guess you have to deform just enough to pop it in...?

Any chance it could "pop" out ,....the same way it pops in?

I have to slide it in sideways and then flip it flat. It would be tuff to pop out with the epoxy in there to help, more or less, seal the edge

Ben

 

[Handeman]

I like the way Ben is doing the nose cone. I just don't see the plastic nose cone coming off from the bulkhead. All the weight (bulkhead, bolt, etc.) is attached to the shock cord. It's just the plastic shell of the nose cone that the epoxy has to hold in place. I'd bet the way Ben does his, he doesn't really even need the epoxy.

 

[ben_ullman]

I like the way Ben is doing the nose cone. I just don't see the plastic nose cone coming off from the bulkhead. All the weight (bulkhead, bolt, etc.) is attached to the shock cord. It's just the plastic shell of the nose cone that the epoxy has to hold in place. I'd bet the way Ben does his, he doesn't really even need the epoxy.

I really don't need it. My dad and I do it just cause it looks cool . Seals the wood and we color our epoxy Plus the foam being "pressurized" with the bulkhead It makes the nosecone stiffer and they actually bounce.

Ben

 

[MaxQ]

I like the way Ben is doing the nose cone. I just don't see the plastic nose cone coming off from the bulkhead. All the weight (bulkhead, bolt, etc.) is attached to the shock cord. It's just the plastic shell of the nose cone that the epoxy has to hold in place. I'd bet the way Ben does his, he doesn't really even need the epoxy.

<"I just don't see the plastic nose cone coming off from the bulkhead>'

Yeah...

until the first time it does.

 

[ben_ullman]

<"I just don't see the plastic nose cone coming off from the bulkhead>'

Yeah...

until the first time it does.

Ive never had one. But Ive only flown them this way 10-15 times. Im not saying it can't but the chances aren't as likely.

Ben

 

[MaxQ]

Ive never had one. But Ive only flown them this way 10-15 times. Im not saying it can't but the chances aren't as likely.

Ben

How big a proect have you done this method?
I can see it on something like a smaller diameter Loc kit...

I don't trust epoxy alone on a load bearing part, especially as the parts get bigger...the load increases likewise.

Many years ago...I had an epoxied bulkhead and eyebolt let go off of a zipperless design plastic boatail...made from a nose cone...
Afterwards I modified the design with small 'L" brackets and screws and it has held ever since (that dual vectored cluster motor Green Weenie design that had two outboards inset in a central 38mm plastic tail cone).

If you slide the BH in sideways it is still the same diameter, just less of it to push through at one time....you don't have to deform the shoulder of the nose cone as much...

I'd be cautious of seating a wide diameter BH against a small rib or lip of plastic that can deform the same way as when you slid it in the first time...

 

[MaxQ]

I'm halfway between Williamsburg and Richmond. What type of foam are you using?

I didn't see where anyone answered your question about two part expanding foam.

Make sure you don't buy the kind that needs a lot of air to cure...(there won't be a lot of it in confined spaces...)

PML and Giant Leap have a brand that may work for you...

https://blastzone.com/pml/images/AdjustableDensityFoamUsageGuide.pdf

https://www.giantleaprocketry.com/products_composites.asp#megafoam

 

[MaxQ]

I like the way Ben is doing the nose cone. I just don't see the plastic nose cone coming off from the bulkhead. All the weight (bulkhead, bolt, etc.) is attached to the shock cord. It's just the plastic shell of the nose cone that the epoxy has to hold in place. I'd bet the way Ben does his, he doesn't really even need the epoxy.

The weight of the rocket ...is attached to the shock cord...
...and the shock cord is attached to eyebolt which is attached to the bulkhead ........which is sitting in shoulder of the nose cone...correct?



Asides from structural concerns......another thing to consider...there may be a diminishing return in putting more parchute volume inside the nose cone itself.

I've seen parachutes fail to open because part of it was still partially bunched up and held inside a nose cone while the rocket fell to earth.
The more room you try and gain by packing more of the parachute inside the nose cone the more likely it is to happen.


Where is the parachute to be attached exactly?

This could make a differece...

 

[blackjack2564]

"THE FINAL SOLUTION" ......pun intended. Now I see what your up against. Simplest, foolproof...it ain't coming out bulkhead....

This is how I put them in. Bear in mind these pics show the NC foamed and carved out for a tracker and the tubes for the antenna. So just ignore that part.

Cut off bottom of NC . Fit some allthread to length needed to go through BP down into NC tip.

AS seen in the photo.. on the tip end of the allthread nut, washer, nut, .....when placed into position, foam poured in, held centered by the BP. No way in Hades when this foam cures, can you pull it out!.

You will gain your 4in. have space under the BP to carve the foam for a tracker if you so desire and have a removable BP to boot!

I used 2-part foam from Wildman [Pro LIne] I think it was 12.00 but PML and GL also have the equivalent products.

WARNING>>>>> when using this foam it can get rather hot....so I always place my NC in a water or ice container to prop it up and keep it from distorting.

Final shot shows how the rod is centered and the eyebolt is offset. Of course yours would be recessed 4 in. into the shoulder.. As you can see this is definitely positive retention.
This foam is an adhesive, We have used it solely by itself to hold fins on rockets. MY Gizmo, flown on K=805 and CTI dual thrust 6grain xl motors no problem!

 

[hardinlw]

I see your in VA. Where abouts are you? If I was doing that nosecone I could get another 4" out of it. The blowmolded NC's have a lip on the inside if you pull the bottom off. I foam the nosecones and as its expanding pop the bulkhead in and the foam pressure pushes it against the lip. I then put a thin layer of epoxy on there just to make it look nice and for easy cleanup.

Ben

If you want a bit more insurance, cut a section of coupler to length and cut a strip out of the side so it fits inside the NC shoulder. That gives a lot of glue surface and it's all in shear, so there is virtually no way it's going to strip out.