Zipperless booster and future DD setup

[slogfilet]

My wife got me a LOC Vulcanite for xmas... bless her! Stats: 2.26" OD, 53.3" long, 38mm motor mount, and about 23oz in stock form.

I was thinking of trying some new techniques on this rocket that will also help future-proof it.

1. Zipperless booster - I was thinking of making the booster section long enough to accomodate a 38/720 motor (which would be waaaay out there anyway) and making it zipperless. That would make inspecting/replacing the shock cord much easier, and it just seems "neater" than the LOC-style cord mount. The zipperless design would also allow for motor ejection, so approx. 5 1/4" holes would be drilled in the bulkplate.

2. Avbay for future DD - I would like to build an avbay into the couple between the payload section on booster. The avbay would be empty for the time being, until an altimeter is procured. I'd be 100% motor ejection until then.

Here's my question:

I was thinking of attaching the avbay to the fore and aft sections of the BT with screws, and friction fitting the nosecone and the booster section.

Is friction fitting sufficient, or are shear pins truly needed? Or are there better arrangements for my attachment points? If I'm using motor ejection for single deployment, where should I break at apogee (i.e., is there anything wrong with the forward section being longer than the aft section at deployment)?

Oh... and does adding an additonal break for the zipperless design significantly weaken the airframe?

Please feel free to comment or share experiences in building similar projects. I'm sure this has been covered to a great extent in other threads (I've found several), but I generally feel better "talking it out" for you fine people in case I'm about to make a huge mistake in any step. :blush: Maybe this time around I can try my hand at a build thread!

 

[n5wd]

The zipperless design would also allow for motor ejection, so approx. 5 1/4" holes would be drilled in the bulkplate.

Instead of just putting in a bulkplate with some holes in it on top of the zipperless'es coupler, consider adding another bulkplate inside the airframe, and making a baffle. There are several ways to do it... I described the method I prefer in this thread on TRF. I'm currently building my 4" Binder Samurai with the zipperless/baffle on top of the booster - just got it finished today as a matter of fact. I've flown both my TARC-task rocket (described and pictured in that thread) about 35 times, now, and my BSD Stretched 38-special 5 times with that baffle arrangement, and couldn't be happier. No wadding - no nomex blankets - no zippers - no problems.

I was thinking of attaching the avbay to the fore and aft sections of the BT with screws, and friction fitting the nosecone and the booster section. Is friction fitting sufficient, or are shear pins truly needed? Or are there better arrangements for my attachment points?

Well, while you're flying single deploy and breaking the rocket at the booster/aft avionics bay payload, you might consider using something like a removable plastic rivet to keep the nose cone attached to the upper payload/parachute airframe. Four of them evenly spaced around the circumfrence of the frame/nose cone would certainly hold it secure.

Once you decide to start going dual-deploy, you can swap in plastic rod or 2-25 nylon bolts in place of the rivets to hold the nosecone in during ascent until you're ready to pop it with the mains ejection charge.

If I'm using motor ejection for single deployment, where should I break at apogee (i.e., is there anything wrong with the forward section being longer than the aft section at deployment)?

I'd suggest you keep it simple and break it where you're going to break it during dual deploy - at the booster junction. A long tether to let the booster section land first, then the nose/payload/AVbay/aft chute combo land next.

Oh... and does adding an additonal break for the zipperless design significantly weaken the airframe?

Nope, as long as you give enough coupler for the airframe to nest upon, you're good.

 

[Handeman]

My wife got me a LOC Vulcanite for xmas... bless her! Stats: 2.26" OD, 53.3" long, 38mm motor mount, and about 23oz in stock form.

I was thinking of trying some new techniques on this rocket that will also help future-proof it.

1. Zipperless booster - I was thinking of making the booster section long enough to accomodate a 38/720 motor (which would be waaaay out there anyway) and making it zipperless. That would make inspecting/replacing the shock cord much easier, and it just seems "neater" than the LOC-style cord mount. The zipperless design would also allow for motor ejection, so approx. 5 1/4" holes would be drilled in the bulkplate.

As mentioned, a baffle is good, but I just used a CR on the top of the MMT and the top of the booster coupler. I had a 54mm MMT in a 4" rocket so I put the U bolt in that top CR. If I was doing it again, I would put two U bolts in it, opposite of each other, so I could put a harness/loop on it instead of the single off-center attachment point.

2. Avbay for future DD - I would like to build an avbay into the couple between the payload section on booster. The avbay would be empty for the time being, until an altimeter is procured. I'd be 100% motor ejection until then.

Here's my question:

I was thinking of attaching the avbay to the fore and aft sections of the BT with screws, and friction fitting the nosecone and the booster section.

Is friction fitting sufficient, or are shear pins truly needed? Or are there better arrangements for my attachment points? If I'm using motor ejection for single deployment, where should I break at apogee (i.e., is there anything wrong with the forward section being longer than the aft section at deployment)?

The tubes attached to the avbay with screws and friction fit the nose cone and booster is exactly what I did with my L2 rocket. It has worked just fine. If you are using motor ejection, you might want to use a wrap of tape on the cone/tube to hold it together.
I haven't used motor ejection on mine, dd only. With dd, I don't think the zipperless design is really needed since the altimeter controls the ejection at apogee. I am glad I did use the zipperless design because after building the booster and lower tube for the longest Aerotech 54mm case, I've gone to a longer tube so I can fit the longer Loki 54-2800 case and the L1400 motor in it.
I would definately consider a longer motor then the 38/720 when you build it, even if you don't expect to use it. The Loki 38-1200 is 24.5" so I would recommend building it to fit that. You may never use it, but when you get the L2 and have the dd installed and someone offers to loan you a tracker and a case on that perfectly windless day when the vendor has the J1000 reload on-hand, do you really want to have to pass that up because you didn't build the booster long enough?

Oh... and does adding an additonal break for the zipperless design significantly weaken the airframe?

Please feel free to comment or share experiences in building similar projects. I'm sure this has been covered to a great extent in other threads (I've found several), but I generally feel better "talking it out" for you fine people in case I'm about to make a huge mistake in any step. :blush: Maybe this time around I can try my hand at a build thread!

This actually sounds like a really great rocket to build and expand on. With the initial build and modification, if you double the weight to 46 oz, with a cd of 0.75, a Hobbyline G64W would still get you 800 ft. With 29mm and 38mm motors available, you should have lots of great flights.

 

[slogfilet]

Thanks for the feedback!

I was looking at the payload section of the Vulcanite, and it may be a bit short to house the main chute:

10" payload section minus ~ 3" for the avbay and ~2" for the nosecone shoulder leaves only 5" to pack the shock cord and 28" chute. Feel free to chime in if you've experienced otherwise, but seems like that would be a tight fit. (I'm open to rebuttal on this point!)

But 5" would probably be enough for packing some tubular Kevlar for drogueless deployment... so here's my thought:

For flying single deployment (the near future), i'll just pack the cord and chute in the aft section of the body tube. For DD flights, I can flip the tubes so that the shorter payload section is below (for the drogueless part) and the longer section is above (for the main, cord, nomex sheet, etc.)

I

 

[troj]

One problem with the "zipperless" method...

If you use motor ejection, then the ejection charge pushes the parachute deeper into the upper airframe while it's pushing the airframe off. This can cause things to get wedge in place, resulting in no recovery.

I learned that lesson on the same flight that I learned that fiberglassed phenolic will still shatter, leaving the fiberglass intact....

-Kevin