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Bat-mite

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Okay, here's my story.

It's three weeks (exactly) till launch.

I have been working on a Rocketry Warehouse (now MadCow) Formula 200 since July. Yes, July. It is my first very large FG build.

I have everything ready for ground testing, except that I discovered I do not have enough room in the payload tube for my main and harnesses. They need to be crammed together in what appears to be an unsafe way, and it requires two people. Not good.

I built my nose cone glue-free, using a stepped bulk plate attached to the bottom of the coupler by the threaded rod from the aluminum tip, tightened with a nylon-insert nut.

It was (wisely) suggested to me to get a new internal bulk plate (which I did) and recess it into the coupler a few more inches.

Here is where I screwed up. I made up a rich mixture of RocketPoxy and chopped carbon fiber, and smeared the inside of the coupler, and slid the bulk plate in.

The epoxy mix was so thick that I assumed I could invert the nose cone and let the fillet form naturally on the inside.

When I checked it hours later, the bulk plate had slid down, turned at an angle, and epoxy was all over the inside of the coupler and the back of the bulk plate.

I looked at this and said, "No problem. I just need to remove the coupler, use the original stepped bulk plate, attach it to the top of the coupler with epoxy, and put the coupler back in. THIS IS WHAT I SHOULD HAVE DONE IN THE FIRST PLACE. Live and learn.

But (if you followed my other thread), I could not get the coupler out. There is no real place to grip anything. Tapping was a failure. Liquid Wrench sprayed into the joint didn't help. Freezing didn't help. That sucker is in there to stay.

So, I guess I am back to needing to insert the internal bulk plate into the coupler. I ground off most of the epoxy from the bulk plate, and it will slide in, but it won't go very deep because of all the gook of epoxy all over the inside of the coupler.

What would you do?

  • Give up?
  • Get a power sander and grind out the inside of the coupler?
  • Find a way to get the coupler out (seems impossible) and use the stepped bulk plate at the top?
  • Take the easy route, slide the bulk plate in as far as it will go (maybe two inches), apply an external fillet and hope it holds?
  • Something else?
LDRS is three weeks away and I haven't ground tested yet. The clock is ticking and I am super-stressed over this. All ideas (and prayers) are welcome!
 

blackbrandt

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If you want to make sure the coupler stays in, you could always just drill 3 holes and tap them for, say, 4x6-32 screws. Then glue your bulkplate in.

Maybe after a few good ejection charge tests it might loosen up some. ;)
 

mikec

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I have everything ready for ground testing, except that I discovered I do not have enough room in the payload tube for my main and harnesses.
Maybe revisit this conclusion, or use a more compact chute/harness or different packing technique? That would allow you to use the original glue-free scheme on the NC.
 

Exactimator

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1. Throw your rocket parts into the street and yell "ROCKETRY'S CANCELLED!"
2. Seeth about it for an hour or two.
3. Change your mind.
4. Go out and retrieve the rocket parts form the street.
5...

I'd get a power sander and sand off as much of the epoxy inside the coupler as I could. Really be patient and try to get down to the bare fiberglass without sanding too much of the FG itself. If you get enough epoxy off the inside, it may actually become flexible enough you could release it from the nose cone. Or maybe if you sand enough epoxy off the forward edge of the coupler, you get the epoxy that's holding the parts together and they'll separate. If you do, all the better. If not, keep sanding the inside of the coupler and maybe the outside edge of the internal bulkplate to get it closer to the forward end of the coupler.

Check the fit of the recovery laundry. If it fits, use a longer allthread lengh to screw into the metal tip, come back through the center hole of the internal bulkplate and fasten with nuts. Sandwich the bulkplate between nuts if you need to. Then either add U-bolts for the harness or a female eyebolt.

m9RljcL7cXAxVJx10LvKbcg.jpg

The biggest issue will be the time and patience it takes to sand all the epoxy off the inside of the coupler. You may not be done by LDRS, but there will be other launches.
 

mikec

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The biggest issue will be the time and patience it takes to sand all the epoxy off the inside of the coupler.
I've had some success with removing epoxy with a small chisel, though I've usually done this with broken fillets and such, not inside a coupler.
 

Exactimator

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I've had some success with removing epoxy with a small chisel, though I've usually done this with broken fillets and such, not inside a coupler.
Good point.

John, maybe if you're lucky you didn't wash and sand the coupler thoroughly enough and the epoxy didn't completely bond everywhere. Maybe you can snap some chunks out and speed up the process.
 

mikec

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You could also get a couple of inches back, probably, by cutting off some of the bottom of the coupler. You really don't need a full diameter of coupler length at either the NC or avbay end. For that matter you could cut off some of the front of your avbay as well.
 

G_T

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I'd revisit the packing technique. Details of what you have for available volume, and what you are trying to put in there, would help. Details on how you are packing would help. One of my rockets for instance has a 54" spherachute in taco with blanket plus small blanket over ejection charge packed into a 54mm tube about 8" long. It's all about how you do it. I prefer the volume filled situations. Things don't shift.

Most people pack chutes somewhere between incorrectly and poorly - the criterion being that the chute must open reliably, consistently, predictably, every time. No exceptions. Treat it as if a person were attached to the chute - as if a life depends on it. And in reality, that may be true. A rocket that comes in hard because of a poor packing job could kill someone. The up part is optional; the down part is not.

I recommend reading/studying up on rigging chutes. There is plenty of info out there in documents, books, and youtube videos, showing how professional riggers do the job. Their methods are based on lessons learned, lessons where people died. It is worth paying attention to what they do, and why, before deciding to do something else.

The often taught technique of wrapping the shroud lines around the chute is a classic example of a common but very bad practice. For some reason people are taught this for model rocketry and then they proceed to use the same method for high power rocketry. It is one of the worst methods of packing one can use. It is unreliable, unpredictable, and has known failure modes.

https://www.rocketryforum.com/showthread.php?37382-Sprite-6-quot-and-a-baby-O/page4 starting with the second post on this page (post 92). This is an example of packing for one of my rockets. I am NOT saying this is how your rocket should be packed; it was specific for this one rocket which had an unusual chute arrangement with three chutes - a single drogue but essentially two mains for separated recovery, all from the same compartment, two from the same d-bag. What I want to indicate here though is consistency matters. Study what the professional chute riggers have done, and then see how to apply it to rocketry.

Gerald

PS - Pictures, please!
 
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patelldp

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You could also try a epoxying the internal bulkhead into the base of the coupler with a fillet and then hitting the bulkhead from tip end with a dead blow hammer and a long dowel. Get the coupler out, fillet the other side of the bulkhead, flip the coupler so the bulkhead is at the fore end, and epoxy into the cone.
 

RocketFeller

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If you have to remove the epoxy with a dremel tool, the flapper wheels work well for that sort of thing.
 

NateLowrie

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I'd revisit the packing technique. Details of what you have for available volume, and what you are trying to put in there, would help. Details on how you are packing would help. One of my rockets for instance has a 54" spherachute in taco with blanket plus small blanket over ejection charge packed into a 54mm tube about 8" long. It's all about how you do it. I prefer the volume filled situations. Things don't shift.

Most people pack chutes somewhere between incorrectly and poorly - the criterion being that the chute must open reliably, consistently, predictably, every time. No exceptions. Treat it as if a person were attached to the chute - as if a life depends on it. And in reality, that may be true. A rocket that comes in hard because of a poor packing job could kill someone. The up part is optional; the down part is not.

I recommend reading/studying up on rigging chutes. There is plenty of info out there in documents, books, and youtube videos, showing how professional riggers do the job. Their methods are based on lessons learned, lessons where people died. It is worth paying attention to what they do, and why, before deciding to do something else.

The often taught technique of wrapping the shroud lines around the chute is a classic example of a common but very bad practice. For some reason people are taught this for model rocketry and then they proceed to use the same method for high power rocketry. It is one of the worst methods of packing one can use. It is unreliable, unpredictable, and has known failure modes.

https://www.rocketryforum.com/showthread.php?37382-Sprite-6-quot-and-a-baby-O/page4 starting with the second post on this page (post 92). This is an example of packing for one of my rockets. I am NOT saying this is how your rocket should be packed; it was specific for this one rocket which had an unusual chute arrangement with three chutes - a single drogue but essentially two mains for separated recovery, all from the same compartment, two from the same d-bag. What I want to indicate here though is consistency matters. Study what the professional chute riggers have done, and then see how to apply it to rocketry.

Gerald

PS - Pictures, please!
I know from the other thread he's using a 5.5 x 10in dbag from fruity chutes for the 15' surplus milatary main chute. Part of the problem is the amount of space in the tube is tight. The Payload tube is 26in but you have 7in lost to the coupler (madcow has switched to a 12in coupler but the originals are 16in), an inch or 2 to charge well/eybolts/avionics bulkhead and 6in with the nosecone shoulder which leaves you with roughing 11-12in all said and done. I believe him when he says it's tight because I had to move my bulkhead back in the nosecone to accommodate both the main and drogue.

John, some pictures of the issue would really be helpful.
 

Bat-mite

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I'll try to get some pics up. Been too busy working on it and not photographing it. No smart phone, so I have to shoot it with my SLR, download the pics, upload the pics, yadda yadda.

My coupler, for whatever reason, is 22". Subtract half of the switchband, and that means 10" inside the payload tube. NC coupler leaves 7" inside the tube. That leaves me nine inches. Subtract charge wells and U-bolts, and I've got about 7".

As Nate wrote, my D-bag is 10", plus harness and chute protector. I need a minimum of three more inches.

I like Dan's idea, but I am afraid that if I still can't get it out, then I am totally screwed.

Gerald, thanks. I will look at your thread. My set-up is a 15" military surplus chute stuffed in a 10" X 5.5" D-bag, shroud lines slipped under the elastic on the outside. 30' tubular Kevlar harness (One Bad Hawk), and a 36" X 36" Nomex chute protector. Oh, plus a 36" pilot chute attached to the top of the D-bag.
 

mikec

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My coupler, for whatever reason, is 22". Subtract half of the switchband, and that means 10" inside the payload tube.
Cut off three inches of the coupler and you're there.

If it were me I would skip the D-bag and the pilot chute, but people who like them usually can't be reasoned with :)
 

Bat-mite

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Cut off three inches of the coupler and you're there.

If it were me I would skip the D-bag and the pilot chute, but people who like them usually can't be reasoned with :)
I have never used one before, so I don't know if I like it or not. But the chute has 18 shroud lines, and I am very concerned about tangling. I bought the military chute because it was a lot less expensive than a Rocketman. In hindsight, maybe that was a bad idea, but I was already spending a ton of my family's money on this....
 

Bat-mite

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Oh, yeah. About cutting off the coupler ... I may end up doing that, although I don't have a cut-off saw. That leaves me 4" of coupler, and with shear pins, it should be okay.

In any case, with several options that have been presented here, my confidence is restored that I can get this up at LDRS. Only thing that could really screw things up now is if it rains on the 25th, 26th, 4/2, and 4/3. Might have to take a day off work to do testing (which won't sit well with the wife).
 

NateLowrie

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Oh, yeah. About cutting off the coupler ... I may end up doing that, although I don't have a cut-off saw. That leaves me 4" of coupler, and with shear pins, it should be okay.

In any case, with several options that have been presented here, my confidence is restored that I can get this up at LDRS. Only thing that could really screw things up now is if it rains on the 25th, 26th, 4/2, and 4/3. Might have to take a day off work to do testing (which won't sit well with the wife).
Why not cut the avionics bay coupler down 3 inches so you have 7in of coupler on each side?
 

G_T

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I haven't read everything pertinent, so this question may be moot:

Have you built the nosecone yet? Put the bulkhead above the nosecone coupler. Now you've got a few more inches. You can put an electronics bay in there as well if you want. You can see details of this sort of thing in the thread I linked to as I did that for space reasons.

Another option, though costly, is to change to a toroidal chute. These have MUCH higher drag coefficient than spherical or elliptical chutes. That allows a much more compact chute to be used. I used a 96" IRIS chute for a recovery weight of around 70#, as an example. It packed into my deployment bag, along with a second chute, the shroud lines... And the bag wasn't long or tight.

You have the option of skipping the D-bag and using the bay itself as if it were a D-bag. Just add a chimney tube from the charge well to duct the hot gasses past the chute. Do NOT make it a tight seal though or you turn it into a shotgun and might do some damage to the inside of the rocket.

Gerald
 

Onebadhawk

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Oh, yeah. About cutting off the coupler ... I may end up doing that, although I don't have a cut-off saw. That leaves me 4" of coupler, and with shear pins, it should be okay.

In any case, with several options that have been presented here, my confidence is restored that I can get this up at LDRS. Only thing that could really screw things up now is if it rains on the 25th, 26th, 4/2, and 4/3. Might have to take a day off work to do testing (which won't sit well with the wife).
Don't worry about the wife John,,
we've got your back..
she's not that tough..
Don't you worry about her..
We here at TRF will take care of everything... lol..

Teddy
 
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