Fixing a cracked nosecone

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Kframe

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This past weekend I attempted L1 certification and I would have achieved it but the 3D printed nosecone cracked in two upon landing on dirt.

IMG_5778.jpeg
It was a weird break, there was no paint loss at all on either section, and it cleaved right along the grain of the filament, so it must have just been a weak spot. But really frustrating because that meant failing the cert attempt.

The printed nosecone also had an integral crossbar for attaching the shock cord, and a couple rocketeers commented that they were surprised it didn’t fail at that point and that for high power they really don’t prefer 3D printed cones.
So I set to repairing AND strengthening the cone so I can attempt L1 again next month.
I first cut off the crossbar, which also gave me better access to the interior for repairs.
IMG_5838.jpeg

Next, and I don’t have pics because my hands got messy, I mixed up some JB Quick and coated the inside or the broken off tip - and then laid in a ‘collar’ of fiberglass cloth that extended above the break about an inch all around.

As that set up I quickly whipped up more JB Quick and dropped a glob down into the cone onto the flat of the epoxy’d BBs , and smeared another big glob onto the nuts of a U-bolt, which I then stuck in, completely covering the nuts with a quarter inch of JB.

I gave that a minute to start setting and then with CA gel I glued the two cone pieces back together.
Then I spread more JB down inside the larger piece, pressed the collar of fiberglass around the walls of it and then spread a copious amount of JB completely over the fiberglass and then around the walls of the cone all the way to the mouth.
This is what it was like:
IMG_5837.jpeg
The BB’s were preexisting from the original building.
Here you can see the JB on the walls and the U-bolt at the bottom (top?)
IMG_5833.jpeg

After the JB fully set I sanded with 120, 220 and 400 until the fault line could not be felt.
IMG_5821.jpeg

After some primer, wet sanding to 800 and then color the damage is invisible!
IMG_5830.jpeg
In a few days I’ll shoot it with some clear and it will be good to go for round two!
 
So... you didn't get your L1 cert... because the nose cone broke? For real? Is that a thing?
Yep. It has to be able to be repacked, reloaded and relaunched without anything but “minor” repair.
I’m told there is a little wiggle room for something like a half inch zipper but if a part actually breaks off or breaks apart it’s a no.
And sure it was disappointing, but I get it and I also know now that that is one more thing I need to make doubly sure is strong enough for high power.
It’s all part of the learning process.
 
Yep. It has to be able to be repacked, reloaded and relaunched without anything but “minor” repair.
I’m told there is a little wiggle room for something like a half inch zipper but if a part actually breaks off or breaks apart it’s a no.
And sure it was disappointing, but I get it and I also know now that that is one more thing I need to make doubly sure is strong enough for high power.
It’s all part of the learning process.
Additive manufactured NCs are not something I'm up to speed with, but I'm curious to hear your intentions for the next one? Supporting ribs? Thicker wall? Switch to commercial blow molded?

TP
 
Additive manufactured NCs are not something I'm up to speed with, but I'm curious to hear your intentions for the next one? Supporting ribs? Thicker wall? Switch to commercial blow molded?

TP
The JB-impregnated fiberglass spanning the fault and the JB quick weld smeared throughout will more than adequately strengthen the cone. And having the shock cord attach to the u-bolt way down in the nosecone will prevent any tension on the 3D filament upon ejection.
 

Additive manufactured NCs are not something I'm up to speed with, but I'm curious to hear your intentions for the next one? Supporting ribs? Thicker wall? Switch to commercial blow molded?

TP
Oh, I should mention, I didn’t print this nosecone, I bought it from a pretty well known rocketry supply house.
 
So... you didn't get your L1 cert... because the nose cone broke? For real? Is that a thing?
Yes, L1 certification is intended to test whether you can build and fly a rocket capable of withstanding the stresses of a flight.
If your rocket breaks during your certification attempt, either during the flight or upon landing, it’s a failure. It’s described pretty clearly in the certification procedures for both organizations.
Slight damage that doesn’t affect the ability to fly your rocket are allowed, like minor zippers or chipped fins.
 
Yes, L1 certification is intended to test whether you can build and fly a rocket capable of withstanding the stresses of a flight.
If your rocket breaks during your certification attempt, either during the flight or upon landing, it’s a failure. It’s described pretty clearly in the certification procedures for both organizations.
Slight damage that doesn’t affect the ability to fly your rocket are allowed, like minor zippers or chipped fins.
Who makes the call?
 
You went a step further than I would have. I would have glued it back with 2 part plastic bonding epoxy. If it breaks, it won't break there.

Nice job on the repair. If it breaks next time, it will be above or below the fiberglass.
 
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