Questions after an ‘almost’ perfect Boosted Bertha launch. W/video

[jongoff09]

This weekend, my wife and I launched a Boosted Bertha for our first two-stage launch. Launched with a C6-0 in the booster and a B6-4 in the sustainer. The launch went perfectly until the parachute failed to deploy. The RSO/LCO (same person on this very small club launch) said that believed the wadding was packed too tightly to push the parachute out. The nosecone popped off, but the parachute was just hanging over the edge of the body tube needing only a tiny tug to all fall out after I picked up the rocket.

Thanks to the nosecone providing some drag and a soft grass after rain the night before, the rocket sustained no damage at all from the fall. What I did find, though, is that the sustainer’s motor mount was pushed into the rocket slightly from the blast of the booster ejection and lighting the sustainer. I had re-glued the sustainer’s motor mount after the initial build because I felt it needed it, and I thought it was super solid after that so I was incredibly surprised to find anything wrong with it.

The sustainer’s motor mount is still very tight in the body, but I’m wondering if we should go ahead and replace it? I’m also wondering now if the booster was too tight and that caused excess pressure on the sustainer motor mount? It is vented so that seems unlikely to me, but I can’t figure anything else that would be an issue. Any thoughts?

I attached video of the launch, (maybe, still learning this platform) I stopped recording after the camera lost visual shortly after booster ejection, but we could still easily see the entire flight with our eyes. There was a very slight wind that we accounted for with the angle of the rod and we got it almost perfect as the rocket went straight up. The picture is of the sustainer motor mount where you can see the ring of glue where it originally was.

 

[jongoff09]

maybe this will work for the video…

 

[rcktnut]

Was your whole MMT pushed up or just the bottom centering ring? Some glue fillets on the top centering ring and bottom one should keep it in place. A thin layer of epoxy spread on the bottom centering ring will also keep it from burning up.

 

[mh9162013]

Looks like you didn't use the right/enough glue for the engine mount. What kind of glue did you use and did you make sure there were some fillets built up on both centering rings?

 

[bjphoenix]

You can possibly add another centering ring at the bottom with new glue fillets, and you can add more glue fillets to the front centering ring through the front end of the rocket.

 

[jongoff09]

Was your whole MMT pushed up or just the bottom centering ring? Some glue fillets on the top centering ring and bottom one should keep it in place. A thin layer of epoxy spread on the bottom centering ring will also keep it from burning up.

I don’t know how to confirm if the front centering ring moved as well, but the back centering ring and the mount tube both were definitely pushed up. The end of the tube was flush with the back of the body tube before the launch and now it is pushed in a couple mm or so. I’d suspect the whole mount was pushed up as one.

Looks like you didn't use the right/enough glue for the engine mount. What kind of glue did you use and did you make sure there were some fillets built up on both centering rings?

I used wood glue per the kit instructions. If anything I over did the glue on the front centering ring. I’m not able to get a good picture of it through the body tube, but there’s plenty of build up around the front centering ring. I wasn’t as liberal with the back centering ring, I figured the front one would be more important with the direction of the forces. Seeing what happened, that may have been a bad assumption.

You can possibly add another centering ring at the bottom with new glue fillets, and you can add more glue fillets to the front centering ring through the front end of the rocket.

I like the idea adding another centering ring to the back, but will it fit around the motor retainer? It doesn’t seem like it would just looking at it. Not sure how to get to the front centering ring through the front of the rocket. It’s a Big Bertha so it isn’t a short body tube.

 

[Azamiryou]

Insert a spent engine, screw on the retainer, then use a dowel to push on the engine from the front. See what comes out.

 

[samb]

Based on your photo the aft centering ring to airframe joint failed. Probably some other motor tube joint(s) failed but hard to tell from the picture. I feel like the way forward is to remove the motor tube and centering rings and re-glue. I think @Azamiryou has the right idea of removing it from the forward end.
[edit]
I believe the failure of the joints occurred when the second stage motor lit. FYI I can't play the video.

 

[bjphoenix]

I like the idea adding another centering ring to the back, but will it fit around the motor retainer? It doesn’t seem like it would just looking at it. Not sure how to get to the front centering ring through the front of the rocket. It’s a Big Bertha so it isn’t a short body tube.

Well gluing a new centering ring to the old one and adding a fillet around the outside could still strengthen things. If there is room between the screw-on retainer and the existing centering ring you might be able to still add a big glue fillet from the new centering ring to the actual motor mount tube.

 

[Azamiryou]

I like the idea adding another centering ring to the back, but will it fit around the motor retainer?

Slit the ring, or even cut it in half and fit the two halves together.

But the standard two centering rings should be plenty strong enough. I'd just take it apart to find where the failures were, then rebuild it making sure I got good glue joints — without adding any additional rings.

 

[lakeroadster]

What I did find, though, is that the sustainer’s motor mount was pushed into the rocket slightly from the blast of the booster ejection and lighting the sustainer. I had re-glued the sustainer’s motor mount after the initial build because I felt it needed it, and I thought it was super solid after that so I was incredibly surprised to find anything wrong with it.

Motor mount wood glue fillets take a few days to actually dry. The glue is trapped in a closed space. Typically this isn't an issue since there are no loads on the mount until launch.

I discovered this on my Space Shuttle America build. I built a display stand for it and used it while building the rocket. The motor hook engages into the display stand. The motor mount actually slid up into the rocket and I didn't even notice it until a few days later.

Before (Note Location Of Motor Hook)

​

After (Again, Note Location Of Motor Hook)

I had to cut the motor hook extension lip to actually install the 29mm motor. I'll likely bolt a metal plate across the bottom for motor retention.​

​

 

[Daddyisabar]

When the nose cone pops off and the chute sticks out but doesn't deploy is what I call an ice cream deployment. Gosh darn! I hate those! Could be a number of causes. Tight wadding pack, too much wadding, sticky plastic chute (not lubed with baby powder,) tight nose cone, weak ejection charge from motor, air resistance from rocket moving too fast up or down, the list goes on!

Welcome to the wonderful world of staging issues. The fact that it staged and you got it all back is good enough for most altitude junkies.

 

[bjphoenix]

When the nose cone pops off and the chute sticks out but doesn't deploy

I've had those too. I think sometimes the ejection charges are just weak. Our launch field is usually pretty soft so a lightweight rocket with the nose popped off can sometimes land without damage.