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Steven88

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Good evening. Today I ground tested my Big Nuke again. The drogue area I extend by 16” from the stock kit. It is a 5.38” diameter rocket. I now have 28.25” of usable space in the drogue area. After putting my blanket, drogue chute and a little dog barf in for good measure there was plenty of empty space left over. I watched it pop on 3.3 grams. That came to about 10 psi. It threw the av bay and main 9 feet which I thought was plenty especially for how heavy it is.

Then on the main test, I used 1.62 grams in 14.5” of usable space. It was about 9.5 psi. By the time I inserted a little dog barf, the deploy bag, 9’ Rocketman chute and shock cord there was NO extra space. It was even a little compressed. The 1.62 of powder didn’t even pop the nose cone! I had used three 2-56 sheer pins to hold it on. I learned something. It must actually take more psi to pop a full tube than one with lots of empty space, seems backwards unless it was actually the compression that caused more friction that got me?
 

Steven88

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I will ground test again and up the powder on the main by 20% I think
 

Steven88

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Yes there were. I’d send the video but it it says it’s too large to upload onto this forum. I’m sure there’s a way to do it
 

Steven88

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Sure! It’s just a video of the actual ground test. You can here the pop but nothing happens. I’ll send it if you like and you supply me your address
 

crossfire

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Good evening. Today I ground tested my Big Nuke again. The drogue area I extend by 16” from the stock kit. It is a 5.38” diameter rocket. I now have 28.25” of usable space in the drogue area. After putting my blanket, drogue chute and a little dog barf in for good measure there was plenty of empty space left over. I watched it pop on 3.3 grams. That came to about 10 psi. It threw the av bay and main 9 feet which I thought was plenty especially for how heavy it is.

Then on the main test, I used 1.62 grams in 14.5” of usable space. It was about 9.5 psi. By the time I inserted a little dog barf, the deploy bag, 9’ Rocketman chute and shock cord there was NO extra space. It was even a little compressed. The 1.62 of powder didn’t even pop the nose cone! I had used three 2-56 sheer pins to hold it on. I learned something. It must actually take more psi to pop a full tube than one with lots of empty space, seems backwards unless it was actually the compression that caused more friction that got me?
Do you have a nice snug fit on the coupler?
 

Steven88

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Yes, I am using charge wells. Seems
like a nice tight fit on the avbay. The NC may be a little loose? Need to check it again... The problem I am running into is the max recommend lbs of force is 300 for this size of tube and that is only 2.24 grams of powder. 1.9 grams of powder ejects my 8’ Rocketman chute and deployment back beautiful about 20’. Now with the added 16” section on the drogue and 75mm motor casing I’ve added enough weight that I need a 9’ chute. Therefore, I purchase a 9’ Rocketman chute and deploy bag for the main and now it doesn’t eject the same as the 8’ setup. Not sure why I’m gettin inconsistent results?
 

Steven88

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I did not put sheer plates on the actual NC, just drilled and threaded those holes. The main tube has sheer plates though. Seems like that should be sufficient.
 

Banzai88

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I did not put sheer plates on the actual NC, just drilled and threaded those holes. The main tube has sheer plates though. Seems like that should be sufficient.
All depends on the quality of the fit where the holes/pins actually are.
Do the pins shear cleanly?
Are both sets of holes round and solid?
 

Steven88

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I’ll take a closer look when I’m home around rocket and update you.
 

Steven88

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Yes, the NC is very loose. The NC and tube are stock. Not sure why I don’t have a better fit? Do you recommend using masking tape around the NC or is there a better alternative on a large bird like this?
 

Steven88

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Adding masking tape to NC won’t allow the NC and sheer plates inside tube to suck up to each other and the sheer pins won’t sheer as easily then 🤔
Maybe I should glue sheer plates to outside of NC shoulder as well?
 

Steven88

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I’m think about adding thin brass shim-stock (see above messages to explain what’s going on) to the NC shoulder. Not recess it, just glue it to the outside surface and then wrap masking tape below and above it on the NC shoulder about the same height and try that. What do you think of that idea?
 

SDramstad

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Yes, I am using charge wells. Seems
like a nice tight fit on the avbay. The NC may be a little loose? Need to check it again... The problem I am running into is the max recommend lbs of force is 300 for this size of tube and that is only 2.24 grams of powder. 1.9 grams of powder ejects my 8’ Rocketman chute and deployment back beautiful about 20’. Now with the added 16” section on the drogue and 75mm motor casing I’ve added enough weight that I need a 9’ chute. Therefore, I purchase a 9’ Rocketman chute and deploy bag for the main and now it doesn’t eject the same as the 8’ setup. Not sure why I’m gettin inconsistent results?
How are you packing your black powder in place and where are you placing the e-match? I always pour in the blackpowder first. Place the tip of the ematch just a little ways into the powder. Pack in dog barf as tightly as possible and take strips of duct tape in an X across the top of the charge well and down the sides. then wrap the charge well with tape and twist it closed at the end of the charge well. If the powder isnt confined it wont burn properly and worse yet, if you put the e-match at the bottom of the charge well it will blow unburned powder out and up to 3/4 of the powder wont burn. It can turn a 1 gram charge into a 1/4 gram charge....
 

Steven88

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That’s a lot the same way I’ve been doing it. I put the ematch all the way in though and then pour in the black powder so that’s maybe something I could watch there. Then I stuff Estes wadding in and place masking tape over it criss cross.
 

Steven88

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Well after pacing three rounds of masking tape around the NC shoulder I have a much tighter fit. Wonder how it would ground test now...?
 

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David Schwantz

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Steven, I like to put blind nuts on the inside of the NC shoulder. This is for the shear pins to screw into. Makes them very easy to remove after the flight. Also holds them secure so that they will shear easy.
 

Steven88

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Thought I’d share how I modified the NC for this rocket to take nose weight and also have a more substantial shock cord anchor. There is a nut epoxied to the back side of the washer and than the washer and nut are epoxied and screwed to the base of the NC. As far as the blind nuts, I suppose you cut the bottom of the NC off and then install the blind nuts and epoxy a bulk head in place on your nose cones?
 

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David Schwantz

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yes, I have done it that way. But you can also epoxy the blind nuts onto the inside of the NC and then use a thin ply plate over them. Your way looks like it should work well also.
 
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