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7.5" nosecone/bt fitment issue, help/ideas

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PokerJones

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I've come to the point in my build when I need to deal with the BT/NC fitment problem. The shoulder of the NC is much smaller than the id of the BT causing a very loose fit. My initial thoughts were 1.) build up the inside of the BT with glass/epoxy 2.) use a small section of coupler inside the BT and sand down the shoulder of the NC until it fits securely 3.) build up the shoulder of the NC with glass/epoxy. The NC has 4.5 pounds of shot/epoxy in the tip which adds to the problem, these are both LOC components.

I'm not sure which idea would work best or if there are better ideas out there. I am leaning towards the coupler idea right now although I am open to any suggestions. Thanks.

First pic is laying horizontally on a stand with me supporting the NC

20170414_093939.jpg

Second pic is laying horizontally unaided showing the large gap

20170414_093945.jpg
 

markkoelsch

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I would start with a layer or two of masking tape around the circumference to get a better feel for how much gap you need to make up. I would add layers, keeping count of the layers, until a satisfactory fit is achieved. Then we can figure out how to fix permanently.

What is the nose cone made of?
 

mccordmw

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If the nosecone shoulder is already very sturdy, there's no need to get fancy and add fiberglass. Depending on the gap, put on a wrap or two of Gorilla duct tape. It's really thick and will add diameter quickly. I like Gorilla because the adhesive is super strong. Looks like you have a ~1-2 mm gap, so just 1-2 wraps of tape should do it. Gorilla tape is 17 mil (0.43 mm), so I assume about 1 mm diameter per wrap.
 

AlphaHybrids

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Duct tape and shear pins.
While this method may be good on something that needs one or two wraps of masking tapes, this is not a good method for something this large.

Say you use a couple bands of duct tape and fly your rocket on a hot day - say 80 degrees. You've been prepping the rocket in the shade, assembly it and then wait for a couple hours to get on the pad. You sit on the pad for another half hour. In that time the duct tape will probably heat up and become pliable. When the charge goes off it could slide and bind the nosecone.

I'd follow Mark's advice and see what the gap needed to fill is. Then we can see what is needed to add and find a fix. Two years ago an IREC team I mentor created their own tube that was supposed to fit 5.5 LOC tubing. It was a bit big (~3/32") They ended up welding plastic strips vertically onto the nosecone in 12 places and then sanding those down to get a good fit.

Edward
 

mccordmw

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I shy away from electrical tape and general use duct tape. Stick with Gorilla. It's rated up to 200 F. Your rocket can bake in the sun on the launchpad without the glue letting loose.
 

AlphaHybrids

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I shy away from electrical tape and general use duct tape. Stick with Gorilla. It's rated up to 200 F. Your rocket can bake in the sun on the launchpad without the glue letting loose.
It is continuous service up to 150 F, intermittent up to 200 F. You'd be surprised how hot a rocket gets in the sun. At IREC some internal temperature sensors were reading 140-160 degrees on an enclosed rocket in the sun that had been sitting there for an hour.

Edward
 

jef955

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I agree tape is a mess. I don't like tape. I had the EXACT same problem with a LOC Doorknob. I took pieces of fiberglass about the same length as the shoulder of the nose cone, about 6" long and laid them around the interior of the body tube a section at a time with finishing epoxy, until I got the fit that I wanted. It worked absolutely perfect. It essentially is doing the same thing as tape, but it's permanent and just adds to durability. sand it out a little to smooth it out.

Basically do the same thing you did outside the tube inside a few inches at a time, plus it will help center up the fit.
 

PokerJones

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Although taping the shoulder may work, I am looking for a more permanent solution. I'm working on either glassing the inside of the BT or using a 5" section of coupler if I can get a good fit with the NC, the coupler fix would be much easier than layering glass on the inside of the BT which would have to be done in small sections. Thanks for the suggestions.
 

madmax

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I would recommend glassing the inside of the tube. Not only does it build up the diameter for a better fit it will add some strength as well. Also it will be fairly easy to glass inside the end of a tube that's 7.5". Lots of room to work. Then sand with a flap sander or similar to achieve a perfect fit.

Also as a general recommendation when using tape I would use actual metal duct tape. I use it for friction fitting motors and have had zero issues with tape removal after a flight. I went to the stuff after I used regular brown masking tape on a fairly hot research motor that not only melted the glue but sort of burned the tape to the case. It was stiff and discolored and it left a few bits on/ embedded in the case.
 

markkoelsch

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Getting to a permanent solution is the idea of the tape. The tape is an intermediate step to figure out how much space you have. Get a good fit with the tape, figure out how thick the tape is, and then figure out what to use to make up this space permanently. Once figured, remove tape and apply permanent solution.

Not really that complicated. It is a form of measurement. Measure first then figure out what to do.
 

PokerJones

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Getting to a permanent solution is the idea of the tape. The tape is an intermediate step to figure out how much space you have. Get a good fit with the tape, figure out how thick the tape is, and then figure out what to use to make up this space permanently. Once figured, remove tape and apply permanent solution.

Not really that complicated. It is a form of measurement. Measure first then figure out what to do.
I was referring to the suggestions to use Gorilla tape as a permanent solution, at least that is how I took it.

I plan on building up the shoulder with 2" painters tape to get my final measurement before I start glassing
 

PokerJones

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Thanks for the suggestions. I ended up using 3, 6" wide strips of 7.5 ounce cloth around the inside of the body tube. Very little sanding and I have a perfect fit of the nosecone.

20170425_113929.jpg

I'm off to do the ground testing starting with 2.5 grams of FFFFG. Although it is a large tube there is only 16" of open space between the MM and NC, should be about right.


Here is the business end.

20170425_114002.jpg

The 6 fin-7 motor Widow Maker, building this for Airfest.
 

blackjack2564

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I LIKE the "Widowmaker" do I see black widow spider vinyl , on fins and body?
 

PokerJones

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I LIKE the "Widowmaker" do I see black widow spider vinyl , on fins and body?
I like that idea but widow maker is just a "working name" not sure if it will stick, I also like "Monstrosity" because that's basically what this is.

I already have the vinyl body wrap from Mark for this one, purple, green and black.

unnamed (1).jpg
 

blackjack2564

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Great color combo, Mark does such fantastic work!

Gonna look super when finished:wink:
 

markkoelsch

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Glad the nosecone fit issue is fixed.

That body wrap is awesome looking.
 

AlfaBrewer

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Jeff, I was able to get great separation on Bob Wilson using 1.5g FFFFg with a similar sized compartment and 4 #2 shear pins. This is with 40oz of weight in the nose.

For the mismatch on the NC to BT, I used a few wraps of painters tape covered with clear packing tape. Mostly 'cause I'm cheap, but also 'cause I didn't want to mess with fiberglass.
 

PokerJones

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Jeff, I was able to get great separation on Bob Wilson using 1.5g FFFFg with a similar sized compartment and 4 #2 shear pins. This is with 40oz of weight in the nose.

For the mismatch on the NC to BT, I used a few wraps of painters tape covered with clear packing tape. Mostly 'cause I'm cheap, but also 'cause I didn't want to mess with fiberglass.
That's interesting Chuck. I started with 2.5gs of FFFFG (video attached) which was just about perfect, blew out everything nicely. I have 3 2-56 shear pins also but the NC weighs in a little over 5.5lbs. I can also add up to 4 more pounds if necessary if I load all 7 motors :p I probably should have done a build thread on this one.

https://youtu.be/MeJ5nA5jOGw
 
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