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Anyone drill holes in their G12 motor tubes to reduce the mass of their fin cans?

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jahall4

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Seems like a contiguous G12 tube is overkill and could be a good location to shed some weight particularly in rockets where motor ejection was not used.
 

TopRamen

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I do that on even lighter things, so yes, the concept is valid.
When something can be skeletonized, do it, and adjust the rest of the design accordingly.
 

TopRamen

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On something like G10 or other composites, you can machine something other than a circle into them, and a square or trapezoid eats up more area, thus removing more weight, so don't waste too much time with drilling lots of tiny holes.
 

jahall4

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On something like G10 or other composites, you can machine something other than a circle into them, and a square or trapezoid eats up more area, thus removing more weight, so don't waste too much time with drilling lots of tiny holes.
Certainly, holes are just easy.

Do you have any photos?
 

jahall4

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Or leave out the mmt completely and go min dia.
Hmmm, joker amongst us :wink: Then how about this… Anyone drill holes in their G12 motor tubes or minimum diameter body tubes to reduce the mass of their fin cans?
 

T34zac

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Hmmm, joker amongst us :wink: Then how about this… Anyone drill holes in their G12 motor tubes or minimum diameter body tubes to reduce the mass of their fin cans?
Just go flying case at that point. Or glue the fins directly to the motor case.

And when built right, you will need to be adding mass to hit that optimal mass for max altitude. My 38mm MD needed to be 12oz (dry) to be optimal mass. I was hoping to achieve 15oz, in reality I got 9.5oz. And that does include electronics and recovery gear.
 
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DavidMcCann

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No. put a bigger motor in it.


The weight savings vs reduction in strength just doesn't do it for me.

but thats just me
 

jahall4

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The weight savings vs reduction in strength just doesn't do it for me.
Its not just about weight reduction. In "unusual designs" it can be about the position of the mass too.
 

dhbarr

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I already replaced the rear g10 CR w/ epoxified lite-ply, and seriously considered a cardboard MMT.

Thrust ring pushes right on the aft CR anyway, and the ejection charge is north of fore. It's more of an alignment sleeve at this point.
 

SaturnV

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Honestly I did not understand anything. After the nozzle and before the front part could be drilled tube of the motor as much as you want. In the middle you can not drilling because it would not withstand the pressure :)
 

cherokeej

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Or leave out the mmt completely.
This isn't a joke. Size the centering rings to fit the motor, and you don't need a motor mount tube.

Some larger projects are built like this.
 
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markkoelsch

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I have said it before- skip the motor mount tube. Have centering rings I.D. sized to match the motor. Have fun tabs longer to reach motor. Pretty sure this will work.
 

jahall4

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This isn't a joke. Size the centering rings to fit the motor, and you don't need a motor mount tube.
I have said it before- skip the motor mount tube. Have centering rings I.D. sized to match the motor. Have fun tabs longer to reach motor. Pretty sure this will work.
This sounds perfectly reasonable if you decide up front to use a certain length case and spacers when you need to use a shorter reload.
 

Forever_Metal

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I have said it before- skip the motor mount tube. Have centering rings I.D. sized to match the motor. Have fun tabs longer to reach motor. Pretty sure this will work.
My school did the "no mmt tube" last year for a project rocket we flew. The only issue was figuring out the thrust ring at the aft end; we ended up with 2 extra centering rings, one of which we mounted the retainer structure to. The other was put in place 2" shorter than the smallest motor we planned to use. Worked well for us, but there is a drawback. If you use adhesives to mount fins, it is possible to compromise that joint when the motor heats up during flight. If using that method, I'd recommend building a fin box for each TTW and mounting them to the CR's. If you're bolting everything together, shouldn't be a problem (that's what we did).

just my :2:...

fm
 

cerving

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Another compromise may be to use very short mmt tubes (maybe 1" or so) on each centering ring. Since the centering rings are already pre-drilled for them you don't have to do anything with the rings themselves. You may want to get an extra centering ring and slot it and the fins to help with the fin alignment, since you don't have the mmt for the fin roots to glue onto. Getting them in alignment during assembly may be a little tricky, though.
 

mccordmw

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How about the function that the mmt tube performs when epoxying the fins to it with through-the-wall fins? Are we giving up too much strength? Would need to supplement with fin lock tabs?
 

cbrarick

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why not just use cardboard? It's lighter then anything you do with G10.

I used to race bikes. In the 80s it was cool to drill stuff out to lighten it, until they started to break. Then it was outlawed because we weren't smart enough to save ourselves from ourselves. I once saw a guy who drilled a ton of holes in his stem - for a 6 corner lightning fast, tight criterium. I think he lasted about 2 laps before he ate a haybale. One of the guys said he saw him drill in, holding his handlebars after the stem snapped. All I saw was the ambulance on the outside of the course. Just sayin' drilling didn't work for him...
 
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