I don't understand the blue tape under the FG...
Stiffening Fins Already on the Rocket
- Thread starter atestani
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It is masking off the top and bottom of the tube so it is clear of epoxy
vulpesjr
Active Member
Looks like you kept the old fillets underneath the tip to tip? How did you handle the leading edges of the layup? Do the glass layers on each side meet at the very edges of the fins?
Yes to both questions.
cbrarick
Wildman CT
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I'm not certain why you think that anything 3d printed is going to add strength. Most 3d stuff doesn't like heat, and even worse, it's extremely difficult to bond to other materials.
tip to tip may help, but you would have been better served to remove the thin wood fins and put some real high powered fins on, even plywood.....
tip to tip may help, but you would have been better served to remove the thin wood fins and put some real high powered fins on, even plywood.....
The extensions are printed with PAHT-CF (high temperature nylon with carbon fibers) which is very strong has a high melting temperature. I use it for bulkheads, thrust rings, charge canisters, rail buttons, etc. These parts have flown many times. The printed extensions have a V-grove to be conformal with the bevels on the existing fins (picture below). The extensions are bonded to the existing fins with West Systems 105. I tested this on a spare fin and I could not break the extension off with a lot of bending force. It took a hard hammer blow to break the PAHT-CF but the bond held.
My initial plan was to build an entire new fin can but the "wisdom" from this thread convinced me to T2T the existing fins. There two cloth layers across the fillet and fins including the extensions. I used West Systems 105 used for the resin.
I've already flown the wood fins with no glassing many times including my L2 with a J350. I plan 3 subsonic flights with this rocket with a I245, I195, and K535 to prove everything out before going Mach 1.2 (sim value) with an L1000. I "believe" what I have will survive but the only way to know is to try, right?
shockie
High Plains Rocketeer
Use a low viscosity Laminating Epoxy with 0.2 to 2.0 mm. Carbon fiber sheet to your fins I.e. "skin them"
The 0.2 to 0.5mm can be cut with scissors and is conformable.
The 0.2 to 0.5mm can be cut with scissors and is conformable.
cbrarick
Wildman CT
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it's a common myth that we need to tip to tip in order to get to mach.
I've flown my bone stock loc vulconite on the J600 with max speed of more then 1000 mph - well above mach, it's only got wood glue....
at BALLS last year i flew a bone stock wildman wildthang extreme to mach 3.2 with standard epoxy filets only
there used to be a great website "strength of HPR Materials" that was a wonderful reference. too bad it's gone.
having said that, it's cool to overbuild if you understand that is what you're doing. maybe you want more durability in transport, the ability to get wet, whatever.
do you have a reference sheet handy for the PAHT-CF? I'd like to learn more about it.
I used MarLander's Fin Flutter Analysis MathCad for asymmetric fins which is based on NACA TN 4197 to get the estimated shred velocity and a lot of reading on the subject to essentially overbuild, as you say. The extensions were added because I couldn't put any more nose weight in for K and L motors. I tend to agree that getting to Mach doesn't necessitate T2T plus, I am probably just going to get to Mach with an OR sim value of 1.2 with this rocket, anyway.
Labels from spools of esun PAHT-CF and QidiTech PA12-CF (which is close to PAHT) filament that I use follow. Both from Amazon. Printing with this stuff is a bit tricky but there is a lot of information available on how to do it successfully. One thing is I always use brass inserts where I need threads even though I could print them. If you want more information, post to the 3D printing forum and PM me and I will respond there.
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This was discussed earlier in this thread and the consensus was it wouldn't help although G10 instead of carbon fiber was proposed. It sure would be a lot easier than what I ended up doing.
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You're welcome. One thing I have found to be very important is to make sure the filament is completely dry. Also, I print on a Garolite sheet on the bed with stick glue applied. The first layer adhesion is very strong so you need to flex the Garolite sheet to get the print to release. One other thing is to use a steel (versus brass) nozzle as the carbon fibers are abrasive. Jack up the print temp by 10C for the steel nozzle.
lr64
Well-Known Member
Any info on the mechanical properties of this stuff once it's applied? I imagine that it's kind of directional.
What stuff are you referring to?
lr64
Well-Known Member
The carbon filled 3D printing filament.
The Z-direction, or perpendicular to the layers, is usually the weakest direction of a 3D printed part. However, with the right print settings, PAHT-CF is stronger than most in the Z-direction, I assume due to the carbon fibers. Because of that, PAHT-CF is used to make functional prototypes, machining fixtures, injection molds, jigs, and low-volume production parts.
However, I tend to print so the main force vector is perpendicular to the plane of the layers, i.e. putting the layers in compression and not in tension or shear. See this post for an example of the thrust rings I print:
https://www.rocketryforum.com/threads/thrust-plates-when-and-why.177113/post-2548491
(PS Since that post, I did fly the thrust ring with a J350W and have the 54mm motor mounts constructed for the K535 and L1000 flights in the next two months)
If you want more information you could look here: https://qidi3d.com/products/qidi-paht-cf-carbon-fiber-filament.
