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What did you do rocket wise today?

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Nytrunner

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My daughter wants to build a new rocket and she already picked a name, Mako.
Roccccket Shark! (Doo doo dadoo da doo)

She likes the looks of Von Karmen nosecones over ogive so we will design it tomorrow night. I'll have to bust out some math since the VK is equation-based.
What modeling program are you using. and does it have an equation-driven line tool?

I know how I'd do this in Solidworks, but bets are off for other programs
 

_kestrel_

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What modeling program are you using. and does it have an equation-driven line tool?

I know how I'd do this in Solidworks, but bets are off for other programs
Professionally, I use Creo. Equation driven shapes can be accomplished using a function called TRAJPAR (trajectory parameter). I've found it to be a bit fussy on past projects. An easy work around is to use Excel to generate an array of points, import that array into Creo as a .pts file, and create a spline through the points. The result isn't mathematically perfect but definitely close enough for a 3d printed nosecone.

For this project, I'm trying to use Fusion 360. Even with the recent changes in Autodesk's license for home use I feel it is a good option for hobbyists, especially if you have a CNC machine. The approach to modeling in Fusion is different than in Creo and it is taking a fair bit of effort for me to learn. It does look like I'll be able to use an imported points file and create a spline through it in Fusion, I just haven't done it yet. I haven't found a direct equation-to-curve function in Fusion, Not saying it isn't there, just haven't found it yet. I wish Creo had a home use license similar to Fusion.

If anybody is looking for the Von Karmen equation, I found it here:

 

_kestrel_

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Wooph, that does sound like an ordeal.

Good luck!
Thanks - I needed that! Creo/Solidworks vs Fusion 360 is like comparing a BMW to a Honda Accord. They'll both get you where you're going, one of them just gets you there with a lot more refinement and comfort. The biggest struggle so far has been getting the constraints and dimensions nailed down. It's almost like the Fusion 360 team looked at how things were done in EVERY major modeling package and did it as differently as they could...
 

Jay Dub 4009

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Last night got the tip to tip carbon Layer on the MDRM to complete the cracked fin repair. When I got up, pulled it all out of the bag and was slightly dismayed at a few wrinkles and frays that the bag didn’t suck down the peel ply that well and didn’t get smooth...but asthetics don’t matter much as it’s going to get repainted back to its sparkly blood red creatix. Also I know that sanding will clean it up rather well. It is very strong now, so the goal of repairing the cracked balsa skin is complete, as well as making it bullet proof for the future. New carbon skins and then the tip to tip added only 2 oz in weight, so happy with that as well. Learning lessons for sure. My next rocket I will be laminating fins before they get installed on the rocket and it’s smaller so will be able to use the food saver instead of the ziplock blanket bag I used this time. Next bigger project I will get a Venturi valve for air compressor and use legit vacuum bag sheeting with bag tape.
D9355133-159A-44A2-98C5-B186F3A0A162.jpeg
3308B99A-FF89-44F0-A320-6407FFD567C1.jpeg
9E694E26-AA83-4AA6-8A73-FBDCE1DE9044.jpeg
 

Banzai88

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I finished sanding the tubes on my L2 attempt project and glued the motor mount in and the fins on.

Post sanding final mock up
1603899275503534041470748402729.jpg

Fins on!
16039152079362011366990223775074.jpg
 

teepot

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Worked on another scratch build. Went over to Balsa Machining. Bill was telling me the cost of balsa has tripled recently. Apparently wind turbine blades have a balsa core and that's where all the balsa has been going. Learned something new.
 

XrayLizard

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Worked on another scratch build. Went over to Balsa Machining. Bill was telling me the cost of balsa has tripled recently. Apparently wind turbine blades have a balsa core and that's where all the balsa has been going. Learned something new.
WOW. Makes me mad actually.
 

Blast it Tom!

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Professionally, I use Creo. Equation driven shapes can be accomplished using a function called TRAJPAR (trajectory parameter). I've found it to be a bit fussy on past projects. An easy work around is to use Excel to generate an array of points, import that array into Creo as a .pts file, and create a spline through the points. The result isn't mathematically perfect but definitely close enough for a 3d printed nosecone.

For this project, I'm trying to use Fusion 360. Even with the recent changes in Autodesk's license for home use I feel it is a good option for hobbyists, especially if you have a CNC machine. The approach to modeling in Fusion is different than in Creo and it is taking a fair bit of effort for me to learn. It does look like I'll be able to use an imported points file and create a spline through it in Fusion, I just haven't done it yet. I haven't found a direct equation-to-curve function in Fusion, Not saying it isn't there, just haven't found it yet. I wish Creo had a home use license similar to Fusion.

If anybody is looking for the Von Karmen equation, I found it here:

What??!?! Excel?! You use Creo and wouldn't generate the nosecone curve in Mathcad?! ;)
We have Solidworks, and are suffering through while PTC plods along achingly slow with Mathcad Prime development- We've stayed with Mathcad 15 forever, it seems, but it's a really wonderful program for every day calculations. Do they not license it for you along with Creo - my understandingwas that PTC was putting (almost all) Mathcad developement into integration with Creo.

Thanks for the Von Karmen equation reference. 👍
 

Back_at_it

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A couple of weeks back I was out flying and had a chance to send up my New Way Flat Boy and Sky Fighter. Even with twice the amount of wadding in the Sky Fighter (8 Sheets) I was still melting parachutes. I posted about this and DavidQ (Qualman Rocketry) over at YORF put together a solution in the form of a baffle system for the square body tube.

I received the baffle and set about retro fitting my Sky Fighter with a baffle system.

Instructions are included and clear but honestly I didn't need them. These are super simply to assemble.

Pic 1. The baffle system comes laser cut and very well done.

Pic 2. The pieces were easily removed with a hobby knife and nubs sanded smooth with 100 grit.

Pic 3. All pieces have slots and tabs that fit together nicely. I placed a fair amount of TB2 on the mating surfaces and inserted the tabs into slots and let it dry.

Pic 4. I glued the reinforcement piece to the top as I will be using a screw eye to attach to the top for my Kevlar leader.

Pic 5. After assembly I gave the joints a quick fillet with TB thick and Quick and brushed the entire baffle with thinned glue to give it some protection from the ejection.

Pic 6. A quick test fit of the baffle in the tube showed a perfect fit. No sanding was required. It simply pushed into the tube and it went down as far as I wanted to send it. Mine is installed just forward of the leading edge of the wings to avoid issues with stability. Still have plenty of room for the laundry.

One note. The reinforcement piece for the screw eye was placed on top of the baffle. In retrospect I think I would put it on the bottom side of the upper piece. Also note that I used a larger than normal screw eye and it caused the top to split. This could have been prevented if I predrilled like I should have. No harm done as I simply hit it with a drop of Epoxy before final assembly.

I'm really happy with the design. The fit is perfect. I also like the fact that you could remove one layer if you were installing this into a something short like the Flat Boy. I'll be ordering these for every New Way rocket I build.
 

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neil_w

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I love DavidQ's baffle design, but gluing it in always seemed a bit dicey to me. Unlike baffles inside couplers, which are incredibly easy to glue, with the Qualman design you have to get the glue in the right spots, and that's often way down in the tube. What approach did you use exactly?
 

Back_at_it

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I love DavidQ's baffle design, but gluing it in always seemed a bit dicey to me. Unlike baffles inside couplers, which are incredibly easy to glue, with the Qualman design you have to get the glue in the right spots, and that's often way down in the tube. What approach did you use exactly?
First thing was to remove the Kevlar I had attached to the motor mount. I removed the attachment from the nose cone and pulled the shock cord and Kevlar out the tail through the motor mount and used a hobby knife to cut the Kevlar up as far as possible. There is about 1 inch section remaining but there is nothing I can do about that. Obviously this step will be more of an issue if you attached the shock cord to the inside of the body tube as that would all need to be removed and sanded smooth.

Next I test fit the baffle and decided where I wanted it to sit within the tube. I then used a tape measure to determine the depth to the top of the baffle. This measurement was transferred to a long handled paint brush. I dipped the paint brush in glue and inserted it into the tube and spread a fairly large about of glue on the 4 walls. Keep in mind that the mark was to the top of the baffle so when inserting, it would push the glue down. The rocket was then stood on it's nose so the glue would sit on the baffle and create a bond.

Once that had dried I moved the shock cord to one side of the body tube and used the paint brush to add additional glue to the top of the baffle. Keep in mind that the square tube does have some minor bowing in the sides while the baffle itself is perfectly square so there the tiniest of gaps around the edge for the glue to get into and create a strong bond. A couple of minor glue drips were cleaned up with a wet paint brush inside the body tube and let dry.


Once dry I pulled on the Kevlar pretty hard (much harder than it would see under ejection) and the baffle is solid.

When adding baffles to rockets I tend to put them forward of the CG for stability but still leave room for laundry. Generally this means the baffle is sitting somewhere between 8 and 10 inches down from the top of the tube. Obviously this is rule of thumb and not always possible do to rocket length or CG. If a rocket comes with a coupler I generally turn that coupler into a baffle. If using these from DavidQ, I would simply slide them in forward of the last coupler.
 
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