New Guy About to start a new MadCow 2.6" DX-3 Build - Need Help!

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markfsanderson

markfsanderson

Model Rocketry Returnee ...
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Greetings,
My son and I are hooked after launching our first rocket together. To that end I purchased a MadCow 2.6" DX-3 to build and launch. I have some questions regarding terminology, building and finishing:

  1. Page 3 of the instructions under Fin Assembly: "
    "Also, spread a thin layer of epoxy on each side of the
    fin tang."​
    What is a 'fin tang'? Is there a good visual representation of other rocket parts that someone could post a link to?
  2. How do I prep the nose cone for painting? I have some Rustoleum primer and fluorescent colors as well as some Tamiya Spray paint as well. Should I prime both the tube and nose cone?

  3. Does the "flameproof chute protector" take the place of dog barf? Should I use both?
  4. What, if any, negative flight characteristics might occur if I didn't round off or bevel the fins leading edge? Can I just slightly round them or just flat sand them lightly and soak the end grain with thin CA? Will paint adhere to thin CA?

Any links to generic/general building instructions would be greatly appreciated!

Thanks Again!

Mark (and Charles) Sanderson
 
you got the 'cardboard & plywood kit, yes? if so the step 2 of the motor mount/ shockcord installation shows a fin w/ the tang/ fin tab labeled (it is the bit that gets glued to the motor tube)
wash the nose with hot soapy water to remove any mold release from the cone, then scuff up the cone with 220 grit sandpaper. rinse to remove sanding residue and allow to dry. prime and paint(priming the rest of the rocket will help the paint to stick).
the Nomex 'hankie' takes the place of dog barf yes.
fins, the rocket will not go as high if you leave the edges square, they might whistle, paint will stick to ca.
Rex
 
Rex R said:
you got the 'cardboard & plywood kit, yes? if so the step 2 of the motor mount/ shockcord installation shows a fin w/ the tang/ fin tab labeled (it is the bit that gets glued to the motor tube)
wash the nose with hot soapy water to remove any mold release from the cone, then scuff up the cone with 220 grit sandpaper. rinse to remove sanding residue and allow to dry. prime and paint(priming the rest of the rocket will help the paint to stick).
the Nomex 'hankie' takes the place of dog barf yes.
fins, the rocket will not go as high if you leave the edges square, they might whistle, paint will stick to ca.
Rex
Click to expand...

Rex,
Thanks for the answers! I have the cardboard tube and plywood 2.6" kit . . . nothing on mine illustrates what a 'tang' is . . . from your description it appears that its the portion that lies entirely inside the rocket?

Mark
 
Yes, the tang is the fin tab, which is the root of the fin, which gets tacked/glued to the MMT.
 
I have the 4" cardboars dx3. I didn't do anything to the fin edges, I didn't want to get it lopsided and induce a lot of roll. It still flew just fine.

Also, I read somewhere the purpose of primer is just to make a nice smooth surface for the paint. The nose cone is already very smooth so I just painted it with no primer and it turned out very nice.

One thing, if you have some flashing on the nose cone where the seams are use a sharp exacto and not sandpaper to take it off. I tried to sand mine and just ended up with a scuffed up side :(
 
Have fun with the DX3! The big 4" fiberglass XL version was the first highpower rocket I worked on

On fin forming, I like to borrow a friends router with an 1/8" radius bit to round the leading edge, then mark and sand the trailing edge to a taper. Maybe it reduces drag, maybe it induces spin, but it looks cool and its what I like to do!
You'll discover what you like to do as you try new things on new rockets!

Chad said:
Also, I read somewhere the purpose of primer is just to make a nice smooth surface for the paint.
Click to expand...

Unless I'm mistaken, primer provides a better chemical substrate for the paint.
Paint gurus can set us both straight, just give it a minute
 
Tang Clik on the link, that will help.
I use filler sandable primer from Rustoleum. Coat, sand, repeat until smooth. you will never see all the flaws until you put the first coat of primer on, so be prepared.

When I built mine, I just hand sanded the fin tips to a round shape, just go slow and steady.

That rocket is a great flier. I love it. H180 for a great flight, I200 for butterflies!
 
roytyson said:
Tang Clik on the link, that will help.
I use filler sandable primer from Rustoleum. Coat, sand, repeat until smooth. you will never see all the flaws until you put the first coat of primer on, so be prepared.

When I built mine, I just hand sanded the fin tips to a round shape, just go slow and steady.

That rocket is a great flier. I love it. H180 for a great flight, I200 for butterflies!
Click to expand...

Roy,
Thanks for the graphic! Makes complete sense now . . . The current plan is to build this one for mid-power and the the 4" for my level one . . . well see how it works out!

Thanks Again!

Mark
 
markfsanderson said:
Roy,
Thanks for the graphic! Makes complete sense now . . . The current plan is to build this one for mid-power and the the 4" for my level one . . . well see how it works out!

Thanks Again!

Mark
Click to expand...
Each rocketeer is on their own journey. I did my L1 with that same rocket and my L2 with my 4" DX3. I learned so much about motors, chute packing, JLCR's, and shock cords by flying my 2.6" half a dozen times before even starting construction on my 4". But that's just me. Good luck.
qm9gFC3Qq0hGxOTfyVbwzDbfXbwZV3KQdWSOS01Cpj5EP6zEeO7HCqQelZRUk_zaX4owKENCGDktIxFFtX7V3GlxT8lcg8fQ_E-ZlkwAe0sjfE2q8vcs4ba2afko02q0QI_9UzW6PcQmy2c8rZoZ1-lHlOVMcLd0Hy22PZcRzCZ9bdYp8h40Xt_MkDrU8OuCaibk0GElcn45favTuegrsbwWAPcIFDdrK8zpDpplSm4Qz0If4hV2e9DwXeRv2aZj45tbbEkUEAR0J14r9jv_6YWG1SBGZrDGDBM_fRblwz-WWigVt-_Wwdsw2WlJ9RD3AguQUgdoM36jLyLHy-44ijlTRnuItZvVJIzvmRqwALxUwDKu3TiNJykiId5hx-P-HMQ_ZUMzmS9udsYNR5NGKUdLFx7tsuxaZjPkkXAgbqM8avJg0xRPhw6DT_zU6G7wFJKq3_xoiTMXlrQvLBA-_XlQKJ33mDXeJFuMxBOckVTTflGeSyrksaEhwBU-4t8MC_LiQsXFj2-m-_QlAzumyZBgBJAjfiEcUVqFzAx-tfg0LIcCJ_UWRlXOFlo7_TxNYa8RijbaBjD5Y7B5pKowNEU8kWHtuxT8bZjimEMpVyC3MEeYLS7pK_KSK7yLzWy0malxd5s_EdEp1rU84oP-C0CmZg=w1468-h906-no
 
roytyson said:
Each rocketeer is on their own journey. I did my L1 with that same rocket and my L2 with my 4" DX3. I learned so much about motors, chute packing, JLCR's, and shock cords by flying my 2.6" half a dozen times before even starting construction on my 4". But that's just me. Good luck.
Click to expand...
Roy,
What is a JLCR? Sounds about what I plan on doing except that I'm going to do my L1 on the 4" DX3. Thanks for the solid advice!
Mark
 
welcome to the wonderful world of mid-power and above rockets (non Estes) where the instructions assume that the builder knows how to build(and thus only tell you what needs to be done, not how) :). always helpful to read through them several times before starting. if you have further questions...please ask, we prefer that people have fun w/o having things go sour.
Rex
 
I did my L2 with the 4" Super DX3.. Great kit! Sadly I got a 4" zipper last flight, so it's been quarantined until fix-it time..

I did a build thread a while back on it.. it might help shed some light & thoughts on your build..

https://www.rocketryforum.com/threads/madcow-super-dx3-patriot-a-build-thread.140215/

Don't tie the blanket to the cord. I make a loop in the cord, near where the cord exits the tube. I then pass this loop thru the hole in the blanket. I then pass the blanket thru the loop and pull tight. You should now have the cord knotted onto the blanket with a cow hitch / lark's head knot. Now, it won't slide up & down, and is easily removed. Tie a loop, an overhand knot is fine, about a foot (or more) behind where it attaches to the NC. this is where you'll attach your chute.

Get a chute release. it's probably one of the most important MPR / HPR purchases we make these days! The altimeters & dual deploy days will come, but this is a good place to start & get back your 2K' flights!
 
dr wogz said:
I did my L2 with the 4" Super DX3.. Great kit! Sadly I got a 4" zipper last flight, so it's been quarantined until fix-it time..

I did a build thread a while back on it.. it might help shed some light & thoughts on your build..

https://www.rocketryforum.com/threads/madcow-super-dx3-patriot-a-build-thread.140215/

Don't tie the blanket to the cord. I make a loop in the cord, near where the cord exits the tube. I then pass this loop thru the hole in the blanket. I then pass the blanket thru the loop and pull tight. You should now have the cord knotted onto the blanket with a cow hitch / lark's head knot. Now, it won't slide up & down, and is easily removed. Tie a loop, an overhand knot is fine, about a foot (or more) behind where it attaches to the NC. this is where you'll attach your chute.

Get a chute release. it's probably one of the most important MPR / HPR purchases we make these days! The altimeters & dual deploy days will come, but this is a good place to start & get back your 2K' flights!
Click to expand...

Doctor, yo
Thanks! I'll study your build thread . . . for sure! Chute release . . . hmm . . .I'll take a look.

Mark
 
Scraping the seam on a plastic NC is also what I like to do, but still sand plastic for prep. It will give tooth for the primer to stick to. Also, do not use the gray fill and sand primer from Rust-oleum for plastic. it WILL peel off. Use their primer that is made for plastic. Works well and is white so any color will go over it. Even yellow.
On sanding and rounding fins, a 90 degree corner creates the most drag on any surface. So rounding ,even just a little will help. I use a 16" sanding block that takes a full sheet of paper, just wrap it around block and tack it on one edge with thumbs tacks. Lay your fin, or any part on the edge of a table to sand. This will support it so that you do not sand a wave into it.
 

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Here are 2 that I just finished the clear coat on tonight. The fins are glass but with sandable primer and a bit of sanding you can get balsa to look just like this. The Scat has a plastic NC that was scraped, filled, sanded with 400 grit, primed and then scuffed with a maroon scotch brite pad. One goos step is before any paint goes on use a tack cloth to remove dust, dog hair ao anything else that is floating in the air.
 

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The latest Apogee newsletter (not posted yet) talks about using automotive adhesion promoter spray as primer for plastic nosecones. It is used to make sure paint adheres to plastic bumpers, trim, etc. It keeps the paint on even if the plastic flexes. I just checked, and places like Autozone and O’Reillys both carry it.

I did my L1 and L2 with a 4” DX3. One thing to consider is to leave the aft centering ring unglued until you have glued and filleted in the fins. That allows you to put internal fin fillets in — otherwise you can’t do it once you glue to motor tube in.

I did bevel my fins. I will try to find the thread that described the method, but basically I marked off 1/2” from the leading and trailing edge with blue tape, and used a sharpie to mark the center of the plywood edge. Then I used a power sander to make a flat bevel between the blue tape and the sharpie mark, then touched it up by hand. That made a nice consistent ~20 degree bevel, and only took about a hour or so for all 3 fins.

Edit: see this thread - https://www.rocketryforum.com/threads/madcow-super-dx3-build-thread.56811/

Good luck!
Bill
 
Last edited:
Bill Hanson said:
The latest Apogee newsletter (not posted yet) talks about using automotive adhesion promoter spray as primer for plastic nosecones. It is used to make sure paint adheres to plastic bumpers, trim, etc. It keeps the paint on even if the plastic flexes. I just checked, and places like Autozone and O’Reillys both carry it.

I did my L1 and L2 with a 4” DX3. One thing to consider is to leave the aft centering ring unglued until you have glued and filleted in the fins. That allows you to put internal fin fillets in — otherwise you can’t do it once you glue to motor tube in.

I did bevel my fins. I will try to find the thread that described the method, but basically I marked off 1/2” from the leading and trailing edge with blue tape, and used a sharpie to mark the center of the plywood edge. Then I used a power sander to make a flat bevel between the blue tape and the sharpie mark, then touched it up by hand. That made a nice consistent ~20 degree bevel, and only took about a hour or so for all 3 fins.

Edit: see this thread - https://www.rocketryforum.com/threads/madcow-super-dx3-build-thread.56811/

Good luck!
Bill
Click to expand...
 
Bill,
Thanks for the word on the adhesion promoter, stopped by the auto-parts store last night and picked some up. My 2.6 DX-3 is strictly for mid-power, I plan on doing my L1 w/the 4" version ( and maybe even my L2, but I haven't thought that far ahead yet ). I didn't know about the rear centering ring trick, but epoxying the fin root to motor tube and putting a filet on the body tube should suffice ( at least I hope so ) for midpower motors. I like this technique for beveling the leading edge. I also have a Great Planes (from my RC stuff) sanding block with a a bevel and rounded edge built in ... I might do that? Not sure yet.

Thanks for the information!

Mark
 
David Schwantz said:
Here are 2 that I just finished the clear coat on tonight. The fins are glass but with sandable primer and a bit of sanding you can get balsa to look just like this. The Scat has a plastic NC that was scraped, filled, sanded with 400 grit, primed and then scuffed with a maroon scotch brite pad. One goos step is before any paint goes on use a tack cloth to remove dust, dog hair ao anything else that is floating in the air.
Click to expand...
David,
What do you 'scrape' the nosecone with? The 2.6" DX3 that i have has 1/8" plywood fins. What did you use to fill the NC with as well? Thanks for the help!
Mark
 
Hi Mark, I use a new #11 exacto blade to scrape. Sand with 320 to 400 grit, this will give a bit of "tooth" for the primer to stick to. On filling the fins I would use the Rust-oleum fill and sand primer, it is gray in color. Spray a couple of coats at a time, let dry, sand with 100 to 120 grit. Repeat until you have the grain filled, use finer grit paper as you go till again about 320 to 400 grit. After the last coat of primer I'll then sand with 1200 or one of them there maroon scotch brite pads. Use a tack cloth right before paint, lots of dust floating around.
On filling the NC it is about the same other than if the seam is very deep I will use a finishing bondo, this stuff sands out very smooth. Can get at most auto parts stores that carry body work supplies. Then just primer as you would do the fins. If you can feel an imperfection, you will see it through the paint.
A good paint job is 99% prep, it's easy to spray the paint.
 
Bondo 'spot and glazing putty' is your friend. apply it after the 1st primer coat (it is designed to stick to primer), sand it smooth and reprime, repeat as needed.
Rex
 
markfsanderson said:
My 2.6 DX-3 is strictly for mid-power, I plan on doing my L1 w/the 4" version ( and maybe even my L2, but I haven't thought that far ahead yet ). I didn't know about the rear centering ring trick, but epoxying the fin root to motor tube and putting a filet on the body tube should suffice ( at least I hope so ) for midpower motors.
Mark
Click to expand...

Mark,

You're very welcome. I did my L1 and L2 both on the same 4" DX-3 with 38mm mount (H123W and J420R). If you are going that route, then I suggest you also get one of the MadCow altimeter bays and use that to join the tubes instead of the provided coupler. You can fly it with an empty bay for your L1, and then add in dual-deploy electronics for your L2 and subsequent flights. (Note: you don't have to do dual-deploy for your L2, but it's a good learning step as you head towards L3)

I didn't use the rear centering ring trick either for my 4" DX-3, but I've incorporated that with subsequent builds. An alternative technique is to drill holes in the airframe close to the fin (before you do fillets) and then inject epoxy to form internal fillets, then cover up the holes with your external fillets. Your method worked fine for my L1, so you shouldn't have problems with your build. I ended up doing a tip-to-tip fiberglass job on the fins prior to my L2 (see @tfish video at ), but that was because I cracked a fin fillet when my rocket found the only fence post in the desert upon landing. Arggh!

Good luck with your build!
Bill
 
Trying to relax after a disheartening setback . . . but probably not too serious. On the payload tube I had just prepared it where it was looking pretty good . . . filled and primed. I manage to find the one Rustoleum Flourescent Red that was malfunctioning . . . it sprayed for about 5 seconds and then it spit a bunch of globs of pain on the surface! Ok, I dabbed the globs with mineral spirits and thought maybe it was something I was doing. I cleaned the nozzle, shook for more than 1 minute and tried again . . . nice spray and then spit. It was as if it were running low on pressure?! I dabbed up the spit again and put the payload section up to dry. I'll be returning the HD purchased paint for a new can and hope for the best . . . Oof . . .

Mark
 
Hey, Mark. Common with rattle cans. Once a nozzle does that, throw it in the garbage. You can take a different nozzle from a like can and replace it. Most of them just pull off the top.
 
David Schwantz said:
Hey, Mark. Common with rattle cans. Once a nozzle does that, throw it in the garbage. You can take a different nozzle from a like can and replace it. Most of them just pull off the top.
Click to expand...

David,
Thanks! First I'm going to check and see if HD will exchange it . . . they should but we'll see. I suppose with enough sandpaper, I can make anything right! Haha!

Mark
 
I would give it 3 days minimum to let the paint dry thoroughly then use 320 grit sandpaper, also don't use a lot of pressure when sanding paint you don't want the paint to overheat and really make a mess. gently warm your spray paint (and keep it warm) to reduce spitting.
Rex
 

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