Plasma Dart II Upscale (a neil_w design)

[mbeels]

If you've perused the Scratch Built forum, you've probably seen one of neil_w's build threads. He has a real eye for design and his rockets are unique and interesting. His meticulous attention to detail and techniques make for quality build threads.

When I saw his Plasma Dart II, I wanted to build one, but larger. I started drawing an upscale (about 2x) version in Rocksim and incorporated some of his earlier design variations (such as the fins). I also ran one tube size through both sides of the plasma core to simplify the arrangement somewhat.

Someone once said, "Give me a fulcrum and lever long enough, and I can move the earth". Well, I say: give me enough filler and sandpaper, and I can fix anything. My building opportunities come in brief stolen moments, or late night binges, so I sometimes choose speed and quick results over quality and precision. But I do appreciate the work of a master craftsman yielding precision tools and using them well. I'm going to capitalize on neil_w's design work, however, don't expect the same results!

Anyway, I started with a BT-80 based rocket (with 3.9" centering rings for the plasma cage) and a 29mm motor mount. However, the 29mm motors that have enough impulse for decent flights are mostly hard hitting, high thrust motors. I decided that this rocket was a much better candidate for 38mm motors, specifically some of the low thrust 1-grain options from Cessaroni like the G46, G50, and G58. Those motors seem to suit this rocket design much better.

I prefer not to overbuild my rockets, instead I aim for "just right", or at least "enough". A lighter rocket accelerates faster, flies on lower thrust motors, and is more fun to build. Strength by design and care of assembly, not excessive epoxy fillets. I'm aiming for 16-24 oz dry weight. If it is lighter, it may even fly alright on a G25.

My box of parts should arrive tomorrow, so it's a good time to kick off this build. This is going to be a fun one.

 

[jqavins]

What size or you warp tubs (the three partial tubes that surround the central tube aft of the warp core)? Do you suppose you could fit 13 mm motor mounts in there? They'd only be for show.

 

[mbeels]

The warp tubes will be BT-55. I'd have to check the cross section, but they may fit 13mm motor mounts without cutting into the central BT-80.

Hmm... that could open up some fun possibilities.

 

[mbeels]

A box of tubes arrived in the mail today. I've developed a "nacho cheese" problem, which is when you run out of nachos, so you need more cheese, and then you run out of cheese, so you need more nachos. I've been doing the same thing with body tubes.

Anyway, I'm going to fast forward some of the first steps which are nothing special. A motor mount from LOC and Aeropack retainer. Kevlar shock cord will be replaceable.



The fins have been cut out of 5/32 plywood. I remembered some of the issues with grain direction that neil_w had with his balsa fins and the "poky things". Plywood wouldn't have the exact same problem, but I decided for strength, simplicity, and appearance to put my poky things on the ends of the fins. The downside is that they will be more vulnerable, as the tips will rest on the ground if the rocket is laying on its side.



I couldn't find 2.6" to 3.9" centering rings, so I bought 29mm to 3.9" rings and used a 29 mm motor mount with BT-80 centering rings as a guide to cut out a 2.6" hole (plus tube thickness).



With the rail buttons, they really do look like rocketry engagement rings, with 24 carrot 1010 rail buttons.

Now I'm getting to the slightly more complicated part. I'm undecided as to the best order of assembly. I have a vinyl wrap for the plasma core, and I suspect it will be difficult to apply once the plasma core centering rings are in place. So I'm considering:

Option A: Prime and paint only the section for the vinyl wrap, apply vinyl wrap, build rest of rocket around it. Fill/prime/paint the rest of the rocket with the plasma wrap masked off.

Option B: Continue assembling the rocket, fill/prime the entire rocket except leave plasma cage off, then apply wrap, and finally add the plasma cage.

Either option has some downsides, but I'm leaning towards option B.

 

[mbeels]

What size or you warp tubs (the three partial tubes that surround the central tube aft of the warp core)? Do you suppose you could fit 13 mm motor mounts in there? They'd only be for show.

Yes, I checked, and there would be room for 13mm motors. The only thing I'd need to do is notch out the TTW fins. Hmm.....

 

[neil_w]

Woohoo!

A box of tubes arrived in the mail today. I've developed a "nacho cheese" problem, which is when you run out of nachos, so you need more cheese, and then you run out of cheese, so you need more nachos. I've been doing the same thing with body tubes.

You just described my rocket life.

The fins have been cut out of 5/32 plywood.

Hot damn those look *nice*. You're gonna make me wish I had stuck with that fin shape.

With the rail buttons, they really do look like rocketry engagement rings, with 24 carrot 1010 rail buttons.

Those button mounts look really good. I guess I was worried about nothing.

Option B: Continue assembling the rocket, fill/prime the entire rocket except leave plasma cage off, then apply wrap, and finally add the plasma cage.

That's what I did (er, "am doing"). Maybe I'm just an optimist, but I don't think that doing the wrap between the two rings is a big deal. You can make it ever so slightly easier by making the wrap slightly narrower than the space in there, and extend the color of the centering rings onto the warp core tube. It won't be noticeable (I think) but will give you a wee bit of room to work. You only need a couple of millimeters on each end to open it up a bit.

 

[jqavins]

Yes, I checked, and there would be room for 13mm motors. The only thing I'd need to do is notch out the TTW fins.

Yeah, I'd forgotten the correct orientation, and I was thinking that the tubes were between the fins. This way is harder than I meant to suggest.

 

[mbeels]

Yeah, I'd forgotten the correct orientation, and I was thinking that the tubes were between the fins. This way is harder than I meant to suggest.

Not impossible, somewhat inconvenient, but still worthy some consideration. I'm not sure the effect from 13mm motors will add very much with a central 38mm G motor. I think it would work out to be a good effect with 4 motors of more equal size. Like 24mm central motor, and 3 18mm outboards, something like that.

You just described my rocket life.

It's not a bad problem to have!

Hot damn those look *nice*. You're gonna make me wish I had stuck with that fin shape.

I'm just copying your design, I agree!

You only need a couple of millimeters on each end to open it up a bit.

And on a painted surface, I should be able to do a bit of repositioning. I'm going option B, it will be a far more straightforward assembly.

 

[mbeels]

Alright, a bit more progress tonight. I glued 13mm tube bulkheads around the centering rings, I plan to use these to hold the cage tubes in place. They'll need to have half the diameter notched out on each end so they can be installed, but I think it will give a little more glue area than just butt gluing them in place. And (if I glue the rings in correctly) they'll be self aligning.



Tubes spirals and fins got the CWF treatment. Boy, I don't miss sanding sealer!

The real genius in this design is neil_w's shroud and tube generators. He calls it an ugly perl script, but the results are beautiful. Here is a test fit, it is really really good. Thanks Neil, spot on.



On to the transitions. Usually I raid the recycling bin for material, but this morning was trash/recycling, so everything is empty. I raided the pantry instead.



I pre-rolled the transition around a motor mount adapter, to give it some shape and prevent creasing.



It was mentioned here on TRF that paper transitions can be sanded at the seams, so I gave it a try. I think it helped.

 

[jqavins]

Not impossible, somewhat inconvenient, but still worthy some consideration. I'm not sure the effect from 13mm motors will add very much with a central 38mm G motor. I think it would work out to be a good effect with 4 motors of more equal size. Like 24mm central motor, and 3 18mm outboards, something like that.

Yeah, as I wrote originally they'd really just be there for show. Four exhaust plumes, even though only one of them really matters.

 

[neil_w]

I glued 13mm tube bulkheads around the centering rings, I plan to use these to hold the cage tubes in place. They'll need to have half the diameter notched out on each end so they can be installed, but I think it will give a little more glue area than just butt gluing them in place. And (if I glue the rings in correctly) they'll be self aligning.

*Love* that. Got me wondering if I could have done that with 1/8" launch lugs on mine, but those bulkheads would have been tiny and hard to work with. Yet another advantage of building bigger!

The real genius in this design is neil_w's shroud and tube generators. He calls it an ugly perl script, but the results are beautiful. Here is a test fit, it is really really good. Thanks Neil, spot on.

Glad those worked. Everything is looking great so far.

 

[mbeels]

Yet another advantage of building bigger!

Yes, bigger is definitely easier in most respects. The only real downside is storage space, I'm quickly running out of room.....

I glued some 1/8" balsa strips down for the warp (plasma? I've lost track of what is which) tubes. In hindsight, I should have beveled them before gluing because shaving them down to the right contour while attached to the tube was tedious and imprecise.



And gluing the tubes down turned out to be trickier than I expected, there wasn't a good way to clamp them in place, so I spent the time trying to hold down loose ends with my fingers. Oh well, watched a few "History Guy" videos while I waited.



When I cut the fins out, there wasn't enough space on the 12" x 12" sheet for fins in their entirety. The front angly bits (there is a word for them....) will come next, followed by another round of filling and sanding.

 

[neil_w]

Wow, you're going fast. Looks great.

Yes, bigger is definitely easier in most respects. The only real downside is storage space, I'm quickly running out of room.....

And that right there is a big reason why I don't build bigger.

The front angly bits (there is a word for them....)

Strakes.

 

[mbeels]

Strakes.

Ah, thanks.

Got the strakes glued on and started the filling and sanding process. I think that the fast progress portion of this build is mostly over, sanding these joints and shapes will take some time. I have one more transition to do, but here is a quick test fit. I think it will be ready for priming next week.

 

[mbeels]

Last transition is on. Now it is just the cycles of filling, sanding, and priming.

The cardboard from cereal boxes seems to work quite well for transitions, it rolls well and is strong in a conical shape. My printer is broken, so I drew this one out by hand. I recessed the top centering ring slightly and inserted a short section of BT-80 coupler so I can get the bottom of the transition more or less flush with the BT-80 body tube.





At this point filling and sanding will take care of the rest. I also have learned recently that white glue can be ironed to reshape it. After the glue dries, I will go over the seams with a monokote iron to persuade them to shape up (or ship out!).

I'm starting to try and brainstorm some paint schemes, I think I want something simple and clean looking. Perhaps a white base coat with some pin striping.

 

[mbeels]

Lots of sanding, time to recruit some extra help.

 

[mbeels]

I expected a fairly time consuming sanding job, and yes, it was. Nooks and crannies may be great for butter and jelly, but they're not awesome for sanding. Primer is on, I'm not going for perfection, but I'll be happy with a 5' finish.

 

[BABAR]

Looking good.

This may be a rocket that can handle two internal Launch lugs around the plasma chamber.

Lining them up is going to be a PITB.

One in forward transition, one in aft transition.

Once in place, cut the edges trim with the forward and back ends of each transition.

Once painted black, you won’t even be able to see them.

 

[mbeels]

This may be a rocket that can handle two internal Launch lugs around the plasma chamber

That's a good idea. The launch rod could even go through one of the cage pieces. And actually, it could also go through one of the plasma tubes (alongside a fin). Had I installed them before the transitions, it wouldn't have been an issue, just two lugs on a section of BT-80.

I often do install both lugs and rail buttons for versatility, but I think this one will only get buttons.

 

[mbeels]

First coat is on, Rustoleum 2x white. The photo is pretty washed out, but the results were decent.

I need to start thinking about a color scheme, I'm not sure what it will be yet. One idea is to do a variation of neil_w's theme, probably in the same colors.

 

[neil_w]

Looks great. If you need any decal art let me know.

 

[mbeels]

Looks great. If you need any decal art let me know.

Thanks, I'm going to see what I can mask and paint, and then figure out what art work is left. Masking was fairly tricky, I did a lot of free hand cutting and eye-balling. It's pretty humid today, but I may just do the black anyway.

 

[neil_w]

Nice. I found the masking to be a pain... but then it always is.

 

[mbeels]

Nice. I found the masking to be a pain... but then it always is.

True enough!

I'm taking advantage of a huuuuuuge nap, and got some painting done. First two quick coats of white to seal up the masking tape edges, then one good coat of black a few minutes later.

 

[mbeels]

My favorite part of painting, pulling the mask off.

 

[BABAR]

Nice!

 

[mbeels]

Well, that wasn't super easy, but not as bad as I was prepared for. I've removed the masking over the cage bulkheads, that is the only structure left to do.

 

[neil_w]

Deja vu.

Did Mark print that for you, or did you do it yourself, or what exactly?

 

[mbeels]

Did Mark print that for you, or did you do it yourself, or what exactly?

Yeah, a big thanks to Mark at Stickershock23.com, he did great work. I just emailed him the texture file and told him what I wanted. The wrap fits just right, and the texture lines up with itself. The vinyl was quite easy to apply, just flexible enough to be persuadable and positionable, but stiff enough to support itself so it wasn't drooping and getting stuck to everything. If that makes sense. I have a couple of extras, so there could be more BT-80 based Plasma Darts .

And your suggestion of cutting the wrap slightly undersized to clear the BT-5 bulkheads worked.

Deja Vu

It's like watching an instant replay, in 2x!

 

[jqavins]

View attachment 390760

That is a beautiful job.