Alcubierre Build Thread

Discussion in 'Scratch Built' started by neil_w, Sep 27, 2018.

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  1. Nov 20, 2018 #211

    neil_w

    neil_w

    neil_w

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    Sadly I've had no opportunity to do anything recently except fiddle with decal designs. You shall see it finished and in action, I always finish up my build threads with flight reports.
     
  2. Dec 3, 2018 #212

    neil_w

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    I have not forgotten about this build. Today I even got to work on it just a bit, for better or worse.

    I was annoyed at some roughness in the paint, so I went in and wet sanded very gently with some 1500 grit paper. I did succeed at getting rid of the bumpy bits; next I'm going to get some 2000 and 3000 and then finish with my polishing compound and see if I can get it back to gloss. I didn't do the whole rocket, just some easily accessible areas, so I don't expect it to be a terrible effort. There are a couple of very small spots that will require a bit of touch-up paint, but no big deal.

    Then I thought it would be fun to do a "complete" dry fit, with the ring pieces squeezed into position and held in by friction:
    Dec-status-1.jpg

    Looks pretty cool! Upon closer inspection, though...
    Dec-status-2.jpg

    My dorsal and ventral fins do not reach the ring, and the gap is substantial, probably 3/32" or so. This is super frustrating because of the amount of time and effort I put in to ensure that it wouldn't happen. Honestly I'm confused how it could be off by so much.

    In hindsight, I should have left the fins too tall until painting was finished, and then sanded them down to size as the final step before gluing. Now I shall have to glue on another piece to the end of each fin, and then sand that to size and shape to match the fin. Fortunately, these pieces will be silver, so I won't need to break out the cranberry again for them. There will however be some significant cranberry touch-up work required in other areas to fill in some of the areas I masked off to preserve gluing surfaces.

    Looks like this rocket will be following the dreaded ninety-ninety rule.
     
  3. Dec 3, 2018 #213

    Bruiser

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    Could you just trim some off the ends of the rings or do you think that would make the ring look out of round?

    -Bob
     
  4. Dec 3, 2018 #214

    Gary Byrum

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    Thta's where my thinking was also.
     
  5. Dec 3, 2018 #215

    Greg Furtman

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    Wouldn't it be easier to tape off one side of the dorsal fin & mix up a batch of epoxy with a filler to make it thicker and then position the rocket so the tape is down and then fill in the gap with the epoxy mix? I have been using WEST System epoxies for 30+ years now and have found that they are always stronger that the woods/plastics I am using them on.
     
  6. Dec 3, 2018 #216

    neil_w

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    I've been very reluctant to mess with the geometry of the rings, but maybe it would be the better way to go here, although it wouldn't necessarily be less work. Would need to sand the two ring ends very slowly and carefully until reaching exact fitment. Might also need to sand off some paint on the outside bottom of the ring where the glue joint goes.

    Hmm, the more I think about it the more I'm inclined to go this route, provided that the ring geometry still looks OK. I'll fiddle around on paper and see if the loss of ring height is really noticeable.

    Interesting idea, but this would be impractical for me for a variety of reasons.
     
  7. Dec 5, 2018 #217

    BABAR

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    Thinking outside the box, take a 1/8” dowel length maybe twice the forward/aft span of the ring, round the forward and aft ends, color it black with a marker (gives it color but won’t prevent glue adherence.). Glue it in the gap, a little sticking out back and more out front. Paint the forward and rear tips silver.

    Instant Antennae.

    This is also called the “I meant to do that” solution.

    What I mean is, rather than look at this as a problem needing to be fixed look at it as an opportunity to be more creative with the design.
     
  8. Dec 5, 2018 #218

    neil_w

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    Interesting idea. I don't think I'm likely to want to go that way, but I'll doodle with it in OR and see what it looks like.

    In the meantime, I'm experimenting with high-grit papers for the first time. I've gone over the body and the dorsal and ventral fins with a wet 3000 grid sanding pad. It's now a very smooth matte finish. Next I'm gonna hit it with some polishing compound and see if I can get it bit of gloss on it, doesn't need too much because the final coat of Future should do it. I actually wouldn't mind if it were a bit less than full gloss anyway. Interesting process; running over the surface with the 3000 grit pad really was very quick and easy, I'm wondering if a run with 5000 grit would make any difference to the final finish.
     
  9. Dec 7, 2018 #219

    neil_w

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    Looks decent after an application of polishing compound, sort of satiny. Plenty good surface for decaling.
    postpolish.JPG

    To keep consistent finish between the nose and the body, I gave the nose the same 3000 pad + polish. It *slightly* softened the paint dams, and definitely ended up with a matching finish.

    I think that after the eventual coat of Future it will look good.

    Still need to work on the situation with the rings. Only get a few minutes at a time to work on it these days, kind of frustrating.
     
  10. Dec 7, 2018 #220

    Amsterdam

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    I have an idea for the ring/vertical fin gap, a piece of balsa to bridge the gap, and then you sandwich two pieces of 1/32nd balsa or 1/64th ply over the extension and a little on the fin, paint them your accent color prior to gluing, cut them in a decorative shape for aesthetics.
     
  11. Dec 7, 2018 #221

    Nytrunner

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    Forgive my ignorance of the tiny wood fractions, but woodn't 1/64 ply just be.....a single ply? Thus being.....a wood sheet?
     
  12. Dec 7, 2018 #222

    Amsterdam

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    1/64 birch plywood is what I should have said.
    Its is at least two ply, there’s an adhesive layer in the middle. If you sand it enough you’ll see a dark brown resin.
     
    Last edited: Dec 7, 2018
  13. Dec 7, 2018 #223

    neil_w

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    1/64 plywood is crazy stuff; it's hard for me to understand how it exists. How the heck do they cut 1/128" thick sheets of wood?

    Anyway, after finishing up polishing the rocket, and inspecting it closely, I'm pretty unhappy with the paint job. There are a very large number of spots that will require touch-up, far too many for my taste. I'm now leaning towards putting a new cranberry topcoat on the whole rocket before moving onto the silver. In the past, when I've put a new topcoat on after sanding down a rocket, it's come out really really good, so I'm optimistic I'll get the results I want this way.

    Unfortunately, given the uncharacteristically cold weather we've been having, I have no idea when I'll get my next painting opportunity. This paint job could take all winter at this rate. Oh well!
     
  14. Dec 8, 2018 #224

    Ez2cDave

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    Space heater for the workshop !
     
  15. Dec 8, 2018 #225

    GlenP

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    at least keep the spray can you are going to use in the house rather than the garage so that they are at optimal operating temperature. You might be able to spray paint on a cold day if the rocket and paint can are at room temperature, and let them dry a little and outgas in the garage until the smell is bearable enough for the house. But, test that out on a scrap piece of cardboard first... temperature and humidity are tricky variables for spray painting outside.
     
  16. Dec 8, 2018 #226

    Gary Byrum

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    I've done that before with success. But I usually heat the paint can in warm/hot water in the sink first.
     
  17. Dec 10, 2018 #227

    neil_w

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    Got a bit of work in over the weekend.

    Found approximately the correct place for the launch lug and cut out a patch of paint and glassine:
    Repairs-1.jpg
    Cut was not as precise as I was trying for, but doesn't really matter.

    Glued on my pre-painted lug and filleted with Quick and Thick:
    Repairs-2.jpg

    In this picture my paint-blocking dowels are still inserted, so you don't see the interior of the lug. In real life, because I beveled the ends of the lug, you can see nicely into the white interior at the ends. I may stop doing that in the future. Now I'll have to color the interior of the lugs, at least at the ends where it shows.

    Then I worked on fixing the dorsal and ventral ring fit situation. I cut small pieces of 3/32" balsa, sanded them approximately to shape and glued them onto the ends of the fins. Then I applied some CWF to blend it all in and smooth it out. I think the end result is pretty good.
    Repairs-3.jpg

    The 3/32" wood was quite a bit thicker than necessary; would have been fine with 1/16". No worries, balsa is easy to sand down. I worked it down until it was just *slightly* too tall:
    Repairs-5.jpg Repairs-6.jpg
    I will do the final very slight sanding to the top of the fin to achieve perfect fit at the very end, right before gluing.

    It's now ready for a new cranberry topcoat.

    Still thinking that a design with a half ring is in my future. Looks cool.
     
  18. Dec 10, 2018 #228

    GlenP

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    here is a really rough sketch of the swept scaled chevrons I mentioned earlier, would look better with some curves to them. Looks like they are compressing into the warp field... just an idea to consider. Could tie in with the shape at the nose in front of the windows.

    Screen Shot 2018-12-09 at 6.08.55 PM.png
     
  19. Dec 10, 2018 #229

    neil_w

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    Ah, now I get it. :)

    Lemme try getting that into OR and see what it really looks like.
     
  20. Dec 10, 2018 #230

    BABAR

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    Something to think about with launch lugs, especially if outer color is dark.

    Problem with paint getting inside the lug is that it may not slide on the rod as well. I have used a sharpie marker reaching as far INSIDE the lug as I can (usually will cover whatever internal surface is visible on finished rocket) to mark it black. THEN put in your blocking dowel in and paint. The sharpie makes the internal surface flat black, so assuming outer color is dark essentially the internal surface disappears from view. May not work as well with a beveled lug.

    Advantages are it is easy, it is IMO fairly cosmetic, and it causes no binding on the rod at launch.
     
  21. Dec 10, 2018 #231

    neil_w

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    Beveling the lugs really does create an issue here that I could do without.

    I have a big set of Sharpies, gonna see if I have a close enough color. I don't think I'm too afraid of a small amount of touch-up paint around the openings, but I do prefer the Sharpie route if I can get close with it.
     
  22. Dec 14, 2018 at 8:26 PM #232

    neil_w

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    Interesting. It's a little busier than I'd like, but it gives me some ideas to play with.
    upload_2018-12-14_15-26-31.png
     
  23. Dec 14, 2018 at 11:21 PM #233

    GlenP

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    I think you have captured the idea. Looks like that warp ring is compressing time and space ahead of it to draw the rocket forwards at light-speed riding that wave, doesn't it?
     

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