Build thread: 1 x 54mm + 2 x 38mm in a 5.54" airframe

Discussion in 'High Power Rocketry (HPR)' started by Tim51, Oct 10, 2018.

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  1. Oct 10, 2018 #1

    Tim51

    Tim51

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    So this will be the build thread to follow my earlier posts in the Plans section, which some of you kindly offered thoughts and feedback on. As yet I haven't come up with a name, but over the summer I've been cutting and fashioning parts, putting together a kit for a slow winter build over the coming months. Since posting in the Plans section, I've made some small adjustments which will become evident as the build progresses.

    Rendering.jpg
    I've already documented some of the basic airframe preparation in the Plans thread, so if any one is interested you can refer back. What follows is basically a summary of the preparation of the other components.
    First off, the centering rings were laser cut, then drilled for inserts and retainers:

    Drilling thrust plate.jpg

    Thrust plate with inserts (outward facing).jpg

    My aim with this build is to attempt airstarting, so each CR was drilled for a aluminium conduit. Also shown here are the bulkplates for the Av bay coupler.

    Centring rings and Bulkheads.jpg

    For the AV Bay coupler itself, I'm using a standard LOC coupler, with a postal tube inserted as a stiffener. bonded with Gorilla Wood Glue, reinforced inside with fibre glass. Wearing a respirator I painted the outside with CA...
    AV coupler.jpg
    And then squared off the edges with a sander: Squared off AV coupler.jpg

    The fins were cut from 4mm birch ply, then laminated with 200gsm fibreglass. This is an initial dry fit of how it will roughly look:
    Dry Fit 2.jpg

    I say 'roughly' because, of course, I've yet to make the cuts for the outboards, which, as in the colour rendering above, bulge from the sides of the main airframe. The outboard 38mm MMTs are designed to take up to 3G casings. Each motor mount and retainer will be streamlined by a 54mm shroud and fairing as indicated: Rendering with outboard detail.jpg

    To make the fairing for the outboards I first made a pattern using balsa and MDF. This was a balsa NC cut and sanded down half way:
    Mould blank.jpg
     

    Attached Files:

    Last edited: Oct 10, 2018
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  2. Oct 10, 2018 #2

    Tim51

    Tim51

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    From the pattern I made a mould using epoxy clay and tooling gelcoat, from which I've now pulled two carbon fibre fairings for the outboards. I'll trim, fettle and fine sand them once I'm closer to fitting them. That's all for tonight... more to follow in due course. Thanks for watching.

    mould and pulled fairing.jpg
     
  3. Oct 11, 2018 #3

    Steve Shannon

    Steve Shannon

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    For some reason this made me think of guacamole …
     
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  4. Oct 11, 2018 #4

    Tim51

    Tim51

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    Indeed! It's a very bright green in daylight, but more like an over ripe avocado under the lamp light...
     
  5. Oct 11, 2018 #5

    Banzai88

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    Where do you get tooling gel coat?
     
  6. Oct 11, 2018 #6

    Tim51

    Tim51

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    I ordered one of these little starter kits
     
  7. Oct 11, 2018 #7

    Andrew_ASC

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    Love the artistic depictions of the concept. Good luck with your build.
     
  8. Oct 11, 2018 #8

    Tim51

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    Thank you.
     
  9. Oct 11, 2018 #9

    viciouspeanut

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    Love the design and impressed with your custom molding. Will be watching.
     
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  10. Oct 11, 2018 #10

    boatgeek

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    The outboard fairings are a nice touch. Did you paint the artist's rendition?

    I've never heard the word fettle used in this context before, but I like it.
     
  11. Oct 11, 2018 #11

    Tim51

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    Thanks! Yes I did the painting - just acrylic on paper. In 'English English' (if you get my drift :)) the verb 'to fettle' does actually mean to trim off sharp edges from a metal casting.
     
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  12. Oct 11, 2018 #12

    Tim51

    Tim51

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    Thanks. I should have noted in the original post that I used 4 layers of 2/2 twill 3k carbon.
     
  13. Oct 13, 2018 #13

    Tim51

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    Ok - time for a little update on this, Ye Olde Englishe Fettling thread, from right here in London's olde East End..

    Yesterday evening I did a quick dry fit of the basic motor mount assembly. As indicated in bright pink on the photo, a section of the airframe will be removed on each side to accommodate the 38mm outboard tubes.

    MMT dry fit.jpg

    But before I get to that, I've decided to epoxy the front and aft CRs to the 54mm motor tube. That will allow me to use it as a dry fit sub frame to support the cut airframe, and make any adjustments whilst dryfitting the two 38s and the fin tabs before installation.

    For the 54mm mount, I'm using a 40cm length of seamless phenolic from Black Cat. I used some little paper stickers to ensure the insert threads were not fouled by the epoxy, and allowed to cure.

    MMT 1.jpg

    This MMT will comprise a total of 4 tubes: the central 54mm, the two 38's and of course an aluminium conduit to allow for airstart igniters. Like the thrust plate / rear CR, the middle CR has two half moons cut out to accommodate the 38s.
    The 54mm tube was marked with a line using an angle, and the two remaining CRs were pushed on to it. The conduit was then inserted, and all three CRs were aligned, using the drawn line:
    MMT 2.jpg

    Fore CR fillet being prepared:

    MMT 3jpg.jpg

    Before the epoxy set, I used an envelope at various points to ensure everything was square:

    MMT 4.jpg

    For the moment I'm leaving both the middle CR dry, so that I can adjust if needed to accommodate the fin tabs. The conduit will also be trimmed down and epoxied later.

    That's all for now. Thanks for watching.
     
  14. Oct 24, 2018 #14

    Tim51

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    After a business trip away had a chance to work a little more on this...

    After some careful double checking and dry fitting to ensure it lined up with forward end of the fin slots, I marked the final position of the middle CR and epoxied into place. The aluminium conduit was also trimmed and fillted with epoxy. I also installed two u-bolts for the recovery harness in the forward CR. Conduit & mid CR.jpg

    Then it was glassine peeling time.. I use wetted 180 grit to remove it from the two 38mm outboards:
    Glassine.jpg

    Then installation of the outboards: scuffed up the interior of each arc, further scuffed the tube with 80 grit, set with 30 min epoxy. Nice snug grip. I'll beef up the fillets later. Installing first ouboard.jpg

    Outboards epoxied and cured. This is a whole new world of MMT construction for me, being the first time
    I've built an HPR cluster (my son and I did several LPRs back in the day), and I have to say it looks quite strange - the shape reminds me of the sort of 'special component' you see in old disaster movies, the missing piece that has to be inserted back into the reactor to stop it going critical...

    ouboards complete.jpg

    Dry fit of the 3 Aeropack retainers:

    Retainers dry fit.jpg
    ...and another shot, just to be gratuitous:

    Retainers dry fit 2.jpg
    Next episode: I'll be starting work on the booster airframe. Thanks for watching.
     
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  15. Nov 3, 2018 #15

    Tim51

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    Ok, time for an update. The past few days and today I've managed to make a little progress on this (I said at the start it would be a slow build...). This week I went ahead and tackled the task which was making me most nervous about this build - cutting gaps in the side of the airframe to accommodate the outboards. Here's a shot of the initial dry fit:
    Cluster MMT Dry Fit.jpg

    I opted to saw the slots by hand, and then filed to get a smooth fit:

    filing airframe.jpg

    Before installing the MMT permanently, there were two tasks: the first was to use the outboards to mark up and cut a set of 54mm centering rings (or rather C shapes) that will be epoxied onto the 38mm outboards, to hold the 54mm shrouds:
    Marking shroud CR.jpg

    Shroud CR marked.jpg

    The second task was more complicated: the installation of the aft rail guide, which has to be installed between the middle and rear CR: it therefore has to be installed when the MMT is partially inserted into the airframe, once the forward and middle CR have been pushed past it. I'm new to using rail buttons, as I've previously used ACME conformals, but this being a 5.54" airframe, I've been unable to acquire conformals for this build. Some months ago I posted a question here on TRF asking if anyone could help identify a set of delrin rail buttons I'd picked up at a local launch, to which I got lots of really helpful responses (thanks again, everyone). It turned out that the threads for the attachment screws, being SC Precision, were UNC. Step forward MPitfield, who having read my thread about the SCP guides, very generously sent me a set of UNC PEM nuts all the way from Canada that would fit the threads, and a couple of long shanked machine screws and washers to tighten them with. No shots of me tightening the PEM nuts into place - that would take more hands than I've been blessed with - but suffice to say it all went to plan. As advised, I drilled the holes for the PEM nuts slightly too small (an M4 drill bit worked well) and there was sufficiently rough edge to the hole in the fibre board for the teeth of the PEM to bite into. I applied a small amount of epoxy to those teeth and left it to go a little stiff before tightening it against the inside of the airframe. It held well:

    PEM nut for rail guide.jpg

    Whilst on the topic of airframe, the forward payload bay and Av bay also got some attention mid week. 3 evenly spaced holes were drilled around the circumference, through the payload bay into the Av bay coupler: Holes for M3 fixings.jpg

    Tee nuts (with the teeth bent flat with pliers) were then epoxied into position using J&B Weld:

    epoxied Tee nuts.jpg

    AV bay threaded insert.jpg

    Shot of the AV coupler and payload section assembled with M3 screws and nylon washers. The switch band has not been epoxied into position at this point, in order to ensure when I do it butts up against the AV tube as flush as possible:
    Payload and Av bay.jpg

    That's it for now, thanks for watching.
     
    Last edited: Nov 3, 2018
  16. Nov 3, 2018 #16

    Nytrunner

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    Good show

    Have you come up with a name? So far its as cumbersome as Apogee's "Dual 18mm rear eject"
     
  17. Nov 3, 2018 #17

    Tim51

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    'Fraid to say I'm still stumped on a name... originally I was toying with something deliberately overblown in a tongue in cheek, Sci-Fi sort of way... the late, great Harry Harrison's In Our Hands, The Stars or something like that, but..basically I'm still undecided.
     
  18. Nov 3, 2018 #18

    timbucktoo

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  19. Nov 4, 2018 #19

    dhbarr

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    Since Ellison just passed:. The Bird that Shouted Fire At the Heart Of the Sky
     
  20. Nov 4, 2018 #20

    Tim51

    Tim51

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  21. Nov 4, 2018 #21

    Tim51

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    Very good indeed. I have an old copy of All The Sounds of Fear somewhere but passed on that as it probably sends the wrong signal...
     
  22. Nov 4, 2018 #22

    dhbarr

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    All the Sounds of Fire?
     
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  23. Nov 4, 2018 #23

    Tim51

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    In addition to the naming issue, I'm still toying with different colour schemes... here's another rendering:

    another rendering.jpg

    Since this is my first venture into airstarting, my inspiration for this build has been the idea of a fairly squat 'test vehicle' as the ALVRJ, the Squirt / Sprint testbed, or the Fastaff
     
  24. Nov 4, 2018 #24

    Banzai88

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    Thunder and Lightning. Launch with a White Thunder, airstart some sparkys!
     
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  25. Nov 8, 2018 #25

    Tim51

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    Some more work on this project: earlier in the week, the C rings I cut were sanded to a snug fit then epoxied into place. I also smoothed and filled in a few little gaps with some epoxy putty.

    outboard spacers.jpg

    The moulded fairings I made from CF were then, err, fettled (this is a shot showing the interior and the inside edges):

    CF Fairing interior.jpg

    ...and epoxied into place. The rear end of the fairing shoulder just hooked under the curve of the airframe, allowing an extra purchase point. The rear edges of the fairing were not perfectly flush with the airframe, but the front portion (about 40%) was:

    CF fairing.jpg

    Fillets of epoxy mixed with chopped carbon fibre were then applied over the relevant joints:

    spacers fillet.jpg

    Likewise, tonight a fillet of chopped CF and epoxy was applied around the fairings.

    fairing fillet.jpg

    I've sliced a length of 54mm LOC tubing in half, and sanded the edges to fit over the outboard c rings and the fairing shoulders. When the fillets applied tonight are fully cured I will measure each and cut to the required length, before attaching them accordingly over the outboards. My plan is to overlay this assembly with either FG or CF - I've yet to decide - bonding it all on to the airframe and fins.

    Sliced 54mm tube.jpg

    Thanks for watching..
     
    Last edited: Nov 9, 2018
  26. Nov 21, 2018 #26

    Tim51

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    A little bit more work on this: outboard fairings fitted and epoxied and fins installed... The four fins are 4mm birch ply, laminated with 200g 2/2 fibre glass twill. So they're now 4.5mm thick.

    fins.jpg

    On my 'to do' list is building a specialised cradle to hold this ... using an old cushion to support it just isn't really good practice..

    fairings and dry fit fins.jpg

    Fin guide cut from foam board, and fins epoxied... two yesterday, two this evening. I don't really like trying to fit them all at once:
    fin alignment guide.jpg
     
  27. Nov 26, 2018 #27

    Tim51

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    Gradually working my way around the airframe, pulling fillets... Fillets.jpg

    (the right one is straighter than it looks - a smear from the previous double buttering stage makes it looks wobbly). In the zen-like reflective mindset of fillet pulling, I've been thinking again about names... it occurred to me at planning stage that this build is a sort of customised Loc Magnum - a kit I very much wanted to build when I first began in HPR but is hard to get hold of this side of the Atlantic. This one's shorter, and with an extra fin and beefed up outboards, so it's a sort of 'Magnum GTX'.
     
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  28. Dec 8, 2018 #28

    Tim51

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    A bit more on this build. Carbon fibre skinning on the booster section in progress... a bit of a glitch on one fin (long story) so not my tidiest CF work.
    CF body work.jpg

    Time was when I could do a seam like this, but clearly those days are gone..my superpowers are failing...
    seam.jpg
    Anyway, my intention is to overpaint the fins on this build ('how convenient' I hear you say :rolleyes:)...
     
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  29. Dec 8, 2018 #29

    Nytrunner

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    What's your technique for hiding the seam?
     
  30. Dec 9, 2018 #30

    Tim51

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    For the seam in the second photo, it was: (1) careful measuring and alignment then blending with chopped cf. The tube (in that case a 3" PML phenolic) was placed on a rotisserie set up and the edge of the CF laid along a line drawn down the length. The cloth was then pulled tight by rotating the tube. No overlap. (2) a few pinches of chopped CF tow were then laid over the join to blend / blur. 3 thin layers of epoxy brushed over, left to fully cure then progressive sanding 120 - 1200 grit.
     

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