Low 'n' slow cluster: 1 x 54mm + 2 x 38mm in a 5.5" frame...

Discussion in 'Plans' started by Tim51, May 9, 2018.

Help Support The Rocketry Forum by donating:

  1. May 9, 2018 #1

    Tim51

    Tim51

    Tim51

    Well-Known Member

    Joined:
    Jul 4, 2015
    Messages:
    569
    Likes Received:
    23
    So I've been thinking around this idea for a while: a relatively short and stubby 5.54" vehicle with a central 54mm MMT flanked with two 38mm outboards, dual deploy with airstart capability.The two outboards would bulge from the sides of the airframe.

    Materials: mainly LOC augmented and strengthened with FG and CF as appropriate, with some Black Cat phenolic (UK company). So it's a kind of foreshortened Bruiser / Magnum cross breed... with four fins.

    As ever I'd appreciate constructive advice based on practical experience of doing similar builds.





    Initial rendering.png
     

    Attached Files:

  2. May 10, 2018 #2

    qquake2k

    qquake2k

    qquake2k

    Captain Low-N-Slow

    Joined:
    Jan 26, 2010
    Messages:
    13,556
    Likes Received:
    10
    Cool design, but it's going to have a heavy butt. Chances are you'll need a lot of nose weight. If it were me, I'd make it longer.
     
  3. May 10, 2018 #3

    MaxQ

    MaxQ

    MaxQ

    Tripoli 2747

    Joined:
    Jan 18, 2009
    Messages:
    4,272
    Likes Received:
    12
    Gender:
    Male
    Location:
    Central Viginia - USA
    I've built some big - short fat rockets, and LOTS of nose weight may not actually be required....the base drag principle explained here is useful when simulating the advantages of base drag for short fat rockets.
    The Simulation of Short Wide Rockets using RockSim Version 8: An Additional Base Drag Consideration for Rockets With Less Than a 10:1 Length to Diameter Ratio
    https://www.apogeerockets.com/education/downloads/Newsletter154.pdf
    There's more to it, been some discussions previously here on TRF....
    http://www.rocketryforum.com/showth...e-explain-it-in-pseudo-scientific-terms/page2
     
    Last edited: May 10, 2018
  4. May 10, 2018 #4

    Tim51

    Tim51

    Tim51

    Well-Known Member

    Joined:
    Jul 4, 2015
    Messages:
    569
    Likes Received:
    23
    Thanks! How much longer are you suggesting? Your point about the length is well taken, but I was set on the idea of a reasonably stubby design, as part of the challenge. The plan as posted was to use c.600g of ballast weight in the NC. I'm intending to use a LOC long 5.38" NC with the base sawn off which I have already, so the dead weight ballast would be augmented with the weight from bulkheads, hardware, tracker battery etc once it had been fitted out with such. My plan there would be to use a reinforced Coker method, securing the bulkheads with epoxy but also small steel screws drilled inserted from the outside.
    Loc long NC.jpg
     
  5. May 10, 2018 #5

    Tim51

    Tim51

    Tim51

    Well-Known Member

    Joined:
    Jul 4, 2015
    Messages:
    569
    Likes Received:
    23
    Thanks very much for digging those out for me - really helpful, and much appreciated! As it stands this design minus fins the airframe is just on the cusp of the 10:1 - in fact, due to the outboards is over (but only just 153cm length / 14.01 cm width), and some of it isn't (153:18 approx taking into account the back end at the widest points). So this issue is very much a moot point for this design. I'll post refinements as I work further on the design.
     
    AndrewW likes this.
  6. Jun 8, 2018 #6

    Tim51

    Tim51

    Tim51

    Well-Known Member

    Joined:
    Jul 4, 2015
    Messages:
    569
    Likes Received:
    23
    Started assembling parts for this project. It will be a slow build probably over the winter, but I like to 'kit' my scratchbuild projects before starting, so I collectted some laser cut CRs and bulkheads today, and some nice stainless steel marine standard u bolts for the AV bay as part of that process. I like marine fixtures on rockets wherever possible, although oar locks do look a bit silly (booboom tsk.. :lol:)

    I've also made some changes to the fin design, partly to give a greater stability margin, and also because aesthetically I felt the earlier design was starting to look a little too much like a V2, even with the outboards. I must confess I'm not much of a V2 fan for some reason (too many memorial plaques in my neighbourhood, perhaps..) Fins will be cut later when I've decided whether to make them solid ply or ply/honeycomb combo.

    The 'nose' of each outboard will probably be an appropriately sized plastic NC sawn in half not flat as in the OR renderings. I don't know how to render half an NC in OR, so I've attached a quick hand drawn comic style sketch.


    20180608_120855.jpg 20180608_120928-1.jpg Screen Shot 2018-06-08 at 12.46.47.png Screen Shot 2018-06-08 at 12.47.36.png
    20180608_124429.jpg
     
  7. Jun 8, 2018 #7

    lakeroadster

    lakeroadster

    lakeroadster

    Lone Wolf... No Club TRF Supporter

    Joined:
    Mar 3, 2018
    Messages:
    782
    Likes Received:
    76
    Gender:
    Male
    Location:
    Central Colorado
    Cool concept, nice sketch!

    You are from London.. I imagine the dislike of V-2 rockets is a genetic thing, inherited from your grand parents or great grandparents :confused2:
     
  8. Jun 8, 2018 #8

    Tim51

    Tim51

    Tim51

    Well-Known Member

    Joined:
    Jul 4, 2015
    Messages:
    569
    Likes Received:
    23
    Thanks!

    Lol - yes these things remain as monsters in the dark gothic corners of the collective memory :wink:. As a kid I was keen on building those great Tamiya 1:35 scale Panzers, although my dad let me, he did sit me down one day and had a stern talk with me... I'm sure there are plenty of German aeromodellers who feel a twinge when building Lancasters or B-17s. But even the V-2 in its post WWII White Sands incarnation - re-painted and really reaching for the stars - doesn't appeal. Maybe after all that it's just a shape thing.
     
  9. Jun 22, 2018 #9

    Tim51

    Tim51

    Tim51

    Well-Known Member

    Joined:
    Jul 4, 2015
    Messages:
    569
    Likes Received:
    23
    Screen Shot 2018-06-22 at 22.58.55.png Screen Shot 2018-06-22 at 22.59.46.png Screen Shot 2018-06-22 at 23.00.19.png
    Some more refinements to the fin design, slightly more Magnum-like. This is starting to feel about right: slightly reduced span and area to the ones in my last post, but still yielding a reasonable stability margin. Stylistically I think I like these the most.
     
  10. Jun 25, 2018 #10

    Tim51

    Tim51

    Tim51

    Well-Known Member

    Joined:
    Jul 4, 2015
    Messages:
    569
    Likes Received:
    23
    Ponderings on fin can construction: my current plan is to construct the outboard motor tubes from LOC 38mm MMT tubing to keep the weight down. However, as they will only be half 'submerged' in the sides of the airframe, I will overlay them with extra reinforcement. Once the MMT assembly is inserted and epoxied in the airframe, the front ends of the outboard tubes will push against the forward edge of each respective AF slot. I'm currently thinking the best option is this: secure the outboards and the fins with epoxy fillets, then overlay with tip to tip 2/2 3K twill CF running from the tip chord of the fins, over the half submerged motor tube. To smooth the surface of the CF, rather than building up layers of finishing resin as in the so-called skinning technique, I'll then overlay with a further layer of 200gsm FG roving. I'll lose the nice CF fabric pattern, but as I see it it makes more sense.
     
  11. Jun 25, 2018 #11

    dhbarr

    dhbarr

    dhbarr

    Amateur Professional

    Joined:
    Jan 30, 2016
    Messages:
    4,512
    Likes Received:
    155
    Aww shucks, you used actual talent to produce that lovely sketch, I was rather hoping for software.
     
  12. Jun 29, 2018 #12

    Tim51

    Tim51

    Tim51

    Well-Known Member

    Joined:
    Jul 4, 2015
    Messages:
    569
    Likes Received:
    23
    Thanks! I'm pretty hopeless with rendering software.. I use Adobe Illustrator for laser cutting but that's about it! I used to love those old 'artist's impressions' renderings that Lockheed, Dornier et al would produce to show aircraft/space transports of the future, so this thread is going to feature old school hand drawn renderings wherever possible. Here's how the back is going to look, with the positioning of the airstart conduit opening in the plywood thrustplate, and Aeropack retainers:
    20180629_150830.jpg

    As my earlier OR renderings show, my earlier plan regarding colour scheme was a sort of alu-silver grey with flourescent orange and white banding, redolent of the kind of scheme sometimes seen on F-104s, but the metallic will interfere with the GPS tracker so I'm thinking now of an adaptation of a blue / off white / black scheme I've used before, with some silver detailing.
    (Now I've posted I can see that thrustplate isn't quite circular - I'll correct it later..)
     
    Last edited: Jun 29, 2018
  13. Jul 7, 2018 #13

    Tim51

    Tim51

    Tim51

    Well-Known Member

    Joined:
    Jul 4, 2015
    Messages:
    569
    Likes Received:
    23
    So last post on this in the 'Plans' section before it morphs into a build thread... Yesterday I cut a 5.54" Loc tube into lengths for payload, switchband and booster sections, 40cm, 4cm and 62cm respectively. This was a tube I slotted 'glassed and sanded some time ago (the charcoal tone is because I used some pigmented resin). I also picked up some 38mm MMT tubing at my club launch last week. I think that's the part I'm most nervous about on this: the cutting of the back end of the booster section to accommodate the 38mm ouboards.
    Anyhow.. I aim to get the fins laser cut later this summer, then I'll start posting a build thread in the HPR section sometime in the autumn.


    20180706_145203.jpg 20180706_145758.jpg
     

Share This Page