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  1. #1
    Join Date
    4th July 2015
    Location
    London, UK
    Posts
    458

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

    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.





    Click image for larger version. 

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    Attached Files Attached Files
    UKRA #1895
    EARS #1329
    L1 6/9/15 Custom built LOC Fantom 438 CTI H125
    L2 3/4/16 Same custom built LOC Fantom w/ DD EXL configuration CTI J410

  2. #2
    Join Date
    26th January 2010
    Location
    Northern California
    Posts
    13,507
    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.

    NAR 91107, Level 2

    I really, really hate bugs.

  3. #3
    Join Date
    18th January 2009
    Location
    Virginia - Central
    Posts
    4,166
    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/educat...sletter154.pdf
    There's more to it, been some discussions previously here on TRF....
    http://www.rocketryforum.com/showthr...ic-terms/page2
    Last edited by MaxQ; 10th May 2018 at 03:36 AM.
    We got two categories of pilots around here. We got your prime pilots that get all the hot planes, and we got your pud-knockers who DREAM about getting the hot planes.
    Now what are you two pud-knockers gonna have?... Huh?
    Pancho Barnes-
    The Right Stuff
    http://www.mwavs.com/0053148414/M4RS...udknockers.m4r

    Tripoli #2747

  4. #4
    Join Date
    4th July 2015
    Location
    London, UK
    Posts
    458
    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.

    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.
    Click image for larger version. 

Name:	Loc long NC.jpg 
Views:	14 
Size:	172.2 KB 
ID:	344324
    UKRA #1895
    EARS #1329
    L1 6/9/15 Custom built LOC Fantom 438 CTI H125
    L2 3/4/16 Same custom built LOC Fantom w/ DD EXL configuration CTI J410

  5. #5
    Join Date
    4th July 2015
    Location
    London, UK
    Posts
    458
    Quote Originally Posted by MaxQ View Post
    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/educat...sletter154.pdf
    There's more to it, been some discussions previously here on TRF....
    http://www.rocketryforum.com/showthr...ic-terms/page2
    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.

    UKRA #1895
    EARS #1329
    L1 6/9/15 Custom built LOC Fantom 438 CTI H125
    L2 3/4/16 Same custom built LOC Fantom w/ DD EXL configuration CTI J410

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