Building the Estes Little Joe II: Tips, Tricks, and Modifications

Discussion in 'Low Power Rocketry (LPR)' started by James Duffy, Jan 28, 2016.

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  1. Jul 8, 2017 #271

    ewg1967

    ewg1967

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    You don't mention it but did you also spray the black over the corrugated wrap as well? I'm curious as to how the black undercoat makes the aluminum look more realistic?
     
  2. Jul 16, 2017 #272

    ewg1967

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    Well I'm an idiot. Somehow I missed post #50 where the black undercoat was applied to the wrap as well.
     
  3. Jul 16, 2017 #273

    James Duffy

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    The theory states that the black undercoat provides additional depth to the metallic overcoat. I've seen the technique used on enough of my own models as well as those of far more accomplished builders to have convinced myself that the process works.

    Yep, the corrugated wrap gets the black undercoat as well!

    James
     
  4. Jul 22, 2017 #274

    ewg1967

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    Thanks James. This is the route I'm taking with my build as well. You are right. The black undercoat does appear to give the metallic layer more depth.
     
  5. Oct 3, 2017 #275

    James Duffy

    James Duffy

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    After opening this thread some 20 months ago, I finally got around to adding the last final little detail to my Little Joe II model. Not long after the model was released, a modeler named Daniel Cavender posted a photo of a display stand for the model that he laser cut from plywood. I thought Daniel's stand was fantastic, so I reached out to him to see if he would share the file so I could cut one for myself. After cutting a kit over a year ago I get distracted by other projects, and the parts started gathering dust.

    A few weeks ago I decided to dust them off and put the kit together. Daniel's engineering was fantastic, and the plywood bits fit together exceptionally well. Construction took just a bit of epoxy, and after some quick sanding the structure was hit with some primer, some gloss white, and finally some bright yellow (all Rustoleum).

    While the stand isn't strictly scale, it is a great complement to the finished model. Thanks to Daniel for sharing the digital file for the stand, and thanks again to John Boren and Estes for modernizing and revitalizing one of the greatest kits in the history of our hobby!

    James

    IMG_2859.jpg
     
  6. Oct 6, 2017 #276

    rocketguy101

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    James, I saw you posted the pdf file on FB, are you going to post it here? I assume the pdf file is full scale, but for double check can you post a couple dimensions?

    EDIT: Follow up...is there any way you can post this file as a DXF file? I have a friend with a laser cutter, and the pdf you posted isn't playing nice with his software. You mentioned an Illustrator file on FB...what is the raw format?
     
  7. Oct 6, 2017 #277

    James Duffy

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    I've posted a pdf version of the plan below with a 1" square added so that you can check dimensions. My original version is in Adobe Illustrator format, and I'm afraid that I have no application that can export a .dxf file. I can send you the .ai file, if you like. (Can't attach .ai files here due to limitations with the Rocketry Forum interface, it seems.)

    James

    View attachment Estes Little Joe II Display Stand copy.pdf
     
  8. Oct 7, 2017 #278

    rocketguy101

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    Thanks for that James, I PM'd you for the AI file...I would like to see what SolidWorks can do with it. Somebody at work converted the pdf -> dwg but when I bring it in to SWX it is huge! The .19 slot was something like 9.3333 inches...I scaled it down using the dimensions measured off the pdf (after you told me on FB those were correct dimensions).

    I made solid models of some of the pieces to do a fit check against a dummy 1/45 LJII and it appears to fit OK.

    Thanks for providing the data, and thanks to Daniel for creating the stand in the first place!

    Little Joe II Stand Base Dim.JPG

    Little Joe II Stand Base Assy 03.jpg
     
  9. Jan 13, 2019 #279

    Araize01

    Araize01

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    I had a problem with the plastruct product. It dries way too fast. The larger pieces didn't stick. I ended up using traditional plastic cement to assemble the parts, then I wicked the plastic weld into the seams.
     
  10. Jan 14, 2019 #280

    James Duffy

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    One thing we may have neglected to mention when suggesting the Plastruct Plastic Weld cement is how the stuff is designed to be used! The parts should first be held together in an assembled position, then the liquid cement is applied to the joint with a brush. Capillary action will draw the cement into the closed joint, allowing the cement to act.

    Sorry about that omission!

    James
     
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  11. Jan 14, 2019 #281

    Araize01

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    Thanks, James.
     
  12. Jan 16, 2019 #282

    Mike Haberer

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    Does anyone have a Rocksim file for this build. I can't find one in any search I've conducted so far. Will build up my own if I have to but would prefer not to. Thanks.
     
  13. Jan 16, 2019 #283

    rocketguy101

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    Here is what I worked up in RS. If you open it up in OR, there are some differences, mainly due to using straight Barrowman vs. RockSim's CP algorithm, plus a little difference in the mass calcs. I used actual as-built mass values for the fins and the LES tower...the placement of the clay is approximate.

    I am also attaching a spreadsheet with comparisons between the two (note I had to add ".txt" extension to allow TRF to upload--something weird about the allowable extensions--just delete that after downloading).

    Somewhere, John Boren told us the balance point should be 6.25" from the end of the main body.
     

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  14. Jan 16, 2019 #284

    Mike Haberer

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    Thanks much. This will save me a bunch of time I proceed to the final build and have to tweak the weight for the balance point.

    I saw John's balance point entry as well, but it can't be 6.25" from the end of the main body (?), it must be 6.25 inches above the CP, which is about what your modeling shows. BTW, which model do you lean toward, it either - RS or OR?

    I'm doing more mods based on what other people have done. I screwed up the front motor mount ring (glued off kilter), so I built my own (beefier, sandwiched 1/8" balsa cross grain with card stock backing) and decided to beef up the bottom one as well. I've never liked the basic Estes motor mounts, they are not all that strong and I've had them fail before (on the original K-30 LJ II kit). I'm going to do the square rod fin mods but am considering doing it in conjunction with adding rings for and aft of the spars for even more strength, then add expanding foam as a last step. I might put expanding foam in the fins themselves as well. I'm going to use a kevlar shock cord anchored to the MM. Finally, I'm thinking I''ll use BB's for nose cone weight (because the aft adds will need top weight added), plus two small ply barriers, one on top of the epoxy/BB weight ( and anchored to the tower legs sticking into the nose come) and another in the shoulder of the nose cone, with expanding foam in between, to hold an eyebolt for the recovery harness. Oh, and I'll use rail buttons since with the added weight I'll likely need a 6' rail to make sure I have stability when it comes off the rail.

    What will this all add up to weight wise? Don't know, but now I can model it before I make final decisions. With the added weight a E30W-4 probably is insufficient because it will need a shorter delay or more total impulse, but with the added strengthening, I suspect I can go with Aerotech F's, which gives you a lot more engine and delay options. We will see...

    If this all pans out I may do another one, but clustered C's with the D/E/F center. That would provide for some interesting flight options, much like the real LJ II could be flown with many configs.

    Cheers.
     
  15. Jan 16, 2019 #285

    rocketguy101

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    Well, to be stable you want the CG ahead of the CP about 1 body diameter, so the balance point should be about 3.4" above the CP. That is 1 caliber of stability (or static margin). An SM a little less than one will still provide a stable flight as long as the rod exit velocity is sufficiently high to offset any cross-wind. I believe that is why the E30 is being preferred over the D12 or E12 (compare the rod exit velocities).

    As far as RS vs. OR...the latter uses straight Barrowman CP calculations, which make a bunch of simplifications and tends to be conservative. RS can run Barrowman, but also has a different algorithm that can take advantage of more complex shapes. If you look at this file with both simulators, you will see OR has this being marginally stable. People have been successfully flying this bird, so I would say OR is being conservative. I've seen people report problems flying w/ the BP motors (D12/E12) but they don't report all the launch conditions (wind speed, rod angle, actual lift off mass) so it's hard to trouble shoot what happened.

    EDIT: I did not have these screen shots at work earlier, but here are shots of RS and OR sims, both empty and with an E30 to show the SM...
     

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    Last edited: Jan 17, 2019
  16. Feb 3, 2019 #286

    jddj

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    I've created a 3D-printed bayonet-mount plate for the plastic nozzles so they can be removed for flight with a quick twist. File is up on YouMagine. Pictured below.

    There's also a nose bulkhead with a hole and plug, for easily adjusting nose weight with BBs.

    Hope someone finds this useful.

    [​IMG]
     
  17. Feb 3, 2019 #287

    GlenP

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    Many thanks to all for sharing details of this build, especially the types of glue. I just got both Little Joes with my SV1969 kit and will probably tackle the Little Joes first.

    I had a question about this part in the display stand/tower, was not sure from the pictures what this "fishbone" in the middle here is for:

    Screen Shot 2019-02-03 at 11.44.51 AM.png
     
  18. Feb 4, 2019 #288

    rocketguy101

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    Those are the cross pieces that tie the two sides of the tower together...you have to cut them apart
     

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  19. Feb 4, 2019 #289

    GlenP

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    Thanks, seems like they were not drawn in that CAD image, but the photo clearly shows them. I see where they go now.
     
  20. Feb 4, 2019 #290

    Brent

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    If you can get someone to laser cut I would love to buy set.
     
  21. Feb 4, 2019 #291

    rocketguy101

    rocketguy101

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    PM me with your email address, I talked to my friend at work and is going to look into what he might charge for cutting these. He added some tweaks like "tab and slot" for the cross pieces. He is going to test some other materials as the luan plywood he used for mine charred pretty badly and some of the center plys fell out. This added some more filling work to finish the edges, but the thing fits together really well...you almost don't need any glue! Once he gets things worked out, I can forward your email to him and let you all work out details ;) He is pretty busy at his day job and has some other things going on, so I don't imagine he would be building a bunch of these in production...
     

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  22. Feb 5, 2019 #292

    Brent

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    PM sent
     

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