Little Joe II A-003 Mission Build

Discussion in 'Low Power Rocketry (LPR)' started by srfrich, Apr 21, 2019.

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  1. May 17, 2019 #31

    srfrich

    srfrich

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    Canting the Elevons for Roll.
    Thought about this for a bit, and the answer became obvious. The actual A-003 mission did a right roll as seated in a virtual cockpit. Fortunately the Estes kit makes this easy to model: the elevons are finely detailed and easily differentiated from the main fins. The elevon actuators are on one side, the side opposite the direction the elevons need to cant to for a right roll.
    1. Using a razor saw was straightforward. The detail of the plastic itself acted as a miter box for the saw. Sawed all the way through between the fin and elevon, and almost (about 1/2 way) through the actuator on the other side. The plastic of the 1/2 sawn-thru actuator is the only thing joining the fin and elevon at this point.
    IMG_0820.JPG IMG_0821.JPG IMG_0823.jpg
    2. Made a jig to hold the fin and stretch some tape to bend the actuator and close the gap made by the saw. Then applied Plastic Weld on the new seam.
    IMG_0824.JPG IMG_0827.JPG
    3. Now the elevon is canted for a right roll. I could try to measure the actual angle and enter it into Open Rocket, but with all the complex angles of the LJII fins, it may not really matter. With luck I'll get a nice right roll.
    IMG_0828.JPG
    Probably will cant just 2 elevons and fly the unfinished model for a test. If the roll is too slow, can cant the remaining 2 elevons. Easy experience with this first elevon suggests that sawing and gluing won't be a problem when fins are attached to the airframe.
     
    Last edited: May 17, 2019
  2. May 18, 2019 #32

    srfrich

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    Better than tape, used a clamp on the second elevon. Easier to apply the glue along the seam without tape standing in the way. The 2 elevons came out looking identical, as best as I could see.
    IMG_0829.JPG
     
    Last edited: May 18, 2019
  3. May 18, 2019 #33

    srfrich

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    Command Module electronics suite - square peg in a round hole.
    This is going to be one of the funner parts of the build, fitting the Spectrum 4-channel receiver, 3S LiPo battery, connectors, and a Transolve Triple Fire which is designed to fly vertically (G-switch), all into the Apollo Capsule. Right away, gotta ditch the huge red piezoelectric buzzer and replace it with a mini (shown next to it, black). The corners of the PCB will need to be clipped off but the mounting holes can be saved - only two traces will need to be rewired, and the G-switch must be reoriented 90 degrees so the PCB can lay horizontally. Spectrum's AR410 receiver has an internal antenna - nice! IMG_0839.JPG

    My beautiful square peg with mounting holes in exactly the right place:

    IMG_0836.JPG
     
    Last edited: May 18, 2019
  4. May 21, 2019 #34

    srfrich

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    Converting the Apollo Capsule into an AvBay.
    Hobby shop sheet styrene, and the Dremel circle cutter.
    DA43E21C-C6C9-45C6-88DE-91614B2EDE94.jpeg
    The 4-40 screws are spaced for mounting holes on the PCB that is shown in the previous post. 43D1DF3A-2C3A-496A-B4D9-7C88A866A4D4.jpeg
    Just the initial step. Still gotta mount female threads, electronics, ports.
     
    Last edited: May 21, 2019
  5. May 21, 2019 #35

    srfrich

    srfrich

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    Cutting, Rewiring the PBC to fit into the Apollo Capsule and reorienting it to fly in a horizontal orientation.

    This work was a bit beyond my experience, so I got a good friend to help. He quickly cut the corners of the PBC, then rewired the 2 traces cut by the Dremel. Gone is the huge red piezoelectric buzzer, replacing its 2 prong plug and leads with a mini piezoelectric buzzer mounted thru-hole on the flip side. Finally, removed the g-switch, added a small insulating pad, and added a small lead so the g-switch can be bypassed for a ground test. Remounted it at 90 degrees so it will point “up” for flight, then added hot melt glue to support it.

    2D083550-DA77-4D19-95A7-476AA02D1134.jpeg 53BD1394-5120-4180-82EA-91F2C90EBF83.jpeg 88DE8FAF-84E9-4B50-8154-A4CE7575425E.jpeg A03EFDCA-5F7A-415B-9F3C-493BE71ABEFF.jpeg 2283FF56-A5D1-437E-A6B8-451D85527820.jpeg
    With this horizontal configuration, there is room in to spare in the capsule for the battery, receiver, leads, etc.
     
    Last edited: May 21, 2019
  6. May 24, 2019 #36

    srfrich

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    Attaching the Vacuform ABS Wrap.
    Made a simple jig: a section of 3" shipping tube attached with construction adhesive to a MDF work surface. In retrospect, this jig was the gem of the process. IMG_0843.JPG

    I wanted to try something different, so I selected Lexel sealant as the adhesive. Reasons: a. fill all the air gaps on the wrap corrugations, including the fin attachment deformations, so there is a 100% surface bond. b. something easy to work with by hand, without overspray and other causes of mess. c. Lexel is a "gorilla glue" of sealants, sticking to wood, plastic, etc. A week ago, I tested it by attaching an Algol plastic nozzle, purportedly made of the same plastic as the wrap, to a scrap of glassine wrapped body tube, to make sure it stuck the two materials together. d. After it cures, Lexel remains flexible, something I wanted for hard landings e. Lexel has a generous working time and has some repositioning ability.
    IMG_0873.JPG
    Rehearsal is key. I did a literal 'dry run' and discovered where to pre-position masking tape. What I initially thought would work, didn't, so the dry run was valuable. Large strips of masking tape were pre-positioned on the reverse side of the wrap to give me something to handle the wrap without actually touching it, and to close the wrap around the airframe while the sealant sets up. Post-Its were laid over where the tape was exposed so no sealant would get on those. All these refinements were as a result of the dry run.
    Narrower strips of masking tape did double duty to hold the wrap flat to the work surface, and also masked off the top and bottom inner sides of the .010" styrene strips I had glued earlier, 'cause I want to use CA to seal those strips against the airframe in case the Lexel didn't perform as hoped.
    IMG_0872.JPG IMG_0878.JPG

    De-glossed the glassine where it would meet the wrap, with a medium grit foam sanding block, then positioned the airframe on the jig.
    IMG_0868.jpg IMG_0869.JPG
    The masking tape on the airframe was removed prior to applying the wrap.
    These pictures were taken during the dry run, to show how I would work the Lexel into all the depressions on the wrap using a putty knife and small squeegee.
    IMG_0874.jpg IMG_0875.jpg
    Then the moment: pumping a generous amount of Lexel onto the wrap, globs on the fin attachment areas, and thick beads every few CM elsewhere. The putty knife was almost perfect for getting the Lexel into the depressions of the fin attachment areas, I don't know what would have worked better. The squeegee was perfect for spreading the Lexel, it filled all the negative (as seen from this side) corrugations. I found the best technique was to work the Lexel from the middle to the edges in all directions and the corners -- it worked well to move the squeegee past the margins of the wrap and over the masking, to get the Lexel to the very edges and corners all around. At the end of this application, I used more pressure on the squeegee to remove all but a thin film of Lexel from the positive corrugations. Excess Lexel built up on the squeegee, which was later removed with mineral spirits. IMG_0879.JPG
    I was pleased that the Lexel felt cooperative and easy to work with; it does not drip, sag, or make strings, and spreads like warm butter. I was surprised by how much of it the corrugations 'soaked' up.
     
    Last edited: May 24, 2019
  7. May 24, 2019 #37

    srfrich

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    The last bit was to gently pull off the Post-Its from the masking tape "handles" and the narrow tape that masked the edges and held them to the work surface. You can see the fresh and dry surfaces of the .010" styrene strips on the top and bottom edges of the wrap that were masked beneath the narrow tape. IMG_0880.JPG IMG_0881.jpg

    Holding the wrap by the masking tape 'handles', I stood it up on its bottom edge on the work surface of the jig, letting it naturally curl around the airframe and standing up by itself, about 1" or more away from any contact with the airframe. The flat MDF work surface and gravity trued up the wrap to the airframe. I gently slid the wrap across the work surface so that it contacted the airframe, then you know what happened after that. Finally finished up by pulling the pre-positioned masking tape "handles" around and sealing the deal, and adding more masking tape along the way.
    IMG_0882.JPG (The glue marks on the MDF are from the construction adhesive that attached the 3" shipping tube to the MDF, not excess Lexel coming from the wrap.)

    Some retrospective thoughts for anyone who wants to try this method: the jig is really solid and if the MDF is clamped to the work table, you get leverage and can put a lot of pressure on the wrap and airframe without any damage to them, really pulling hard on the masking tape to squeeze the wrap to the airframe. I probably used too much muscle at the start, and accidentally moved the wrap off center, so had to pull off and re-attach. The Lexel made strings when I did that. If you go slow and gentle in the beginning, you should be able to get it right the first try, and then pull hard on the masking tape after the wrap is all the way on.
    This assembly is now sitting on the top shelf of my workroom; I will get it down next week, peel off the tape, and see how this method worked. At worst, I can buy another kit for $39.99 and start over using one of several proven methods on the main LJ thread.
     
    Last edited: May 24, 2019
  8. May 26, 2019 #38

    srfrich

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    More work on Apollo Capsule as an AvBay.
    The Estes Apollo capsule appears to have an angle of about 57 deg. A carpenter's square was handy for measuring and cutting.
    IMG_0922.jpg
    Cut styrene tubing at 57 deg angles, then screwed in 1 cm lengths of 4-40 all thread, then cemented the tubes into the capsule. 0FE6D400-D69A-4BEC-A4BE-37D1004A1F23.jpeg
    IMG_0920.jpg
    IMG_0923.JPG

    IMG_0925.JPG
    IMG_0926.JPG
     
    Last edited: May 26, 2019
  9. May 27, 2019 #39

    srfrich

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    Time to drill the Capsule for LES attachment.
    To drill a 7/16" hole thru the nose of the capsule, started with a 9/32" pilot hole, drilling from inside the capsule forward through the nose tip. A pilot hole is not really necessary, but I'll always take a practice lap if the rules allow.:cool:
    A wide 9/32" standard twist drill was selected because the heel of the cutting edge touches the sloping sides of the capsule before the point reaches the nose tip. Reason: the capsule walls will center the drill point for me.
    Used my go-to jig for drilling nosecone bases: a bulk pack of masking tape rolls. Lower the bit into the nose and let the heels find center; true up the nose to level (eyeballing it) by moving the masking tape stack while the drill bit keeps the nose center - it's sort of a dance. Then, power up the drill press, and slowly lower the turning bit through the plastic, holding the plastic gently to keep it from spinning but loosely enough so the nose naturally obeys the centering force of the drill bit. You can stop before going all the way through if you're nervous (like I was) but that would mean having to do the leveling dance all over again before finishing the cut. (this set-up photo was taken before switching to the 9/32" bit)
    IMG_0931.JPG
    IMG_0932.JPG IMG_0933.JPG
    I was a bit concerned that the hole looked a smidgen off center. Followed up with the final 7/16" drill bit, again, the bit's heels against the capsule's inner walls found center and probably more accurately because of a larger diameter bit.

    A 7/16" hole is a perfect slip fit for 7/16" styrene tubing, which telescopes inside the LES core tube. Gotta admire the folks at Evergreen Scale Models - their styrene is machine shop grade.
    IMG_0936.JPG
    Also shown is a beautiful 1:45 scale BPC made in collaboration with The Aerospace Place.
     
    Last edited: May 27, 2019
  10. Jun 11, 2019 #40

    srfrich

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    Igniters. Specifically, air-starting 3 D10's with 10 amps.
    Estes Sonic II igniters (I can hear the boos from the bleachers) were a no-go trying to light a 3-cluster of BP A8-3's for a static test, with my Transolve Triple Fire board and 1 3S LiPo battery. The Sonics cooked the pyrogen without lighting it.
    IMG_0948.jpg The one on the left is virgin.
    Sonics are labeled as 3.8 amp igniters. Shoulda read the label. 3 of these igniters draw 11.4 amps. The Transolve's output smartFETs are 10 amp. I thought about swapping in a larger transistor, but...

    NSL this past weekend was a convenient place to shop vendors and talk igniters. Chris of Chris' Rocket Supplies sells a small batch "Tiny" igniter that isn't on his website (yet). No stats published, but I bought 3 to test. Their resistances were significantly higher than the 2 ohm Sonics: 8.7 ohm was the lowest, highest was 30 ohm.
    V = I R This should be interesting.
    The lack of consistency gave me some concern, but the 3 test motors lit instantly in a static test. What a beautiful sight considering the frustration using Sonics.
    IMG_0949.jpg
    The igniter problem for the airstarts is licked if I fly BP motors for the airstarts. How the "Tiny" igniters perform on D10s, the intended motor, remains to be seen, but there is a lot more confidence now.
     
    Last edited: Jun 11, 2019
  11. Jun 11, 2019 #41

    srfrich

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    Tried again to machine a 6-motor centering ring using a drill press.
    Forstner bits were the key, not only for drilling, but for marking the centers. 5/8" - with a little tape - centers nicely inside a BT-20 coupler.
    IMG_0938.JPG IMG_0942.JPG
    The tip of the bit centers on the bulkhead, which magically has a center pinhole. Tack the coupler to the bulkhead with a drop of CA.
    IMG_0963.jpg
    Add seven 18mm motor tubes, and tack a few of them to the bulkhead with small drop of CA, so they don't move. Then use the taped 5/8" forstner bit again with a 2nd coupler (the 1st coupler glued to the bulkhead and now holding the center motor tube), and mark the center of each motor tube by pushing the tip of the bit down against the bulkhead like a center punch.
    IMG_0964.JPG
    Ugly after the CA-glued components are removed, but here are 6 geometrically exact center holes for an 18mm cluster.
    IMG_0965.JPG
    Then, just a matter of gently drilling each one with a 3/4" forstner bit. I don't recommend milling a centering ring out of cardboard like I did; plywood is probably a better choice. Ugly, but here it is, after not much work: IMG_0966.JPG

    Oh, and has anyone else tried making himself a supply of LJII-sized bulkhead disks out of BT-101 bulkheads (cardboard and plywood) using a Dremel and a sanding block? (and a dust mask?) It's crazy fun. IMG_0937.JPG
     
    Last edited: Jun 11, 2019
  12. Jun 11, 2019 #42

    Mugs914

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    This is such a fun thread, keep up the good work!
     
  13. Jun 12, 2019 at 5:00 AM #43

    srfrich

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    Thanks Mike! Appreciate that you used the word 'fun' - that's what this build is supposed to be all about.
     
  14. Jun 15, 2019 at 4:57 AM #44

    srfrich

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    Unmasking the vacuform wrap.
    IMG_0971.JPG
    The Lexel is strong, but my method wasn't perfect.
    IMG_0969.JPG
    First off, I noticed that I should've used .015 styrene strip instead of .010 on the top of the wrap. Secondly, noticed that I shoulda used the body tube gap filler that was in the kit for the bottom edge.
    IMG_0970.JPG
    Decided to fill the top edge gaps by dusting them with micro balloons and sealing with thin CA, which went well in some spots and required a lot of sanding in others. It looked as if the CA wicked the micro balloons out of the gaps when I placed the drop directly onto the balloons in the edge of the wrap. What worked better, I found out, was to apply the drop of CA onto the airframe tube just above the balloons, and let the CA fan out into the balloons. Per build parameter #2, I'm not going to sweat it. I bought a second LJII kit at NSL, and will probably try the Lexel method again for bonding the wrap to the airframe, trying to improve on the technique.
    IMG_0972.JPG IMG_0975.JPG
     
  15. Jun 16, 2019 at 5:01 AM #45

    srfrich

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    6-cluster "motor can" with canted motors - getting closer to reality.
    Some kit parts, specifically the 24mm motor tube, the 24mm thrust ring, and the aft centering rings, can be used to complete the motor can.

    Top view with the fore centering ring, made in post #41. The central tube is just structural, not for a motor. IMG_0977.JPG
    The middle centering ring is the BT-80 seven-cluster ring that can slide up and down to adjust the angle of the motor tubes. (Build parameter #5 is to thrust the motors through the CG.)
    IMG_0978.JPG IMG_0993.JPG
    Side view with Estes LJII parts used to attach kit aft centering ring to complete the motor can.The 24mm thrust ring centers the 24mm tube around the central 18mm tube, and the 24mm tube centers the aft centering rings. It's not glued together, just test-fitting the parts. The 24mm motor tube will need to be shortened so it doesn't stick out like in these pictures.
    IMG_0987.JPG
    It's convoluted, but it works...the bi-layered aft centering rings (per kit instructions, laminate the two together) can be offset to 'squeeze' the aft ends of the 18mm motor tubes where they protrude, since the holes were cut to accept the Algol plastic nozzles and are too big for 18mm motor tubes.
    IMG_0982.JPG
    IMG_0983.JPG
    Motor can won't be glued up until I know the actual CG location.
    IMG_0985.JPG
    And this is a 24" parachute 'cause I'm thinking of jettisoning the motor can, to save the fin can from the stress of landing with 6 spent D10s inside. :oops:
    IMG_0990.jpg
     
    Last edited: Jun 17, 2019 at 2:49 AM

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