Wild Goose Chase - Modifying a LOC/Precision 3" Black Brant X for staging

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LithosphereRocketry

Pining for the Fjords
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This is an idea I've had kicking around for a while now. My plan is to start with the LOC 3" Black Brant X and build a custom Terrier booster for it. My approach will involve a lot of wood glue and laser cutting, and should hopefully be able to take just about anything I can throw at it.

Since the Black Brant isn't intended for staging, it's less than forgiving in terms of stage couplers. My plan is described in a thread that I can't find at the moment- basically, four 1/4" aluminum rods that mate with launch lugs embedded in the sustainer motor mount. Extra support will be provided by a stepped ply "thrust plate".

The entire interstage structure is going to be based on stepped CRs and bulkheads so all of the load is mechanical rather than on the glue. This is one of the advantages/reasons I'm spoiled for having access to laser cutting- I can make a million centering rings with 0.1" diameter differences without a lot of hassle. In any case, the booster will look something like this:
interstage.JPG
The upper stage will be a pretty much stock LOC BBX with a couple exceptions: First of all, the aforementioned embedded launch lugs. I'll be using rail buttons instead of launch lugs (this thing is 9ft tall with the booster, a 6ft rod won't help it much) and adding an avbay of some kind. I'm also ditching the tailcone- it's not to scale, and the part it was meant to represent is taken care of by the interstage.

I haven't drawn the paint scheme in OR, but here's an "unfinished" render:
bbx_render.jpg
You know that thing people keep talking about, whatever it is, "incremental development" or something? Yeah, I can't figure out what that is either. Meh, it probably isn't important. (backstory: I got my L1 less than a month ago.)

Parts have arrived, and I'll be starting the build this weekend assuming nothing explodes. In the meantime, suggestions are welcome!
 
Subscribed and watching with interest. I really want to build a booster for my Madcow 2.6" fiberglas arcas now and put it up on two J motors
 
Subscribed and watching with interest. I really want to build a booster for my Madcow 2.6" fiberglas arcas now and put it up on two J motors

Which version? I made a 1.6" Boosted Arcas a while ago... It's a lot of fun. 1000 feet on a C11-0 to D12-7 or 2000+ on a D12-0 to E9-6... That configuration just keeps going!
 
The build has officially begun!

I started out with a bit of sanding. Giant collective sigh.

I just got a new belt sander, so I thought I'd try it out on one of the small canards. No dice- made a complete mess of it. I was able to get one of the main fins nicely rounded though, and I sanded another canard by hand to a very nice curve. Belt sanded one on the left, hand sanded on the right.

It's not a big deal- I'll be lasercutting a lot of plywood so I'll just cut myself another.
T6KwNSJAUNwlBJQoOiWfcVMlvMpr7GMj0muODD_9EN5cv1gTIWnhjxZj-VzXoTa33u2sIiRduLj7dWY5mL-BiIihzRdPZT2B0gjnFp-TbAwIudc2Xm_1wq_eql8-mXpvvSklBEJY9BwIiz_TKaa--STfM-zXSE7PsjumSIbo7132nVdlyIgyc1sN_EfHSaOaHAIAJOnbZNexaAtIM6vNEhd14_QAOCB1-10m0_PPFBPp3tFCVnhP0ylExnUQJ6dVA92Y_6qxo58O2rrM-i81xmKdIc5JgCUvZcpeaU6n-Vw5v2Mu7IRF9hfTZkqNTQjzPDk6KwesEdo1vP_fAYM1cmLa6voLrMZsNdnq49zoaQ6blLd6zdx-B4oWhpbUt7dtNyKIAJM8GWYGMoO2dA-_iL2hB30gTuajoxY79c6Llt09P3idXXuDm87J_Ia2-y68OMd6Q6jB79rXdikNV6xsHtqQYme7SLWSPA9xShyVgwPubOs5Zbpr-QdK9IUZqhBnjEgt3Ve9RkcBSDMR0UV0KmzR5l3cQvibBEt-UPM11_zrb592FrbBvvQuLPu0hor-puRkqKzvnCWXFNth3PuWT0aVblJ80PKeDPDxrYk=w1709-h961-no


Then, I epoxied the coupler insert into the upper body tube. I would usually use wood glue, but I went with epoxy for the extra working time. No major fails here, just pushed it in with another coupler:
DmYKnpp1-uBAN-jjYaR68_Kg2ZmO2XO19XuTFIC50lTQEhZCzLOwoKgx-d4N_32B751hOxoNvRGzlyco8dtjNd_I2tLNpNPZKQrfxZ5QEG486_1KFzyLUx28k34nt4MnHtD8P9RZywFai4zOsQzrVOyuz9oINMMq1pC9g-DlGwJ_G3cABkBFkbRjUC6FFqptYRYzxocXml1OAX4UDK6yHPn7STLeGOVi3bYG-3u9KVt9aoxlZIZHP2vgpyR33cIeIzRg4Yn6BdlXLfMSKXHPbmFR_W4R1hCLD8OHFXC10vqEqhbgLr5sw84LwDZRbGoD4JX6ElEzdSAQiCd0dpgFC9cE6o-NMxGMRN_RnR_V9rigb_NThcCPwL6_ZlME7UD3yndTEoh8dBPvf0z85bgS5TuFKGvkqKg8pPywaKmgV3e1VJfSVODBJQ8qzebdy_2BpyfFy43qdLWQa6xfWpLBVKXJ5XMJ07oOWPq26zb6CBIEmXMx2WF5TIJr0QvmA-KnNrwSOOoVu34XpUKxekYCQcvOVlHG2VKTJUvJwOfXXVYlOpABwYooDPvLbd63ez0F2u06wdL8vyRAkZjrG0_qWZASgdb-_adzgg1pK2U=w541-h961-no


And Titebonded the nice canard into place:
kw4rFTzY9kb2B0SZ84AD5Yj4GRw1H1FfUcTBr6I4A5iAdx6Y6hPEZwchynSLmFeIkHxsNsnVwYazcOb_U7KHpFw0VVU6EQeYBrz2EbG1mnDn1E_klJ_V7Lr1cP91NJ1d5W_rxDjpKnH1YMjL8lJLOa1WXdHC-452XSDJCs3yjaUF66BE6RAshXdW1_0V2uOnhzHWMcb5MGjQxCewTeXdqLZAvX823wKw2j8UymyqrSoRsd02HM1ynfPIrfsf2S43-SEY6vy1GmOc9MmHi4waF-Ed5UaXddOSXwEsJPHthka-rEYUXyx5JXe59CwLdSV_PSKt_h2MGCQ7Bu0ojVbrmjfIJ9RjRdCccHDIDQCMXx_5fkpY-sf3mkNctS8bYpPSNCGwMVKULWu3OQCV4cd-H888dTwcG0gJRKspEUS8GYrH0U3HF_oUe0pvUmZZshzFOzXTwE4tUreo2_gXOJ2iqBtr8OCC2g5705JzRO4kJ2O1fmzWs5rb5OLcQJTWPVOZeTMq_IxSIiBNZ8ZgmF07DcBAW4-YebWBDhXEOayESeouPjxcUyH5yciTJQpg7o-hG_WZVkNk_h-i_son3LmpvMHSkgtsnpVAs7ACRAk=w541-h961-no


A lot of this build is waiting on laser-cut parts, but I have a start at least.
 
More progress...

Got another canard rounded and glued on, but forgot to take a picture of it. It looks basically like the first one. I'm debating how I want to do fillets- the canard I glued yesterday feels pretty solid, so I may be able to get away with straight wood glue. I'm almost definitely going with epoxy on the main fins, so I might just do the canards while I'm at it.

In a fit of generosity, LOC gave the Black Brant a 17" motor mount. There's no way I need that much, so I cut it down to an 8" section for the top and a 5" section for the bottom, with an extra 4" for a future project. I had ordered a full-length 34" 38mm tube thinking I'd need more MMT... I guess not. Ah well, spare parts are an excuse for more rockets...

I am definitely a big fan of LOC tube. It's plenty strong and cuts beautifully... I got a near-factory edge with a somewhat old hobby knife.
92CJCO052fH4CDLeL4-kYntzXSmgrERe62f6ve-CytAeeGPINmirKiQ58dhkZbsLILN-vJhyUMvbqa7vLohTs4ya3fhOhSAbRuPobI4AaFow50R6sw2EdGuCRafymsb_U79ZkUkohXsrJW7ulOE55BMuYdV9rEfawCd9vT2aLUrJereaa4SSI1gi-M26vyn2q3XEM8565G4hhvkM1suLYB-EZYhZRA4IYpkxHGc5jSFfC1QUs1tPCGaZ3AaLl2btyAusAifjSG1FgZT8TJIZ_3OVYyH8zrFaL7ln80xHSy6nrtWMsoBt2ubBhzMvgYxORVHDuQ8k4o3osJqTDoN25GkG3Tt3RvDwPv9Qz6vNFC5ZPfqixWeRLqvmmk-eJfmdiRpIVmr93XHWJWF11Y_Vqvuz-LINvZoKT7QSeJChR1VehO_sr4e08hUxDUEpRtrOqdGVUnuBsI7hlT-6NLCji6ms95caWVUsGNjbkF6iYiLJG7KjGhiyGRlOyKOnDjO_SJj7NJ3m9CHGxmWfkLySZ_SxqfxdIqBKKYXm4sEnonyHTSyfjwdJp5ASyJv59shjwnODyP1puq96Ro4lmNVaWjet3C55Uz82y9R3EXg=w541-h961-no


An important thing to consider is how the sustainer MMT goes together. My current thought is to use the "petal" technique, where the fin slots are cut to the base of the tube and the entire motor mount is assembled separately and installed, then the "petals" are reinforced with a bit of coupler. Any thoughts? The trick is that there will be 1/4 centering "wedges" in the middle of the MMT to hold the 1/4" launch lugs... Sadly nobody that I could find sells launch lugs long enough to reach the entire length of the mount.
 
It would be my first attempt at staging a rocket. Where would you recommend I start my research?
 
It would be my first attempt at staging a rocket. Where would you recommend I start my research?

I really don't know. I build my own altimeters, so I'll be using one of those. My Arcas was just gap staged with Estes motors- this is my first HPR staging project as well. I'll be doing some practice flights with my LPR staging fleet before attempting this, but I don't have any experience as of yet. There was a thread a month or two ago about HPR staging basics:
https://www.rocketryforum.com/showthread.php?144260-Multi-stage-motor-selection

Lots of stuff here:
https://www.rocketryforum.com/showthread.php?144667-2018-the-year-of-multistage-awesomeness

For my first full-up flight I'm planning on an H399 White Thunder to an H54 White Longburn to about 2500 feet. I'd love to put it up on Loki I's to 29-3G loads but that's a lot of hardware investment compared to just a 6-grain 29mm case.
 
Not much new on the build, but I had a spare hour and got started on the Eggtimer WiFi switch that will eventually handle the avbay control duties. That avbay's a pretty long way off the ground...0502182206.jpg
 
Finally got the laser cutting done for this project, so I can really get started.

This thing has a lot of CRs.
y2qInK1juweZtGhoxrMtoiJoZx17iMUD9_CEpjyAfG1vLL9gsYOIWlko4hxBmQ5FujyvFViIo240WGtnwTXALu-0x-y2txm7c5tVY3UXj146QO-96ciEPVPbm-3C_xhiUFpVLcEjzbpoAvfgyK1sRPfAd8uduE5bGU9gyiQdhqPyruBK9OdaGNEld60HAUAynuyQMyv848YBFFz6o_Em1kw9wmbtqycM2-0zPyp7DzWyZdWcba3sJ7sWXh61-zlPzNjT1BobEOg1VeTmcoP0Qlg1U7hLhWPPWqy48mhQ4xBsTO7-_rpl30bPB-CzH7fl4f5YTiENzit8UH_uiFcQH-H6jvVvFz2CV5jrQupwZRkVA08oCJ_rIO0vkNwtK1GaDN64WMKQIj7VdqDqES_m8cXVtW_9vDORmM1k3_5l-one1ai4A7OEB1GcPcMJfXG3nutOUwJdzl36Aw6LSS4dBdxfT1NxFQoJFqrSzjT2-0N7dwQoaeB-mskC0LKNVW14kigm63Dz5WfKpk7lvlAzRNf6F7-VwvQZHoSacoukEE1RpTr46aM5NEBCcuw5d0pJZBeV6KXww60LCL4gclJu1Yz09Pya88nowFe8npc=w1705-h959-no




I did a bunch of laminating CRs together to start with. First up is the bulkhead for the booster, which gets a 54mm to coupler CR glued to it. This will be the back end of the "nosecone shoulder" of the booster.



MY2zOXbpME8g4_ZWWlJXJ1ugaS2TG_BfbphHLUpix99BMyLOWOfEzTH3HqOvi03YHRjh1-8pXYsyAbssxRIJcMUEVzLkXclOPb0WZcy2UDlOZdwzxCA-h8DoBx-8H9BUxxaKFJET5xEnWzzU3xtcjIKOj-NPAVEg7h49Osk0Vxk7Y3pNeTfDKgDu8AQK68Gf8OfGlU_H6PV4Rj3MO_SyqeBcZccQUA9-AvzEcLN6It9o_MuLdXn8pUTGHkPN8RcRYCiRzAmHvqUBiHBH-CbR6tuAfp4LPQvIPommxlUaoa-uooBQiohq5FYQ-BiC0sXOgP2Lri1bIsboK026TUZZCw4I0rt84sLRgNUSnt60hAswBnR1M2effb36kJ1R-ay6-4o9k1Rj0NF2-03aJaqnou3WX5ATbSt6oF7ACDJPO-1Z5sqCe5_Zn04ny5UfyFL7Jwt0Q6nJSMOada5aSqScqi8ET4GZCvI7Q4EsqKN5I2fLCfI4oiixLwIKCGeafrCIZ2ZsWipSvfU8VV-IeA4ZxANoRHYlzQviSTepXcTYdaH8MlParOxF19rmoYypPS2GJ94H3L0O-LYrQFnxVBMXT0iPUPGkpuzt2IRCW4o=w1705-h959-no


Next will be the other end of that shoulder, a coupler CR to an outside-diameter CR to form a lip:
jOdmMN7pUUmHqVT3hGIEz6mGn8B1Pg98t2c-bZm1Cv6N_TQNGfEvWG15ZN0Nlx8M9Um_t98o91hgrWgxhPK6QicvF_Np8O5CeJqivwCHoLW2DB17T-Wijfxjwx7uku649X4PDQkfERHDJjvquAO5ehrKuwGG0p6eBN0ZJvfZi2oSFoDc-d7W9nrcaeCq8fgh2td699H4R8WvvkW4cts8VMofMtidnGUvXtZ271azfh-_BlBgwo_aJ2ghSRxoe7zXJYR1n58tp_iYtWgpbTCBcq1_XaD72g3qfOOARP9AQMztRgW8jQbaAAE1pLYaT-EMqv1zscjXk2LONZtYCj6LU8frXp3XqarX-gQNb_L0Tba9dTlAcKRhBp-I8pc8QBFom9oAOWC91dRZPfdukyREPusQ_Hd23LHNOrjEjV_i3TTSdDWLnWByT3qHUwm0j9g_T-bpcqpwehk5yYraUNu_j2t8BMSMFZRtPkYZKsYagXwv7ODXExGw2y65gDgmRFODjM1DauG6kT52p8e35wCTF16Cuyp6Ef-2oyAnOme4OCgpVA1L4_W5ijDSB4bw23ggNOfsy23ftWYioUHbyRfHVOvTALSshGQ0L4HJuBg=w1705-h959-no


Then the other end of the interstage section. A standard CR with 1/4" holes gets glued to an OD CR:
QSyef2J1JQQMHrk27vbpDtgRGVV7HzDbnyNLT4samsu8SbMDkAXMcsSYbgBND0foZ-v2aJQdFLvRjnwWaVSI8uJPgqE1XGWrRjV5g9MtUe8I2c3ngOWcsiSvUS2xNGAqymzPQThK2LlQutVBw-TlU1itWv4ssUhDh3fDePQSY5RyHjxTqDK1-YHXVgls6SezrO1MKeq6QavvF6N6UMzCIFVcjEjtfOgg1FTdQQoR1qDyEmIHU_-k-GPdg2dTCpnd7jEHVePhSBStrbdUqw2aAVqn88dZuYKtyvyCCvIIb8yi8AjsaJtJ_NazDXIYO-txGa-80xXAonA4Ro90oOp62xFJEoxC_Ii53hBFZ09tECxdsPvKb3-fmhCjcJzRAvPhgANoA4geT0YOToJ1Chdh6wy_JIVTD7OSdqcsbiguX8m-k87g-ebfBU19zxV4eWULAcdZ6ymJeklGiY6aJihT8xnWmvIN129vXr5k2S7WWsAYzLeVu48KqUFMaFii6z0eKVtUu0zXLvsAMzi3RinhQE2mXd_ZYAD9DUshs-WshCjNCiMiHK6GierScZ8bgyt-Ai4KolykR-YvmD3S57tY6Ll9PMymGMEYzBSmNBs=w1705-h959-no


Then the interstage thrust plate- the same combo, but with the 1/4" holes all the way through:

W54GEKfzO41u-3Se0wM_CC6dZRS4n5oVjr7Lp3MXwYnhMzISAKntfJA77QZoC7f1uWbwGK9k68d_FboTCtqMqcJqsV5bp5wtC7kfJ3e_MumRkmro5HAVtsxU_95TJKRuCDrpf_CpRhl-LelRvY9NVaVoBVKVuSb307vtUL5nYVAxujgvEUwNQzpZ5mJso3274vk-H9_TVagiEgUkvidXd1dKgxB_YBn2ZBlLtRyipJGVm46teRmEytQonxObYtHAr0pXxHBXfnvUlyFZTFCsCj8cQVtXBH5aRgBBxgI9-o0ifiBVaP2p2P-8CfqeCGbPujMNHsZFpU6wVp7eGbv8epjupF77JDe4L90VXGivOYIseBcKrwIqm50_lDhSRwbwu7HJle4-9Ud-zlEtOo2kZARZXnF0G302FeBWJIVLcTwIqnva51AYjtGlj4gEwFz5CS1J2NM8K_NPWQXC6zMURhhhOHN9uicyWMQyVGOv8vS00xrCQjBsyEl_cO8vvSkZjegfV--S-yMbNlsZFwhfFFHZw5E_MyP_iJ3RF3J0dgL25dhWLaj20g21VEDU4UmokKVo7v-B4f50BxizmRPNLfcuIGirUfVORZlXhgQ=w1705-h959-no


The other side will be a coupler CR with a 54mm coupler ID to engage with the end of the 54mm interstage tube.

And the last canard, a replacement for the one I screwed up:
EaF_6ucCasgdM3fmc1EUTIupsPsS4aTTLRN_gj5lqlQNPzo23pm8f86Jth0ab7OHRAGWVIMKMhc7-Dsg3Docs2G-2uG2LM8GwgB3mQsPjCZ3fqv6TWRnqzjlqCSjl1dObOffRFraA34YK1dN8-j1RZaDUhbxSZodLKlU3t4FgJaSzpOo3-D27OryZ8vGT-gONG95-7RmEx4iaGpT5cFHrZvHMHW3NxoOunig_wftqrPlnxXCbS_HL6s-a6RQUexolKtrCg0hQaEGGgSdAd0c-0mra8ZSQhW7ouHmzsyvcGgmegmI_AJTlUGGXWSG8Jet4Zvfog8b_7SjWezWBMUGO5UxqYUFlgGC6km6Q_XeafRmw6IwvhmN1nVtJ5FGs5WWb47LW-y3_1MoglwA3vmDH7IZB3Z7djwD2VjrH-TzYsqQKa0PAlC7Fds3NipBIfbVD06IyetJiOjySjs8WBrc_NuZt1w_GQbgU90wN-xPPB_vnRmwPfaaeA2dzmweG8tVR53Qy8sY4RClPadxhxjH0xdvHYfrHj7R79QiV4OVBhrh3JfMF8mcQ8SO1bGiqU33-m07dJU08BRT3IV-R0OyHxo0FXJMVGaEa0PY6mY=w1705-h959-no
 
Man, I've been away from this forum for a long time.

Long story short, the Goose is back on the run, and pursue it I must. USLI competition is over (at least for our team :/ )and I no longer have all of my rocketry time occupied by that, so I'm going to make a solid effort to get this build completed. Along those lines- my college club owns an Aerotech 38/720 case, so I'm switching the plan up a bit in terms of power: an I600R booster to an H159G or similar sustainer (have to stay CTI for the BP pellet).

Unfortunately not documented, but I finished up the LOC portion of the kit and painted it in traditional BBX colors:
1649832576749.png

I did take some very slight liberties with the colors as listed by the wonderful Peter Alway- he lists the canards as brown and the checkered segments as fluorescent red, while most scale models I see have the canards in gold and most actual photos I've seen show a very muted red (or solid black) for the booster. I went for copper and dark red as a compromise, and I think it looks reasonably true.

The only significant deviation is the addition of four 10-32 screws at the avbay-to-payload and payload-to-nose joints. Very overkill, but they're what was lying around in the shop. I don't have pictures but the avbay was set up in conventional threaded-rod form with a small MDF sled for my homebrew altimeter.

Aside: I also forgot younger-me came up with such a good name for this project. I'll be sure to remember that next time I fill out a flight card.

Update part 2 to come soon...
 
Looks good.
How is the 1st Stage booster coming along?

Very little progress on the first stage so far- I haven't had the time to get started on it, and I forgot I was short a tube for it since I stole it for another project (which unfortunately I have no build photos for.) This is how it ended up:
1649895527641.png
(After some damage from mishandling the 3D printed railguides were replaced with normal ones; other than that, it's been a great flier on Loki H's and definitely worth delaying the main project.)

Back on topic, the promised Part 2 update. I forgot I hadn't posted the pictures of the fin assembly before being installed in the main tube:

After surface-attaching the fins to the motor mount, internal fillets were (messily) done and the full-length launch lugs were installed using small plywood spacers:
1649897422150.png
(Cameo by my other main project in my time away from the forum, which I may write about sometime, motivation depending)

Anyway, after full assembly, I headed out to the cornfield to give it a try -- hmmmm, that flight card feels a little heavier than it used to, and my wallet a little lighter...
(we'll see if this video embeds)
https://www.youtube.com/shorts/6S50yWO7wUg
The Indiana mud and stiff wind were not kind to the paint job, but it'll clean up OK.
mud.jpg
 
Dragged out the box of parts again to get started on building again.

1650291050316.png
From left to right, top to bottom:
- Booster airframe
- fins
- centering rings
- Booster shoulder coupler
- Booster bulkhead, with centering ring for interstage section
- Interstage section airframe
- Shoulder upper centering ring
- Lower half of thrust ring assembly with centering ring and pin mounts
- Top centering rings for thrust ring asssembly (all 3 are unique)
- Aluminum interstage pins
- Sustainer avbay and coupler

A dry fit of how all this fits together:

The pins go in the 1/4" holes in the thrust ring assembly, and pass through all 3 top centering rings, arranged so as to create a stepped joint on both sides:
1650291466293.png

The whole assembly goes at the top of the interstage tube, with the centering ring and bulkhead on the other end:
1650291553954.png

The shoulder coupler goes over that:
1650291585180.png

And then the whole thing goes at the top of the airframe:
1650291614960.png

Actual gluing coming soon...
 
Updates! (Definitely not several months late... imagine all of this progress is happening during the chaos of finals week.)

First order of business was to get the avbay in working order. I got myself a cute little 3S LiPo battery so that I could drive enough voltage to light a full-size APCP igniter. Shoutout to my drone-enthusiast friends for recommending Tattu to me -- I'm gradually standardizing to them after I lost a couple of my usual Turnigy Nanotechs in a disagreement with gravity and have had nothing but good experiences. (Well, one complaint: they only ship this particular battery with JST termination instead of my preferred XT30. That actually will end up being important later.)
1657336801972.png
The avbay layout is pretty straightforward: flight computer on one side, battery and WiFi switch on the other.
1657337047491.png
1657337064929.png

I also started work on the booster stage. The lower half of the interstage and motor mount were epoxied together as normal with minimal fuss:
1657336648723.png1657336661023.png

Fin slots were hand-marked and cut:
1657337217344.png
1657337261940.png

Originally I had wanted to retain the motor with a bolt and threaded insert, but that ended up being too flexible and would just bow out of the way whenever a motor was installed. Instead, I went back to my old standard of slapping a threaded rod on the motor mount and liberally soaking it in epoxy.
1657337406219.png
1657337419348.png
The forum has nicely informeed me that I've used all my attachments for this post. Part 2 soon...
Apparently I had a stray attachment, so here's one more step: fins installed, nothing particular to note.
1657337632311.png
 
The promised Part 2.

As I looked more closely at the interstage section, something didn't seem right- I was running into the same friction issue I had originally before remaking the parts. In fact, looking at the pins as compared to the lugs, it almost looked like they were closer together. I went back to my original design, which I hadn't touched in 4 years... yep I designed it to the wrong radius. Facepalm.

Oh well, redesign time.

The new design uses three parts:
- A plywood top plate and cardboard shell, adapted from parts I had already made
- A dense-infill 3D printed retaining ring, meant to be the main structural member
- A light-infill 3D printed transition and centering ring, meant only to stop the pins from sliding backwards

All parts were printed in PETG and aside from needing some aggressive sanding due to swelling they came out excellent.
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First, I used the structural ring as a drill guide to drill correctly spaced holes in the top plate:
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The pins were then press-fit into the ring. The wood had a tendency to bow the pin inward slightly, but not nearly as much as the old misaligned parts.
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Fit test- it works!
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The whole assembly was then epoxied together, along with an additional transition cone on the back end of the interstage. No pictures here, my hands were very messy at the time.

Obligatory full stack - this thing is pretty sizable!
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Next up was running the staging wire. A small notch was cut in the upper airframe to pass wires through:
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Old ematch wire was then threaded through a passthrough in the fin can and forward to the avbay, using electrical tape to keep it neat:
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I could not have planned this better.
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And with that, the rocket was ready for test flight!
 
I had mentioned in another thread that I was planning to fly this at MiniMWP in May. Well that did happen... Sort of. Since I was using under-development electronics, I figured I would give it a "dry run" with only one stage and make sure it ordered all the right flight events. I picked an I357T since that gave roughly the same acceleration profile as the I600R with both stages, and successfully flew without incident (save a brief panic Walmart run after the photographers on the team relocated all my SD cards). Pulling up the data showed that all (simulated) events were right on time. Flight log is attached if anyone is interested.

Next it was time for the big flight. I got my motors built, got my electronics tested and wired up, and started the walk out to the pad. Due to the heads-up nature of this flight, I got put on the further rack of pads -- I honestly was planning to ask for it if I didn't get it automatically. I get out there, get everything stacked up, pull out my phone... where is my phone? On top of my toolbox in the prep area. Long walk back, long walk out again.

I'm all set, go to arm the altimeter... no WiFi network from the switch. Sigh. I tear down the rocket and bring the avbay back to the prep area. I unplug things, plug them back in, and I have WiFi again. Long walk back to the pad.

Get it all stacked up again, get my phone connected... connection immediately drops. Double sigh. It eventually reconnects but it won't stay up for more than a few seconds at a time. I tear it down as before, and manage to figure out what is actually causing my issues. Remember my complaints about JST connectors? A big gripe about them is that they're primarily sold as pigtails rather than loose connectors, which are typically made using fairly subpar wire. Turns out my JST pigtail had been worn down to the point that the few reliable strands weren't making reliable contact, and poking around ended up breaking it completely. I didn't think to bring spares so that was a full scrub, and I'm not sure I'd want to trust another one anyway after that one failed so easily. So, no flight, but no failures and a straightforward fix -- overall a success. Next flight attempt will be soon(tm); with IRI not having a summer HPR site as far as I know, it'll probably have to wait until the fall at least unless the USLI gang is up for a road trip. In the mean time, I'll be working on refining my altimeter code as well as maybe starting a new project, depending on what my wallet says...
 

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Update: Once again tried to launch yesterday at ROCI. After being delayed a couple times due to my phone losing connection to the Wifi Switch, I ended up taking a look at the wind, my altitude charts, and the forbidding wall of corn next door and saying "no, thanks". Oh well, will try again next launch.
 
At least your rocket came home with you. May not have happened if that corn wanted it.

We have one or two more launchs at local club before the corn is cut.
 
Another update, tried to fly again earlier this month at IRI. This time I had planned to step down the booster motor to an H550ST since I had somehow goofed up my simulations for the I600R; somehow I had put down the projected altitude on that motor as about 3000 ft when the actual prediction was closer to 4500 ft. That's a bit farther than I'm comfortable chasing this thing without GPS, at least for now, so the H550 brings it back in line with my 3000ft target at around 3300 ft predicted. At the end of the day, this didn't really matter; despite good outlook at the start of the day, the cloud ceiling prediction kept getting pushed forward to the point that by about noon it was predicted to stay <1000ft until 8pm or so, and at that point I decided it wasn't worth the wait. Better luck next time...
 
The goose finally flew Saturday, on the H550-H159 combo planned for last launch. The flight wasn't a perfect success but nothing was damaged and I think I know everything that needs to change for next time.
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First stage boost was beautiful - I was a little worried about flex in the staging joint but it ended up flying beautifully with zero signs of undue stress. After that is when things started misbehaving.

The separation charge went off right on time, but from video it doesn't seem like the stages actually separated. The recorded separation charge lines up with a small puff of smoke in the video, but both halves are pretty clearly still attached throughout coast. I'm not super surprised - since the interstage uses pins instead of a coupler, there's not much of a seal between the two parts, so the BP exhaust just leaks out around the sides. For future flights I'm probably just going to skip the separation charge entirely.

After booster burnout, there is no second-stage ignition; the rocket coasts to apogee and then the booster motor eject and sustainer altimeter charges fire within about a second. The deployment of the booster parachute shakes the booster loose from the sustainer and the booster recovers without incident. The sustainer chute is tangled and never fully deploys, but the rocket lands in soft dirt and takes no serious damage, the only casualty being the launch lugs used to secure the avbay sled. My guess on this is that because I added a beeper to the shock cord on this flight along with a JLCR, some combination of the 4 things on the main chute quick link caused it to tangle; for future flights I will either move the beeper elsewhere on the cord or use GPS.

After retrieving the data from the altimeter, it turned out that I had mistakenly loaded a test version of the flight code that had a very low liftoff trigger threshold, about 1.2 gees. (This version existed because it's much easier to test on the ground if I can fake a liftoff trigger by shaking the altimeter.) It also turned out that the accelerometer had either not been calibrated or had been calibrated badly, with about 0.3 gees of offset in the X and Z axes. Because of these combined issues, it had detected liftoff almost immediately, meaning that the gyro orientation wasn't reset to vertical at liftoff; this in turn meant that its calculated orientation had drifted by almost 90 degrees by the time it launched, and the flight logic (correctly) rejected staging.

Overall, I feel like this is a pretty good result. The main parts I was worried about (interstage structure, altimeter decision logic) worked as intended, and all of the issues are pretty straightforward fixes. I don't have another H550ST on hand, so the next flight is probably going to be with the I600R and GPS tracking, weather permitting.

Addendum: A huge thank you to Paul Wolak for his advice on stage couplers - his incredible WAC Corporal flew just after mine on two M's in one of the coolest flights I've ever seen.
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Thanks for detailed report and good video.

Overall, this was a successful flight for first time air-start 2-stage since all parts recovered without damage.
 
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