Another LPR gap stager- Standard Aerobee BT-60 sport scale

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LithosphereRocketry

Pining for the Fjords
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I've wanted to make an Aerobee sounding rocket for quite a while now. I have an Aerobee 170 scale drawing downloaded off the Interwebs timestamped 11/16 that I never even put mouse to OpenRocket for... Fast forward to recently, I got a copy of Rockets of the World. One of the first models in the US chapter was the Standard Aerobee... Ran a few numbers: BT-60 with a BT-55 booster is pretty darn close to scale. Uses 17" of BT-60, so less than one "full" tube, and 5.25" of BT-55, easy to get from a 6" scrap I had lying around.

BT-60 is also (roughly) the minimum tube size for my ArdIU project... Intriguing. Let's see if we can fit that in there.

The only problem is the Aerobee has those conduits that go up to the payload area. My solution- a HED style "stretched" NC shoulder:
payloadbay_render.JPG

Here's what the final result looks like:
sim_scale_updated.jpg
sim_render_updated.jpg
I'm going with the paint scheme from Air Force Round 1 because it's interesting without being too hard to paint (e.g. AF Round 2).

Yes, I have a motor block in the sustainer. Basically, since the motor is also the interstage coupler, an E9 is the biggest motor I'll be able to fly anyway (composite thrust rings won't fit), so there's no point planning for bigger. An E9 with ArdIU driven ignition with an F24 first stage gives me about 2500'- plenty for me, especially given that I can't fit an Eggfinder anywhere. More typical would be something like a C11-0 to C6-5 in an adapter, to around 800'. I'm planning on rear eject with a streamer or something for the booster, as I've had bad experiences with boosters of this style...

Build has started and documentation will begin given one or two more round tuitts...
 

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Love gap staging.
Look forward to seeing how you rig streamer on booster.
For first flight, consider A8-5 in the sustainer. If the whole point is just to successfully pull off a two stage flight, you don’t need more altitude on the sustainer (you won’t see it well anyway) and it may save you a walk in recovery. Also the A8 engines have a wider nozzle and therefore will gap stage more reliably.
Best
Tom
 
Finally getting back to this thread!

I haven't had a lot of free time lately, and most of my free time has been devoted to trying to get the next ArdIU PCB finished, but I've made some progress here and there.

Being the lazy person I am, I started by doing everything I could with the parts I had ready to go- namely, setting up the avbay. I decided to use some 6-32 nylon screws I had lying around to secure the NC to the "switchband".

(I can't get this image to be anything smaller than full size... Sorry!)
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Then the sustainer motor mount... The motor intentionally hangs out 3/4" to act as a coupler. For electronic staging, I'm planning on copper foil tape on the sides of the motor, or possibly just Copperheads. Motor block is a mutilated D12 casing- I'm down to about 1.5" left on this one at the moment...

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Next, I SLA 3D printed a boattail and booster transition. They came out slightly oversized but otherwise nice. (I apologize for the crappy photography.)

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Next up will probably be fins, but I'm not sure yet.

Love gap staging.
Look forward to seeing how you rig streamer on booster.
For first flight, consider A8-5 in the sustainer. If the whole point is just to successfully pull off a two stage flight, you don’t need more altitude on the sustainer (you won’t see it well anyway) and it may save you a walk in recovery. Also the A8 engines have a wider nozzle and therefore will gap stage more reliably.
Best
Tom

Interesting that they're bigger- I would've assumed they were smaller with the low thrust (same nozzle as the B4)

800' isn't that high, and I love long burns. That's basically my only reason for picking the C6-5. I'd use a B4-4 but I don't have any on hand- I get the mixed 24 pack from Estes, which skips over B4s.

Honestly, I don't think it'll make too much difference. This rocket is a heavy sustainer on a light booster, so it'll probably fly somewhat like an airstart in terms of performance- barely-noticeable difference at staging.
 
This looks like a really cool project--the exact reason why I wrote "Rockets of the World."

Your rendering sort of implies that the space between the booster and sustainer is closed. You can leave it open and it will work. You cna even set the upper stage nozzle all the way up flush with the rear of the sustainer and it will work. You can download "The Art of Scale Model Rocketry" free from the NAR site and look for the Aerobee 150A plans to see the mechanics of it, but without the upper stage boattail.

Peter Alway
 
This looks like a really cool project--the exact reason why I wrote "Rockets of the World."

Your rendering sort of implies that the space between the booster and sustainer is closed. You can leave it open and it will work. You cna even set the upper stage nozzle all the way up flush with the rear of the sustainer and it will work. You can download "The Art of Scale Model Rocketry" free from the NAR site and look for the Aerobee 150A plans to see the mechanics of it, but without the upper stage boattail.

Peter Alway

Thanks, and thanks for putting it together!

The interstage is closed on this model. I'd love to have an open interstage, but this rocket has no interstage coupler- the only stage retention is the motor, so that tube is needed.

On the build side, I got the fins & conduits done. I had all the materials I needed, and everything worked perfectly with no screwups.

Everyone said:
Haha, you expect us to believe that?

Fine...

Yesterday, I was searching for my 1/8" balsa. I could've sworn I had a sheet of it somewhere, but it was nowhere to be found. I managed to scrounge up enough scraps for the booster fins, but that was about it.

Fast forward to this afternoon- I was talking to a friend on the phone, and asked if he had any spare balsa. As I was asking, I looked down, and the sheet I was looking for was right there...:bangpan:

As I was sanding, I also managed to snap about 1" off the corner of one of the booster fins. I reglued it with Titebond, and it's now barely noticeable. You can see a slight yellow line on the top left fin, but that's about it...



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Next up, conduits. My original thought was to use some 1/4" dowel I had lying around and split it in half. That didn't work at all. My solution was to use more scrap balsa to make some 1/8" x 1/4" "planks" that I can sand into semicircles.
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Progress is being made!
 
Getting back to this thread.

Glued on the conduits and the avbay bulkhead:
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And sanded them round-ish:
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I had to put a wrap of tape on the sustainer motor mount in order to get it to fit, but it worked fine.
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While I do want this rocket to be capable of "regular" staging, I also want to be able to use it as an electronic staging testbed for my ArdIU flight computer. To that end, I chiseled out the edge of one of the scale conduits in order to use it as a real one. I used an old ematch wire tacked in with CA:
vD3CnVZNGTaTtTFtHGQk31-Ff0UQfXeTmbJ5CoYfU6GRJH-HPWM48zeHbubML5eL-R99qQntZkx3sc_BV4-Pj-a3yVRjhvO6V21kj4sowr04LO4MVKm3gyxwy9X2VOp7_uaf8eVJq-1xODi3L7CvZUyTuWiDI-ykNXf7Y6vW0q4ISHCOedr0fySfiyfF--u1n7LFHbR6aApuyDGHybLcRznJRA8e5gZN15mWrZsjIJpu9uS41cqBDir59Mt7K5UKUvpzUg_phtaCMVsyoBpYsIQWQFYomTHPOjoYURdb-ABroUnXtcCfB02o3Tso1uv4Z5uSC95fwOYrLMHl-ZZiuXw1E9NXwZRdTAQ1-dToVIEKm6lODPSSi3KKYMBiUjkRUbkSta5gqOVz5FHpttDonpHmXBCJ9jgrN40yHu9YkhjIT7nLTuajCObt5kxS6y_imA31ydDk91aV4JIUMlJ7ZmL-pb-ESGm1lyqahVcy4DcZP-dHw-9hcLsePanDvK6Vmi44_YbgLg9PH_gKe5nYJYYHWalxqwOCaIOh1j4sL0Omp6H82lHg5H3L_IYcn-YhQpCx_yfnov7MHGiOYbZxx9TXJW1djbaY05ExlXc=w1705-h959-no


Since this is for the most part motor deploy, the electronics have to be on the nose end, so I needed to make some kind of breakaway plug for the igniter wires. I decided on a technique I saw here a while ago, bare wire to a female JST connector:
zGCNW5eEvDQg5bvm6nCR5y6-bi_2AOpk94ABbJQ4v5jIyetNC2v20OdYD6kqyaASgsMMC2SE5xhVP4BpbxOpqYEdDnJ7JvIBhZmE4Fnvt_q75MuF9BbB-TN2Y2pDPdpLoC6GGvlEzFSDnENZAMCIT9Ow7zc_ly_RYMdDq_qVRhrE15qloqexo-OHVxgbOfVIuAhF9zBE2PyVI52oSkYiVRCi-L1VSlC9TrdCRnDJV8hR0DaRbm9S-0UkWAA07v54dSpGGZmgoZQnRsY6mnKtFUA6eBv2oY5dlY5VwVGmU_70weXUhFWJQu8xvC6il0WABoiNsHv5CsfnAaGzzjLSG7kiorL5t5PKkeRq_Mnz-UUmS6-78UDyXvK4Mji66pD0ROvGMereU9Lrvnt4g7RorpzBUvy7NTProWeLDhmHGNaXmD-VMZrbOycPU7JSev0esz9sQ4V_uqCGvUZVa56PMKLL78nzNsXA99Le23hmL4btTRoBhMIzpFMKdowq-vPvWBh6okGA3iqeUC2Oc_rJ5M_rIRWp12hAfH11p1Bf5tjVw_-qXvrbm3FHsWSt48AXhUICEoaMup_Jtu34Tq53IovR5eWdYJhVzJsu2Aw=w1705-h959-no

It seems to work pretty well, and I'm quite happy with it.

Finally, I epoxied on the fins with no major mishaps:
VQHvdke56qbJfZkIASoBuk72nbnBiReirT1c7dr8f-lZBtLp_MeTwAcZfVbo12W-n1bl0v-Jd8ecOUxrV7xopkMse2fkVJMlbDtmVazFGk23Li0zcHxGobQ5JHB1xIzp0Fo48DkSdqdbK-1re8KYDvpCPX5wf63XQX-fiyYBhOTija1DUsZ18mfNf3c3_B07LEYX86GHFZXa2Tcw517-A9nIsIbaK-py0B3sxFNiBvqAiKqT0ON9Q3-QvQ1JCOvjP4zSlP09lw4bMnhnJPGCuj05LtO090jhomANcbHSu7PuRV7MakxCvPVIq7LcJswxCxsOQnkbOLuZoyp-njl2vBc1TEKAtcdQyNjGf7KJB5o11vgx7pW4uDOchpnyYE1UEKS4BEgOU6Ken5t1psZFwmtn7vHZz-rG330ITGuPIFJQXWqvo3r8yBTa3OdqE7_ipDlj1jecC_dsFmr6ykzzQ4iA3dheDpUd0jy6XLXNA-8d73YPXviXPzZW3GdmLP0BnUCk8TQfE4cslgqRmg7S8EsUAoVPvPGK6lMD3eVI6GgzPeKjZHxyHjakemwcSOff8FyATrGwkq9RGHOr1WgNLJcByVZjSifwuyERQ4U=w1705-h959-no


That boat tail really plays tricks with your eyes when it comes to alignment. From the side, the fins look horribly misaligned, and I sometimes have to double check that they are, indeed, at 120 degrees.

I've decided that I want to put slightly more than my usual halfhearted effort into getting a somewhat smooth finish on this one. So the next step is everyone's favorite- CWF and sanding... I might back off a bit on my finish expectations, but I want to put at least some effort into getting it smooth.
 
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