Someone mentioned a tube-finned rocket. I think a BT-55 rocket with tube fins and a cluster of three 13mm A10-3T motors would be a great fit. Four 13mm tubes can be crowbar'd into a BT-55 but the airframe would have to be distorted. Plus, my instincts tell me the ~3 second coast time is better suited to the impulse of three motors rather than four.

I'd swag that 9" or more of BT-55 oughtta be stable with 6 tube fins (of BT-55) and a nominal nosecone.

You could readily bash such a bird out of a Tuber, but that'd be a waste of a dang fine rocket

Doug

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I'm intrigued by this one myself. Do you have an electronic version of the plans, or a link if they exist online?

It'd be a good complement to my Viva Italian (7 C's).

Thanks,

John B.

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John Buscaglia
NAR 27366
SAM 63
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solo:

consider this:

http://www.apogeerockets.com/rocket_grant_money.asp


terry dean

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"Old Rocketeer's don't die; they just go OOP".....unless you 3D print them.

I'm curious about rockets built with fin-sets already available on Semroc.com. For instance, Carl has a standard Alpha finset. I know from experience the stock Alpha is a bad choice to convert for the A10-3T; it doesn't work well on the A8-3 either. (Best engine for the Alpha? Quest A6-4. Go figure.) But a rocket using those fins, for instance, would be cool.

It's a balancing act. I'd like to see designs that are relatively easy to build, but on the other hand I want to emphasize traditional materials and building techniques. I see no problem with a beginner rocket using laser-cut fins.

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Once upon a better day... SAM #0076
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Regarding a 3-cluster in a BT-55: I don't know for sure, but I'd almost be willing to bet you can't design such a rocket to fly well on A10-3T engines (i.e. have a low DV) without somehow intentionally adding drag. I.e. (3,4)FNC is, I'm almost certain, out of the question.

You're talking, effectively, a 3/4C10-3 (three-quarter C). Standard BT-55 rockets tend to like B6-4 and C6-5 engines; so I'd expect that the 3 second nominal delay (probably 2.35 seconds plus the .6 second almost-no-thrust tail, for 2.95 seconds effective delay) will be too short.

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NAR # 115523
Once upon a better day... SAM #0076
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I couldn't resist tackling this one. You need to think bigger than BT-55, if you're going to get the Dv down to below 10 FPS. The one I'm posting here adds Solo's criteria for pre-lasered fins, using the Alpha standard fin shape.

Length: 29.25"
Diameter: 2.04" (ST-20)
Fin Span: 5.04"
Weight: 4.46 oz

Launch Rod: 36" x 1/8"

(3) A10-3T......221'......Dv 2 FPS (or lower)

I didn't think even three A10's would get something this large to move, but RockSim says otherwise. It must be the kick in the pants the A10 has.

Enjoy!

And... Don't let this entry stop anyone else from trying! I'm trying to show what is possible, not just the only solution!

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Attached Files

XFNC Challenge #5.rkt (131.7 KB, 90 views)

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Craig McGraw

BARCLONE Rocketry -- http://barclone.rocketshoppe.com
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SAM 0044
AMA 352635

Yeah, I agree. For BT-55, you can't keep it a conventional 3 or 4 fins. It's either gotta be tubes, or lots of fins, as in Craig's next post (#36). And in that case, a much draggier tube was employed as well.

Doug

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YORF member #11

But Craig, if you're gonna use ST-20, you gotta use more motors - there's room for nine

Doug

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YORF member #11

Wow, ST-20! I like that!

and 2 FPS DV is really cool also. I can't wait to show that one to my students.

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Once upon a better day... SAM #0076
My site: http://rocketry.gonnerman.org

Thanks for the invitation. Craig's designs look really good, so I wasn't sure Solomoriah was still looking for alternatives.


How about a 3-engine cluster, BT-60 tube-fin rocket to use up your A10-3T's?

All I have is the Rocksim v5 demo, so I can't save the file. Also, I simulated the tube fins with 6 1/8" balsa fins as noted below. The weight of the balsa fins was set at 0.001 oz., and I believe Rocksim v5 doesn't take the drag of the tube fins into account.


Parts List:

- Nose cone Estes - PNC-60MS, Len: 2.500 In., Mass: 0.390 oz.
- Body tube Estes - BT-60, OD: 1.637 In., Len: 18.000 In., Mass: 1.244 oz.
- Parachute Estes - 12 in. plastic, Mass: 0.072 oz.
- Shock Cord - Material: 1/8 In. flat elastic, Len: 36 In., Mass: 0.066 oz.
- Launch lug Estes - 1/8 in., Len: 1.250 In., Location: 11.000 In., Mass: 0.002 oz.
- Centering Ring 1 - CR-5-60 Cluster, Mass: 0.039 oz., Loc: 12.500 In. from the front of Body tube
- Centering Ring 2 - CR-5-60 Cluster, Mass: 0.039 oz., Loc: 17.750 In. from the front of Body tube
- Motor tube 1 Estes - BT-5, Len: 6.000 In., Mass: 0.084 oz., Loc: -0.125 In. from the base of Body tube
- Engine block Apogee - CR 10-13 ring, Len: 0.188 In., Mass: 0.006 oz., Loc: 4.500 In. from the front of Motor tube 1
- Mini engine hook Estes - Mini size, Mass: 0.036 oz.
- Motor tube 2 Estes - BT-5, Len: 6.000 In., Mass: 0.084 oz., Loc: -0.125 In. from the base of Body tube
- Engine block Apogee - CR 10-13 ring, Len: 0.188 In., Mass: 0.006 oz., Loc: 4.500 In. from the front of Motor tube 2
- Mini engine hook Estes - Mini size, Mass: 0.036 oz.
- Motor tube 3 Estes - BT-5, Len: 6.000 In., Mass: 0.084 oz., Loc: -0.125 In. from the base of Body tube
- Engine block Apogee - CR 10-13 ring, Len: 0.188 In., Mass: 0.006 oz., Loc: 4.500 In. from the front of Motor tube 3
- Mini engine hook Estes - Mini size, Mass: 0.036 oz.
- Fin set - Custom, 6 Fins, Material: Balsa, Trapezoidal, Root: 3.000 In., Tip: 1.750 In., Semi-span: 3.500 In., Loc: 0.0 In. from the base of Body tube, Thickness: 0.125 In., Mass: 0.001 oz.
- Tube fin, Quantity 6, Estes - BT-60, Len: 3.000 In., Mass: 0.207 oz. each, Loc: 15.000 In. From the front of Body tube


Performance:

Performance looks reasonable, though the DV is just over 30 fps with one engine misfiring. Please see the attached screenshots for details. To simulate a misfire, I added a mass objects with mass of 0.269 oz. for each bad engine.

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John Thro, NAR #84553 SR
I was too old when I started! Now I'll *never* become a BAR!