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  #11  
Old 02-17-2009, 09:31 AM
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I wonder about a short, fat rocket for the 3 cluster. BT-80 perhaps, simple swept fins, etc.
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  #12  
Old 02-17-2009, 09:49 AM
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Quote:
Originally Posted by Solomoriah
RockSim, as I understand it, uses the thrust curve data as well as the certified delay value... it doesn't take the designation at face value.
It's a mixture of both. It uses the thrust curve from NAR datasheet, but not the tested delay. Rocksim uses exactly 3 seconds (in the case of the A10-3T) instead of the 2.35 seconds measured during the test. The user would need to key in the 2.35 in order to more exactly simulate the delay.

Doug

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Old 02-17-2009, 10:00 AM
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Quote:
Originally Posted by Solomoriah
I suspect the 3 second delay will severely limit clustering the A10-3T. It's a hard-kicking engine with almost no follow-through; a heavy enough rocket to hold it down to a low DV might be too heavy for the low tail of the thrust curve.

Just musing, no simulations or data to back it up.
Think drag, not mass.

I've run many sim's trying to adjust the coast time to fit a given motor only to learn that coast time is surprisingly flat over a wide range of mass values. The heavier rocket will burn out at a lower altitude with a lower velocity, but with the added mass, its coast time will be about the same.

So if you want a rocket to have a short coast time for use with a cluster of A10-3T's, use draggy construction: large but light body tubes such as the BT-100 or BT-101, unswept fins with no airfoiling, six fins instead of 3 or 4, a ring tail or tube fins. These are the tricks for cutting the coast time.

Doug

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Old 02-17-2009, 10:09 AM
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Default A variation of the challenge...

BTW, FWIW, I was given a challenge a few years ago to use the A10-3T in an upper stage, without zippering or shredding. Here's what I came up with. It uses BT-55 and it works pretty good. Doug




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Old 02-17-2009, 12:07 PM
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Exclamation Parts Lists for XFNC Challenge #1, #2, #3, #4

Quote:
Originally Posted by Solomoriah
Excellent, Craig, thanks! Can I ask a favor? A parts list would be nice. I can probably guess my way through it, but it would be much quicker with a list.


Here's the basic #1:

BC-1031 Elliptical NC
ST-10180 Main Body
(2) CR-510 Rings
ST-530 Engine Tube
TB-5 or TR-5 Thrust Block
EH-1 Mini Hook
SE-10 Screw Eye
SCE-24 Elastic Chord
SCK-24 Kevlar Thread
CPK-12 12" Parachute
LL-122 2" Launch Lug, 1/8" x 2.25"
1/8" Balsa Sheet


For both #2 and #3, add:

HTC-10 Coupler


For only #2, add:

ST-10100 Body Tube


For only #3, add:

ST-1080 Body Tube



I didn't use a stuffer tube on #2 or #3, as the ST-10 is small enough that I don't think it would be necessary.


For the #4:

BC-1344 Ogive NC
(2) ST-13180 Body Tubes
HTC-13 Coupler
(2) ST-5150 Engine Tubes
(2) TB-5 or TR-5 Thrust Blocks
(2) EH-2 Standard-length Hooks
(3) Custom CR-513 Rings for 2-engine clusters
(2) LL-110 1" x 1/8" Launch Lugs
CPK-16 16" Parachute
SCE-24 Elastic Chord
SCK-24 Kevlar Thread
1/8" Balsa Sheet

This is a deviation from the given design, by using two 15" lengths of ST-5 instead of the short 3" lengths shown in the original design. Add one extra centering ring at the very top of the stuffers for internal support and to close off the volume around the tubes. Use the standard hooks instead of the mini hooks, as the second ring is used to "clamp down" on the hook. Use a touch of epoxy (or JB Weld) to hold the hooks down, and you shouldn't have them come loose.

The changes this makes to the design increase the mass to 2.79 oz, drops the altitude to 226', but more importantly, drops the Dv to a mere 2 FPS over the top. All of the simulation runs for this Mk II version show the parachute symbols with no arrows in any run. See the attached files.
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  #16  
Old 02-17-2009, 02:45 PM
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Hey, I like that cluster! Very cool. Thanks for the parts lists, also.
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Old 02-17-2009, 03:53 PM
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Quote:
Originally Posted by Solomoriah
Hey, I like that cluster! Very cool. Thanks for the parts lists, also.


Ask Carl really nice, and I bet he could laser-cut those centering rings for you on that cluster, that way they'd be accurate with no thrust vectoring...
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  #18  
Old 02-17-2009, 04:06 PM
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Probably he'd do it. I feel rather guilty asking him... I can't imagine my business is worth the effort he's put into it thus far.

Placed a small order with them last night, just a kit and a couple of couplers, and it had already shipped this morning first thing. DANG they're fast.
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  #19  
Old 02-17-2009, 05:04 PM
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if you're looking for really inexpensive rockets that fly with A10-3Ts, try the Art Applewhite 13mm paper flying saucer, a 2" diameter mini Sputnik (use bamboo skewers for the 4 legs), or a spool rocket made of a pair of CDs and an interconnecting tube.
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  #20  
Old 02-17-2009, 05:48 PM
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Actually, I'm not concerned about price (well, not so much anyway). I want rockets that require traditional construction, but that will fly acceptably on the engines we have in abundance. Craig has done an admirable job here.
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