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  #1  
Old 01-30-2012, 09:43 PM
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CPMcGraw CPMcGraw is offline
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Exclamation Estes Super Alpha -- On Steroids

So, I thought I'd try shoving a 24mm mount into this one and see what the results would be. I'm getting a good feeling already...

Something I suspected from the start was the SA would be very stable. I just didn't know how stable. Using RockSim's equations, even with an E12-6, the rocket has a stability margin of 7.05! I took the time to carefully work up a nose cone that matches what this kit has in the bag (a plastic NC, like the ones found in the Screamin' Mimi), so that the mass distribution would be more like a finished item. I used CenturiGuy's method of simulating a rounded-tip ogive.

I found a faux pas in the art card of this kit. They list the length as 19.5", and it's actually 21.5" measured to the trailing tip of the fins. However, they were very close on the weight, at 2.2 oz. The difference here appears to be in the thickness of the plastic used in the NC. For 2.2 oz, the plastic cannot be more than 0.01". This gives an empty static margin of 13.08!

Specs:

Length: 21.50"
Diameter: 1.637" (BT-60)
Fin Span: 7.137"
Weight: 2.2 oz


C11-5.......647'......Dv 8 FPS.......requires 31"
D12-6......1225'......Dv 6 FPS.......requires 30"......This is, of course, a fantasy engine.
D15-6......1383'......Dv 14 FPS......requires 16"
E12-6......1826'......Dv 20 FPS......requires 29"
E9-6.......1857'......Dv 19 FPS......requires 36"......Use a 48" rod


A 24mm mount works very well, with the C11-5 providing great performance as the "weakling" in the list. The altitude of 647' is 47' greater than the maximum expected altitude of 600' on a C6-5.

If someone could get us a 24mm D12 with a 6-second delay, the deployment would be ascending just ahead of apogee.

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  #2  
Old 01-30-2012, 10:07 PM
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hcmbanjo hcmbanjo is offline
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Craig,
Thanks and your timing is perfect!
I'm working on a 24mm version of this one right now.

I thought the C11-5 would get much more altitude than the C6-5 though.
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  #3  
Old 01-30-2012, 11:08 PM
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I'm sure the cover card art (and the dimensions) apply to the original balsa nose cone version....or so I thought until I measured mine. It stands 20 3/8 inches tall. It weighed 3.01 ounces without motor initially - and is stock except for installation of a Semroc BT-60 baffle.

It has been to around 1100 feet on a D12-7 18mm composite motor (and while carrying an AltimeterOne). Seven seconds is too long, but 5 is not quite enough.
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  #4  
Old 01-31-2012, 12:26 AM
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Quote:
Originally Posted by CPMcGraw
I used CenturiGuy's method of simulating a rounded-tip ogive.

I found a faux pas in the art card of this kit. They list the length as 19.5", and it's actually 21.5" measured to the trailing tip of the fins. However, they were very close on the weight, at 2.2 oz. The difference here appears to be in the thickness of the plastic used in the NC. For 2.2 oz, the plastic cannot be more than 0.01". This gives an empty static margin of 13.08!

Specs:

Length: 21.50"
Diameter: 1.637" (BT-60)
Fin Span: 7.137"
Weight: 2.2 oz
Craig,

A gentle reminder here when using this method: Your "Static Margin Reference" needs to be the...

Maximum Frontal Diameter, instead of the...

Nose Cone Base Diameter, which is actually the base of your rounded nose cone tip.


*Believe* me, I've done this several times before, and gotten *fabulous* results... until I noticed my *little tiny error*...


Cheers,
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  #5  
Old 01-31-2012, 02:08 AM
Rex R Rex R is offline
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heh I built mine with a 24mm mmt(and baffle) flys great on D12s, one of my friends built his as a tripple cluster(iirc he uses A8-3s). I haven't felt the need to try anything bigger than a D12-5 though .
rex
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  #6  
Old 01-31-2012, 07:33 AM
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Quote:
Originally Posted by Rex R
heh I built mine with a 24mm mmt(and baffle) flys great on D12s, one of my friends built his as a tripple cluster(iirc he uses A8-3s). I haven't felt the need to try anything bigger than a D12-5 though .
rex

It's hard to resist not clustering BT-60 rockets, it's just so easy! I've flown my SA on clusters of A's, B's, and C's without any weight compensation for any configuration. It's a great flyer, one of my favorites.
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  #7  
Old 01-31-2012, 09:14 AM
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CPMcGraw CPMcGraw is offline
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Quote:
Originally Posted by CenturiGuy
Craig,

A gentle reminder here when using this method: Your "Static Margin Reference" needs to be the...

Maximum Frontal Diameter, instead of the...

Nose Cone Base Diameter, which is actually the base of your rounded nose cone tip.


*Believe* me, I've done this several times before, and gotten *fabulous* results... until I noticed my *little tiny error*...


Cheers,


Ahem... Yes, well...

The Super Alpha is still highly stable, using this corrected measurement. The dry margin is 3.98, and with an E12-6 (which is probably one of the two heaviest engines in the list) the margin is still 1.88, which is plenty.

Thanks for catching my goof, Jay!
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  #8  
Old 02-01-2012, 01:59 PM
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CPMcGraw CPMcGraw is offline
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I've started mine, got the fins papered and attached to the tube, but came to a grinding halt when I discovered I had no spare long hook for the mount.

Rings I've got (plenty), a length of BT-50 I've got, Kevlar thread I've got, even an engine block I've got...

Long hook? (grumble)... I've no got...

Something else to add to my next SEMROC order...
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  #9  
Old 02-01-2012, 02:57 PM
Rex R Rex R is offline
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well I suppose that one could (GASP) make an engine hook . I've collected a few strips of springy metal from discarded wiper blades.
rex
edit
here are my 'alphas' (yes I know the executioner isn't really an alpha...but I painted it like one)
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  #10  
Old 02-01-2012, 03:07 PM
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There's always friction fit.
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