Question about 'instability'

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Not mine, the rocket's!
I am attempting to add a payload bay to an existing rocket which will make the fin area far more than necesarry for the particular rocket. Since the biggest problem with 'overstable' is it's vulnerability to weathercocking, if I cut the bulk of the fins out leaving only say 5/8" on each outside chord and 3/4" along the root would that theoretically take care of the 'overstable' attitude? The wind should blow right through the fins and affect it minimally. Theoretically.
Chuck
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Chuck Rudy

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www.v-serv.com/vcp
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Jerry Irvine, Box 1242, Claremont, California 91711 USA
Opinion, the whole thing. <mail to: snipped-for-privacy@gte.net>
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He is talking about cutting "lightening holes"... not trimming down the fins.
Does VCP have the capability to handle this kind of modification? I have never used it, as I have both RockSim and SpaceCAD, so I don't know it's capabilities... but my guess is that VCP probably wasn't designed for that level of complexity... am I wrong?
I too am interested in the effect of lightening holes through the fins. I know Randall Redd is plenty well known for some of his custom creations, and has made plenty which have center-cut-out style (lightening hole) fins... maybe you could try to get ahold of him?
Also, RockSim seems to be able to model it if you draw a "custom fin set", and connect the dots by drawing the root chord first, and then plot around the outside fin area. I tried it just now on a 29mm G80-10 simulation. For these example pictures, see (watch for URL wrapping):
http://www.aharrt.org/rocket_fin_lighteninghole_solidview.jpg
and
http://www.aharrt.org/rocket_fin_lighteninghole_designview.jpg
Simulation flight seems to be stable and good, although I expect I lose a bit of altitude by having a greater forward surface area causing slightly more drag, vice just using smaller fins... I dunno... when I tried it in RockSim, it actually shows *less* altitude with smaller solid fin of same weight/total surface area... very odd... not to mention it was calculated to be slightly less stable... something here doesn't seem to add up...
Comments?
~Duane Phillips.

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Duane Phillips wrote:

Absolutely correct! I'm looking at 'holing out' the fins to remove material which would promote smaller lateral force windcocking. The outline will remain the same as far as vertical flight, but wind shear should be minimial......yes? No? \ Chcuk
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Chuck Rudy

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Chuck wrote: The sims haven't been so kind to those of us in the Mac world......my latest version of Virtual PC is too long in the tooth to keep messing with......I need either a mathamatical answer which I can confirm myself, or a Mac program w hich will reinforce the common sense idea..........soon I will go to 'seat of the pants' rocket design........it could be worse.... :-P
What could be worse than using a Mac? >;-)
Mark Simpson NAR 71503 Level II God Bless our peacekeepers
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Mark Simpson wrote:

Being from New Jersey and using a pee cee? :-D
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Chuck Rudy

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Jerry Irvine wrote:

Jerry, I'm not the Mac user, Chuck is. And I don't think he's from Joizey. ;-)
Mark Simpson NAR 71503 Level II God Bless our peacekeepers
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Mark Simpson wrote:

So true, so true.....we've threatened to cut the bridges into Joisey and let it float away! :-) , we're looking for seafront property.........I thought of something worse than being a Mac user!! Getting a flat in the old Ferarri! Getting Brie dropped into your caviar! Not making the minimum food payment at the county club.....ah yes, there are things which are worse than being a Mac user, but just marginally.
Chuck
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Chuck Rudy

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I hate when I get Brie in my caviar. The flat in the Freeari is no big deal though. I just have my bodyguard change it. :-)
Mark Simpson NAR 71503 Level II God Bless our peacekeepers
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