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  #21  
Old 10-04-2011, 03:22 PM
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Doug Sams Doug Sams is offline
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Quote:
Originally Posted by bernomatic
If I tell you the design is stable and has been string and flight tested, should I be allowed to fly it or should I still need a RS file showing it viable?
Yes, in my book. Furthermore, a good RSO should be able to say, "That looks about right", and let it fly.

Doug

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  #22  
Old 10-04-2011, 04:22 PM
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Quote:
Originally Posted by bernomatic
I didn't mean for this to become a trash RockSim thread, by any means...

If I tell you the design is stable and has been string and flight tested, should I be allowed to fly it or should I still need a RS file showing it viable?...


FWIW, as one of the RockSim "wonks" here on this forum I'm not insulted. It's a bug in RS, plain and simple, that hits when we want to design ring fin and tube fin models. We just grind our teeth and crawl forward anyway; a good string-swing beats a RS calculation any day.

The best reason for using RS, aside from the reasonably-good-otherwise flight simulations, is the ability for other users to see how a design comes together, and not just how it looks assembled. The parts tree and part descriptions offer a lot of information that might otherwise be overlooked, especially if we designers remember to use it right. Since Apogee allows the program to be "demo" run for a while (30 days?), others can at least view the files we create. It's also a file format that can be used across all three computer platforms.

It's easier to work with than, say, trying to create individual TIF/PNG/JPG files for components and fitting them together into a single image. Been there, done that!
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  #23  
Old 10-08-2011, 09:13 PM
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RandyT0001 RandyT0001 is offline
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For the past few months I've been using RocSim for some preliminary work on a ring tail design for my L3 certification. I want to fly low without high mass and I had heard ringtail designs have high drag hence my starting point. My first design used a 7.7in airframe and 11in ringtail (7in AF LOC 11in Ringtail fin rocket V1) which RocSim said would be stable with 3+ calibers of stability using a CTI M1400. I had doubts about the stability and the calculated drag on the design. To test the the stability (and if stable to backtrack/zero in on the drag using an altimeter and RocSim) I built a 22% scaled down version (22% scale 7in AF 11in Ringtail V1) that used some BT-60 1.64"dia airframe tubing with a BT-80 2.6" tube for the ringtail. It was unstable.

My second design still uses a 7.7in airframe but I've increased the size of the ringtail to 16" in diameter (7in AF LOC 16in Sonotube Ringtail fin rocket V1). The stability margin decreases to slightly over two calibers but I had a better TLAR feeling as to the stability of the design. I still questioned the calculated drag on the design so I designed and built a scaled down version (7in AF LOC 16in Ringtail 35% scale). The stability margin is different but I was more interested in making some flights to determine the drag on the design. I had bought some G64's and G53's so decide to use them for test flights. On my first flight I packed the parachute too loose and it didn't deploy though the NC popped off ruining the aerodynamics enough for it to drop in a flat spin to the ground. From this one flight's altimeter data I used RocSim to backtrack the drag to about 1.05 instead of the calculated (approx.) 1.7 from RocSim. Unfortunately the ringtail got busted on when it hit the ground and I haven't had time to repair it these past few weeks in order to continue the tests. Hopefully over the winter months I will be able to repair it and finish the tests.
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  #24  
Old 10-09-2011, 04:18 PM
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Talking Invoking Bruce S. "teflonrocketry1" Levison

Quote:
Originally Posted by CPMcGraw
Ring tails and RockSim have never quite gotten along together for several iterations of the program. RS shows a higher drag value, for one thing, and definitely doesn't calculate RTs the same as primary tubes. Jay Goemmer (CenturiGuy) might be able to pass along some comments, as this was an issue with his "Tau Zero" design.
Quote:
Originally Posted by bernomatic
So... basically, go back to Levison's stuff?
Bernard,

Yes.

Craig and I will be among the first to tell you that while RockSim is a great design tool, sometimes you have to jump through mindboggling hoops to get it to sim correctly (or display decals, or...[fill in the blanks]).

Sometime in the last year I tried to put two different sized sets of tube fins on the same rocket, and managed to "break" RockSim. [RockSim programmer] Paul Fossey asked, "What are you trying to do?" I replied, "I just want the tube fins to act the way they do in the real world."

So it's far from perfect, but it looks cool. But plenty of us "old guy" rocketeers slap together stuff That Looks About Right (TLAR), and it flies okay. (shrug)


As with everything else, your mileage may vary.

Not to mention your airspeed.

Cheers,
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Last edited by CenturiGuy : 10-17-2011 at 11:10 PM.
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  #25  
Old 10-11-2011, 06:10 PM
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Quote:
Originally Posted by jharding58
The design above is indeed stable and the pylon definition is pretty reasonable to specify. Also the Tau Zero has been modelled effectively. Which version and build are you using (118)? I would imagine that the changes adding pods in 9 should have some impact on the calculations - specifically drag components off the main tube.

But isn't that the idea? I am not a programmer by any stretch of the imagination ('cept for a little ActionScript and HTML) but if there is a 'design philosophy' behind the programming intentions (basic 3/4FNC) it currently doesn't rise to the level of creative design and implementation I've seen nowadays... but that sort of stuff may be difficult to add.

I had been dinking around with a free version for as long as it let me, but I don't have the financial wherewithal to get a real version (although I'd like to, I suppose).
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  #26  
Old 10-11-2011, 06:42 PM
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Then there is the difference between RS and RS Pro...
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  #27  
Old 10-12-2011, 12:49 AM
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Quote:
Originally Posted by jharding58
Then there is the difference between RS and RS Pro...


what? about $876.?

It was hard enough to justify the upgrade price of $41 to the wife.

I see the conversation now.

me: "dear I just bought a new rocket software program.

her: "that's nice. HOW MUCH DID IT COST? "

me: "it allows me to design my rockets with more accuracy and be able to guess where they're gonna land."

her: "HOW MUCH?"

me: "Only a mere thousand."

her:

me: (silence except for blood slowly seeping out of deep chest wound)
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  #28  
Old 10-12-2011, 06:19 PM
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Quote:
Originally Posted by bernomatic
what? about $876.?

It was hard enough to justify the upgrade price of $41 to the wife.

I see the conversation now.

me: "dear I just bought a new rocket software program.

her: "that's nice. HOW MUCH DID IT COST? "

me: "it allows me to design my rockets with more accuracy and be able to guess where they're gonna land."

her: "HOW MUCH?"

me: "Only a mere thousand."

her:

me: (silence except for blood slowly seeping out of deep chest wound)

Yes, this is exactly how it would go in my house.
The only difference being not having a DIVORCE emoticon to use here...
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  #29  
Old 10-17-2011, 11:10 PM
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Red face Jay 'fesses up...

Quote:
Originally Posted by bernomatic
It's not that I can't get a ring tail to work, it's just one that I know works shouldn't according to RockSim.
And that's *my* gripe, as well.

As Craig often says, welcome to the asylum.


"Gather inmates, while ye may..."
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