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  #11  
Old 09-21-2007, 12:52 AM
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CPMcGraw CPMcGraw is offline
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Quote:
Originally Posted by Bohica
That's what I do! If I have a design...I build it and tweak it until it works. I have at least 3 designs that fly great that certain Sim programs said would never be stable. Of course just like with any program the "garbage in, garbage out" rule applies.

Bo


Agreed. I think I have a couple or more such designs in my folders right now. But the ones that really get my goat are those that proclaim their stability in bold numbers, then promptly perform cartwheels just above my head.
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  #12  
Old 09-21-2007, 01:30 PM
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Quote:
Originally Posted by CPMcGraw
Agreed. I think I have a couple or more such designs in my folders right now. But the ones that really get my goat are those that proclaim their stability in bold numbers, then promptly perform cartwheels just above my head.
So this *is* rocket science, after all.
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  #13  
Old 09-21-2007, 03:39 PM
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Quote:
Originally Posted by PaulK
So this *is* rocket science, after all.


Yup. Sometimes BARCLONE field looked a lot like Canaveral in the early days...
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  #14  
Old 09-21-2007, 04:29 PM
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Quote:
Originally Posted by CPMcGraw
Yup. Sometimes BARCLONE field looked a lot like Canaveral in the early days...


Been there, done that buddy!
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  #15  
Old 09-22-2007, 06:11 PM
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Here is the "Dead Ringer". I actually built this years ago. It's the ultimate back yard flyer. On a 1/2 A your looking at 75 feet straight up/straight down with a streamer on board. But....it will really haul the mail on an A10! Sorry for the poor pic!

Bo
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  #16  
Old 09-22-2007, 09:19 PM
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I believe I'm going to build it, then swing test it the old fashioned way. If it seems like it's going to work, perhaps with some nose weight, I'll finish it as is. If not, I'll notch some regular fins (maybe just rectangles) and slide them over the rings to make it flyable.

... today I calculated the CP location of my Bandito using the Barrowman equations. Cost me fewer brain cells than I expected. But Jim didn't provide a method for calculating the effect of rings either... probably why RockSim can't do it.

Do you suppose that the pressurized air in front of the first ring might act like a conical shoulder? That would yield a benefit to the CP, if it were true.
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  #17  
Old 09-23-2007, 12:32 AM
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Quote:
Originally Posted by Solomoriah
I believe I'm going to build it, then swing test it the old fashioned way. If it seems like it's going to work, perhaps with some nose weight, I'll finish it as is. If not, I'll notch some regular fins (maybe just rectangles) and slide them over the rings to make it flyable.

... today I calculated the CP location of my Bandito using the Barrowman equations. Cost me fewer brain cells than I expected. But Jim didn't provide a method for calculating the effect of rings either... probably why RockSim can't do it.

Do you suppose that the pressurized air in front of the first ring might act like a conical shoulder? That would yield a benefit to the CP, if it were true.


I have no idea. I am not a RockSim user. I do the equations and swingtest...and I use cutouts if necessary...but most significant of all....I build em' and fly em'. The rocket pictured is one of the most stable critters I have ever flown. Matter of fact, after flying 4 times today (after it sat for at least 3 years) I decided it deserved a better paint job than simple silver. The "Dead Ringer" is now sporting a metallic green top fading to metallic purple on the bottom.

Main body tube = T-50 @ 18"
Nose Cone: PNC 50
1st ring: CR5060
2nd ring: CR5070
3rd and 4th rings: CR5080
13mm mount
Streamer recovery.
No nose weight required.
Stable and able from 1/2A to A10.

Bo
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  #18  
Old 09-23-2007, 07:42 AM
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Hey Bo....distance between rings? Looks like an interesting build....
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  #19  
Old 09-23-2007, 10:35 AM
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Exclamation New Plan -- Dead Ringer

Quote:
Originally Posted by Bohica
I have no idea. I am not a RockSim user...

Main body tube = T-50 @ 18"
Nose Cone: PNC 50
1st ring: CR5060
2nd ring: CR5070
3rd and 4th rings: CR5080
13mm mount
Streamer recovery.
No nose weight required.
Stable and able from 1/2A to A10.

Bo


Bo,

I worked up a simulation of Dead Ringer, using an invisible paper transition with no mass and no CG to simulate our suspicions about how the rings work. The components are not exactly as in your design, but they should be close.

Nose Cone: BNC-50K
Body Tube: BT-50
Ring 1: CR-5060, 3.50" from rear
Ring 2: CR-5070, 1.75" from rear
Ring 3: CR-5080, 0.63" from rear
Ring 4: CR-5080, 0.10" from rear
EM-59 motor mount (SEMROC package)
12" Parachute (or 2x20 streamer)
SE-10 screw eye
Snap Links
SC-24 elastic
SCK-24 Kevlar

Length: 22.35"
Diameter: 0.976" (BT-50)
Span: ~2.80"
Weight: 1.16 oz

1/2 A3-2T......90'......Dv 2 FPS.......requires 25" of guide length
A10-3T........215'......Dv 10 FPS......requires 20" of guide length

Margin with A10-3T motor installed: 2.29 (VERY STABLE!)
Margin with 1/2A3-2T motor installed: 2.08 (VERY STABLE)

CG with A10-3T: 15.54" from NC tip
CG with 1/2A3-2T: 15.75" from NC tip

Let me know if this comes close to your observed performance with the prototype.
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  #20  
Old 09-23-2007, 10:42 AM
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Solo,

Your version using BT-20 simulated out to nearly 400'. Lighter design, but still highly stable. Both designs look like stable mates next to each other.

Like minds thinking alike...
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