Not a specific link, but the Barrowman paper on calculating CP should cover something like this, shouldn't it?

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John Thro, NAR #84553 SR
I was too old when I started! Now I'll *never* become a BAR!

John,

I did say "pull up and read"...

I took one look at the Barrowman paper...

I want to keep what hair I still have on my head on my head, not intertwined in my fingers...

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Craig McGraw

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Here is another one of my unusual designs. The fins themselves might be a bear to cut and attach. I wonder which way would be best to run the balsa grian?


Hope you all enjoy, Thanks JP

James Pierson
NAR #77907

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Attached Files

Sparrow Dart.rkt (62.7 KB, 109 views)

Another "Schoolyard Sounder"...

Taking the cue from our fin shape discussions, this design is a simple 3FNC with matching canards. I wanted something along the lines of the old Estes Aerobee, but with better styling. I also wanted it to be flown with 13mm motors, in keeping with my small-field-capable theme.

Skill Level 1...

Length: 15.5"
Diameter: 0.908" (ST-8)
Fin Span: 3.91"
Weight: 0.85 oz

1/2A3-2T......799 FPS/S......140'......21 FPS......36" Rod
A10-3T.......1433 FPS/S......350'......16 FPS......36" Rod
A3-4T.........562 FPS/S......365'......12 FPS......36" Rod

Enjoy!

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Attached Files

Pathfinder.rkt (52.1 KB, 92 views)

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Craig McGraw

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Have you thought about using that thick cardstock Carl uses for centering rings and rocket racks? He cut out a set for my Lil' Battle Axe design, and they turned out great. Don't confuse this with that crap Estes uses for their fiber fins. Carl's cardstock is much better and hold up to a lot more abuse.

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Craig McGraw

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Good idea with the card stock for fins Craig. Where can I get some of Carl's cardstocks material? I wonder if this cardstock is compariable in wieght to 3/32 balsa?

Also Craig, notice the difference between Scrappy and Thunder Strike designs. The center tube in Thunder Srtike is classified by Rocsim as a regular BT and not an inside tube like Scrappy has. I needed the center BT to be a regular BT to be able to put the fin set on the center Bt. It took me a long time to figure that one out. Just thought you might be interested.

James Pierson
NAR #77907

Lately I have been copying a few design files, deleting specific parts, and changing and rearranging. Have also discovered the ability to copy from one design file and paste it into another, like a favorite fin set etc... I came up with the Thunder Stick which is actually a highly modified Thunder Strike. This design looks like a large stick one might wack a seal in the head with or something.

Criag,
It might be modified into a pretty nice payloader with a clear upper payload tube???

Thanks Again, JP

James Pierson
NAR #77907

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Thunder Stick.rkt (55.8 KB, 104 views)

There's a trick to that, too...

You define a "reference tube" of the same dimension as the inside tube, which has no weight (actually, make it 0.0001 oz) and 0.00 opacity (in other words, it's weightless and invisible) and which fits in place directly between the front and rear sections. You make it the same length as the distance you want the sections to be apart. You can then stick fins onto this tube as if it were actually there...

Study the attached file...

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Hidden Tube With Fins.rkt (14.6 KB, 90 views)

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Craig McGraw

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Uh, from Carl?

He also happens to have a fabulous LASER CUTTING TOOL, BTW, which he occasionally uses to cut very crisp fins in balsa, plywood, and occasionally, even cardstock...

The thickness is 0.05"...

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Craig McGraw

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Another Schoolyard Sounder...

OK, folks, I know these 3FNC designs are not the most interesting, but there is a purpose behind them. Especially this one, as it again uses that stepped fin shape to reach the lowest Dv possible with a rocket of this shape and weight. Altitude was not a priority, but keeping it stable and getting the softest deployment possible were priorities.

You will notice a full dozen runs on a single motor, which demonstrates the range for the Dv better than a single run. It took me over two hours to tweak the shape to get those low numbers; even the slightest shift in the fin plot points could alter the Dv by as much as 200% from what you see here (or, the Dv's would easily double to 8 and 10 FPS).

Take this one as an academic study in fin shapes and their respective flight characteristics...

Length: 15.0434"
Diameter: 0.908" (ST-8)
Fin Span: 3.2272"
Weight: 0.822 oz

Average range:

A3-4T.....397'.....4.75-to-6.19 FPS Dv.....576.70 FPS/S.....36" Rod

I think it still makes a great flying design, even if it is just 3FNC...

Enjoy!

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Prowler.rkt (104.2 KB, 104 views)

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