Long and pointy

Seems to work well on C and D engines.

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Attached Files

Long Dart.rkt (61.3 KB, 116 views)

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Dale Marshall, San Antonio Texas
NAR #90990
Semroc SAM #083

BAR Since 2008
Enjoying model rocketry since 1977.
The Spotted Dragon
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Looks nice! It's a single-stage design, right?

I like long thin rockets with multiple sets of fins. I built one with two sets of fins several years ago and am working on another even as we speak.

Since your design has 15.70 calibers of stability without engines, how overstable is it *with* engines?

Which C and D engines did you use? Can you show some simulation results?

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

Thanks!

Yes, it's a single-engine/single-stage design.

See the attached image for some simulation runs.

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__________________
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Dale Marshall, San Antonio Texas
NAR #90990
Semroc SAM #083

BAR Since 2008
Enjoying model rocketry since 1977.
The Spotted Dragon
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It's also light enough to reach safe flight V on just a 36" rod.

Feyd, have you found the Rocksim simulation run detail screen, where it shows you the "Launch Guide Data"? The last line in that block lets you know if the rocket clears the rod with enough velocity that the fins are working.

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Craig McGraw

BARCLONE Rocketry -- http://barclone.rocketshoppe.com
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SAM 0044
AMA 352635

C11-5 : Minimum velocity for stable flight reached at: 28.7609 In.
D12-5 : Minimum velocity for stable flight reached at: 27.6568 In.
E9-6 : Minimum velocity for stable flight reached at: 33.1296 In.
F12-5 : Minimum velocity for stable flight reached at: 20.6862 In.

Looks good!

Oddly enough, the E engine takes longer to get up to safe speed.

__________________
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Dale Marshall, San Antonio Texas
NAR #90990
Semroc SAM #083

BAR Since 2008
Enjoying model rocketry since 1977.
The Spotted Dragon
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That's because it has less power during the burn, but burns longer. The Estes E9 is the weakest engine in the group. The D12 and F12 have about the same power, the F burns longer. The C11 has almost as much power as the D12, but burns for a shorter time. It can almost compensate for a B14...

...Almost...

__________________
Craig McGraw

BARCLONE Rocketry -- http://barclone.rocketshoppe.com
BARCLONE Blogsite -- http://barclone.wordpress.com
BARCLONE Forum -- BARCLONE Forum

BARs helping BARs

SAM 0044
AMA 352635

I have one rocket to build for the EMRR contest, then I think I'll try this one. It looks fun. I have another idea but I don't think it can be done in RockSim.

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Dale Marshall, San Antonio Texas
NAR #90990
Semroc SAM #083

BAR Since 2008
Enjoying model rocketry since 1977.
The Spotted Dragon
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This beast is in "build" mode now!

I've got the body tubes done and the engine mount (24mm) built. After looking at the fins again, I've decided to change the design to rear-ejection to protect the pointy ends. So I doubled the length of the engine mount and added a couple more centering rings. Also, I added a solid balsa coupler just past the first hollow tube coupler (why didn't I make it the coupler instead? Good question.). And I added a centering ring behind the engine mount to act as a thrust ring for the mount.

Now... since this thing has an 18" parachute, any suggestions for how to tie it all together? I was thinking of using the extended engine mount for wadding. I already have a kevlar string attached to the end of the engine mount.

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Dale Marshall, San Antonio Texas
NAR #90990
Semroc SAM #083

BAR Since 2008
Enjoying model rocketry since 1977.
The Spotted Dragon
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I think what I'll do is create a really long shock cord and attach it beyond the thrust ring. Attach the parachute to the shock cord with a snap swivel, and attach the kevlar cord to the snap swivel as well.

Do y'all think that work?

I'm also thinking a nomex blanket might be in order. Would I need one with the wadding in the engine mount?

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Dale Marshall, San Antonio Texas
NAR #90990
Semroc SAM #083

BAR Since 2008
Enjoying model rocketry since 1977.
The Spotted Dragon
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-

The basic build is complete and I just managed to insert the shock cord (should have thought this through before building) just past the thrust ring. Hopefully it'll hold up when the ejection charge fires

Here are photos of the completed rocket ready for priming.

Second photo shows the Long Dart beside a yardstick for reference.

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__________________
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
Dale Marshall, San Antonio Texas
NAR #90990
Semroc SAM #083

BAR Since 2008
Enjoying model rocketry since 1977.
The Spotted Dragon
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-