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  #1  
Old 05-10-2005, 02:02 PM
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CPMcGraw CPMcGraw is offline
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Talking Cherokee Double-D

All,

Back in August of 2004, on the OldRockets list, we had this discussion about a two-stage version of the Cherokee-D. Our general consensus was to start with the C-C Express...

I've sent Scott a set of modified decals and a set of fin templates to build one version of this model. This version has the booster fins reduced in size to 85% of the originals. The booster fin decals on the new sheet are reduced accordingly.

Thanks to James Gartrell for his original "Cherokee DD" name decal. The decal sheet I created borrows from his pattern, but uses the "D" of the original Cherokee-D. Since I can now post the images here on the Forum, I'll attach them to this message so anyone who wants a set can try it out...

The decal sheet here is in JPG format, but the version I sent to Scott is a TIF, with perhaps a bit more resolution.

Also included is a copy of an alignment guide that works well. Attach the pattern to a thicker piece of cardboard and remove everything inside the outline (you may have to use some sandpaper to adjust the opening...), and it will hold the fins in their correct positions while the glue dries.

Enjoy!


Craig McGraw
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File Type: tif Cherokee DD Fins.tif (65.3 KB, 317 views)
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  #2  
Old 05-10-2005, 02:21 PM
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Eagle3 Eagle3 is offline
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Why are the booster fins reduced and not the upper stage? I don't recall the discussion on oldrockets, so I don't know the history.
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Old 05-10-2005, 02:42 PM
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CPMcGraw CPMcGraw is offline
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Quote:
Originally Posted by Eagle3
Why are the booster fins reduced and not the upper stage? I don't recall the discussion on oldrockets, so I don't know the history.


I had to look hard to find the thread, myself. Mid-August, message numbers between 21500 and 22000...

There were several suggested fin patterns in the discussions, but the thread died out without a final accepted booster pattern. One plan version used a set of fins similar to the main fins of the #2174 Polaris, while another suggested enlarging the original fins to use for the booster.

The reduced-area "booster" fin idea is not uncommon, and has been used by several Estes' kit designs, including the Clipper, the SARK, and the Guardian. I saw this version as just one more design in the list of possible solutions.


Craig...
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Old 05-10-2005, 02:47 PM
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Gotcha. The SARK and Clipper came to mind when I visualized this. I just thought that with two 24mm Ds that one might want the added fin area aft, especially if you build the original shorter tube Cherokee D. I'll have to rocksim it and see how it looks. Thanks for the image uploads!
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Old 05-10-2005, 02:56 PM
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Quote:
Originally Posted by Eagle3
Gotcha. The SARK and Clipper came to mind when I visualized this. I just thought that with two 24mm Ds that one might want the added fin area aft, especially if you build the original shorter tube Cherokee D. I'll have to rocksim it and see how it looks. Thanks for the image uploads!


Since we started with the CC Express kit, this offered the chance to do a long-body version (full 18" BT-55 tube), so the reduced fin area really shouldn't be a problem. The decal I sent uses the modern Estes logo, making this version more like an extension of the #1247 version rather than the "K" version.

I need to sim up the short-body version with this booster, but I still think the stability is OK. At the very least, the short-body version might need some weight added, but probably not much. The original Cherokee-D is a very stable design as-is...


Craig...
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Old 05-10-2005, 09:10 PM
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either way , I like to make sure the booster is unstable enough to tumble ,
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Old 05-10-2005, 11:39 PM
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Quote:
Originally Posted by CPMcGraw
I need to sim up the short-body version with this booster, but I still think the stability is OK. At the very least, the short-body version might need some weight added, but probably not much. The original Cherokee-D is a very stable design as-is...

Craig...


OK, the sim is in! (AGAIN)

In fact, if you've already read this message once, I've updated the RKT file. Found something out that I didn't notice before, and had to correct it. The design is NOT naturally stable in two-stage mode, and DOES need some weight in the nose (0.25 oz at the tip). This gives the full-up rocket a 1.0 calibre margin.

The new RockSim 8 [Beta 3] gives me a 2155' altitude for this bad boy, using a D12-0/D12-7 combination. This is for the LONG-BODY version. Deployment is within a foot or two of apogee!

I'd say this confirms the stability of the (corrected) design...

ZIPped RKT file is attached...

Craig McGraw
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File Type: zip CDD Project.zip (6.1 KB, 274 views)

Last edited by CPMcGraw : 05-11-2005 at 12:07 AM.
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Old 05-11-2005, 12:10 AM
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CPMcGraw CPMcGraw is offline
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Quote:
Originally Posted by ScaleNut
either way , I like to make sure the booster is unstable enough to tumble ,


The booster is about the same size as the one for the Astron Avenger, so it should have the same (or similar) tumble characteristics....

And yes, I know, Famous Last Words...

Craig...
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Old 05-11-2005, 12:30 AM
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Quote:
Originally Posted by CPMcGraw
OK, the sim is in! (AGAIN)


Third time usually gets it right... Just ask Scott!

Sorry about the confusion with the RKT files. I'm still trying to learn some of the new features of the program...

I made a mistake by doing this after midnight, too. My brain says I should be in bed...

RockSim 8 B3 says 2181.6' this time, with a two-stage flight stability margin of 1.02, and a sustainer-stage post-booster-seperation flight margin of 2.05. My mistake was in attaching the nose weight to the booster (trying to show the sustainer in a single-stage mode without the added weight...) instead of directly to the NC. Problem with this is, in the simulation, the nose weight drops out at staging, which we know it doesn't do in reality...

And howdy, do I love those rendered images of the Cherokee Double-D! I was able to apply the decal wrap to them, with only a few minor glitches...


Craig...
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  #10  
Old 05-11-2005, 09:48 AM
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Oh, man. Not gonna get into the tech discussion, but seeing as this is a combination of my two favorite things (the Cherokee-D and two-stagers), looks like I have a new project on the horizon.
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