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mycrofte
07-16-2009, 10:12 AM
Guess I put mine in the wrong area. I finally finished my Ascendant design. I 'loosely" based it on the Andromeda Ascendant from the TV show. I love that ship design!

http://i629.photobucket.com/albums/uu15/Mycrofte/Current%20Build/Ascendant_02.jpg

Sorry about the picture quality. It was storming and my lighting was bad. I had to touch it up in Paintshop Pro since it was nearly black and white.

This was the last RockSim file I made (by file date), so I hope it is the correct one.

CPMcGraw
07-16-2009, 07:53 PM
I've downloaded the file, looking it over...

The Barrowman calculation for stability says the model is 'in range', but the RockSim math says otherwise. Loaded with a B6-4, the model shows 0.16 static margin. It needs to be above 1.00 to be safe... :(

Having said this, RockSim has been known to make a few mistakes using its own math... :o

Important question: Have you actually built and flown this design?

This design is similar to another we have in the Master Collection -- the Sky Captain W.A.M design (Water-to-Air Missile). Look in one of the old "Scrounged" threads, there's two or three interpretations of it. Study where the CG and CP locations are on those designs, and compare the length of those designs to the total fin area (and how that area is distributed). It is also similar (maybe larger) to one of James Pierson's many creations (I can't remember the name of it right now, sorry).

Without changing your outlines at all, I had to add 1 full ounce of ballast to the nose cone shoulder to achieve a proper CG/CP ratio (static margin); however, this much ballast blew out the deployment velocity to an unsafe value. What I would suggest is decreasing the fin size by scaling it down a bit, and shifting the smaller fins as far to the rear as possible. You might also adjust the fins a bit in shape to move the bulk still farther to the rear. This has the additional effect of shifting more of the tube ahead of the CP, which is a good thing.

I try to adjust the mass distribution in a new design over the addition of ballast (nose weight). One or two inches of additional tube length ahead of the CP weighs virtually nothing (just the additional inches of tubing), but this can have the same effect as adding ballast without all of the additional mass. You might also try adding some length to the main tube, with the additional length at the top. It shouldn't hurt the appearance, but it will improve the stability.

If you have not already picked up a copy, I would highly recommend grabbing "The Handbook" by G. Harry Stine (currently the Seventh Edition). The chapter on stability is a must-read for all model rocket designers.

Thanks for placing this design in the BARCLONE studio area. Let's get the model 'tweaked' for stability, and then it will get added to the catalog list.

mycrofte
07-17-2009, 05:01 AM
I had originally designed it with a longer tube. I shortened it to where it was just stable, since it didn't make "much" difference.

I have built and painted it. It is waiting for a parachute now. Since my RockSim Demo ran out all I can do is string test it and maybe add a short tube topside...

I can add an older file for you to look at and see if it is better! Since I can't even look at them I will have to rely on someone else. It would be nice if the demo would at least let me open them to look at (hint, hint, next version)

mycrofte
07-17-2009, 06:08 AM
Thanks for the thread tip! There was a lot of cool stuff there. I didn't even know that thread was there. Let alone all the hollow fin designs.

The was another, the Sparrow Dart, looked like mine with the fins upside down...