# Thread: Aspect Ratio (BT L to W)

1. ## Aspect Ratio (BT L to W)

I have searched on here and EMRR. I have found that the rule of thumb is from 10:1-30:1.
I trying to built a something a bit shorter. More like 5:1. It will be a much more drag rocket then usual. Heck maybe even 2:1 if I can get away with it.
Will this be okay? Or is there something I have to do in order to adjust stability?
Last edited by mkmilion; 27th June 2010 at 05:52 AM.

2. I've found a lot of nose weight maybe required...ALOT... I just built my 'Peanut' by feel. The CG felt about an inch into the NC, completely ahead of the BT...

Are you using any type of Sim program? (RockSim, OpenRocket) Maybe check this out... http://www.rocketryforum.com/showthread.php?t=12306

Just build it, it will fly!

3. In general stumpy rockets (<10:1) are actually more stable than you would think, and as a result, they tend to not need as much of a stability margin as you would normally need.

4. ## Thanks for the link

The link answered many of my questions; to the degree I get the concept. The short answer was: They just do, because they're in their own class. Of course base drag too.
Mine will be a tiny bit longer and a tiny bit fatter then yours so I think I'll be safe.
BTW I do not have a simulator just the old school swing test.
Last edited by mkmilion; 27th June 2010 at 07:23 AM.

5. The same rules apply -- Center of gravity must be in front of the center of pressure, preferably with some extra margin so that things like the parachute shifting aft or a bizarre gust of wind won't cause it to become unstable. The trick is figuring out where the center of pressure on a short, fat rocket is. I know that the CP on saucers can be completely aft of the saucer, rendering them stable no matter where the CG is.

Short, fat rockets are much more likely to require nose weight. They also benefit greatly from swept-back fins since that puts the fin area farther from the center of gravity. Also, try to avoid things like canards foward on the rocket.

6. ## Thanks MattieShoes

I probably should let you know that; this is a scale of sorts and the in order for me to do the same aspect I figured I need a lot of nose weight. It's similar to McKaila's Dad's Peanut.

BTW here's the ratio: 1.2857142857142858:1 = 4.5:3.5

That's without the nose cone. I don't know if the nose cone counts as part of it. Does any one know? If that's the case I might be in the clear for sure. Well maybe after I adjust it to account for that.

7. The nose cone is usually counted.

Oh, and MattieShoes, as I said before, you actually need less margin with a stumpy rocket, rather than extra margin. With something like a Fat Boy or similar, you are usually fine with something like 0.5-0.6 calibers rather than the 1 caliber normally recommended.

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