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Old 04-18-2009, 01:02 AM
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Royatl Royatl is offline
SPEV/Orion wrangler
Join Date: Mar 2005
Location: Atlanta, GA
Posts: 2,549

Originally Posted by MDorffler
James, nothing personal, but I have never had any need to use 'model rocket design software' to design my model rocket kits. Never. Ask yourself what software I would have used in 1968, or 1973, or even 1990? I have always designed all my models using my natural skills. Normally I conceive a design totally in my mind driving either to or from Estes. That's the truth. I can tell you whether a model will be stable by simply looking at it, or hefting it, or whether it needs a pinch of clay in the nose to correct any CP/CG imbalance.

I've noticed a trend that a lot of people trust RockSim implicitly. However, like you, I design the old fashioned way!

I always build several flight test versions of any new design. The first test round is with parts from inventaory, then with parts from pre-productions. I build the first test model with all the parts in positions as if built by a serious and carefull modeler. The next are built as though the the modeler is clumsey. Any flight of any test model has to be arodynamically stable, even when parts are glued on crooked. Only when I am totally satisfied that all of these versions fly absolutely straight, do I release it for the next production steps.

In the past few years, however, I've seen a few kits that have ended up unstable as built. The well known example was the first shipment of SpaceShipOnes. Admittedly, that was probably a difficult design to deal with, but I was surprised when, after building mine as stock as possible, it immediately went unstable. Then we found that it needed an extra 1/2 ounce of nose weight, that later kits had. There was the E2X military kit -- can't think of the name -- but, built stock, it too was unstable on C6-5 and sometimes on B6-4. There was the SR-X, which I've only seen fly stably once out of five flights. I've heard of problems with the Solar Flare, though I haven't seen one fly yet (gotta get around to building mine).

Or how about the lower stage of the original Renegade, that was heavy and stable, and would spike into the ground (at one of our launches, a stock Renegade lower stage lawndarted within a couple of feet of a spectator. Later that day it flew again and spiked the tail lens of the rear door of a van. We banned the Renegade from our launches after that day). I guess you saw the problems with that rocket, since you redesigned it.
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