Thread: After the Fire
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Old 06-08-2005, 01:33 AM
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Carl@Semroc Carl@Semroc is offline
Junior ??? Rocketeer
Join Date: Mar 2005
Location: Knightdale, NC
Posts: 1,470

Originally Posted by Tweener

... data says "User specified minimum velocity for stable flight: 43.9993 ft/sec".

That converts to 30MPH. At some point in the past, someone determined that 30MPH was the minimum velocity for stable flight. In 1961, Vern Estes designed a wind tunnel (TR-5) that produced 22 fps air flow and said it was "ideal for stability tests." G. Harry Stine in his first edition used the figures 30-40 MPH not as a minimum, but as typical.

I think RockSim is very conservative. Minimum velocity varies with the geometry of the rocket. Maybe RockSim needs a plug-in to CALCULATE the minimum velocity and launch rod length.

Another consideration for launch rod length. It should be measured from the bottom of the lowest launch lug to the top of the launch rod. Many taller rockets with launch lugs high up the side and engines raised off the blast shield only have an effective usable length of 2 feet from a 3 foot rod.
Carl McLawhorn
NAR#4717 L2
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