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Old 09-24-2012, 01:54 PM
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Quote:
Originally Posted by CPMcGraw
What I've been trying to do with my more recent stuff is to design for low-Dv. Simply put, to achieve a low velocity at the apogee so that the parachute(s) don't open "explosively". I've got a few like that where you think the chute is going to rip itself off; the sound of the chute opening (even 300-400 feet up!) is as loud as a gunshot. If I design to avoid such, then the end result is usually a better-flying rocket overall, even if I have to sacrifice some top-end performance to get it.


Has anyone done any testing to determine how accurate the deployment velocity predictions are? With things like the Altimeter Two available, it should not be a difficult research project.



Quote:
Originally Posted by CPMcGraw
I've used random-length tubes in some designs, placing a coupler at known tube lengths to keep the mass correct, but not breaking the long tube down otherwise. From the POV of the program, it doesn't care. It calculates aerodynamics on the total exposed length(s), not the individual lengths that may be internal. It calculates the mass on the total of all the parts based on their area totals and the mass values per unit in the database; not on any specific part. We've run into issues with the database on this already; some component materials have bogus entries, or values that are at best whacked. It catches us occasionally...


Do not be surprised if smaller kit manufacturers who cut their own own tubes use seemingly random lengths of tubes in their designs. For example, 17", 11.3", 8.5" and 6.8" are 34" tube stock divided into two, three, four and five even pieces.


Bill
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