#21
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Tweener, RockSim either calculates a value here, or there is a "pre-set" value in the program. I believe I can change that value, but I did not select that value. I've just run the simulations with mostly default values. What I did change was the temperature at launch time, the launch guide length (note, this doesn't necessarily mean a rod), and the Latitude of the launch site. Craig... |
#22
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Pig(skin) Kickin'
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Quote:
http://www.rocketreviews.com/virtual_contest5.shtml http://www.rocketreviews.com/reviews/descon8/ncaa.html Quote:
Cheers, --Jay |
#23
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I think ours is about a four footer. |
#24
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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.
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Carl McLawhorn NAR#4717 L2 semroc.com |
#25
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Thanks Carl,
My gut-feeling was that an over-stable design like the Thunder Roc wouldn't need much velocity at all to keep headed in the right direction - as long as it was still accelerating. I can't wait to try that Aerotech E15! BTW, my order for a set of laser-cut fins will be in as soon as I decide what else I need/want to make at least a minimum order.
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John Lance Ladd Yoyodyne Propulsion Systems Grovers Mill, NJ Established 1938 lladd.netau.net |
#26
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I built the motor mount and fin can for the Thunder Roc this weekend, but decided to order a BT-60 ejection baffle from Flis Kits to replace the tube coupler in the middle of the two uppermost BT-60 sections. This T-Roc should be quite a bit lighter than my first clone because I cut out the epoxy clay, basswood fins and huge nylon chute right off the bat. Next launch is in two weeks. (I was "under the weather" this weekend. In a completely different way than Craig was. )
I also ordered several other parts, including a "complete" set of the canted cluster mounts. They now stock them in 13mm, 18mm and 24mm for BT-50(?), BT-60 and BT-70 respectively. Not sure what project they'll become a part of at this point, but that's part of the fun. (Although that dual 24mm BT-70 mount sounds like it would make an a$$-kicking SPEV for starters.)
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Bill Eichelberger NAR 79563 http://wallyum.blogspot.com/ I miss being SAM 0058 Build floor: Centuri Mini Dactyl Estes - Low Boom SST Semroc - Marauder, Shrike, SST Shuttle In paint: Canaroc Starfighter Scorpion Estes F-22 Air Superiority Fighter, Multi-Roc, Solar Sailer II Semroc Cyber III Ready to fly: Estes - Solar Sailer II Semroc - Earmark, Groonie Der V 1/2 |
#27
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That was my thinking exactly. Kill two birds with one stone, so to speak. The added mass would only be the perforated bulkheads, since the coupler's needed anyway. The only concern I'd have is that only half the baffle is effectively anchored in the tube against the ejection pressurre. Make sure it's glued 'real good'.
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John Lance Ladd Yoyodyne Propulsion Systems Grovers Mill, NJ Established 1938 lladd.netau.net |
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