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#1
09-22-2010, 04:21 AM
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Old Semroc Swift fins?
Hello All,
Looking at the laser-cut balsa fin set (see: http://www.semroc.com/Store/scripts...p?idproduct=179 ) for the "Retro-Repro" Semroc Swift model rocket kit (see: http://www.semroc.com/Store/scripts...s.asp?SKU=KV-24 ), I noticed that the fin set has 4 fins while the kit is illustrated as being built with 3 fins. Also, the illustration of the Swift in the Semroc catalog (in the May 1970 issue of Astronautic Modeler, see: http://www.ninfinger.org/rockets/ca...70semroc34.html ) shows it with what looks like 4 fins. Did the original Swift kits have 4 fins? If so, the "extra" fin would enable the builder to build it as either version, rather like the Black Brant VB (with 3 fins) versus the Black Brant VC (with 4 fins). In addition, the kit specifications page in the 1970 Semroc catalog (see: http://www.ninfinger.org/rockets/ca...570semroc8.html ) says that the original Swift was 12.5" long (0.6" longer than the 11.9" long "Retro-Repro" version). I'm sure this is due to the 9" long ST-790 tube being used in the new kit, as it is a standard length that is also used in other "Retro-Repro" kits. (I'm certainly not criticizing Semroc for this; why increase their already-large total number of in-stock tubing lengths when they don't have to, since the slight difference in the new Swift kit's length causes no stability problems nor any noticeable difference in its appearance?)
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Black Shire--Draft horse in human form, model rocketeer, occasional mystic, and writer, see: http://www.lulu.com/content/paperba...an-form/8075185 http://www.lulu.com/product/cd/what...of-2%29/6122050 http://www.lulu.com/product/cd/what...of-2%29/6126511 All of my book proceeds go to the Northcote Heavy Horse Centre www.northcotehorses.com. NAR #54895 SR Last edited by blackshire : 09-22-2010 at 04:28 AM. Reason: This ol' hoss done forgot somethin'. 
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#2
09-22-2010, 02:11 PM
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The original only had three fins. When we first started back up, I included the extra fin because there was room on the fin sheet and it provided a spare. The original 1/16" balsa would break easily. Later batches of the Swift only have three fins on the sheet.
The length was incorrect from the beginning. I think the original prototype in 1965 or 1966 used the Estes BNC-20N, long before we did the nose cone machine. The closest we got to the 20N with the new machine was 2.1" long. I thought someone had gone back and corrected the lengths once we had the production nose cones, but it was missed. The only tube we had close to it was 9.0" long, We did not cut tubes back then, but ordered them all to length.
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Carl McLawhorn NAR#4717 L2 semroc.com
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#3
09-22-2010, 04:10 PM
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Quote:
Quote:
__________________
Black Shire--Draft horse in human form, model rocketeer, occasional mystic, and writer, see: http://www.lulu.com/content/paperba...an-form/8075185 http://www.lulu.com/product/cd/what...of-2%29/6122050 http://www.lulu.com/product/cd/what...of-2%29/6126511 All of my book proceeds go to the Northcote Heavy Horse Centre www.northcotehorses.com. NAR #54895 SR
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#4
09-22-2010, 04:18 PM
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Quote:
__________________
Carl McLawhorn NAR#4717 L2 semroc.com
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#5
09-22-2010, 04:21 PM
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Quote:
__________________
Black Shire--Draft horse in human form, model rocketeer, occasional mystic, and writer, see: http://www.lulu.com/content/paperba...an-form/8075185 http://www.lulu.com/product/cd/what...of-2%29/6122050 http://www.lulu.com/product/cd/what...of-2%29/6126511 All of my book proceeds go to the Northcote Heavy Horse Centre www.northcotehorses.com. NAR #54895 SR
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