12-10-2007, 09:02 AM
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Forest Sprite
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Join Date: Dec 2006
Location: Back Up in the Woods
Posts: 3,657
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Quote:
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Originally Posted by Ltvscout
Mark,
The engine mailing tubes and the BT-40 were two different animals. The BT-40 was from what I recall leftover stock from MMI. I have some scratch-built rockets here that I bought off of eBay six or seven years ago that have BT-40 tubes and those old, rubber nose cones. This tube had an inside diameter of .765". They had a balsa cone, a plastic skyrocket cone (fit over the outside of the tube) and two rubber cones available for this tube. The BT-40 size derived from the skyrocket size tube if I'm not mistaken.
The engine mailing tubes were much larger in diameter and much thicker-walled. Estes only offered one cone for the engine mailing tubes. That was the BNC-MTD. This tube had an inside diameter of .937".
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A-ha! My knowldege of early model rocket history is even sketchier than I thought! I had read about the old mailing tubes, and had also read about BT-40, and had assumed that they were the same thing. I stand corrected. In any event, back in the day I never saw either one.
BTW, when I went to build my Li'l Augie (EIRP-10) this summer, the plans called for cutting the augmenter tube out some mailing tube, by which I assumed they meant the engine mailing tube. I thought that I would need BT-40 for that, but it turned out to be the wrong diameter and I ended up using ST-10, which worked fine. Now you have cleared up that mystery for me. Thanks!
Mark K.
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Mark S. Kulka NAR #86134 L1,_ASTRE #471_Adirondack Mountains, NY
Opinions Unfettered by Logic • Advice Unsullied by Erudition • Rocketry Without Pity
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