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[02/01/05 note - this is a very important page to read. Learning to select different sizings of bottle is going to help you more than just about anything on this web site.]
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[02/01/05 note - this is a very important page to read. Learning to select different sizings of bottle is going to help you more than just about anything on this web site.]
THE REMOVEABLE FIN ASSEMBLY SLEEVE:Another thing I have been doing lately is to make another outer sleeve for the bottom of the rocket and putting the fins on the outer sleeve.
I also do a "CURLED EDGE" on the very bottom of this outer sleeve for ridigity. I tape this "finned sleeve" around the circumference to prevent it from sliding off. I also pick a tighter fitting outer sleeve. My feeling is that by "sleeving" the bottom section too (with a tighter fitting sleeve), it will force more pressure to the upper section of the rocket body for improved deployment action. ALSO, I'm getting double duty "explosion jacket" because now both top and bottom of the rocket body is "jacketed". This is much easier that using filiment tape.
Another reason for liking this "finned sleeve" is that I can now EXTEND the position of the fins LOWER than I could when attaching fins directly to the body of the rocket. Also, I can SWITCH this "finned sleeve" to other rockets, thus reducing my required fin inventory.
Whenever a rocket falls to the ground and distroys the booster portion of the rocket, this removeable fin assembly is very easy to slide off the booster and slide onto another booster (soda bottle).
The picture above shows three lexan fins, but lately I've been using Coroplast Plastic (fluted signboard material). It's much lighter and cheaper than lexan. Look at the photo (right) of the colorful Coroplast Fin assembly.
Now that we know that you can select different size 2 liter bottles for specific purposes, you can pick an outer sleeve that won't bucket the walls of the rocket body. I'm betting the with the right selection, you will be able to find telescoping sleeves that won't buckle each other.
In determining the circumferences of the bottles, first remove the labels and debris. I use a nylon strap that is marked with ball point pen lines. Then I use a felt tip marker to write the size (my own code) of each bottle on the side of the bottle. Then I sort the bottles according to their sizes.
Stanley brand tools as a nice 1/4" measuring tape that is 1/4" wide and 10' long. If you look closely, find the tape with the DIAMETER SCALE on the reverse side. This is VERY HANDY. Just flip your measuring tape upside down and wrap it around a soda bottle. You can get measurements to the nearest 1/64 of an inch.
I have found that in surveying circumferences of many 2 liter soda bottles, there appears to be THREE predominant SIZES, (and sometimes sizes in between). The prevailing circumference sizes are 13.5, 13.563, and 13.625 inches. Since the thickness of one wall is only .0123 inches, there is room for all three of these sizes to freely "telescope" inside each other. I was using these "telescoping size" differences to make perfect "butted curled edges & circumference splice" joints for multiple bottle rocket bodies.
Since a 2 liter bottle expands about .188 inch in circumference when pressurized, there is enough expansion to interfer with the telescoping of an outer sleeve, even when using the extreme differential sizes of an 13.625" sleeve over a 13.5" bottle. The ideal of course is to use sizes that allow EASY telescoping, yet as tight as possible. The 13.563 inch circumference is more plentiful on the average, so I like to make that the body of the rocket, and the 13.625 inch circumference is chosen for the outer telescoping sleeve, in this case the removeable fin assembly.
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