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Model Forum / General / Rockets / December 2009Model rocketry tips and techniques?
I haven't seen many postings in RMR lately, so I thought I would try to get a thread started. Do you have a tip or idea for your fellow model rocketeers? If so, post it, and let's see if we can make RMR useful again. To start off, here's an idea I haven't seen elsewhere. The narrowest roll of masking tape I've seen is 3/4 inch, but sometimes you need it to be thinner. For example, to make a thrust ring on a 13mm engine, or to secure an engine hook to a 24mm reload engine. In those situations, I use floral tape -- the green tape that florists use to make flower arrangements. It's cheap, available in any craft or floral store, and comes in 1/2 inch widths. Anyone have any other tips? Leslie Use slow-setting epoxy for larger body tubes - yellow glue grabs too quickly, risking an incomplete connection between parts if it grabs before you're done inserting the BT. To make sure your fins and launch lugs are straight on your body tubes, you have to make sure your guide lines are drawn straight along the length of the tube. My favorite way to do this is by using angle irons -- "L"-shaped lengths of metal -- as a guide when drawing the lines. My local Ace Hardware store sells 1/2" x 1/2", 3/4" x 3/4" and 1" x 1" aluminum angle irons in 4' lengths. If you don't have a local hardware store that carries them, one online source is http://www.onlinemetals.com, which sells 6063-T52 aluminum angle irons in various widths and lengths. (I'm sure there are other sources, but that's the first one I found while searching online). White glue is great for model rockets, but when you start building mid- power and larger rockets, you need to use epoxy. When I use it, I tend to repeatedly mix small amounts -- for example, mix a little up and make fin tang fillets inside the body tube, wait for them to dry, rotate the rocket 90 degrees, and repeat three more times. I've found it handy to keep a box of toothpicks and a box of kitchen wax paper in my workshop. When I need some epoxy, I tear off enough wax paper to give me a mixing surface, and use a toothpick to mix it. The toothpick is also good for applying the mixed epoxy to accessible areas, but for applying it to recessed areas in a body tube I use shish kebab skewers. You can get a bag of 100 ten-inch skewers at most grocery stores for a couple of dollars. > White glue is great for model rockets, but when you start building mid- > power and larger rockets, you need to use epoxy. A common fallacy. While I'd use yellow glue instead of white glue for my models, yellow glue works fine on any size rocket as long as the materials being bonded are wood and paper. In fact, any good yellow glue is going to make a stronger bond between wood and paper than 5 minute, 30 minute, and even the aircraft/boat building epoxies like West and System3. The mass market epoxies just won't hold up to motor mount heat, even on a rocket as small as a Mosquito. I tested this to the extreme over a decade ago, building a THOY Hornet (same size as a Graduator or Initiator, 29mm MMT, I added a baffle system to the MMT) with nothing but Titebond. To date it's flown on everything from a D to an H238, which is the limit of what will fit in the motor mount. A rocket like a LOC Magnum, a popular L2 kit, would have no problem flying on a J or more even built with Titebond. Of course regardless of glue, you need to use proper building techniques everywhere, such as fillets and reinforcing where needed. When you switch to materials like G10, fiberglass, and the like, then you do need to use epoxy. But not until then. > > White glue is great for model rockets, but when you start building mid- > > power and larger rockets, you need to use epoxy. [quoted text clipped - 3 lines] > When you switch to materials like G10, fiberglass, and the like, then > you do need to use epoxy. But not until then. I stand corrected. Thanks for the tip! > I haven't seen many postings in RMR lately, so I thought I would try > to get a thread started. Do you have a tip or idea for your fellow [quoted text clipped - 10 lines] > > Anyone have any other tips? One of my favorite tips is to use Future floor wax for the clear coat. After the flying season is over I use Windex to remove the clear coat and redo the process for the next flying season. Ted Novak TRA#5512 >> I haven't seen many postings in RMR lately, so I thought I would try >> to get a thread started. Do you have a tip or idea for your fellow [quoted text clipped - 14 lines] > After the flying season is over I use Windex to remove the clear coat > and redo the process for the next flying season. Not a tip as such, but - has anyone tried dimpling a rocket, like a golf-ball? It's been tried with cars, and they do go faster ... -- Peter Fairbrother > Not a tip as such, but - has anyone tried dimpling a rocket, like a > golf-ball? > > It's been tried with cars, and they do go faster ... > > -- Peter Fairbrother No one else has replied yet? I haven't heard of anyone trying this. My off-the-cuff thought is that any gain in a rocket's aerodynamics would be offset by the additional weight of the rocket coating, but that's just a guess. This sounds like a possible NARAM R&D project. Build a couple of rockets, one with dimpling and one without, and see if one performs better. >> Not a tip as such, but - has anyone tried dimpling a rocket, like a >> golf-ball? [quoted text clipped - 9 lines] >Build a couple of rockets, one with dimpling and one without, and see >if one performs better. One of my favorite rockets was a Big Bertha painted white and covered with metal flake blue punched paper computer tape (an old altitude prediction program). It was purely cosmetic, but it may also qualify as a dimpled surface. In your research, be sure to learn about separated flows, and how the type of boundary layer affects separation. If you find a rocket design that may benefit from inducing boundary layer transition, you can research more effective ways of tripping the boundary layer on the rocket than dimpling. You might also discover that using vortex generators can be even more effective. Dimpling etc. will not improve a typical well designed rocket, although you may find an exception. In general you just want a well built and finished model with a rubbed/waxed finish. Alan Jones >>> Not a tip as such, but - has anyone tried dimpling a rocket, like a >>> golf-ball? [quoted text clipped - 27 lines] > >Alan Jones Well, it is clear by the lack of replies, that there is no interest in doing R&D, not even for a NARAM entry. Even though I view with disdain those awful R&D projects where the "researcher" simply flys two rockets with some difference between then, "observes" that A went higher than B, and concludes that the difference was effective. Nevertheless, I encourage R&D. At least the "researcher" benefits from going through the motions of writing an R&D report. I was prepared to offer some additional key words, and other help. I would also like to suggest the opposite approach. Instead of dimpling to hasten boundary layer flow from laminar to turbulent, consider using riblets to try and stabilize the flow and extend the laminar region or lessen turbulence. Riblets are fine surface ridges parallel to the airflow. They are typically W ridges, similar to old phonograph records. I think the idea originated with shark skin, yet the technique is much more recent than the dimpled golf ball. I think 3M makes riblet tape that can be easily applied. Alan Jones Pet shops sell 12" and 16" long "tweezers" used to reach into spider tanks. They work great for grabbing things inside those small diameter airframes. Kevin I have never liked sealing balsa fins. I know everyone has his or her favorite method, and I know that someone will chime in with "but it's really simple to..." But I just get discouraged when I take the time to carefully sand my balsa fins into an airfoil shape, then spray Krylon Sandable Primer onto them, only to watch the air bubbles form due to all the air in the grain. So what do I do? Replace the balsa fins with basswood ones. Basswood sheets are available in most hobby stores, and basswood has a much finer grain than balsa. A single light coat of Krylon Sandable Primer is usually quite sufficient to give me a smooth finish. > I have never liked sealing balsa fins. I know everyone has his or her > favorite method, and I know that someone will chime in with "but it's [quoted text clipped - 7 lines] > finer grain than balsa. A single light coat of Krylon Sandable Primer > is usually quite sufficient to give me a smooth finish. Back in the day I brushed on coat after coat of sanding sealer, balsa fillercoat, and Aerogloss dope until I got mirror like finishes. Then I did the same with an airbrush. PITA! The best method I've used lately is to fill the grain with Elmers Fill & Finish (or whatever they call the product today), then prime & paint. For the fins, use a plastic squeegee or an old credit card to spread it around. For the tube spirals, a glue bottle will deposit a fine line along the spiral better than a brush. One technique I learned from former Estes employees but never did myself is to coat the balsa surfaces with a thin layer of finishing epoxy, then sandwich between glass sprayed with Pam or some other release agent and weigh down with phone books. The epoxy hardens to a glass smooth surface that is easy to prime and paint. They used this for many of the catalog photo models. A few years ago I got a roll of transparent return address labels with my name, email address and NAR member number on them. I put one on all of my model rockets, so that if someone comes across a rocket I lost, they can get in touch with me. > A few years ago I got a roll of transparent return address labels with > my name, email address and NAR member number on them. I put one on > all of my model rockets, so that if someone comes across a rocket I > lost, they can get in touch with me. As long as the email address doesn't point to a CompuServe or GeoCities acoount... <G> David Erbas-White |
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