Reference / Paper · 2008
Peak of Flight #215: How to convert a plastic nose cone into a drag reducing boat tail
Apogee Components' Peak of Flight newsletter, issue 215 (2008-08-12).
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- apogee-components
- model-rocketry
Reference / Paper · 2008
Apogee Components' Peak of Flight newsletter, issue 215 (2008-08-12).
Apogee Components' Peak of Flight newsletter, issue 215 (2008-08-12).
How to Convert Apogee’s Plastic Nose Cones into Boattails Step-by-step instructions on designing and building rockets with boattails Sunward Aerospace Solar Eclipse 2-Stage Rocket Kit www.ApogeeRockets.com/solar_eclipse.html Apogee Components, Inc. — Your Source For Rocket Supplies That Will Take You To The “Peak-of-Flight” 3355 Filmore Ridge Heights Colorado Springs, Colorado 80907-9024 USA www.ApogeeRockets.com e-mail: [email protected] ISSUE 215 AUGUST 12, 2008 How to Turn a Plastic Nosecone Into a Boattail By Tim Van Milligan “Hi Tim and crew! Thanks again for the newsletter. I appreciate the time you take to pass on your knowledge to the rest of us. Something I’ve been interested in is how to best utilise your fantastic BT-70 (P/N 20070) & BT-80 (P/N 20080) nose cones as boattails. What is the best way to cut them? How can I make accurate fin slots? What about motor retention? What sort of glue works on the polystyrene for bonding and fillets? What is the best way to mount the motor tube? Thanks and regards.” -- Matt Small You’re in luck! I just happen to be working on the instructions for a new DynaStar kit that uses one of our nose cones as a boattail. This new kit, due out in a couple of months was designed by Shrox and will be called the Lexx-Jet. So I’ll borrow from the instructions and show you how to take one of our nose cones and turn it into a dragreducing boattail. First off, in case you’re wondering, you can find these two nose cones from the Apogee Components web site at: Figure 1: Rocket designer “Shrox” holding a prototype of the new Dynastar Lexx-Jet rocket. http://www.ApogeeRockets.com/nose_cones.asp. What makes the two Apogee nose cones special is that they were designed to be easily converted to boattails. I don’t know of any other manufacturer that has created nose cones like ours. We think ahead and try to make our parts extra useful and as easy to work with as possible. The features that makes them unique is we’ve included the cut lines on the tip and on the shoulder to make it easier to cut them. On the rear end of the nose cone is a V-groove that you simply run a hobby knife along. You only need to score the plastic, and it with a little flexing it will snap off. Figure 2: The V-groove on the shoulder makes it easy to cut off the rear end of the nose. About this Newsletter Continued on page 3 Newsletter Staff You can subscribe to receive this e-zine FREE at the Apogee Components web site (www.ApogeeRockets.com), or by sending an e-mail to: [email protected] with “SUBSCRIBE” as the subject line of the message. Page 2 The other feature on the nose cones are two little raised beads near the tip. We put these on the nose cone ISSUE 215 Writer: Tim Van Milligan Layout / Cover Artist: Tim Van Milligan Proofreader: Michelle Mason AUGUST 12, 2008 Continued from page 2 Turn a Plastic Nosecone Into a Boattail Why did we use a raised bead instead of a “V-groove” like we did on the rear shoulder? That is a great question. The V-groove definitely makes it easier to cut the plastic. But what if you don’t want to cut the plastic? Now you have a groove in the nose cone that has to be filled prior to painting. That can be time consuming if you want a sleek-looking nose cone. By making the cut line a raised bead, it is really easy to sand off if you want the smooth surface. It is much easier to sand it smooth than it would be to try to fill a groove line. Makes sense, doesn’t it? Creating the boattail Figure 3: Raised beads on the tip of the nose make it easier to cut off the correct length for both 24mm and 29mm tubes. to make it easier to cut off the correct amount so that the hole left will be sized to allow the engine mount tube to slide through with a nice slip fit. The bead near the tip is used as the cutting guide if you want to use a 24mm (BT50) size tube, and the further aft bead is a cutting guide if you want to use a 29mm diameter engine mount tube. I’ll give you the main steps in creating the boattail in this article. Since every rocket is unique, your particular design might be configured differently than what is shown here. Step 1: Cut off the tip using a razor saw. Because of the way blow-mold nose cones are made, the plastic is much thicker at the tip of the cone than at the bottom. Normally, this is a good thing. It puts more weight near the top of the rocket and also makes the nose cone stronger so it can survive hard landings. Continued on page 4 Available Online & Worldwide through Quality Hobby Shops & Online Retailers Trust Sunward for a complete line of Model Rocket Kits and Parts including: Tubes, Baffles, Connectors, Mounting Kits, Balsa & Plastic Nose Cones, Nylon Parachutes, motor cluster cables, and NOMEX flame resistant blankets and shock cord protectors. NOW AVAILABLE FROM APOGEE ROCKETS! Browse online our large lineup of BT50, BT56, BT60, and BT70 based Model Rockets Kits. www.sunward1.com [email protected] Direct 416-953-1847 fax 416-245-7985 ISSUE 215 AUGUST 12, 2008 Page 3 Continued from page 3 Turn a Plastic Nosecone Into a Boattail But the extra plastic near the tip makes is much harder to cut the tip off. It is possible to use a hobby knife, but the plastic is so thick that it would take a long time and you’d have a good chance of snapping off the tip of the knife blade. That Figure 4: Keep the blade on the is why I recommend forward side of the plastic ridge. using a razor saw to cut off the tip. The teeth on the razor saw will quickly cut through the plastic, and you’ll have the tip off in about 30 seconds. The only caution is to make the cut on the nose-tip side of the raised plastic bead. The goal is to create a hole that is just big enough for your engine mount tube to slide through with a nice slip fit. Because of this, you want the hole to be slightly small after the initial cutting process. Figure 5: Sand the inside edge to Then you can come create a slip-fit for the engine tube. back and either shorten the length of the boattail, which opens up the hole bigger, or you can sand out the inside of the plastic. Because the plastic is so thick near the tip, sanding out the inside edge of the boattail is what I prefer and recommend. Just wrap some sandpaper around a dowel (1/2” to 3/4” dia) and work the inside edges as shown in figure 5. boattail. Step 2: Cut off the shoulder end. As stated previously, there is a “V-groove” on the shoulder of the nose cone, just forward of the parachute attachment loop. Cutting this end is much easier. All you have to do is deeply score the plastic in the bottom of the groove with a hobby knife. Then flex the plastic by gently squeezing the shoulder. This flexing will open up the crack, and eventually the end of the shoulder will separate from the part. Step 3: Build your engine mount. Because the nose cones are very long, there are a couple of options when it comes to designing and installing the engine mount. You an either have a short engine mount tube, or a long one. I prefer the longer engine mount tube in the boattail because I want to make sure that it is centered concentrically with the outside body tube. As I mentioned previously, the manufacturing method used to make blow-molded nose cones has a drawback that the wall thickness of the part is not perfectly uniform. Because of this, it is possible that Continued on page 5 Launch Success Begins with RockSim • Economical Educational Software • Kid-Friendly: Easy-to-use Design Interface • Determine if Rockets are Stable and Safe to Fly • Find out How High and Fast They’ll Travel The wall thickness of the plastic will not be uniform because of the way the nose cone is manufacturered. So sanding out the inside edge is a good way to control the thickness and insure that the engine mount tube will Figure 6: You can cut off the aft be concentric inside the shoulder using a hobby knife. Page 4 ISSUE 215 • Dream It! • Design It! • Simulate It! • Build It! • Fly It! Get your free demo today! AUGUST 12, 2008 Continued from page 4 Turn a Plastic Nosecone Into a Boattail the engine mount might be cocked slightly in the tube. This would result in canted thrust from the engine which might Centering rings Making the short engine mount will mean that the forward centering ring will be much larger in diameter than the aft ring (sorry to state the obvious). You can see a picture of what the engine mount will look like in Figure 8. Optional centering ring The engine mount is a critical part of the rocket, so I would test fit everything a couple of times before applying any glue. You’ll notice that in both in Figures 7 and 8 that I use a second ring Figure 7: It is preferred that a long engine mount tube be used just to make right behind the most forward centering ring. This is the ring that anchors sure the engine mount tube is straight and concentric. the Kevlar® shock cord. I found that possibly cause the rocket to go unstable. you need the extra gluing surface area to prevent the shock The long engine mount tube alleviates this problem. Sand this edge for fit The engine mount tube is made long enough so that you Align hook with seam will have two centering rings inside the big tube that will dges hold the engine mount tube perfectly concentric (see Figure rear e n o e 7). After that assembly is glued into the big tube, the plastic A glu Put C boattail is slid on and glued in place. Shock cord anchor ring Boattail shoulder Just one small caution; make sure the centering rings are deep enough in the tube so that they don’t interfere with the shoulder of the plastic boattail. If space inside the rocket is limited, and you need more room to house the parachute, then you can make the engine mount shorter. This is the case in the Dynastar LexxJet kit that I’m working on right now. Figure 8: Anatomy of a short engine mount tube in the plastic boattail. Here are a couple of other simple ways to strengthen the centering rings without adding a lot of mass. Remember, it is really the glue joint holding the rings in that we need to strengthen. If you are using through the wall fins, you won’t need these extra strengthening methods. It would be redundant. 1. Put a short (only 1/4 inch) length of tube coupler inside the tube, just in front of the front centering ring on the engine mount. This gives the ring something to butt up against and prevents it from sliding forward in case the glue joint fails. 2. Similarly, put a ring over the engine mount tube - again positioned just front of the forward ring so that it can’t slide forward if the glue joint fails. Inner stiffening ring (use an adapter ring) Outer stiffening ring (use a coupler) Preventing glue-joint failure, can be done with short stifffening rings on the inner and outer edges of the disk-type centering ring. To prevent the rocket from sliding forward in the rocket,the typical method is to glue a thrust ring (also called an engine block) into the engine tube. It is positioned directly in front of the motor, so the engine can’t slide forward into the rocket. See Fig. 2- , and Fig.6-29 on page 53. But note that a thrust ring glued in the rocket will prevent longer motors from fitting completely in the engine mount tube. For example, an Aerotech G35 Econojet is 98mm (3-7/8 inches), while the “Thrust Ring” glued in front of the motor to prevent it from sliding forward. 3rd Edition COMING SOON! PRE-ORDER NOW. Nozzle end A B C Fig. 6- Thrust rings on the aft end of the motor allow different lengths of motors to used in the same rocket. (A) Reloadable motor nozzle end piece. (B) Masking tape wrapped around a case to build up a thrust ring. (C) Thrust ring molded into a single use motor. G80 is 124mm (4-7/8 inches long). Both are 29mm diameter, so they would both fit into the same engine mount tube. But since the G80 is significantly longer, it would stick too far out the back of the rocket. There are two possible fixes for this. First, you could position the engine block deep enough in the rocket to accomadate the longest rocket engine the rocket will use. For engines that are shorter, you would put a spacer tube in front of the motor that fills the gap between the engine block and the front of the motor. The drawback of this approach is that sometimes you don’t know the length of the spacer you would Fig. 6- A thrust ring on the back of the engine butts against the aft edge of the motor mount tube. This prevents the engine from sliding foward while it fires. 61 • 328 pages of concise information on designing and building rockets • Double the size of the 2nd edition • Learn to build stronger rockets that last longer • Make them more aerodynamic so they fly higher and faster with cheaper motors • Use unique recovery techniques to enhance the flight and gets applause from your friends • Use the information to teach others about rocketry and how to do it safely www.ApogeeRockets.com/design_book.asp ISSUE 215 AUGUST 12, 2008 www.ApogeeRockets.com Model Rocket Design And Construction Page 5 Continued from page 5 Turn a Plastic Nosecone Into a Boattail cord from pulling through the front centering ring. One word of caution here about this shock cord anchor ring. Use only wood glue to assemble it. I had a customer that thought that CA glue would be better. But the CA made the shock cord stiff and brittle, and it cracked and failed on the first flight. Wood glue is more plyable and allows the shock cord to flex without making the fibers brittle. Because you will be using wood glue, make sure everything is bone-dry before gluing the mount inside the plastic boattail. Once the assembly is inside the plastic boattail, air cannot get to the rings to dry the wood glue. So you need to let it dry completely before gluing it in. The glue to use when putting the engine mount into the plastic boattail is thick (gap-filling) CA. The CA will harden inside, and the thick viscosity adhesive will help to center everything up nicely. Engine Restraint There are a number of different methods of engine restraint you might consider when using a boattail. My favorite is to extend the motor mount tube out the back of the boattail by 1/2 inch (12.7mm). The motor sticks out of this tube 1/2 inch, and you simply wrap masking tape over You get: (4) AT 41/18 (2) AT 56/18 (2) AT 66/18 (1) AC-56 (1) AC-66 the motor and the tube that extends past the boattail as shown in Figure 9. Rocket engine You’ll notice that in Figure 8, Masking tape there is an Figure 9: The simpliest engine retention aft centering method for boattail rockets. ring inside the boattail. This ring serves a double purpose. Not only does it center up the mount in the boattail, but it also holds down the metal engine hook. From personal experience, I’ve found that the hole on the back end of the boattail is never perfectly circular and is always a little big. So there will probably be room for the metal engine hook to fit through the opening along with the engine tube. If there isn’t, you can use a hobby knife and carefully cut a notch for the hook. If your engine mount includes a metal engine hook, I would try to orient the hook so that it aligns with one of the Continued on page 7 Dollar for dollar, you’ll see the most results by advertising in the Peak-of-Flight Newsletter. In fact, I guarantee it. If you don’t see more results from your advertisement in the Peak-of-Flight Newsletter, I’ll run your advertisment for two more issues at NO COST! Call us at: (719) 535-9335 Price: $18.00 You Save: $3.34 You get: (4) AT 13/18 (4) AT 18/18 (4) AT 24/18 (4) AT 29/13 Price: $25.00 From Estes, you would spend over $43.60! http://www.ApogeeRockets.com/body_tubes.asp Page 6 ISSUE 215 AUGUST 12, 2008 Continued from page 6 Turn a Plastic Nosecone Into a Boattail seams on the outside of the boattail. This is only for aesthetic reasons, but you’ll see why later on. At the end of this article, under additional information, you’ll find a link to another article I wrote on engine retention in boattails. It is a little more complicated, but it can be used to give you an even more aerodynamic boattail. Masking tape Step 4: Glue the boattail on to the body tube. This is a pretty simple step, but I just wanted to point out that you need to use that thick (gap-filling) CA adhesive. The reason is that wood glue won’t stick to the plastic of the boattail. I also recommend orienting the seam line on the boattail with a fin line on the tube (if you’ve already drawn them on the tube). This will make attaching the fins easier. Step 5: Mark the body tube and then the boattail for correct fin spacing. Align fin line with seam Figure 11: Use masking tape pressed down on the boattail as your straight edge for marking fin lines. Drawing straight lines on a boattail is very difficult. In fact, I consider it in the range of a Skill Level 3 technnique. To make the process easier, I recommend marking fin locations the body tube first, and then extending the lines onto the boattail. And use the seam lines on the plastic boattail as much as possible. If your rocket has four fins, you can use the seam lines as two of the locations for the fins. Then you only need to draw lines for the other two fins. I have yet to find a fixture that is good for drawing lines straight down a curved boattail. I’ve tried using an aluminum angle as a guide along with a mechanical pencil with the graphite sticking out really far. But no matter what CA glue I tried, the pencil line curved to the side as it Figure 10: Use thick CA glue to attach the bottail to the tube. Thread got close to the small end of the boattail. If you the shock cord out the back temporarily so it doesn’t get glue on it. Continued on page 8 RS-PRO is a 6-degree-of-freedom rocket simulator to find the behavior of high-performance rockets. It picks up where RockSim leaves off: • Speeds up to Mach 10 • Altitudes up to 392.7 miles • Reads RockSim design files • Create landing zone patterns in Google Earth • See a 3D trajectory path Model Rocket Design and Simulation ©2007 Paul L. Fossey, PKF Systems www.RockSim-Pro.com Windows and Macintosh CD Version: 1 www.ApogeeRockets.com 3355 Fillmore Ridge Heights Colorado Springs, CO, 80907 • Developed for university researchers and aerospace professionals. www.ApogeeRockets.com/RS-PRO.asp ISSUE 215 AUGUST 12, 2008 www.ApogeeRockets.com Sim Your Rockets With The Confidence of 6-Degrees-of-Freedom Page 7 Continued from page 7 Turn a Plastic Nosecone Into a Boattail have a good way please let me know. The only technique that gives acceptible results is to use a very long strip of masking tape. Position one edge along the fin line on the body tube, and then press that edge of the tape down the length of the body tube.You do have to sight along the tube to make sure the tape went down straight. But once you’ve confirmed that, you can draw the pencil line for the fin line. Step 6: Design your fins in RockSim Why RockSim (www.Apogeerockets.com/rocksim.asp) to design the fins? It makes getting the exact curature on the root-edge of the fin very simple to do. Without it, you’ll probably have to go through an extensive trial-and-error process of drawing the curvature and then cutting out a template to see if it matches the curvature of the plastic boattail. Figure 12: Use RockSim to design the fins, so the root edge matches the curvature of the plastic boattail. RockSim makes the process much easier because it is so accurate. But before you can start, you need to measure the exposed length of the boattail, and the small diameter at the base (you already know the big diameter, because it is a standard size tube). Figure 13: Print out the fin With these numbers, you template using RockSim. can quickly create a design in RockSim to draw the boattail. Then it is just a matter of designing the fins onto the boattail. Another nice feature is that by using Rocksim, you can add those fin tabs if you want them. Once you design your fins, it is just a trivial task to print the template so you can start cutting wood. The result is a fin that nicely matches the curature of the boattail. Step 7: Attach the fins to the boattail Since wood glue will not stick to the plastic, you’ll need to use CA adhesive or epoxy. I recommend that you use the CA adhesive. With epoxy, you would have to hold the fins in place for a long time for them to grab. And it is harder to attach fins to a curved boattail, so you might as well use the quicker setting CA adhesive. Use the thick (gap-filling) variety of CA glue for this Continued on page 9 • Designed to ignite the top motor in two-stage rockets. • Provides an easy way to stage composite propellant motors • Fires off igniters after a preprogrammed amount of time following liftoff • G-switch senses liftoff and insures against a false launchdetection • Small, lightweight design is great for skinny rockets • Easy-to-use, and will fire off any igniter, including clusters! Battery, battery connector, mounting board and igniter are not incuded. Page 8 www.ApogeeRockets.com/Staging_Timer.asp ISSUE 215 AUGUST 12, 2008 www.ApogeeRockets.com Staging Electronics Continued from page 8 Turn a Plastic Nosecone Into a Boattail your own disk-type centering rings. www.ApogeeRockets. com/education/downloads/Newsletter126.pdf task. There may be small gaps under the fin root, and the thicker variety will fill them easier. Want to learn more about designing model rockets? Get the 328 page Model Rocket Design and Construction book at: www.ApogeeRockets.com/design_book.asp The original question from Matt Small also asked how to cut slots for through-the-wall fin tabs. I will skip that answer for now, because this article is already long and that is a much harder task to accomplish. But it can be done, although it requires a lot of skill and patience. A nice alternative to through-the-wall fin tabs is to use the Fix-It epoxy clay (www.apogeerockets.com/epoxy-clay. asp) and create nice fin fillets around the joint where the fin attaches to the boattail. Not only will you fill any remaining gaps along the joint line, but the Fix-It epoxy will really make the attachment strong. I don’t recall when any fin popped off a rocket if it had a fillet made from Fix-It epoxy clay. Usually the fin will break somewhere else further out from the tube. Conclusion I tried to show in this article the simple steps needed to convert the PNC-56 (BT-70 size) and the PNC-66 (BT-80 size) nose cones into drag-reducing boattails. I say “simple” because the nose cones were designed from the beginning to be easily converted. They differ from other nose cones in that they have V-grooves and raised ridges that can be used to guide the cutting process. They are also made from polystyrene plastic, which can be easily glued and painted. About the only other advice I can give you in designing the boattail is to sit down and really give some thought into the layout of the parts. You have to decide where the internal centering rings will go. You can’t just slap things together, or you will probably find that the parts don’t fit properly. It is highly recommened that you use the RockSim software as a design aid. It allows you to see the general layout of the parts before you start the process of building. It doesn’t do fit-checking, but I believe that it will help things go together better and faster. Let me know how your designs turn out. Send me a photo and a note saying what you might have done differently. I’m sure our other readers would love to see it. Additional Information: Peak-of-Flight Newsletter #203: Learn how to build a engine restraint system inside a boattail that eliminates that ugly metal engine hook sticking out the back end of the rocket. www.ApogeeRockets.com/education/downloads/ Newsletter203.pdf Get all your building supplies from Apogee Components. We carry only the highest quality parts, because they save you time and energy when assembling your rocket designs. www.ApogeeRockets.com/building_supplies.asp. About The Author: Tim Van Milligan (a.k.a. “Mr. Rocket”) is a real rocket scientist who likes helping out other rocketeers. Before he started writing articles and books about rocketry, he worked on the Delta II rocket that launched satellites into orbit. He has a B.S. in Aeronautical Engineering from Embry-Riddle Aeronautical University in Daytona Beach, Florida, and has worked toward a M.S. in Space Technology from the Florida Institute of Technology in Melbourne, Florida. Currently, he is the owner of Apogee Components (http://www. apogeerockets.com) and the curator of the rocketry education web site: http://www.apogeerockets.com/education/. He is also the author of the books: “Model Rocket Design and Construction,” “69 Simple Science Fair Projects with Model Rockets: Aeronautics” and publisher of a FREE ezine newsletter about model rockets. You can subscribe to the e-zine at the Apogee Components web site or by sending an e-mail to: [email protected] with “SUBSCRIBE” as the subject line of the message. Kevlar® is a registered trademark of E.I. du Pont de Nemours and Company for its brand of aramid fiber. Only DuPont makes KEVLAR® Advertising in This Newsletter REALLY Works! If you want more rocketry customers and don’t have a big advertising budget, then the Peak-of-Flight Newsletter is an answer to your prayers. Reach over 14,000 modelers - NOW - when you need it most. Plus, there isn’t a lower priced way to advertise to this many rocketeers on the planet. I use it, and so should you! For more details and our bargain rates visit: http://www.ApogeeRockets.com/newsletter_advertising.asp Peak-of-Flight Newsletter #126: Learn how to make ISSUE 215 AUGUST 12, 2008 Page 9