Reference / Paper · 2009
Peak of Flight #245: Rocket Plan - the 'Kink' Superroc
Apogee Components' Peak of Flight newsletter, issue 245 (2009-10-06).
- peak-of-flight
- apogee-components
- model-rocketry
Reference / Paper · 2009
Apogee Components' Peak of Flight newsletter, issue 245 (2009-10-06).
Apogee Components' Peak of Flight newsletter, issue 245 (2009-10-06).
Feature Article: Plan: The “Kink” Superroc Also In This Issue: Reader Comments, Questions and Answers Cover Photo:Red River Rocketry’s Red Star rocket kit. To get one today, visit: www.apogeerockets.com/Red_River_Red_Star.asp Apogee Components, Inc. — Your Source For Rocket Supplies That Will Take You To The “Peak-of-Flight” 3355 Fillmore Ridge Heights Colorado Springs, Colorado 80907-9024 USA www.ApogeeRockets.com e-mail: [email protected] ISSUE 245 OCTOBER 6, 2009 Rocket Plan: The “Kink” Superroc Rocket Written By Tim Van Milligan In Peak-of-Flight Newsletter 243 (www.ApogeeRockets.com/education/downloads/Newsletter243.pdf), I showed the development of the Fly-Apart Rail Guides. As I began writing that article, I thought there would be room enough in the issue to present plans for the 13 foot tall Superroc-style rocket. Unfortunately, there wasn’t. So in this issue, I will give you the plans for the model. I actually flew this rocket, and unfortunately, it bent in three places. The reason it crimped is that the top five feet of the rocket were unsupported and bending in the wind while the rocket sat on the launch pad. Because the tip of the rocket was going in one direction and the rear in a different direction, it didn’t stand a chance. It kinked about 20 feet after it cleared the launch rail. Hence the name: “Kink.” I decided to have a little fun with the name. If you can’t poke fun at yourself when things go wrong, you might be in the wrong hobby. Will it kink for you? That is a good question. There is always a chance that these supperroc models might kink. I think that if you fully support the entire length of the rocket prior to launch, there is a much better chance that it will fly fine. That was the whole purpose of using the rail launcher in the first place. There are a few other things you have to watch out for when building with these long superroc models that have a bearing on if it will kink. First of all, you have to make sure that the tube joints are absolutely straight, and second, you want the tubes as stiff as possible. A layer of fiberglass cloth over the tubes isn’t a bad idea, although it will add weight to the rocket. Figure 1: The 13 foot tall Kink superroc. Design Philosophy When I created this design, I wanted the rocket to be pretty light weight, since it was for a rocket contest, and yet use off the shelf components. It was designed for F-engine motors, which meant I had to make the engine mount section at least 29mm in diameter. But to keep the weight low, I decided to transition the diameter down to something smaller near the top of the rocket. If you take a look at Figure 2, you’ll notice that the diameter steps down three times from the largest diameter of 29mm at the base of the rocket. About this Newsletter What is Different in This Design? In reality, this is a fairly simple rocket, other than a requirement for having three transition sections in the rocket. Basically, it is just a longer model rocket—really long! 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 trade-off of doing this is that the rocket will be less rigid than a rocket with a constant diameter for its entire length. That is a common trade-off in rocketry; strength versus weight. I decided to go for reduced weight. ISSUE 245 Writer: Tim Van Milligan Layout / Cover Artist: Tim Van Milligan Proofreader: Michelle Mason OCTOBER 6, 2009 Continued from page 2 The “Kink” Superroc Rocket Plan About the only thing that is unique is that I designed the rocket to come apart in four sections. The reason for this is so that it is easier to transport to and from the launch site. Obviously, it would be difficult to strap a 13-foot tall rocket to your car and drive it to the range. But it is reasonable to have four sections that are each a little over 3 feet long stowed in the truck of your car. In fact, it should easily fit inside your trunk, and can be assembled on the field in about five minutes. Rocket Design and Construction (www.ApogeeRockets. com/design_book.asp) for making a removable transition. When it is done, it will look like Figure 3. Transition Assembly As I mentioned, the only modestly challenging part of this rocket is making the transition sections and the shoulders where the parts of the rocket are assembled on the field. I like to use a technique that I have in the book Model A Figure 3: The rocket separates at each transition section. This plugs in to the larger tube below it and is friction-fitted so there is no wobble in the joint. C B D 400 cm (13 feet, 1.5 inches) Figure 2: The Kink superroc is built in four sections that are designed to separate for easier transport to and from the launch site. Continued on page 4 Roam In Our Forest of Over 170 Different Types • Unique and exotic kits from over 20 different manufacturers • Skill Levels range from “easy” to “fiendish” • Sizes from 1/4A motor to level-2-high-power • We build & fly them to find out what they’re like, saving you grief • More new ones arriving all the time • Educational bulk packs available too www.ApogeeRockets.com Looking For A Fun Rocket Kit? www.ApogeeRockets.com/All_rocket_kits.asp ISSUE 245 OCTOBER 6, 2009 Page 3 Continued from page 3 The “Kink” Superroc Rocket Plan What this technique reminds me of is making a custom nose cone. We need a nose part, which will be our paper transition, and then a shoulder that will fit into the tube. The shoulder will be made from a tube coupler, since it is already sized perfectly to fit into the lower tube. To make sure the upper tube is perfectly straight and concentric with the tube coupler, we’ll actually extend the smaller forward tube all the way through the coupler. We’ll use a couple of centering rings to align the tubes perfectly. But the standard centering rings are the same outer diam- Figure 4: The standard centering rings are the same diameter as the coupler, so they need modification. eter as the coupler (see Figure 4). To make them fit inside the coupler, you’ll need to peel off a few layers of paper. For this, I usually use a hobby knife, as shown in Figure 5. Once the rings fit into the coupler, go ahead and dry assemble the coupler on the end of the small tube. Don’t glue anything up yet, until you have the paper transition created. Assembly of the paper transition is the tricky part, es- Figure 5: To make the centering ring fit, you’ll need to peel off a few layers of paper with a hobby knife. Continued on page 5 TM NOW ON SALE - Available Online & Worldwide through Quality Hobby Shops & Online Retailers 25% off selected model rocket kits - available from Apogee Rockets and Sunward! 25 ® NOW ON SALE % off Nylon Parachutes, NOMEX Flame Resistant Blankets and Shock Cord Protectors available from Sunward - www.sunward1.com JOIN US IN CELEBRATING th OUR 6 YEAR OF BUSINESS Thank you for your support. Watch for new items in 2010 www.sunward1.com™ [email protected]™ SALE EXTENDED! TAKE ADVANTAGE OF GREAT SAVINGS Page 4 ISSUE 245 OCTOBER 6, 2009 Continued from page 4 The “Kink” Superroc Rocket Plan pecially if you are looking for a nice smooth surface where the edges come together. I’ve found that it is more “technique” than anything else, which is the secret of getting a good edge joint. If you want to see my personal techniques, you can find it on rocketry construction video #12, which is found on the Apogee web site (www.ApogeeRockets. com/Rocketry_Videos/Rocketry_Video_12.asp). Once the transition is made, you’ll slide it onto the small tube and over the edge of the tube coupler. I like to have Figure 6: The forward centering ring hangs out of the coupler a tiny amount to give more surface area for the transition to attach to. the forward centering ring hang out of the coupler by about 1/20th of an inch, so that it gives more surface area for the glue to attach to. That is why I told you not to glue anything up yet. You want the rings to slide around a little bit so you can get everything in a proper position before you apply any glue. You’ll notice that on the upper two transitions, the inner tube is open, and not capped off. This means that the ejection charge gases could pass through the entire length of the tube if we wanted. In this design, that is OK. But we’re actually not going to let that happen. Figure 7: The bottom transition is the only one to be capped off. We’ll also need to attach a shock chord to this section to keep the rocket together. Continued on page 6 • Won’t Shatter Like Brittle Phenolic Tubes! • Super Smooth Surface With Tight Spirals • Standard LOC Diameters Up To 6 inches • Cut and Slot With Standard Tools • No Fiberglass Wrap Needed • Sands and Paints Easily • Cheaper than Fiberglass Blue Tube From Always Ready Rocketry www.ApogeeRockets.com High Power Tubes & Couplers www.ApogeeRockets.com/blue_tubes.asp ISSUE 245 OCTOBER 6, 2009 Page 5 Continued from page 5 The “Kink” Superroc Rocket Plan The parachute is going to be placed in the lowest body tube. Because of this, we only need to cap off the bottom of the lowest transition. We’ll also need to attach a shock cord to this transition so that the entire rocket stays together during descent. Capping it off is easy. One way is to use a balsa block and a metal screw eye, onto which you can attach the shock cord to the upper section. Unfortunately, balsa blocks are expensive, so I capped if off with a disk made from cardstock. I also choose to use 100lb-Kevlar® shock cord (part number 30325 from www.apogeerockets.com/shock_ cord.asp). What I did is to tie the cord around the tube, and pass it out the bottom of the coupler through a little notch cut in the aft centering ring. Again, a little notch is cut along the edge to allow the shock cord to pass through (see Figure 8). In the lower body tube, the shock cord is anchored using the classic Estes-style paper shock cord mount. That is sufficient for this size rocket. Cutting the Tubes to Length If you use full-length tubes for all the components in this rocket, the overall length of the rocket will actually be too long. Why? One rule of superroc competition events says that the rocket has to be a certain length. For example, the F-Engine class of events says the maximum length Figure 8: Exploded view of (as measured from the base the aftmost transition section. of the motor to the tip of the The Kevlar® cord is tied around the nose) is 400 cm. Actually, the body tube in front of the aft centering ring. Cut rocket can be longer than a notch in the aft centering ring to allow the cord to this. But since you don’t get exit out of the bottom. Before putting the tube coupler on, any extra points for the extra work some wood-glue into the knot on the shock cord, and where it touches the body length, you might as well tube. This will make it a secure anchor point to keep the rocket together. Continued on page 7 Model Rocket Design and Construction By Timothy S. Van Milligan New 3rd Edition Now Shipping! This new 328 page guidebook for serious rocket designers contains the most up-to-date information on creating unique and exciting models that really work. With 566 illustrations and 175 photos, it is the ultimate resource if you want to make rockets that will push the edge of the performance envelope. Because of the number of pictures, it is also a great gift to give to beginners to start them on their rocketry future. For more information, and to order this hefty book, visit the Apogee web site at: www.ApogeeRockets.com/design_book.asp Apogee Components 3355 Fillmore Ridge Heights Colorado Springs, Colorado 80907 USA telephone: 719-535-9335 website: www.ApogeeRockets.com Page 6 ISSUE 245 OCTOBER 6, 2009 Continued from page 6 The “Kink” Superroc Rocket Plan these was covered in Newsletter 243. cut it back to 400 cm. This will make it lighter weight, and should help a little bit with the overall stiffness of the rocket. Since the rocket breaks down into four sections, you can wait until you have everything together to make the final length cut. I’d cut off from the forward body tube. Therefore, don’t glue on the nose cone until after you’ve measured the overall length of your rocket and have cut that forward section to the correct length. You’ll be cutting it down to approximately 13 inches, but the exact length will depend on your construction skills when assembling the transition sections. The only other unusual thing about the rocket is that it requires the Fly-Apart Rail Guides. The construction of As I said at the beginning of this article, make sure all your tubes are perfectly straight when you glue them together. You might consider applying a layer of fiberglass over the tubes to stiffen them up, but that is a topic for a future article. In conclusion, I think that you’ll find that this is actually an easy model to build. And when you fly it, let me know how it does. I’m interested in knowing if your’s kinks too. Parts List (1) 13mm nose cone (Apogee P/N 19700) (2) 13mm X 18” long tubes (Apogee P/N 10063) (2) 18mm X 18” long tubes (Apogee P/N 10086) Figure 9: Full-size pattern sheets for the transitions, fins, and shock cord anchor. Continued on page 8 Your Cool Rocket Designs Look So Much Better In RockSim Version 9! Launch It. v9 www.RockSim.com Space Foundation certified as an excellent teaching aid. For further information, call Apogee Components at: 719-535-9335. ISSUE 245 OCTOBER 6, 2009 Page 7 Continued from page 7 The “Kink” Superroc Rocket Plan (3) 24mm X 18” long tubes (Apogee P/N 10100) (3) 29mm X 13” long tubes (Apogee P/N 10111) (1) Airframe Coupler AC-13B (Apogee P/N 13014) (3) Airframe Coupler AC-18B (Apogee P/N 13015) (4) Airframe Coupler AC-24B (Apogee P/N 13009) (3) Airframe Coupler AC-29A (Apogee P/N 13010) (2) Centering Ring 13-18 (Apogee P/N 13028) (2) Centering Ring 18-24 (Apogee P/N 13032) (2) Centering Ring 24-29 (Apogee P/N 13037) (1) 24” diameter plastic parachute (Apogee P/N 29116) (1) Centering cardstock for bulkhead (Apogee P/N 44002) Balsa Sheet for fins - 1/8” thick 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. FREE Rocket Construction Videos RockSim File The RockSim design file for this rocket can be downloaded at: www.ApogeeRockets.com/education/downloads/ kink-superroc.rkt.zip A new Apogee video every two weeks to help you become a better modeler! 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 www.ApogeeRockets.com/Rocketry_Video_tips.asp Pratt Hobbies GO BOX Launch Controller Launch controller for mid-power rockets. Hooks right up to your car’s battery. No more dead AA batteries! Plenty of electricity to set off any type of rocket motor igniter. 24 foot cord, allows you to stand far back for launch safety. Audible continuity buzzer lets you know the circuit is armed and ready for launch. Flat-jaw alligator clips Only $39.99 P/N 7705 Brought to you by: (for easy hook-up of igniter.) www.ApogeeRockets.com/go-box_controller.asp Page 8 ISSUE 245 OCTOBER 6, 2009 Reader Questions and Answers Responses By Tim Van Milligan Josh Barnett asks: “I am in the process of designing my own rocket and I was wondering if long rod-like fins could provide some stability. I have the latest copy of your book; and while it is not listed inside, you would probably know something about it. I was thinking that they would cause less drag and while not providing the amount of lift of the other fins the rocket could be configured so that the small amount of extra stability the fins provided would be all that is needed. Is that possible?” The dowels could provide stability. But they are far less effective than the lift created by fins. To understand this, you’ll need to review how stability is defined and how it works. In Figure 1, you see the classic definition of rocket stability. It is when the CG (center-ofgravity) is forward of the CP (center-of-gravity). The CG is where the rocket balances, and is the point on the rocket about which the rocket will rotate. Figure 1: A force at the CP will cause the rocket to rotate around the CG location. Figure 1: A lift force is created when the rocket travels at an angle-of-attack. The CP is an imaginary point on the rocket where all the aerodynamic forces are said to be concentrated. In real life, there are forces (lift & drag) that are created by all the different parts of the rocket. But to make things simple, we find the balance point on the rocket where the forces in front of this balance point equal the forces behind the point. We call this imaginary point the CP. The CP point is actually dynamic. That means it shifts positions on the rocket as the forces acting on the rocket fluctuate. For example, if the rocket begins flying at an angle-of-attack, such as shown in Figure 2, the CP will move a little bit further aft. Why is this? The big reason is that the fins create a large lift force. In response to this lift force, the rocket will rotate around the CG point until the model points its nose back to Continued on page 10 Continued on page 10 • 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. www.ApogeeRockets.com/Staging_Timer.asp ISSUE 245 OCTOBER 6, 2009 www.ApogeeRockets.com Staging Electronics Page 9 Continued from page 9 Reader Questions and Answers zero-degrees angle-of-attack. This is good, and is what we expect. What I want to point out is that the distance between the new lift force and the CG is quite large. The result of this is that it doesn’t take a very big lift force to start the rocket turning back into the direction of travel. In Figure 3, we see that an increased drag force also arises as the rocket travels at an angle-of-attack. But the distance away (the pivot arm length) from the CG is a lot smaller. Figure 4: Rocket with dowel fins. the dowels have to be made quite long so they stick out a distance from the centerline of the rocket (such as shown in Figure 4). What this means is that it will take a larger drag force to get the same result for the rocket to turn back into the direction of travel. Because of this, we can say that the lift force is much more efficient than the drag force in getting the rocket to behave like we want it to. The disadvantage of dowel fins is that the drag is constant throughout the entire flight. You can’t turn if off if the rocket is flying straight and true. Lift, on the other hand, does turn on and off during the flight. If the rocket is flying perfectly straight, there isn’t any lift force created. So you’re not robbing from the speed of the rocket to create a force to stabilize the rocket. But if you are going to use a drag force, it is possible. You just have to make the drag force big, and you have to move it further away from the centerline of the rocket. That is why when you see a rocket that uses dowels for fins, The badminton shuttlecock (birdie) rocket is very similar to a stick-fin rocket. They do work in keeping the rocket really stable, but you pay for that stability in lower altitude (because of all the excess drag). In conclusion, if you want your rocket to go high, use fins instead of dowels. The lower drag is the reason it will fly higher. Figure 3: A drag force will also cause the rocket to rotate and try to get it back to 0° angle-of-attack. 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 Page 10 ISSUE 245 OCTOBER 6, 2009 www.ApogeeRockets.com Sim Your Rockets With The Confidence of 6-Degrees-of-Freedom