Reference / Paper · 2003
Peak of Flight #116: Simulating Pop-Pod Boost Gliders In RockSim v7 #1
Apogee Components' Peak of Flight newsletter, issue 116 (2003).
- peak-of-flight
- apogee-components
- model-rocketry
Reference / Paper · 2003
Apogee Components' Peak of Flight newsletter, issue 116 (2003).
Apogee Components' Peak of Flight newsletter, issue 116 (2003).
N I S S U E 1 1 6 , E S W L D E C . E 5 , T 2 0 0 3 T E R Simulation of Pop-Pod Boost Gliders Using RockSim v7 Part 1 1130 Elkton Drive, Suite A Colorado Springs, CO 80907 USA www.ApogeeRockets.com orders @ApogeeRockets.com phone 719-535-9335 fax 719-534-9050 Page 1 ISSUE 116 - DECEMBER 5, 2003 P E A K O F F L I G H T Simulation of Pop Pod Boost Gliders Using RockSim Version 7. Part 1 Bruce S. Levison Bruce S. Levison has asked us to share this article with other RockSim users. It describes a method that he feels will help to simulate the fight of a Pop Pod Boost Glider in RockSim. Bruce feels that the neutral point (CP) will be in the right location on the boost glider. Please note: The user assumes all risk for the information obtained with this method. This article contains links to download the RockSim version 7.01 designs. After downloading, place these files in the Design folder within the RockSim Folder on your hard drive. These files cannot be viewed using older and demo versions of the RockSim software. This article describes how to use RockSim version 7 to simulate pop pod boost glider rocket designs where the motor (pop) pod separates from the glider at apogee and the glider glides back to the ground. The motor pod is typically recovered separately. A word processing program (such as Microsoft Word or WordPad) is used to edit a RockSim version 7 .rkt file to simulate the glider design, be sure to read my previous work on the Simulation Fins on Fins with RockSim 7 by Bruce S. Levison in issue #113 of the Apogee Peak of Flight Newsletter, October 27, 2003 http://www.apogeerockets.com/education/downloads/Newsletter113.pdf . The glider is actually simulated as a boosted dart, boosted dart simulations are described in Apogee Technical Publication #14 Software Simulation Tricks by Tim Van Milligan http:/ /www.apogeerockets.com/technical_publication_14.asp and in the article on Strap-on Boosters by Tim Van Milligan in issue #109 of the Apogee Peak of Flight Newsletter, August 22, 2003 - page 5 http://www.apogeerockets.com/education/downloads/ Newsletter109.pdf also talks a little bit about boosted darts. It is a good idea to read over and become familiar with the simulation tips these articles before attempting your own pop pod boost glider simulation. A peculiarity of this boost glider simulation is that the motor pod, which actually behaves as a booster stage, is located on top of the dart (glider) opposite how RockSim wants this relationship to be in a simulation. The program can even be made to place a nose cone on top of the booster section. The descent rate of the glider is simulated using a square parachute with a surface area equivalent to that of the projection of the wing and stabilizer surfaces on to a horizontal plane. The lift of the glider wing can be augmented with thermals available on the “Launch Conditions” tab of RockSim ver- A P O G E E Page 2 sion 7, this is one of the new software features. The Cd of the glider is estimated using the Cd analysis tab under the “Rocket” menu in the RockSim program. Part one of this article covers the simulation of the glider from the Quest Flat Cat boost glider see Figure 1. Part two covers the simulation of the pop pod and the glide recovery flight. The Quest Flat Cat was chosen since it is a simple generic pop pod boost glider design that has been simulated using other software programs. Overall design of the pop pod glider see Figure 2. Open RockSim version 7 and select File-new. On the rocket design attributes tab select; Use RockSim method for static stability analysis, for simulation method select; Use Continued on page 3 Figure 1. Quest Flat Cat Pop-Pod Boost Glider R O C K E T S ISSUE 116 - DECEMBER 5, 2003 P E A K O F F L I G H T Pop-Pod Gliders Continued from page 2 Figure 3: Create a phantom body tube to offset the glider from the Pop pod. Figure 2. Design Attributes screen for the Quest Flat Cat Pop Pod Boost Glider. this case BT-20, 0.736" +2* 0.5" = 1.736" pod mount height) that is only 0.001" long. To keep the weight down specify the inner Diameter (ID) to be .0001" less than the OD and specify this as a motor mount tube for any motor diameter. Be sure to remember or write down the motor diameter you used since this value will be used in a later step. Assign the tube to be a lightweight material such as Balsa and for the second part of this article indicate that the tube is a motor mount for 13mm diameter engines. Select a Custom fin set design for the phantom body tube Continued on page 4 RockSim equations in the simulations and set the number of stages to; Two stage rocket. This is a good time to name the design and set the launch rod length, I used 36 inches. Next click on the rocket design components tab and for the sustainer, which will be the glider or boosted dart, create a phantom body tube that has an outer diameter (OD) equal to that of the pop pod plus twice the height of the pod mount (for Figure 4: Specify the Glider Body. Are You New To Rocketry? Want To Learn More? Have You Tried The Apogee Components website? It is your "How-To" source for rocketry information. Check Out These FREE "How-To" Articles How-To Get Started In Rocketry http://www.ApogeeRockets.com/beginner_rockets.asp How Do Multi-Stage Rockets Work? Read Newsletter #98 How-To Start A School Rocketry Program See Newsletter #112 How-To Track A Rocket's Altitude Jump to Newsletter #93 A P O G E E R O C K E T S PAGE 2 Page 3 ISSUE 116 - DECEMBER 5, 2003 P E A K O F F L I G H T Pop-Pod Gliders Continued from page 3 and specify the dimensions of the glider body, be sure to set the fin count to 1 on the glider body thickness to 0.25". The points in the Fin Plan are (counter clockwise from left to right): 0.0, 0.0 0.0, 6.5 0.125, 14.5 0.25, 14.5 0.25, 0.0 Select another simple trapezoidal fin set for the phantom body tube and specify the dimensions of the glider wing for just one side, be sure to set the fin count to 1 and a fin thickness of 0.125" also set the location to zero (see Figure 5). Figure 7: Create the Rudder. ness of 0.0625" also set the location to zero (see Figure 7). For a more complex wing, stabilizer, rudder, and/or pod mount shapes the “Free Form Custom Fin” set could also be used. For two (or more) out board rudders at the tips of the stabilizer you would have to design two fin mounts and locate them to the tip edge of the stabilizer and assign a rudder fin to each one of them. Specifying the Glider Body Wing Mount Assign an inside tube to the Phantom body tube with a minimal diameter and thickness the same length as the root of the wings on the glider body; set the location to zero. See Figure 8 below. Figure 5: Specify the Glider Wing. Specifying the Glider Stabilizer Select another simple trapezoidal fin set for the phantom body tube and specify the dimensions of the glider stabilizer for just one side, be sure to set the fin count to 1 and a fin thickness of 0.0625" again set the location to zero. Figure 8: Create a phantom body tube to mount the wings. Set the radial distance to 0.868, which is half the phantom body tube diameter (or the radius of the pod plus the pod mount height) see figure 10 below. Repeat this step assigning one more inside mount tube to Figure 6: Create the glider stabilizer. Specifying the Glider Rudder Select another simple trapezoidal fin set for the phantom body tube and specify the dimensions of the glider rudder for just one side, be sure to set the fin count to 1 and a fin thick- A P O G E E Page 4 Figure 10: Set the radial position of the phantom tube. R O C K E T S ISSUE 116 - DECEMBER 5, 2003 P E A K O F F L I G H T Pop-Pod Gliders Continued from page 4 Figure 11: Create a phantom tube to attach the stabilizers. the Phantom tube to serve as a common mount (2 inches long) for the rudder and horizontal stabilizers. See Figure 11. Set the radial distance to 1.118, which is the radius of the pod plus the pod mount height plus the thickness of the glider boom 1/2*0.736" + .5" + 0.25" (see Figure 12 below). Figures 13 (top) and 14 (Bottom): Change the radial position of each wing to set the dihedral. Figure 12: Set the radial position of the tube. Use a word processing program like Word Pad to change these two inside tube mounts into regular body tubes. Convert: <IsInsideTube>1</IsInsideTube> to <IsInsideTube>0</IsInsideTube> Review my previous work on the simulation of “Fins on Fins” http://www.apogeerockets.com/education/downloads/ Newsletter113.pdf for details on how to do this. Save the edited file and open it again in RockSim. Open the wing mount (which used to be an inside tube) and change the location to12 inches from the front of the owning part. Now copy and paste the wing to the wing mount; do this twice, once for each wing. Be sure to delete the wing that was originally assigned to the phantom body tube. Open each wing file and assign one of them a radial position angle of 104 degrees and the other a radial position angle of 256 degrees for the 14-degree dihedral angle of the wings see Figures 13 and 14. Open the stabilizer/rudder mount and assign the location A P O G E E of 18 inches from the front of the owning part. Copy and paste the stabilizer to the stabilizer/rudder mount do this twice one fin for each side of the stabilizer. Be sure to delete the stabilizer fin that was originally assigned to the phantom body tube. Sequentially, open each stabilizer fin and assign one of them a radial position angle of 90 degrees and the other a radial position angle of 270 degrees as you did for the wings above. Copy and paste the rudder to the stabilizer/rudder mount. Again be sure to delete the rudder fin that was originally assigned to the phantom body tube. Open the stabilizer fin and be sure it has a radial position angle of 0 degrees. The parts tree should now look something like Figure 15. Continued on page 6 Figure 15: Parts tree after modifying the glider. R O C K E T S Page 5 ISSUE 116 - DECEMBER 5, 2003 P E A K O F F L I G H T Pop-Pod Gliders Continued from page 5 This completes the design of the boost glider it is lacking only one more detail that will make it “glide” in the simulation of the recovery phase of the flight - a parachute! Before we add this last component, and explain how it works, lets take a look at this glider design and its neutral point or CP . Figure 17: A 3D view of the Flat Cat Glider. Figure 16: The stability of the glider. RockSim indicates a CG of 14.217 and a CP of 13.863 giving a static margin of -0.2. Taking a look a Bob Kaplow’s work on this very same model (I used the same dimensions and only changed the glider body slightly to reflect its tapered shape) http://www.ninfinger.org/~sven/rockets/ rmrfaq.8.html This article indicates: “The Neutral Point is located at 85.38% (2.348 units) from wing L.E., NPg = 1.1540 Stability factor 0.20 Put CG at 70.65% (1.943 units - in this case “inches.”) from wing L.E., NPb =0.99614” RockSim gives the CP at 68% (=100%*(13.863-12)/2.75) or 1.86 inches from the wing leading edge (L.E.) and the CG at 81% (=100%*(14.217-12)/2.75) or 2.217 inches from the wing leading edge. Although the two neutral point values are Continued on page 7 Newsletter Archive On CD-ROM - FREE! Tech n 36051 $35.0 0 6 P/N s ion at Get the entire collection of Peak-of-Flight newsletters on CD-ROM in pdf format. It’s absolutely FREE when you buy the Apogee Technical Publications (#1-#35) set. Not only do you get the great technical reports, you get all of the first 112 u P b issues of the Peak-of-Flight newsletter on a seperate CD-ROM for no extra l l icReaports #1 through i#2c charge. The Peak-of-Flight CD-ROM gives you much more than the web-site archives. You also get: All issues are in PDF format. This allows you to print them out quickly so you can share them with your friends. Images are high-resolution, so they print out great. Many of the earlier articles have been re-written and updated with new information and illustrations. QuickTime videos have been embedded into many issues to show action sequences (11 movies total). Many extra reference articles included - So you don’t have to Newsletter #1 to #100 download them from the internet. Order Today, and also receive #101-#112 Shrox plans, decals, and RockSim design files included. http://www.ApogeeRockets.com/technical_publications.asp Plus excel spreadsheets, programs, and much more... www.ApogeeRockets.com R eq 20 03 - Ap ogee Comp on en ts er © ne uir www.ApogeeRockets.com e s: or v4 Adob an e A cro b at er dA ew i p ple V QuickTime w P/N 01084 Re er qui ew res: or n and Adobe Acrobat v4 er Apple QuickTime View A P O G E E Page 6 R O C K E T S ISSUE 116 - DECEMBER 5, 2003 P E A K O F Pop-Pod Gliders Continued from page 6 close to one another, RockSim calculates a value that is 15% closer to the wings leading edge than this published value. This difference may be due to the fact that RockSim is taking into account the area of glider body when it determines the CP value. The other method does not take the lift from the body of the glider into its calculations. (See also Newsletter #115 for another explaination.) While this simulation indicates a slight negative stability you can always trim the glider by adding nose or tail weight for a better flight. For a level glide the Neutral point or CP of the glider should be the same as the glider’s CG or center of gravity. The negative stability case presented here may be the best case for a stable gliding flight; the glider would have a tendency to fly nose up since it is slightly tail heavy! The correct placement of the CG will have to be determined empirically by hand launching the glider and adding or removing nose or tail weight until a stable flight is obtained. Once the amount of this weight is known it can be incorporated into the simulation as a mass object. The actual CG of the glider can also be incorporated on the mass override menu for the sustainer once the glider has been trimmed out for a level F L I G H T (stable) flight. Here is a copy of the RockSim version 7 file for the Glider: (link to Quest_Flat_Cat1.rkt) Now that the glider has been simulated and its trim has been accounted for, the next step is to use RockSim to account for the glide phase of the recovery. Part two of this article will cover the techniques to fly this glider with a pop pod and use RockSim to simulate the glide recovery. About the Author: Bruce S. Levison (NAR #69055, MTMA #606), A.K.A. Teflon Rocketry, is a rocketeer from Ohio, a member of the National Association of Rocketry (NAR), and NAR section #606, the Mantua Township Missile Agency (MTMA). He has published articles on ejection charge proof expanded Teflon recovery systems (hence the nickname), camera tripod mounted launch pads, ablative blast deflectors, a horizontal painting swivel for model rockets, a method for the simulation of tube fin rocket designs, a RockSim method to determine how far away from the launch pad a parachute recovered model rocket will land, the simulation of ring fin designs using RockSim and the simulation of fins on fins using RockSim. Bruce earned an advanced degree in chemistry, and works as a research scientist at the Cleveland Clinic Foundation "How To" Series Bonus #1: Designer's Resource Pak ($8.95 value) Bonus #2: Journal of the International Spacemodeling Society - 12 issues ($24 value) ww.ApogeeRockets.com I Goofed... So You Win! Building Skill Level 1 Model Rockets Learn how to construct model rocket kits by watching video I didn't watch my inventory close enough, and I ran out of the printed versions of the book: "Model Rocket Design & Construction." I've ordered more, but they won't be in until late January. In the mean time, I'll distribute the book on CD-ROM as a pdf document. Everything is included! And you'll also recieve $45.90 in free bonus items! One of them is the "Building Skill Level 1 Model Rockets" video book. To see the others, visit: www.ApogeeRockets.com/design_book.asp About this Newsletter You can subscribe “FREE” to receive this e-zine at the Apogee Components web site (www.ApogeeRockets.com), or sending an email to: [email protected] with "SUBSCRIBE" as the subject line of the message. A P O G E E R O C K E T S Page 7