Reference / Paper · 2009
Peak of Flight #230: Increase Tracking Precision With Vernier Scales
Apogee Components' Peak of Flight newsletter, issue 230 (2009-03-10).
- peak-of-flight
- apogee-components
- model-rocketry
Reference / Paper · 2009
Apogee Components' Peak of Flight newsletter, issue 230 (2009-03-10).
Apogee Components' Peak of Flight newsletter, issue 230 (2009-03-10).
Increasing Tracking Precision with Vernier Scales Your RockSim Questions Answered Aerotech’s G-Force kit is now in Stock! www.ApogeeRockets.com/Aerotech_G-Force.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 230 MARCH 10, 2009 Increased Tracking Precision with Vernier Scales By Bernard Herman In Peak-of-Flight Newsletter 164 (www.ApogeeRockets.com/education/downloads/Newsletter164.pdf) I wrote about the precision of your readings for determining the height your rocket attained. In that article I mentioned creating a vernier scale for your scopes to help make readings more precise. In issue 222 (www.ApogeeRockets.com/education/downloads/Newsletter222.pdf), Tim Van Milligan talked about finding the possible landing place of your lost rocket, and in Issue 223 (www.ApogeeRockets.com/education/downloads/Newsletter223.pdf) he talked about building a triangulation station scope. Well, to finally fulfill my promise of the first article and to assist in the finding of your lost rockets, I have undertaken the writing of this article. In the first part of this article, I will teach you how to use and read a vernier scale with the triangulation station scope shown in issue 223. In the second part, I will show you how to design and create a vernier scale of your own for your own particular tracking theodolite. Getting Started The first step in using the vernier scale for the triangulation station scope is to copy the degree numbers from the outside of the dial to the interior. This will make it easier to read your final angle when using the vernier scale. At this time I would consider renumbering the degree numbers on the protractor rosette so that they number 0 to 350 (Figure 1). Figure 2: Having the Rosette numbered this way could lead to a mistake in the field, especially around the 0 degree mark and the 180 degree mark. If you do use this one, make sure you and your trackers remember to also record if the angle was turned to the right or to the left. Renumbering is a preference issue and not absolutely necessary. However using the full 360-degree count is a way to help eliminate mistakes in the field. It’s easier to write down 185 degrees than 175 degrees left or to try and remember which way the angle was turned. If you do use the original numbers, make sure you write down if the angle was turned to the right or to the left. This is not which tracking station that you are at (as signified by the big “R” or big “L” on the protractor rosette.) This is the way you turn the scope from the zero degree mark toward the point you are looking at (See Figure 2.). Using the zero to 350 numbers (Figure 1) may require a little extra math (subtracting the reading from 360 to get the angle to the left), but it’s easier to catch a mistake, especially when using the vernier scale. Errors and Mistakes, not the same Figure 1: While helping to avoid mistakes, this style of numbering requires additional math work by the person trying to compute the location of the rocket. 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 As a quick aside, as I mentioned before in my earlier article, words have specific meanings, especially in scientific fields. There is a difference between errors and mistakes. ISSUE 230 Writer: Tim Van Milligan Layout / Cover Artist: Tim Van Milligan Proofreader: Michelle Mason MARCH 10, 2009 Continued from page 2 Tracking Precision Using Vernier Scales Errors for the most part are things that we can analyze and correct for. Mistakes are things that are caused by a misunderstanding of the problem, by carelessness, or by poor judgement. Usually the only way to correct for a mistake is to re-do the work leading up to it, not always possible with a rocket launch! If we misalign the zero scale when setting up the tracking station, that is an error and could be corrected for later on by noting the amount the sight was misaligned and adjusting our reading. If we write down left when the angle was turned right, that is a mistake and we may not be able to be correct for it. is different from use with the scope and protractor rosette provided in Newsletter 222. I would suggest printing the scale out on light cardstock or possibly photo paper to give it a little stiffness and durability. After printing it out, you should check your vernier scale at this point. If you align the 0’ mark with the 0 degree mark, the 60’ mark should perfectly align with the 29 degree reading. If it doesn’t, there may have been a problem with the printing of either the rosette or the vernier, or there may have been some stretch of one or the other due to humidity or the glue used to place the rosette on the instrument. The Vernier Scale Next print and cut out the vernier scale (see attached). Be very careful when cutting along the base arc section. The vernier scale referenced here is a new one that Figure 4: The easier to use vernier scale. After sighting the rocket’s last visible location, read and record the degree reading at the pointer. To avoid making another common mistake, view the pointer along its axis, not from the side as shown in Figure 5. Next carefully align the base arc of the vernier scale along the outer edge of the protractor rosette circle and align the 00’ mark with the pointer (See Figure 6). Figure 3: Make sure you use the side of the vernier scale appropriate to the direction the angle was turned. Taking the reading is a little tricky, and you may want to use a magnifying glass to help you. What you want to do is find the mark on the vernier scale that best aligns with one Continued on page 4 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 230 MARCH 10, 2009 Page 3 Continued from page 3 Tracking Precision Using Vernier Scales Figure 5: To avoid parallax, another common mistake in taking readings, sight along the axis of the needle and not from either side. As shown in this view, looking at the needle from an angle to the side, we might record a reading of 272 degrees. Note however, the line on the end of the gun sight is at the 270 degree mark. ate side of the vernier scale for the direction you turned the angle. Recall that the direction turned refers to which way you turned the scope from the zero degree mark printed on the rosette. Figure 6: Align the base arc of the vernier scale along the outer edge of the protractor rosette circle and align the 00’ mark with the pointer. of the degree marks on the protractor rosette, like seen in Figure 7. If you can’t quite determine which marks align, a helpful trick is to look on each side of the vernier until you are certain the lines don’t align by about the same amount and then pick the line midway between them as shown in Figure 8. The vernier scale we are using here is calibrated to two-minute marks (remember the ‘ symbol in reading angles stands for minutes, not feet), from zero to sixty minutes (a full degree). We then determine what this number is and add it to our degree reading. If you are using the right/left reading rosette, make sure you read the appropri- Figure 7: Find the mark on the vernier scale that best aligns with one of the degree marks on the protractor rosette. FREE Rocket Construction Videos A new Apogee video every two weeks to help you become a better modeler! www.ApogeeRockets.com/Rocketry_Video_tips.asp Page 4 ISSUE 230 Figure 8: If you can’t quite determine which marks align, a helpful trick is to look on each side of the vernier until you are certain the lines don’t align by about the same amount and then pick the line midway between them. MARCH 10, 2009 Continued on page 5 Continued from page 4 Tracking Precision Using Vernier Scales Conclusion Vernier scales have been around for a long time and are not just used for angular readings. The vernier scale is a useful tool to help give us more precise readings and maybe, to help us find a lost rocket or determine which rocket flew higher. Like with all tools, a little care and understanding of how it functions are needed. Figure 9 shows three examples to test your ability to read vernier scales. Remember that the vernier scale I have provided here can only be used with the protractor rosette for the triangulation tracking scope from Peak-of-Flight newsletter 223 (www.ApogeeRockets.com/education/downloads/Newsletter223.pdf). You can download modified vernier scales attached to the rosettes at: www.ApogeeRockets.com/education/downloads/Vernier_Grids.pdf About the Author: Bernie Herman has worked in the land surveying field for over twenty years. He doesn’t consider himself a BAR since he never gave up rocketry since his mother bought him his first model rocket kit in 1973 at the age of ten. He has been married for over seventeen years. He has five children, three girls and two boys. Figure 9 (Right): Some examples of vernier measurements to gain some practice making readings. 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 ISSUE 230 MARCH 10, 2009 Page 5 RockSim Questions and Answers By Tim Van Milligan Ronald Zacher writes: “In my new RockSim version9 design I am using pods and body tubes for fins. The rocket’s CP moves to the nose cone, which can’t be right. Do tube fins made from body tubes not register as fins?” That is RIGHT. Pod tubes are not the same as TUBE FINS. According to the Barrowman Equations, normal tubes do not contribute to the CP of a rocket. The parts called “Tube Fins” do. You must make them tube fins if you want them to contribute to the CP of the rocket. See the image below that compares external tubes to “tube fins.” Tony Cannin asks, “When I click help then index, my RockSim 9 shows page not found. Could you please advise me what to do next?” There is a folder called “Docs” in the Rocksim folder. Inside of it, you’ll find a pdf called RockSim.pdf. That is the official PDF manual that you can print out. Additionally, in the folder is a folder called “htmlrocksim.” Inside that folder are the html versions of the manual. Just open the file called index.html in any web browser and that will be the start page of the manual. Pod Fin Rocket Length: 20.6250 In. , Diameter: 1.3200 In. , Span diameter: 3.9600 In. Mass 57.000 g , Selected stage mass 57.000 g (User specified) CG: 12.0000 In., CP: 0.8750 In., Margin: -8.43 Unstable Shown without engines. Tube Fin Rocket Length: 20.6250 In. , Diameter: 1.3200 In. , Span diameter: 3.9600 In. Mass 57.000 g , Selected stage mass 57.000 g (User specified) CG: 12.0000 In., CP: 13.4019 In., Margin: 1.06 Shown without engines. If you get an error, click on the RockSim book to open the help file manually. TM Available Online & Worldwide through Quality Hobby Shops & Online Retailers NOW ON SALE - 25% off selected model rocket kits available from Apogee Rockets and Sunward! NOW ON SALE - 25% off Nylon Parachutes, NOMEX® Flame Resistant Blankets and Shock Cord Protectors available from Sunward - www.sunward1.com LIMITED TIME ONLY www.sunward1.com [email protected] TM Direct 416-953-1847 fax 416-245-7985 Page 6 ISSUE 230 MARCH 10, 2009 TM