The day started out pretty well. I had a car load of untested rockets and Ol’ Faithful, my BDR 4.0 that I used for L1, & L2 certifications as well as my first dual deployment. Our club has a couple of contests going, a 2000′ and 9000′ challenge. I started the day with the maiden flight of my Aerotech Cheetah on an F52T-8 motor. It flew well to 2018′. I wish I had entered it into the 2000′ challenge. Next I flew the Lil’ Rascal on its maiden flight with a CTI H400 Vmax motor. Woah, Zero to giddy-up in a blink. The rocket suffered a severe case of road rash by being dragged across the broken concrete of a WWII era runway by its parachute. The crowd loved the flight! I then flew yet another maiden flight with my stretch Vulcanite. This one I did enter into the 2000′ contest with an H90 motor. It only went 1811′ – much lower than the 2025′ in the sim (the Cheetah simmed out at 2022′). It was an exciting flight because the electronics bay pulled out of the upper tube but did not deploy the main parachute. Being a dual deploy rocket, it looked like it was going to be smashed to bits. Fortunately, it hit very wet grass and suffered absolutely no damage. Now it was time to break out Ol’ Faithful. I had built and installed a keychain video camera in an external pod on the sustainer. I prepped the rocket and took it out to the launch pad. I forgot one crucial thing and this is what happened. The electronics bay and payload section survived. All else was a total loss.
Archive for the 'Hobbies' Category
Accomplishing one of my goals (dual deployment) on the very first day of the year has me in search of a replacement. Something a bit more challenging. Looking to later in the year when I hope to make my Level 3 certification flight, I realized that flight will result in a number of firsts for me, if I am successful. It will be the highest, probably just shy of 13,000′, and the fastest, Mach 1.5. However, that is all being done by sheer brute force of a 75mm M3100 motor. Certainly there must be a way to finesse some of these. I started playing around with some simple designs and simulations with the quick realization that I could go a lot faster with far less motor. So my goal is to do Mach 1.8 with a 38mm motor. This is actually fairly easy as well so, I added a little twist. I want to do this with a tube-finned rocket.
I spent yesterday evening searching for good information on the specifications of various materials used to make the airframes. There really is a bit of a void here and I think I see an opportunity to make a contribution. I’m going to make several, at least 4, identical rockets that differ only in the materials used and see how they perform. There is quite a range of specifications too which should make this interesting – perhaps even exciting if material limitations are surpassed in flight testing. A tube-finned rocket is ideal in this respect for several reasons. The tube fins create a lot of drag and will be put to the test, structurally, when the rocket is pushed through Mach 1. I plan to choose a fin geometry to accentuate that. The geometry of tube-finned rockets spreads the loads in such a way that my ability to achieve uniform glue properties and proper bonding of the fin to the main body tube should not be the limiting factor – at least for the weaker materials.
Right now my list of tubes includes: LOC/Precision tube, Blue Tube, G12 fiberglass epoxy, and Carbon Fiber epoxy. I may add Quantum tubing after a little more study to see if it warrants inclusion. The initial consensus is that CF is the obvious choice – lighter weight than fiberglass and stronger. G12 will certainly work but is the heaviest. G12 is a safe bet. LOC tube is standard thick-walled kraft paper tubing. It is the lightest and also the weakest. Most people expect it to fail at high speed. Blue Tube will be interesting. It is strong and light, lighter than CF epoxy, but begins to yield much earlier that CF. All of these tubes have the same wall thickness so, this should be a fair test.
I plan to use motors in the Vmax series from Cesaroni (although the White Thunder and RedLine series have interesting thrust curves). These Vmax motors burn for less than one second with very high thrust. In these minimum-diameter, high-speed rockets powered by high thrust motors, weight is of the essence. The lighter it is, the faster it will go with a given motor and rocket geometry. Lighter rockets will not go as high as the heavier rockets, however, because more of the energy put into the system ends up as momentum in the heavy rocket rather than being “wasted” pushing the air out of the way with the lighter, faster rockets. I could have decided to use mid-thrust longer burning motors but, that would be mainly a test of the drag differences between the rockets as much as it was about structural stability. I could select altitude as the metric but, that would favor heavier rockets. The proper metric must be chosen for this test and I think it will be top speed – fastest rocket wins. I want to see which material is the lightest that will survive. You can think of this another way. The lighter the rocket, the greater the fraction of the total thrust that must be dissipated as drag (i.e., stress to the structure). The lighter materials will be tested harder than the heavier ones.
This should be fun!
January 1 brought good weather for flying rockets. My club SEVRA had obtained permission to fly at Fentress Naval Auxiliary Landing Field and an FAA waiver to fly to 10,000′ so, I decided to go fly rockets on New Year’s day. Dana, Eva, Steve, Kelly, and Spear also came along. Eva and Spear built rockets the night before and flew their Estes Gold Streaks several times. Eva also flew her HiJinks. To start the day/year off, I flew my Big Daddy on an E28-7T. Although the simulations indicated an altitude of 1100′, the rocket only went 835′.
I flew my first dual deployment today. I modified my BDR 4.0 by adding an electronics bay and installed a Featherweight Raven 2 altimeter. The ejection charges were constructed from a 1.5 cc centrifuge vial, a Q2G2 igniter, and 1 gram of FFFG black powder. The Cesaroni H225 White Thunder motor delay was set to 1.5 seconds past the predicted apogee as a back up. The flight went without a hitch, perfectly straight up. The yellow rocket was stunning against the unusually haze-free, deep blue sky. On the H225 motor, the peak acceleration was 11.5G and the maximum velocity was 346fps. Apogee was measured at 1264′ and was, once again, higher than simulation. The max speed and altitude both support a CD lower than I’ve been using and much lower than calculated. Because of southerly winds, a lot of the rockets flown were headed for, over, and occasionally into the trees so, I decided to use a smaller parachute. The rocket was flown without a drogue. The apo charge separated the rocket and the resultant descent rate was 50 fps. The main parachute was set to deploy at 500′. The decent rate on the main chute was 25 fps and the rocket hit a concrete taxiway. Modest damage was sustained but, the rocket was repaired this afternoon and is ready to go once again. Despite the high descent rate and damage, I think the larger chute would have carried it into the trees. All in all, this was a good start to the new year.
Time for a rocketry update. I’ve been building quite a few rockets, each intended to be used in my Level 1 or 2 certification attempts. I built a LOC/Precision Vulcanite first but, on an H motor it looked like it would fly at least 2000′ – a bit high for single deploy at our site. I then built a Performance Rocketry Lil’ Rascal. For various reasons, I was still looking for another design, one that could be used for both Level 1 and 2. Two weeks before my planned Level 1 attempt, I saw an article for a BDR 4.0 and decided to build one. The article indicated a very high CD, 2.4, that would result in very low flights on both H and J motors.
I flew the BDR 4.0 on an H90 on November 6, 2010 at our Boy Scout Rocket-Ree event. NAR president Trip Barber was present and I asked him to be my Level 1 certification official. The flight went perfectly but there were indications that the rocket went much higher than expected. Unfortunately, I did not remember to turn on the altimeter and had no flight data. During the following week, there was extensive discussion among club members as to what the CD should be for a rocket like the BDR 4.0. There was a wide range of opinion, simulation results, and a void of published work on the CD of tube-finned rockets.
With great uncertainty as to what the CD actually was, I decided to go for my Level 2 certification two weeks later, November 20, 2010. I passed the written portion of the test with a perfect score and was antsy to fly before the winds were predicted to become unfavorable. I had selected a J285 motor and had run many sims. My expectations were for an apogee of between 2000′ and 2500′ with a modest range of optimal delays. I split the difference and went with a delay in the middle of the predicted range, 8 seconds. I should have known something was amiss when the igniter did not go very far into the motor but, I guess I was fairly nervous. With a puff of smoke, the rocket failed to come to life and sat on the pad. Jeff Goldstein, my certification official, offered me a spare and I made certain the igniter went all the way in the second time. This time the motor started and the rocket roared off of the pad. Once again, it seemed to go much higher then expected. The parachute deployed near apogee in a strong wind. I watched the rocket descend slowly and drift far off behind a row of trees. We jumped in the back of a pickup and headed off to the NE corner of the field. After a brief search, we located the rocket in a field of winter wheat and in perfect condition. The successful flight meant I had passed on to Level 2. I did remember to turn on the altimeter for this flight. The BDR 4.0 flew to 3010′! Follow up simulations could replicate this performance only if the CD was a rather low 0.67.
When I was in grade school I started flying model rockets. I won’t say how long ago that was, but I will say that a C6 was the biggest motor you could buy. I do remember when the D’s and E’s were introduced. It was a simple hobby back then and I had a nice big park across the street where I could fly them. Fast forward to today, I’m getting back into the hobby along with my daughter (7th grader). I built a couple of small Estes and Quest kits to revive my modeling skills. These are small enough to fly from my big yard. Well the bug bit. I found a club in the area that flies out of a Navy auxiliary landing field. Poking around some of the rocketry websites, I see that the hobby has changed quite a bit. Folks are flying L motors or bigger, FAA waivers are required, and the rockets have electronics or computers that monitor the flight and deploy a series of parachutes at specified points in the flight. This is just the sort of techno-hobby that I like to get into. I have a few mid and high power kits that I’m building and have set the goal of achieving Level 2 certification. I plan to document my progress as well as review some of the products I’ll be using.
I’ve been doing sudoku for a couple of years now and I have developed a simple notation that keeps track of what numbers can go where in the 3×3 blocks. I do not track all combinations, only 6 basic “shapes” and their various permutations (rotations and reflections). I have found these simple shapes are all that is needed to work almost any puzzle. The more complex patterns you may think are important eventually simplify to one of my basic shapes as your solution for the puzzle progresses. The notation is very simple, easy to learn, and easy to manage (alter/edit as the solution progresses). A key property of any notation is that it needs to be easy to interpret and unambiguous in its meaning. I’ve seen a lot of people working puzzles by filling each block with all of the possible numbers that can go in each square. That is hideously busy, difficult to read, and impossible to manage. It can be an effective technique near the end of solving some of the most difficult puzzles though, so I won’t completely deny its value because I have resorted to using it exactly twice.
First a bit on how to read my figures. The black numbers are the numbers that the puzzle either started with or we have added in trying to solve the puzzle. The blue numbers are the ones that limit where in a 3×3 block that same number can be placed. The possible locations are denoted by numbers in gray. Finally, my notation is indicated in red. When working a puzzle I use a very fine mechanical pencil. I prefer 0.3mm lead, but that can be hard to find. A good clean soft eraser is also a must. With that out of the way, here are the six basic shapes I use to work sudoku puzzles.
The first I call Adjacent. When a number’s location is limited to only two cells that are adjacent, either in the same row or column, I place that number in the center of the line shared by the two cells. In this example I’m considering the possible locations of the number 2 in the Left Middle 3×3 block. The bottom two rows are blocked and the top row already has one value filled. The only two possible locations are next to each other. So, I place a small 2 on the line between those cells.
The next shape I call Line. It is an extension of the Adjacent shape in that it is comprised of three cells in the same row or column instead of just two as found in Adjacent. If the pattern falls in a column, I place the number centered vertically and near the left edge of the center cell. If it is a row, I’ll place the value centered at the bottom of the center cell. It is important to apply the notation consistently since the primary meaning is derived from the location of the values. It will be hard at first to remember where everything is supposed to go. It will also be difficult to read what the notation is telling you. As with anything, practice makes a big difference and I hope you’ll find this can be learned quickly.
The third pattern which contains cells within a single row or column I call Ends. It is exactly what is sounds like. The possible locations are at opposite ends of a row or column. Since the pattern spans the full length of a row or column, I’ve chosen to place the value in the center block. If the pattern is found in a column, place the value centered on the right side of the center cell (yes, in the cell where the number cannot actually go). If it is in a row, place the value centered at the top of the center cell. You should note that this is exactly opposite from where you’d place the value if the pattern was the Line and this demonstrates the importance of applying the notation consistently.
The next pattern is the Block. It is formed by a 2×2 sub-square in the larger 3×3 sudoku cells. The notation places the value on the intersection of the lines where the four cells of the block share a common corner. Each of the 4 cells does not have to be empty for the notation to be valid. If one of the cells already had a value filled in, you would still use this notation to indicate that the value could go in any of the remaining three cells. There is also one way to have two of the cells already filled in and still use this notation. If the two empty cells touch only at the common corner, like two white squares on a checker board, then this notation applies. The other pattern of two squares is actually the Adjacent shape.
The Corners pattern is somewhat similar to the Block. For this pattern, the locations are found in the 4 corners of the 3×3 sudoku cell. As was the case with the Block pattern, one or two of these cells can be filled with a value already and the notation is still valid. The two empty cell form has the two possible cells in different rows and columns (kitty corner, catty corner, cady corner, … whatever you call it). The notation goes in the outer most corner of one of the corner cells. I prefer to place the notation in the corner of a cell that is on the outside edge of the whole 9×9 puzzle grid. If that is not possible (e.g., the center 3×3 grid) then I go with the upper left if it is empty. Which cell you select is not too critical for this pattern.
The last pattern is a three cell pattern that has many permutations. It is called the L. It is a combination of the Adjacent and Ends patterns where one of the cells is common to both. This means that the long axis of the two patterns forms a right angle, hence the name L. The notation places the value in the cell at the corner of the pattern. The value is placed in the outermost corner of that cell which is also between the two touching cells (of the Adjacent pattern). Just look at the image.
As you use the notation, you will eventually need to place multiple numbers in the same pattern (e.g., both 2 and 8 need to be in the same Adjacent). Simply place the numbers close to each other, either side-by-side or one over the other, you’ll quickly learn which way works best in each situation. Being able to write small is a big help. The real power of the notation is that it allows you to see at a glance that some of the cells are not available. If two numbers are assigned to the same Adjacent (or Edge) pattern (e.g., 2 and 8 as in the previous example), then the cells of that pattern cannot be used to make any other pattern for another number. Four values assigned to the same Block means those four cells are out of play for any other numbers/patterns. You may not yet know where each number goes in these full patterns, but you do know that they do end up in there somewhere. The beauty of the notation is that there are no conflicts in position so the placement and interpretation of the notes is unambiguous.
So that is my notation. Try it out and let me know how it works for you. I’m always interested in hearing about more tips and tricks too.
I received a book of Sudoku puzzles for giftmas 2007. The title is “X-treme SUDOKU” by the editors at Nikoli Publishing. The book offers 160 difficult puzzles and 160 more very difficult puzzles – 320 in all. I found the book to be a fabulous waste of time when I had no choice other than to waste time (e.g., waiting in the doctor’s office). I just finished the book and feel like I have accomplished something. There were two puzzles that stood out as being deviously difficult – at least for me. (Hint: try solving the puzzle in my first figure!)