A literal description of my state of mind
A literal description of my state of mind
Here's a simple and inexpensive way to get a fair estimate. There are three diagrams, so expand the extended entry to read the surprisingly easy method we use.
You actually only need a couple things to figure out the altitude of your flights. A theodolite, a tangent table, and a pencil. For reasonably accurate readings, you can make the simple theodolite shown in figure 1. It's basically a 1"x2" piece of wood, 2 foot long, with a plastic protractor screwed to the side. Add a couple finishing nails to sight along, a string with a fishing weight at the end to indicate the angle, and you're set.
The tangent table can be found in any trigonometry textbook. Use the one shown in figure 2, or find one to your liking, they're all the same.
Still with me? Good, believe me, this is simple. In fact, this explanation takes longer than the process.
Figure 3 shows the basic concept of determining altitude:
The 'tracker' takes the theodolite and stands a known distance from the launch pad. In the diagram, it's where the black and blue lines meet. This distance is the baseline, and the farther the better (as long as you can see the rockets from there). Our usual launch area is a football field, so our tracker is usually 300 feet (100 yards) away from the pad. The tracker on one goal line, the launch pad on the opposite goal line.
When the rocket launches, the tracker follows the rocket with the theodolite, sighting it like a rifle, until the rocket reaches apogee (it's highest point). The angle is read (where the string marks it on the protractor), and this angle is written down.
Time for some simple math. The formula is on the diagram. Look up the tangent for the angle on the table, multiply that number by the baseline, and that is the altitude in feet. Simple!!!
An example: baseline is 300 feet. measured angle is 40 degrees. The tangent for 40 degrees is .839, so 300 * .839 = 251.7 feet.
This is only one method, there are many others. But this one is cheap, simple, and accurate enough for our purposes. You can find more information about altitude tracking in the Handbook of Model Rocketry, by G. Harry Stine.
Accuracy can be improved by using two trackers placed at 90 degree angles to each other to compensate for rockets that don't fly perfectly vertical. This is the usual method used at altitude contests. We don't bother when we're flying for fun. Truth be told, we seldom worry about altitude anyway, we just guesstimate using the good ol' Mark I eyeball.
Several years ago I put together a web site devoted strictly to model rocketry. One of the most popular pages was an introduction set up in question and answer format. Looking back on it, I can see that we've come a long way since those early days. I've copied that page into the extended entry, and added links where I could.
Q: Why do you think rockets are such a great thing to do with your kids?
A: If I sit down to play video games with the kids, or we watch sports together, or read in the same room, we might be spending time together, but it's not necessarily 'together' time. Model Rocketry is more interactive for us, there is a give and take, and an exchange of ideas. It's not just spending time together, it's spending time with each other.
My kids have picked up some very good habits from rocketry; setting goals, planning, following directions, working together, teamwork, and keeping records.
They've also felt satisfaction. Imagine the look on 9 year old Rachaels' face as her U.S.A., designed, built, and launched all on her own, roared off the pad for a perfect flight. As it drifted down on its pink streamers, everyone was cheering and congratulating her. I don't know who was more proud at that moment, her or me.
And they've learned how to deal with the minor tragedies of life. The lost rockets, and the ones dinged when the parachute didn't deploy (because Dad forgot the baby powder).
Flying rockets teaches about science too. You'll see practical demonstrations of aerodynamics, physics, chemistry, and more. The kids become engineers, meteorologists, photographers, and journalists, without any pain, and possibly without even realizing it.
One thing we've discovered about rocketry is that the only way to get bored with it is to quit dreaming. We've yet to launch anything bigger than a 'C' motor, but that's ok. We've still got clustered rockets to try, and staged rockets, and 'gap' staging. We haven't done near enough glider or helicopter recovery. How about night launches, how can we make these smaller rockets visible in the dark?
My kids have a million ideas, to go along with my one or two.
I probably should also mention that model rockets are fun.
Q: Isn't model rocketry like launching fireworks?
A: There are some basic differences between rocketry and fireworks.
To start with, model rockets are never launched by lighting a fuse. The ignition is electrical, with the power supplied by batteries. This lets you stand back a ways from the rocket when it is launched. Much safer.
A second difference is that model rockets are designed to be recovered. This means that you can reuse a rocket over and over. There are various ways of recovering a rocket, such as parachutes, streamers, gliding, and more (there's more about recovery later).
Another difference is the use of a launch rod. This is simply a guide for the rocket to follow for it's first few feet of flight, keeping it straight up until it's going fast enough to be stable on its own. Once again, it's a safety thing.
Q: Is this really safe enough for kids?
A: Model rocketry is an amazingly safe hobby, provided you follow the Safety Code. When you read it over, you'll find most of it is just common sense. Over the years, there have been literally millions of rocket engines fired safely.
As for kids doing rockets, if you insist on following the safety code, and have adult supervision, it's almost impossible to get hurt. Explain that each and every one of them is responsible for safety when launching rockets.
I have normal kids, they get into their share of mischief. But when we launch, they know what is expected of them, because it's been that way since day one. A brief example that really happened:
My youngest, Rachael, was doing the countdown. When she got to '3', her brother TJ yelled 'STOP' from where he was standing (about 100 feet away). Rachael immediately pulled the safety key and put the launch controller down. Then we saw a mom chasing a toddler, who was running full steam towards the rocket.
After mom corraled her child (he never even got within 20' of the rocket), we made sure the area was clear again, and started the countdown over. It was a perfect launch.
Some rules we use:
The countdown is LOUD.
ANYONE can stop a countdown at any time, for any reason.
When someone yells 'stop', that's it. No exceptions.
The only time the safety key is in the launch controller is during a countdown.
We don't resume a countdown from where it stopped. We start over.
Before a countdown starts, everyone has to give an 'OK', meaning they're in position, ready, and the area is clear.
We have never had anyone hurt, or been even remotely close to having an accident. It's not luck, it's designed to be that way. And by the way, that mom and child stayed and watched us for about an hour that day, and still stop by occasionally when we are launching a few.
Q: What's the easiest way to get started?
A: I'd suggest an Estes Starter Set. They start around $15.00 [~$20.00 in 2003], and you can get them at stores like Wal-Mart, K-Mart, Toys-R-Us, hobby shops, and even some craft stores like Michaels or MJDesigns. The starter set includes almost everything you need, except batteries and glue. There are even some 'Ready To Fly' starter sets out now, where the rocket is pre-built for you. Other sets have a variety of rockets (1 or 2) that you have to build yourself. Rockets like the Alpha 3 and Sabre goes together quick and easy. Other sets have 1 simple rocket, plus another that takes a bit more skill to assemble. Another company, Quest, also makes starter sets, but I've never seen one. I hear they're pretty much the same.
Q: Launch controller, recovery wadding... What's all this stuff really do?
A: I'm going to assume that you are looking at a starter set, and I'll just run down the assembled parts.
* Launch pad - Usually has 3 or 4 legs, with a blast deflector and launch rod sticking up from it.
The launch pad holds the launch rod and blast deflector. The wide legs keep it from tipping over in a breeze, and you can adjust the pad to tip the rod a few degrees for launching into the wind. The launch rod is what guides the rocket until it's moving fast enough for the fins to keep it stable. In the starter sets, the launch rod is usually sectional, always use both pieces. The blast deflector keeps the engine exhaust from hitting the pad and ground. Safety again. There is also a rod cap included. Put it over the tip of the upright launch rod, and it helps prevent injuries where someone leans over the top of the rod while preparing a rocket for launch. Make sure you remove the rod cap just before the countdown, and replace it immediately after.
* Launch controller - This is where the batteries go, usually 4 AA size. It has a continuity light or buzzer that tells you when the rocket is set up properly for launch and the safety key is inserted. The safety key must be inserted before pushing the 'fire' button has any effect. In other words, keep the safety key with you when you work around the rocket, and no one can accidently launch it when someone could get hurt. Coming out of the launch controller is a long wire (about 15 feet) that ends in two small microclips. These clips connect to the ignitor, explained below. When you launch, the length of the wire makes it easy to stand back at a safe distance.
* Rocket - A simple rocket is 3 or 4 fins and a nose cone. These are connected to each other by the body tube. On the side of the body tube is the launch lug, a small tube or loop which is slipped over the launch rod prior to igniting the engine. Connecting the nosecone to the body tube is the shock cord. This keeps the pieces of the rocket together as it comes down. Inside the rocket is the recovery system, often a parachute (there is a whole section on recovery later on). The recovery wadding protects the parachute from the ejection charge, which is what deploys the recovery system. Finally, at the bottom of the rocket is the motor mount. This is the place where the engine goes, and it transfers the thrust of the engine to the rocket itself.
* Engine - The 'whoosh generator', also called a motor. This small cardboard cylinder is actually quite complex in design and function. That doesn't mean it's complicated to use. First turn the engine upright so the small hole is facing up. That's the nozzle, the business end of the engine. The ignitor is a small U or V shaped piece of wire. Drop the point of the ignitor into the nozzle, and gently make sure it goes in as deep as possible. There will be two wires sticking out of the nozzle quite a bit. Next take an ignitor plug (color coded, check the directions in the set), and gently push it into the nozzle. This holds the ignitor where it needs to be to fire the engine. Insert the engine into the rocket motor mount and you're almost ready to go!
When ready to launch, connect the controller clips to the ignitor. After everyone is away from the rocket, insert the safety key, and the light should light (or buzzer buzz, depending on your controller). This means that the rocket will be launched when you push the button.
Q: What do the motor numbers and letters mean?
A: This is an easy code to provide complex information. Here's the bare minimum needed to start with.
A sample engine code might be: B6-4
The 'power' range of an engine is indicated by the letter, in this case a 'B'. The codes start with 'A' and keep right on going up the alphabet. So B is twice as powerful as A, C is twice as powerful as B (and 4 times more powerful than A), and so on. This is overly simplified, but you'll absorb the details as you gain experience.
Bigger engines (higher letters) achieve higher altitudes, or lift heavier rockets.
The '6' is the average thrust of the engine. It's measured in 'newtons', but don't worry about it for now. Just keep in mind that a '6' has a higher average thrust than a '4'.
The '-4' is the delay, measured in seconds. This means that 4 seconds (more or less) after the propellant burnout, the ejection charge fires. That deploys your recovery system.
There are '-0' engines. These are booster engines designed for multi-staged rockets. As soon as burnout occurs, the ejection charge fires to ignite the next engine. Don't use these on a single stage rocket. '-P' engines are plugged, and have no ejection charge. They're made for gliders.
Some Estes engines have a 'T' listed after the delay time. This means it's a mini-motor, and has a smaller diameter casing.
Q: Where can I launch a rocket?
A: We launch at the local middle school (Jr. high) field. This is a football field, a baseball diamond, and 2 soccer fields, all bent around an L shape. The bigger the field, the better your chances of recovering the rocket. We've had a few rockets drift away on the wind into, or over the trees. Be aware that it can be calm on the ground, and fairly windy a couple hundred feet up! Because of the L-shape of our regular launch field, we limit ourselves to A and B engines on most rockets. We've got a few heavier birds that fly normally on C's, and on one spectacularly calm day, we launched our little rockets on C's. Straight up well over 1000', and recovered on a parachute less than 30 yards away. For more information, read about rocket clubs below.
Q: How do the recovery systems work?
A: You spend time to get your rocket looking good, and to fly well. You hate to lose them! Recovery is one thing that keeps this hobby from being glorified fireworks (I'm not knocking fireworks hobbyists). There are many ways to recover a rocket. Here's the most common:
Featherweight - for the lightest rockets. The have such a high surface area compared to weight that they 'float' to the ground, like the name says.
Tumble - for very light rockets that are too stable for featherweight recovery. Usually the nose cone is ejected (it's all connected by the shock cord, remember), and the whole thing comes down. If something wasn't done to ruin the stability, it might come down like a dart. At best, hitting the ground like that could damage or destroy the rocket. At worst, it could hit and hurt someone. There are terms for rockets that accidently come down hard, they're called Prangs or Lawn-Darts. No fun, and very hard on the rocket.
Streamer - this is a long, thin piece of plastic or crepe paper. It creates enough drag to bring the rocket down gently. These are good for days when the wind causes too much drift in a parachute.
Parachute - these range in size from 8" up to 24" for model rockets. To minimize drift, you can cut a spill hole in the center of the canopy. This will help the rocket come down faster, but it hits harder when it reaches the ground. If you cut a spill hole, cut it large because too small a hole can actually increase the lift the parachute generates as it descends. Estes parachutes have a spill hole marked with dotted lines, just cut it out if needed. Another technique to minimize time in the air is to 'reef' the shroud lines. Take a piece of masking tape and wrap it around all the parachute lines about halfway between the rocket and the canopy. This prevents the chute from opening fully.
Glider - It goes up like a rocket, and comes down like a glider airplane. Really cool.
Helicopter - Ever see a maple seed fall? Spinning on one wing is one method of helicopter recovery. Another is to have rotors deploy at ejection, causing the whole rocket to rotate.
Q: What about rocket clubs?
A: The National Association of Rocketry (NAR) is America's model rocket organization. Their site can be reached from my links page, and from there you can find a local chapter near you. Flying with a club is a great way to learn from others' experience. The NAR also offers insurance for rocketry activities. Sometimes the deciding factor on whether you can fly in some areas (a public park, for instance) is whether or not you have this insurance. On top of that, you receive the NAR rocketry magazine, full of useful tips, plans, and articles. NAR also offers it's Technical Services division, called NARTS. This is where you can get anything from rocket designs to wind tunnel plans to baseball caps. Check out their site, it's worth it!
Another organization devoted strictly to high power rocketry (HPR) is the Tripoli Rocket Association (TRA). Since this is Q&A for beginners, I'll mention that they're there, and not go into HPR. You can find a link to TRA from Rocketry Online.
A new organization is just starting out, the Independent Association of Rocketry (IAR). They are very new, and not yet completely organized. They're worth checking into. [years later, I take this back. they've gone nowhere.]
Q: Can you recommend a book or something to learn more?
A: Some very good books:
The Handbook of Model Rocketry by G. Harry Stine.
Model Rocket Design and Construction by Tim Van Milligan.
The Art of Scale Rocketry by Peter Alway. [out of print]
At least the first two can be found in your local library, NARTS also offers these books and more for sale. See my links page for Saturn Press, they have the entire collection of Peter Always' rocket books. There's also a link to Apogee Components, where you can find Tim Van Milligan's books. Apogee has a complete line of educational rocketry publications, including 69 Science Fair Projects with Model Rockets: Aeronautics.
The Rocketry Online webpage has all kinds of links to good sites on the web related to rocketry. See my links page for a link to them.
The Rec.Models.Rockets (RMR) newsgroup is a vast source of experience. I've always found the folks there to be willing to answer questions without talking down at you. A great group of people.
The RMR FAQ (frequently asked questions) file will answer many questions you may have. I keep a copy of this handy by my workbench, because it's that useful.
Q: Couldn't I save money by making my own rocket engines?
A: No. When you factor in the cost of the chemicals, equipment you'd need, and materials, the store bought motors are actually a pretty good deal. Also consider that a home-made motor is more likely to malfunction, which could destroy your rocket or, worse yet, hurt someone. The commercial motors are reliable and consistant performers, and you'd have to make literally hundreds of motors yourself to even come close to that kind of reliability.
Now let's talk about safety. It's dangerous to deal with some of these chemicals unless you know what you are doing. Even among experienced rocketeers, there is a surprising amount of 'lore' and common knowledge that is just plain wrong. It's not safe to try to make your own motors, please don't do it.
If you absolutely have to make homemade motors, check out the RMR FAQ (links page) where there is information about a course in making rocket motors. The Rec.Pyrotechnics newsgroup has folks that can help too.
Simply put, Model Rocketry means using commercially available motors. To save money on these, you can mail order them (or order from companies on the internet), or buy them in bulk packs at your local store.
Q: I remember these cool rockets I saw as a kid. Are the old companies still around?
A: Estes is still with us. They absorbed Centuri a while back, and once in a while release an old Centuri design. There are many small companies producing quality rocket kits today, check the Rocketry Online website for links.
Q: I can't believe that white glue is strong enough for rockets. Shouldn't I use model glue or epoxy?
A: For gluing plastic to plastic, model airplane glue is best. There are some times and places where epoxy is handy. But for Estes kits, white or yellow glue is king (yellow is superior). A bond you make between the cardboard body and the balsa or cardstock fin will be so strong that the tube itself will tear before the glue joint breaks. Two secrets to getting even stronger joints; lightly sand the body tube to remove the glasine coating (the glossy stuff), and use the double glue method. The way to double glue is to apply a small amount to the pieces to be joined and press them together. Pull them back apart, and let the glue dry for a few minutes. Apply a little more glue, then join like normal. This technique results in super strong bonds that will easily handle A-D engines. I've heard of rockets built with just yellow glue that fly on G motors. [I've flown H motors this way.]
Q: It goes up, it comes down. What's next?
A: If you look at rocketry webpages out there, you will find a hundred people experiencing rocketry in a hundred ways. I mentioned in passing cluster rockets, staging, scratchbuilding, high power rocketry, scale modeling, gliders, and more. I didn't mention payloads, or contests, or arial photography, or altitude records, or... The list just goes on and on, and you can decide what suits you best.
Do it safely, and have fun!
Don't confuse these terms with 'scale' modeling, which is building a detailed version of a real rocket. Rather, 'scaling' a rocket design means building a larger or smaller version of the original, like a big Mosquito or miniature Big Bertha.
When scaling a model (or anything else), the first step is determining the scaling factor. We'll upscale an Estes Mosquito to demonstrate. The original BT-5 tube measures .544" in diameter, and the desired BT-60 tube measures 1.637" in diameter. Dividing 1.637 by .544 results in a scaling factor of 3.00 (rounded, use more decimal places and/or forget the rounding for more precision). In other words, a Mosquito built using a BT-60 body is three times larger than the original, or 300% bigger. Sometimes you’ll see this mentioned as a 3x upscale.
This scaling factor is what you will multiply every measurement by for the new model. So the original 3" length of BT-5 would become a 9" length of BT-60, and you would multiply each of the fin dimensions the same way for the upscaled version. There are two possible exceptions to this. One, you don’t always want to upscale the thickness of the fins, or that upscaled Mosquito will have fins 3/16" thick. It’s up to you. The second exception is nose cones. Unless you have a truly scaled version of the original nosecone, the length is probably wrong to some degree, or the shape is slightly (or not so slightly) different. What I do in these cases is to measure the length of the true upscaled nosecone, compare it to the length of the available nosecone, and then adjust the length of the body tube to make up the difference. For instance, if the upscaled nosecone should be 4" long, but the nosecone you have is only 3" long, my solution is to make the body tube 1" longer to compensate. Close enough is usually good enough.
To reverse the above, and downscale an Estes Big Bertha, we’ll take 1.637" (diameter of the original BT-60) and divide it by .544" (diameter of the desired BT-5), which gives a scaling factor of .33. So a BT-5 Big Bertha would be a 1/3 sized downscale, or 33% as large as the original. Just like above, all dimensions are multiplied by the scaling factor, which makes the original 18" long BT-60 a 6" long BT-5. Adjusting for fin stock thickness and nose cone/body tube lengths are done the same way as well.
Doing the measurements and calculations in metric (millimeters), makes things much easier.
That’s the theory and the math. Below is a table I keep handy by my workbench with measurements and scaling factors for many common sizes of tubing. To use the table, find the original size body tube down the left hand column, then find the desired size tubing along the top row. Cross index the column and row to read the scaling factor to use. The two columns farthest left on the table have the metric and standard diameter measurements for the body tubes. Adding other sizes to the table is easy to do by using the techniques above. Obvious additions are Apogee 10.5mm tubes and tubes for the Micro Maxx sized rockets.
One neat thing about the table is using it to help scale fin templates using a photocopier. The copier I have access to will make reductions/enlargements from 64% to 155% of the original size. Suppose I want to upscale an Estes Alpha to use BT-80 sized tubing. Looking at the table, this means the scaling factor is 2.72, or the fin template needs to be enlarged 272%. Looking at the table (and knowing the capabilities of my copier), I see I can enlarge the original fin template by 154%, making the template the correct size for a 1½" tube. Next, I take that new (enlarged) template and use it as the original, enlarging it again by 148%, for a BT-70 tube. Finally, I’ll enlarge this new template by 117%, giving me a fin pattern perfectly sized for the BT-80 tubing I’m going to use. It’s easier to do than to explain, so just follow it through using the table to see the steps.
Upscales and downscales are fun and interesting. The Mosquito is a classic that’s done often, and makes a good first project. After that, the possibilities are endless, just look through past issues of Sport Rocketry and High Power Rocketry for examples, and old catalogs for ideas.
| 0.544 | 13.8 | ... | 1.36 | 1.80 | 2.04 | 2.44 | 2.48 | 2.79 | 3.01 | 3.72 | 3.90 | 4.12 | 4.64 | 4.76 | 5.57 | 7.43 | 10.22 | 11.14 | 13.93 | 21.18 | |
| 0.544 | 13.8 | ... | 1.36 | 1.80 | 2.04 | 2.44 | 2.48 | 2.79 | 3.01 | 3.72 | 3.90 | 4.12 | 4.64 | 4.76 | 5.57 | 7.43 | 10.22 | 11.14 | 13.93 | 21.18 | |
| 0.544 | 13.8 | ... | 1.36 | 1.80 | 2.04 | 2.44 | 2.48 | 2.79 | 3.01 | 3.72 | 3.90 | 4.12 | 4.64 | 4.76 | 5.57 | 7.43 | 10.22 | 11.14 | 13.93 | 21.18 | |
| 0.544 | 13.8 | ... | 1.36 | 1.80 | 2.04 | 2.44 | 2.48 | 2.79 | 3.01 | 3.72 | 3.90 | 4.12 | 4.64 | 4.76 | 5.57 | 7.43 | 10.22 | 11.14 | 13.93 | 21.18 | |
| 0.544 | 13.8 | ... | 1.36 | 1.80 | 2.04 | 2.44 | 2.48 | 2.79 | 3.01 | 3.72 | 3.90 | 4.12 | 4.64 | 4.76 | 5.57 | 7.43 | 10.22 | 11.14 | 13.93 | 21.18 | |
| 0.544 | 13.8 | ... | 1.36 | 1.80 | 2.04 | 2.44 | 2.48 | 2.79 | 3.01 | 3.72 | 3.90 | 4.12 | 4.64 | 4.76 | 5.57 | 7.43 | 10.22 | 11.14 | 13.93 | 21.18 | |
| 0.544 | 13.8 | ... | 1.36 | 1.80 | 2.04 | 2.44 | 2.48 | 2.79 | 3.01 | 3.72 | 3.90 | 4.12 | 4.64 | 4.76 | 5.57 | 7.43 | 10.22 | 11.14 | 13.93 | 21.18 | |
| 0.544 | 13.8 | ... | 1.36 | 1.80 | 2.04 | 2.44 | 2.48 | 2.79 | 3.01 | 3.72 | 3.90 | 4.12 | 4.64 | 4.76 | 5.57 | 7.43 | 10.22 | 11.14 | 13.93 | 21.18 | |
| 0.544 | 13.8 | ... | 1.36 | 1.80 | 2.04 | 2.44 | 2.48 | 2.79 | 3.01 | 3.72 | 3.90 | 4.12 | 4.64 | 4.76 | 5.57 | 7.43 | 10.22 | 11.14 | 13.93 | 21.18 | |
| 0.544 | 13.8 | ... | 1.36 | 1.80 | 2.04 | 2.44 | 2.48 | 2.79 | 3.01 | 3.72 | 3.90 | 4.12 | 4.64 | 4.76 | 5.57 | 7.43 | 10.22 | 11.14 | 13.93 | 21.18 | |
| 0.544 | 13.8 | ... | 1.36 | 1.80 | 2.04 | 2.44 | 2.48 | 2.79 | 3.01 | 3.72 | 3.90 | 4.12 | 4.64 | 4.76 | 5.57 | 7.43 | 10.22 | 11.14 | 13.93 | 21.18 | |
| 0.544 | 13.8 | ... | 1.36 | 1.80 | 2.04 | 2.44 | 2.48 | 2.79 | 3.01 | 3.72 | 3.90 | 4.12 | 4.64 | 4.76 | 5.57 | 7.43 | 10.22 | 11.14 | 13.93 | 21.18 | |
| 0.544 | 13.8 | ... | 1.36 | 1.80 | 2.04 | 2.44 | 2.48 | 2.79 | 3.01 | 3.72 | 3.90 | 4.12 | 4.64 | 4.76 | 5.57 | 7.43 | 10.22 | 11.14 | 13.93 | 21.18 | |
| 0.544 | 13.8 | ... | 1.36 | 1.80 | 2.04 | 2.44 | 2.48 | 2.79 | 3.01 | 3.72 | 3.90 | 4.12 | 4.64 | 4.76 | 5.57 | 7.43 | 10.22 | 11.14 | 13.93 | 21.18 |