Rocket Stability - or - What Happened To Homer's Rocket? (Part 1)

A few months ago, because of a recommendation from Chad, I read Homer Hickam's book Rocket Boys. This was adapted into the film October Sky, starring Jake Gyllenhaal.

In 1957, after the launch of Sputnik, Hickam became obsessed with building his own rockets. But model rocketry hadn't really been invented yet - in fact, the hobby got its start that same year - and a lot of kids tried building their own rockets at home, sometimes with tragic consequences. Cooking up propellant isn't something kids should do in the kitchen. Nobody should do it, unless they really know what they're doing, and most people don't.

If you've read the book, or seen the movie, you know Homer's first few rocket flights didn't go well. The first "flight" blew up his mother's fence. The second didn't blow up - but it flew out of control.

Since his rockets were made of metal, he was really lucky he didn't kill anybody. This is why we make model rockets out of paper, balsa and plastic. Their destructibility is a safety feature, in case something goes wrong in flight.

But what happened to Homer's rocket? Why did it fly all over the place, rather than straight up?

Reading the book was fascinating, and since I'd been studying rocketry for several months, it was fun to see how Hickam came up with a lot of innovations that we see in modern model rocketry today - electric ignition systems, tracking altitude from the ground, using a launch rod and launch lugs - all on his own. Model rocketry was invented in 1957, and it didn't get really popular until the 1960s, so a lot of young rocketeers did not have the benefit of its innovations or safety features, but many of them discovered better practices along the way.

I'd seen the movie years ago. But when I read the book, I thought, I bet I know why that happened. Actually, the reason why could have been one of several things.

There are a number of things to consider when designing, building and launching a rocket to ensure a stable flight. If you are merely building a kit, you probably don't have to worry about it that much. Most model rocket kits are well designed, and designed to be stable.

But if you'd like to design your own rockets - and it isn't that hard, as long as you understand a few simple concepts - it is very important to know something about stability. Also, sometimes we like to hack a rocket kit so it will take a larger, more powerful motor than the kit was designed for. I did this with the Estes Cosmic Explorer, because I love the way the rocket flies with standard motors so much, and I wanted to see it go higher.

My two Estes Cosmic Explorers - the stock kit build on the left, which accepts up to a
C motor and flies to about 600 feet, and the upgrade on the right, which accepts a much
more powerful E motor, and can top 1800 feet.

A larger motor is heavier, and so stability issues come into play - this is another time it's important to understand the basics of rocket stability. I was able to upgrade the Cosmic Explorer with confidence, knowing that it would have a stable flight, because I understood the basics of rocket stability.

Stability is covered in depth in G. Harry Stine's Handbook of Model Rocketry, which I highly recommend reading.

But I want to cover some of the basics here.

What keeps a rocket stable in flight? The answer might seem obvious: the fins. But simply slapping a set of fins on a rocket is not enough. You need to understand why the fins work, and what might prevent them from working.

The two most important concepts to understand with regard to rocket stability are the following: Center of gravity and center of pressure.

Center of Gravity

Every object has a center of gravity. This is also sometimes called the center of mass. It's a theoretical point somewhere on, inside, (or sometimes outside) the body of the object around which the mass is equal in any direction. This is also known as its balance point, because if you can balance an object - a stick, for example - on your finger or the back of a chair (or whatever), you've found its approximate center of gravity.

Any object in space, whether it's in the vacuum of outer space, or tumbling through the atmosphere, will rotate around its center of gravity. If you flip a stick in the air, it will rotate exactly around its balance point. A gymnast doing a somersault rotates around his or her center of gravity.

Remember how I said that sometimes the center of gravity is located outside the body of an object? That's how a boomerang operates. It rotates around its center of gravity, which is located somewhere in the air between its two arms.

A rocket will also rotate around its center of gravity. Keeping that rotation under control is what stability is all about. Although gravity is pulling equally on all parts of a rocket, from the tip of the nose cone to the end of the motor hook, it acts through the center of gravity.

In rocketry, the center of gravity is often abbreviated CG.

Center of Pressure

 The center of pressure is the average location of pressure variation on an object. It's another theoretical point on a rocket - this time, the theoretical center of all the aerodynamic forces operating on the rocket. It is determined by the total surface area of the rocket, and in a way, it's similar to the center of gravity; it's the point where all the aerodynamic forces are in balance. The surface area in front of the center of pressure is equal to that of the surface area behind the center of pressure. Much like the center of gravity, air pressure acts on all parts of a rocket equally, but because the forces are balanced before and behind the center of pressure, we say that aerodynamic forces act through the center of pressure.

But the center of pressure is tricky, because while the center of gravity of an object mostly stays put*, the center of pressure can move around, as we'll see.

In rocketry, the center of pressure is often abbreviated CP. CG and CP are very important concepts, so keep them in your mind.

*(On a model rocket, the center of gravity does move forward slightly during flight. More below.)

The center of gravity is usually indicated with a blue and white checked circle, and the center of pressure is indicated with a red dot, often with a red circle around it, as in the picture below. Notice where the CG and CP are in relation to one another.

Click here for Part 2.

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Build It Yourself - Quickie Launch Pad

Sometimes you find you need a new piece of equipment in rocketry, because what you have isn't the right piece for a particular rocket. Or maybe you want an extra this or that. Launch pads are one of those - maybe you want to be able to set up multiple rockets at one time, or you need a pad with a fatter launch rod.

If you go with building Estes kits, and you build a larger rocket with an E-sized motor, the kit instructions tell you to launch it only on an Estes E-sized launch pad. The basic launch kit has a 1/8 inch rod. Rockets with an E motor really should be launched with a 3/16 inch rod.

The Estes V2 - a semiscale model of the historical rocket - uses E motors
and needs a larger launch rod than your typical Estes Skill Level 1 kit.

Great, you think, now I gotta go out and get a whole new launch pad!

Not so.

There are a lot of things you can build yourself in rocketry - most things, in fact, once you get enough experience and know how things work. Launch pads are particularly easy.

I realized I needed a launch pad with a 1/4 inch launch rod - and quickly, for a launch the next day. For most of my rockets, I use a camera tripod with the Odd'l Rockets Adeptor - a kind of threaded rod connector with a thumbscrew in the side.

You screw one end of the Adeptor to the tripod, stick the launch rod in the top, and use the thumbscrew to secure the rod in place. It's great! And only about 10 bucks from JonRocket.com. However, it only takes up to a 3/16 inch rod.

No problem! I threw together a little list, ran to Lowe's and Michael's Crafts - I needed to go anyway - and built a new launch pad. Whole thing took me 15-20 minutes to build, plus an hour to allow some glue to dry.

There are a lot of cool launch pad plans on the internet - with legs, adjustable rod holes, swivels for changing the angle of the rod. But if you just need something basic, this works great. It only takes one sized rod, but you can make multiples of these for different sized rods, easily and quickly.

Here's how you build mine. You can design your own - it just needs to be wide enough to be stable, and thick enough to hold the launch rod securely. I designed this on the fly, and it's really easy.

What You Need

• 12-inch square plywood base, 1/2 inch thick (Michael's Crafts - $5)
• 4-inch square wooden plaque, about 3/4 inch thick (Michael's - $0.99)
• 1/4 inch steel rod - you can use whatever size rod you need for the rockets you're launching. (Lowe's - price varies depending on thickness and length of the rod. Mine was less than $4)
• Steel electric box cover plate (Lowe's - $0.50)
• Pencil
• Straightedge (I needed an 18-inch ruler. Didn't have one, so I used a piece of basswood I had)
• Wood glue
• Drill with a bit the same size as the launch rod - 1/4 inch, in my case
• Steel wool
• Paper towels
• WD-40

 Step 1: Use the straightedge to mark diagonal lines from the corners on the plywood base:

Step 2: Place a ring of glue around the center:

Step 3: Line up the corners of the small wooden plaque with the diagonal lines on the base, and glue the plaque to the base. Place a heavy book on top and allow it to dry for 30 minutes:

While the glue dries, it's time to clean up the launch rod.

The steel rod is found in a section labeled "metal shapes and rods," and I think it's for welding or something. I don't know - I only use it for rockets. In the same section, you'll find aluminum angle - useful for lots of applications in rocket building. For this pad, I used a 1/4 inch rod, but you should get whatever thickness rod you need. For your basic kits, a 1/8 inch rod is standard. Just make sure it's long enough - a 3 foot rod is right for most low power kits with A-C motors. I have a 3/16 inch rod which is 4 feet long for slightly bigger stuff.

Note: I do have to get a longer launch rod for this pad - the rocket I built it for needs a 4-foot-long rod, and all they had in stock that day were 3-foot. Easy fix.

The rod is covered with some nasty black oils, and may be a little rusty. This is fine. Just make sure you get the straightest rod you can find - some of them are a little bent.

The rod is covered in oils which will turn your hands black, and may be a little rusty.

You'll need to remove the label.

First, you remove the paper label on one end of the rod. Then you'll get out some steel wool, paper towels and a can of WD-40.

You're going to rub the rust and oils off the rod with the steel wool. Work from one end to the other - this doesn't take too long, but you want to scour the rod until it looks shinier. It took me perhaps five minutes.

Now the rod is shinier and smoother.

After that, you need to clean the rod. Spray some WD-40 onto one paper towel, and begin rubbing down the rod. All the oils and steel shavings will be collected onto the paper towels - it gets pretty messy.

Once one paper towel is thoroughly dirty, switch to a new one. Spray on some more WD-40 and repeat the process. You'll repeat this a couple of times with a new towel until the towel remains clean, and doesn't show any oils when you rub it down with the WD-40.

Finally, with a clean, dry paper towel, rub off the excess WD-40. Just rub the rod down until it doesn't feel greasy any more.

Now, let's go back to the base of the launch pad. Take the book off the top, and with a pencil and straightedge, extend the diagonal lines from the corners of the wooden plaque so that you find its center.

With a hand drill, drill as straight as you can down into the center, through the block and a little into the base.

If you have access to a drill press, that's even better. I do not, so I had to eyeball it.

Check the fit of the launch rod. It should go right into the hole. Then, see how easily it comes out. If it comes out too easily, just drill a little deeper into the base - but not all the way through. That will provide more friction against the launch rod, so it doesn't accidentally pop out of the hole at launch.

The electric box cover serves as your blast deflector. If it's large enough, you can drill a hole in the center, and it will be perfectly centered on your launch pad.

But mine came with a screw hole on one corner, which was perfect.

Insert the launch rod into the hole on the base, and slide the blast deflector down over it. If you use a corner screw hole like I did, then it will hang off at an angle - this is great. It'll direct the blast away from the pad, and not just back up at the rocket. Just make sure you place your rocket over the blast deflector when you launch!

Boom. You're done. Launch pad.

If you need to angle the pad at launch, or you didn't get the center hole perfectly straight, you can adjust the angle of the pad by placing a small rock underneath one side.

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Launching Your First Rocket (For N00bs) - Part 2

[Click here for Part 1]

It's time to launch some rockets!

(Quick safety note: I took the following pictures on my back patio, with lots of trees, buildings and dead leaves around. BUT, I was using a used motor, so there was no chance of an accidental ignition! These pictures are merely for illustration. In case it needs to be said, do not do the following steps until you are out in the flying field, away from trees, houses, etc., and that the ground is clear of fire hazards like dry grass and dead leaves. The NAR website has the appropriate site dimensions on its safety code page for flying rockets of various-sized motors.)

The rocket is prepped, but before we place it on the pad, it's a good idea to make one slight adjustment.

If you slide the rocket onto the launch rod now, you'll see that it goes all the way down and rests right on the blast deflector. This might be fine with some rockets, but generally, it's not a great idea.

An Estes Hi-Flier rests directly on the blast deflector.

When you press the launch button, a surge of electric current will run from the batteries in the launch controller, through one of the wires leading out to the pad, through the igniter, and back to the launch controller, completing a circuit. The igniter is a high-resistance metal, and that resistance is what causes it to heat up - just like the wires in a toaster.

But, electrons are lazy; they always take the path of least resistance. If the clips on the launch controller wires touch the blast deflector (or each other), suddenly there's a path around that resistor, and current won't flow through the igniter.

The launch controller microclips are touching the metal blast deflector. The electrical current will go
through the deflector, and not the igniter at all. Your rocket won't budge an inch if this happens.

So we need to raise the rocket off the pad just a little bit.

The common way to do this is with a little masking tape. Just take a long strip of tape and wrap it several times around the launch rod until it's thick enough that it holds the rocket up by the launch lug. This is what Estes recommends, and it works fine, mostly.

However, if you don't get the tape on straight, or if you've already launched several times, you might expose some of the sticky side of the tape, and it will stick to the rocket. This could cause the rocket to have trouble lifting off, or worse!

Chad once launched his Crossfire ISX, and it had the weirdest, unstable flight. It didn't fly very high, and it arched over and flew in a weird twisty spiral until it crash landed a few hundred feet away. What we didn't notice until we ran to recover the rocket is that it had taken the launch rod with it!!

Model rocketry has an extraordinary safety record, but this could have been really dangerous! If that metal rod had landed on someone (or someone's car), there would have been some real damage done! (It also goes to show how powerful these little motors can be!)

We think the culprit was the engine hook. It's on the same side as the launch lug. The Crossfire is a pretty narrow rocket, and I said I thought the hook might have grabbed the seam on the launch rod (this is why, when I built my Crossfire, I put the lug on a different side from the hook, just in case). Another possibility was a crooked lug. Make sure your launch lugs are straight when you build your rockets! If they're not properly aligned with the rocket body, the lug can bind the rod at launch.

But I worry that if your rocket gets stuck to the tape, this could perhaps happen. This was a freak accident, but happening once was more than enough.

I add an alligator clip to my tape, and use that as a little ledge to hold the rocket up by the body tube or maybe a fin.

I clamp an alligator clip to the launch rod, just above the tape.

Now the rocket has plenty of support while sitting on the pad. Make sure
you keep the clip well away from the igniter leads, so you don't get a short.

Slide the rocket down to the tape (or alligator clip). Make sure it slides freely along the rod, and can come right back off again without getting stuck. Then, carefully hook up the clips from the launch controller to each of the leads of the igniter.

 
I say "carefully," because you don't want to pull the igniter out! If it happens to fall out, remove the clips, reinstall the igniter, and make sure the plug goes in firmly. If it's too loose, you can put a small piece of masking tape over it to hold it. The tape will come off with the force of the blast from the rocket motor.

Step back. The NAR model rocket safety code says you should stand at least 15 feet from the launch pad when launching a rocket with anything up to a D motor, and 30 feet away when launching something larger. If you're using the Estes launch kit and your standard motors, 15 feet is enough (that's as far as you can go with an Estes launch controller anyway).

Insert the safety key, and press it down. The continuity light on the launch controller should come on. If it doesn't, check your connection - are the clips in place? Do you have a new igniter, or did you accidentally install a used one? Once you get the continuity light, you're good to go.

Insert the safety key into the launch controller. On an Estes controller, this is spring-loaded, so you'll
have to press it down with your thumb. Wait until you're ready to launch before you do this.

If all the connections are good, the continuity light will turn on. Then it's go time!

Make sure everyone is at least 15 feet away from the launch pad, and knows you're about to launch. Then, do a countdown. The NAR safety code says that you should count down from at least 5. This is for a couple of reasons. First, you want any spectators to know what's about to happen, and be aware should anything go wrong. Also, imagine you have a little kid watching (or a not-so-bright adult), and suddenly they walk up to the launch pad! If you're counting down, you can hold while you get that person out of harm's way.

Once you reach zero, press the button and hold it down. If everything is correctly installed, the rocket will take off at incredible speed! The first time you launch a rocket, you'll be surprised how fast and high it can go!

Note: If nothing happens after you've held the launch button down for a few seconds, release the button and remove the safety key. You must wait 60 seconds before approaching the pad, to prevent being right on top of the rocket if it suddenly ignites!

This is particularly true of composite motors, which we're not discussing here, but it's also true of black powder motors. Now, black powder doesn't really smoulder. It's lit, or it's not. But one reason for a misfire is that the igniter might not be touching the propellant. I believe the reason for waiting 60 seconds is that the igniter wire may still be hot, and if it suddenly comes in contact with the propellant, you could have an unexpected ignition, so you want to let that wire cool down.

Approach the rocket and inspect it. Are the clips still in place? Did the igniter fall out? If those aren't the problems, remove the clips and take the rocket off the pad, and flip it over. The igniter wires should not be touching each other. They're not insulated on Estes igniters, so if they're touching, you have a short circuit. You can simply spread the wires apart slightly, or use a new igniter.

Here, the igniter wires are touching each other. That's a short circuit - the current won't go all the way to the tip of the
igniter, where it's in contact with the propellant. Try spreading these apart and re-installing the igniter.

If that's not the problem, your igniter probably isn't touching the propellant. Pull it out of the nozzle and look at it. If the igniter is still intact, re-insert it into the nozzle, making sure it touches the propellant, then reinstall the plug, hook everything back up, and do your countdown again. It will probably work. If not, then just install a new igniter.


Once the rocket has left the pad, while you've got your eye on it, remove the safety key by feel. This isn't hard. The Estes controllers now have a spring-loaded key which pretty much pops out on its own when you're not pressing it down.

Watch the rocket ascend into the sky. Once the burn, or powered flight, is over, it will keep going up. It goes further just by coasting than it does during the burn time! The delay charge will leave a trail of white smoke which will help you keep your eye on the rocket. Smaller rockets are really easy to lose sight of!

When the rocket is at or near apogee, assuming you've installed the correct motor, the ejection charge should go off, and the nose cone and parachute will pop out. If you used a ton of baby powder, there may even be a puff of white "smoke."

The parachute should open and the rocket will slowly descend to the ground. Keep your eyes on it. Don't trip while you follow it! Let it come down to the ground. Don't try to catch it. You want to examine how it performed once it hit the ground, and besides, you can accidentally damage a rocket by catching it, if you trip, or grip it too hard.

Chad loves to catch rockets. He's like a golden retriever. It's fun to watch. But not best practices, according to most rocketeers.

Now, if the rocket gets hung up on a power line, forget it. It's gone. Don't try to get it back. But hopefully the majority of your rockets will not land in trees, power lines, roofs, etc. The goal is to get them back safely.

Most of your flights will go just great. Sometimes a parachute won't deploy, or the rocket will behave oddly, or it won't lift off at all. Figuring out what the problem is and correcting it is part of the fun, actually. Analyzing a crash is kind of fun. Of course, that sometimes means you need to repair (or completely trash) a rocket, but even when things go wrong, rocketry is awesome. After your first launch, you'll want to do a lot more.

Here's a successful launch of my Estes Cosmic Explorer, from liftoff to touchdown, plus a slo-mo replay of the liftoff:

Launching Your First Rocket (For N00bs)

Let's assume you've got a rocket. Maybe you built your first Skill Level 1 rocket, like the Big Bertha, or maybe you have a Ready-To-Fly or E2X (Estes' term for "easy to assemble") rocket. In any case, it's time to launch this sucker.

This post will be long, so I'm breaking it into two parts. I don't want you to think it's really complicated, or that launching a rocket takes a long time - it doesn't. But there are some details you need to get right to have a successful, safe, awesome rocket launch, and I don't want to leave anything out.

Rocket Flight

Here's basically what'll happen. You'll load up the rocket, put it on the launch pad, hook up the launch controller, press the launch button, and it should take off into the sky. The motor (or engine) will burn for a second or two (this phase is known as powered flight), and when it stops burning, the rocket will continue to coast upward. You'll see white smoke coming from the back of the rocket for several seconds as it does; this is the delay charge burning. The delay produces no thrust, but it allows the rocket to coast up to its apogee - the uppermost part of its flight. Then, the motor will fire the ejection charge - a tiny explosion that will push the nose cone off and eject the parachute. The parachute should open, and the rocket will drift back to earth.

What are you going to need?

Here are the basics:

• A rocket
• A launch pad - with a launch rod
• A launch controller
• Some rocket motors - or, as Estes and many people call them, engines
• Some igniters - these usually come with motors or engines, so you shouldn't need to buy any
• Some recovery wadding
• Something to carry all this stuff

What is this stuff?

Well, as I've recommended in the previous post, you might want to get launch kit. You can get a basic Estes kit - or Quest - which will have the launch pad and rod, the launch controller, and a rocket for less than you'd pay for the pad and controller plus no rocket at all, if you'd bought them separately.

An Estes launch pad - with a round metal
blast deflector and a 33-inch launch rod. The
cap at the top of the rod comes off - it's to prevent you
gouging your eyes out when prepping the rocket!

A launch pad comes with a metal disk called a "blast deflector," and it's not optional! This will deflect the hot gasses and burning propellant away from the ground, and protect the plastic from melting.

The launch rod is usually about 3 feet long. The purpose of the rod has to do with rocket stability. The only thing keeping the rocket going upward instead of straight at the crowd is the fins. And for the fins to work, the rocket has to be moving upward, so there's wind moving past them. The launch rod keeps the rocket moving straight up until it is going fast enough - at least 30 miles per hour - for the fins to do their job. With model rockets, it takes only a fraction of a second to reach that velocity or much higher, so a 3-foot rod is usually plenty.

The Estes rods are 33 inches - close enough - and come in two parts which you have to push together. There's a narrow, curved bit of metal shoulder material in one half of the rod which you push into a hollow onto the other half. I found I had to crimp mine with pliers to get the halves together.

Tap one end of the rod on a concrete surface to get the pieces completely together - but don't try to hammer them. The rod will bend, and if that happens, you need a new rod!

Estes recommends using sand paper to smooth out the joint between the rods. Don't do this. What happened when I did this was that I scuffed the chrome coating off the rod, making it rougher! You could try some steel wool, but honestly, unless the joint is way off, you'll be fine.

The rod gets inserted into a little hole in the top of the launch pad. There's a little safety cap included which you place on top of the rod when you're not actually launching a rocket - this is to prevent you bending over the rod and gouging your eyes out. I've mentioned that rocketry has a great safety record - I read once that the most dangerous thing about launching rockets is that rod!

Arr! Don't be the guy who loses an eye launching rockets!

The launch controller is a plastic box with a button, a light, and a removable "key" - usually a bit of wire or metal with a plastic button on top of it - and a couple of wires coming out one end with little clips on the ends of them. The controller takes batteries, and it ignites the motors electrically. The key is a safety feature. Once you hook the rocket up, you cannot launch it accidentally by hitting the launch button with your thumb, because you have to put the key in the launch controller and press it down before it will work.

The light is known as a continuity light, and when you hook up the rocket igniters to the launch controller, and put in the key, this will light up. It tells you that electricity is flowing through the system, the batteries are good, and the igniters are not broken.

Typical Estes launch controller, from Chris Michielssen's
modelrocketbuilding.blogspot.com. If you haven't seen his
blog, you need to check it out!

The launch button... uh, launches the rocket.

***I do have to say something important here, in case you are not going strictly the Estes route for your first rocket launch. Currently, Quest motors and igniters are out of stock, but once Quest motors are back out again, this is very important: You cannot use an Estes launch controller with Quest igniters. Quest makes a very sensitive igniter. They require very little current to flow through them to actually cause them to fire - which is a good thing, for certain applications. But an Estes launch controller doesn't have enough resistance in it, and as soon as you put the safety key into the Estes launch controller, instead of just the continuity light coming on, a Quest igniter will get enough juice to fire prematurely. If there's someone at the launch pad making an adjustment, that can be dangerous!***

A rocket motor is a heavy paper cylinder  which encases a solid propellant - in this case, black powder. One end has a little hole in it - the nozzle - and the other end has a clay cap in it.

A typical 3-pack of black powder motors - in this case,
Estes B6-4. That's an average thrust of 6 Newtons
and a delay of 4 seconds.

The nozzle end - this sticks out the back of the rocket.

The clay cap end - goes into the rocket pointed toward the nose cone.
In A and B motors, this is further recessed into the motor, because
there's less propellant inside.

(If you don't see a clay cap, and instead see the dark black powder in the non-nozzle end, look at the side of the motor. Is the last number a 0? Then you have a special motor used only for the first stage of multistage rockets. Put that away for now - we'll get to those later. For now, it's definitely not what you need!)

The motor on the left has no clay cap - you can see the black powder propellant. This is
only for multistage rockets. Put that one away for now. We'll do staging later!

Rockets for beginners come in three basic classes - A, B, and C. The basic explanation of this is that each letter class is roughly twice as powerful as the previous one. C is twice as powerful as B, and four times as powerful as A. They are described by a letter and two numbers. The first is average thrust, and the second, after the dash, is the delay time, which is the time between when the motor stops burning propellant and the ejection charge going off. So, a C6-5 motor has an average thrust of 6 Newtons, and a delay time of 5 seconds. A Newton is about 0.225 pounds.

Your first rocket will come with a list of recommended motors to use. Read these. First time I launched the Big Bertha, it was kind of windy, and I didn't want to lose my beautiful new rocket. So, I put an A motor in it.

Problem is, the Bertha is kind of heavy. An A8-3 motor doesn't have enough power to properly lift it. It flew about 30-50 feet into the air, took a nose dive, and straight down for 3 seconds (that was the delay time!). The nose cone ejected about 5 feet from the ground, and the rocket drove itself into the damp earth.

The fancy, homemade launch controller makes me look like an "expert,"
but the crash landing goes to show that I'm still kind of a n00b.

I thought I knew what I was doing, but hadn't realized that the A8-3 is not on the list of recommended motors for this rocket! The weakest motor for the Bertha is a B-something. Oops!

There will be a list of appropriate motors with your rocket. There's usually one with an asterisk (often the least powerful one) that says "first flight." This is so that, if, say, it's windy, you're less likely to lose the rocket when the parachute drifts too far, or if you made some kind of catastrophic error in the construction of your rocket, the damage will be minimal.


The igniter is a little wire thing that comes with the motors. It's usually made of high-resistance nichrome wire. The resistance is important, because when electricity flows through a high-resistance wire, the wire heats up. This happens in an incandescent light bulb, and in the wires of a toaster - which are also made of nichrome. Most Estes igniters are also tipped with a combustible material called pyrogen.

To igniters - you snip these apart before using them.

Motor packs include tiny plastic plugs for
securing igniters into the nozzle of the motor.

You insert the motor into the back of the rocket with the nozzle end - the little hole - pointing out the back of the rocket. Secure the motor with the motor hook (or sometimes you tape it in, if the kit instructions tell you to do that). The motor hook should lock into place once the motor is all the way in. Tug on the motor gently to make sure that when it moves backward, the hook holds it in firmly by the edge.

Now, pull out the nose cone, parachute and shock cord. You need to protect the parachute from the burning particles of the ejection charge, or it will melt together and won't open. Into the rocket body, you put recovery wadding. Tear off individual sheets, and roll them loosely into little wadded balls of paper - not too tight! The instructions on your kit will tell you how many pieces you'll need for your particular rocket. Put them one by one into the body of the rocket, and if you need to, push them down very gently with a dowel rod.

Picture from stormthecastle.com

Next, you need to fold the parachute and insert it and the shock cord into the rocket. There are lots of ways to fold parachutes, but some ways are better than others. Doing it by the instructions in the Estes kits is terrible - mine do not deploy at least 50% of the time when I do it this way. We're going to do it another way.

The Estes "fold over and roll both ends to the center"
technique - terrible. The shroud lines get tangled, and
the chutes often fail to deploy.

Plastic parachutes sometimes have problems deploying. This can be due to static electricity, or cold, or bad folding. In any case, you'll help the parachute properly deploy if you give it a few dashes of talcum powder or baby powder.

I prep my rockets before going to the flying field by laying the parachute open on a table. 

The Big Bertha 18-inch parachute ready for prep

I sprinkle a bit of baby powder on the underside of the parachute and lightly spread it around so it coats the whole chute. 

Sprinkle a little baby powder or talcum on the chute to aid deployment

Next, fold the chute in half, with two of the corners being at the top of the fold. Now you'll have half a hexagon, with four corners showing - two at the top and two at the bottom.

Take one of the top corners and fold it down to the bottom corner on the opposite side. Then do the same for the other top corner. You now have a triangle, with all the shroud lines - the strings on the parachute - coming off the two corners at the bottom.

Fold one of the top corners down to the opposite bottom corner - in this case, top right to bottom left.

Then do the same for the opposite top corner - here, top left to bottom right. You now
have a triangle with shroud lines coming from the bottom two corners.

Fold the parachute in half so that all the shroud lines are together. Now, you'll have a scalene triangle, with all the shroud lines coming out the bottom.

Take most of the extra slack that leads from the parachute to the nose cone and gently lay it on top of the parachute.

Gently lay the slack from the shroud lines on top of the folded parachute.

Fold that outside corner over the shroud lines, then fold the top corner down about a third of the way, then fold what you have down again.

Fold that outside corner over the shroud lines

Fold the top third of the parachute down.

Fold that down over the bottom third.

Next, roll the whole thing up into a little packet and gently wrap whatever is left of the shroud lines around the parachute into a helical shape, making sure you don't cross over what you've already rolled.

Roll the folded chute down into a sausage shape

Wrap the shroud lines in one bundle around the chute, moving from one end to another, in a helix.
Don't cross lines back over what you've already rolled!

Once this is done, you stuff the parachute and shock cord into the rocket. Some say you should put the shock cord in first - which is probably better. Some say the shock cord goes on top. It probably doesn't matter a ton, and in some small-diameter rockets, it's hard to get that shock cord in there - it's just rubbery enough that it doesn't want to go in on its own unless you're pushing it, and that's hard to do when you've got your rocket in one hand and a perfectly-rolled parachute in another. If I can't get the cord in first, I stuff in the chute, then pack the cord on top. I've rarely had a deployment problem with this.

The shock cord in a larger rocket like the Big Bertha goes in quite easily - put that in first.

Put the nose cone on top, and make sure it's snug, but not tight. You should be able to easily pull it out with your hand, but it shouldn't be so loose it falls out if you turn the rocket over and give a little shake. If it's too loose, add a little strip of masking tape to the shoulder. If it's too tight, sand the shoulder down a little bit.

The nose cone of my Cosmic Explorer is just a little too loose. A few
bits of masking tape makes it snug enough to fly.

You then insert the igniter into the nozzle of the motor, making sure it touches the propellant inside. It doesn't have to go very far, and you don't need to force it. Just set the tip of the igniter gently into the nozzle until it stops.

Don't insert the igniter until it's in the rocket and at the launch pad!I'm just doing it on the table here for the purpose of taking pictures.

Next, you'll secure the igniter into the nozzle with either a little plastic plug that comes with the motor (in the case of Estes motors), or with a piece of masking tape. Either way, this will bend the igniter's leads into a 90 degree angle. Make sure the two wires leading into the nozzle don't touch each other - this creates a short circuit, which means that when you press the launch button, nothing will happen.

Now, you'll bend the ends of the igniter wires away from each other. You can bend them into little rabbit-ear loops, or simply bend them away from each other at a wide angle. The rabbit ears are easier to connect to the clips, but as long as the two wire leads aren't near each other, you'll be fine.

The rocket is now prepped for flight.

In Part 2, we'll launch the sucker!

[Click here for Part 2]