Wednesday, December 17, 2014

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:


  1. Back in the day, we used clothes pins to a) attach to the launch rod to keep the rocket up a couple inches off the blast deflector, and b) another one to clip the controller wires to either the blast deflector or to a launch pad leg, so that there was some slack in the controller wires & alligator clips, and so you didn't accidentally yank out the igniter when you were straightening out the controller wires.

    I keep meaning to pick up some clothes pins at Michaels...not exactly the sexiest tool, so I keep forgetting them...


    1. My current launch pad is a camera tripod topped with a steel electric box cover, which has four little curved slots for screws. The slots are a good place to hold the controller wires, and I keep them in place, with slack, with a couple of binder clips. I'll put up a picture in a future post.