Friday, September 18, 2015

Igniter Tip - Q2G2's Keep Falling Out?


If you look at the comment section below, you'll see a few rocketeers have corrected my big dumb mistake here. Turns out, I was mis-reading the instructions for the Q2G2 igniter, and inserting it all wrong in the first place.

My initial reaction was to delete this post. But I've decided to leave it up for two reasons.

1 - It's a good example of a n00b mistake - not reading the directions.

2 - It's full of pretty pictures.

For the correct method of installing Q2G2 igniters, see this post by Chris Michielssen.

My apologies for not doing my homework!

. . . 

In May, I went to launch some rockets with Chad. I took along several I'd built but never flown before. It was breezy, and I lost a few. Against my better judgment, I put the Quest Quadrunner on the launch pad.

This beauty of a rocket from Quest Aerospace is a four-motor cluster capable of pretty high altitudes for a model rocket. It took me a long time and some heartache to build, but in the end it turned out really beautiful.

I installed four standard EC6-7 motors in the rocket. But clusters are tricky. The trick is getting all the motors to ignite at once. Estes motors (or "engines") all come with igniters, but they're not as reliable as you want for a cluster rocket.

There are a couple problems that prevent Estes igniters from being ideal for clusters. One is their size - they're pretty small and don't have much reach. But the main problem is that they require too much current.

Getting one Estes igniter to fire is one thing, but when you have the current from your launch controller split between two or more igniters, the total current reaching each igniter tip is less and less. What can then happen is that sometimes one motor might fire, and take the rocket with it, ripping out the other igniters before the other motors light.

Quest Aerospace has a much better igniter for this job. It's called the Q2G2 igniter.

These were off the market for a while, but they're back. The supply still can't quite meet the demand, but they are on the market.

Two things make this igniter much better for cluster rockets.

The first, is that the igniter has a black pyrogen on the tip.

This is a flammable substance. When the igniter tip heats up, the pyrogen creates a small flash or flame, aiding in the motor's ignition.

Estes igniters used to have a pyrogen, but they stopped making them like that in the last year. I still have a few, but I save them for special occasions.

But what makes the Q2G2 an even better igniter for cluster ignition is that they are low current igniters. That means it takes much less electric current to make the tips hot enough to ignite the rocket motors. You can send the same amount of current through several Q2G2 igniters as through one Estes igniter, and they will all fire pretty much simultaneously.

I put the Quadrunner on the pad, inserted the safety key into my launch controller, counted nervously down from 5, pressed the ignition button... And there was this loud puffing sound signifying ignition.

And then the rocket just sat there. Fortunately! I'm sure I would have lost it otherwise!

But what had happened?

As you can see in the above photos, the Q2G2 comes packed in a little red straw. This is actually what keeps the igniter installed in the motor before ignition. This is a different method than the plastic plug method seen in the Estes igniter photos.

Quest Q2G2 installed in an Estes C6-7 motor

I really like the straw method. It allows you to insert the igniter until you can really feel that it's in contact with the propellant.

I looked at the rocket. The Q2G2 igniters - all of them - had slipped downward a little inside their straws. The straws were blackened, and the puff of the pyrogen had actually ejected them from the nozzles of the rocket motors without igniting any of the propellant.

OK, so that saved me losing a beautiful rocket on its first flight.

On other occasions, I've used multiple Q2G2 igniters successfully, but only after fiddling around with them, then placing the rocket gingerly on the pad, hoping nothing would disturb the igniters before I pressed the launch button. Then I'd have to rush to launch the rocket before any of them fell out.

Rushing is not a good idea with rockets.

I've got a big launch coming up in a large field, and I'd love to see the Quadrunner finally take flight, and have a reliable ignition system securely in place.

If you've had trouble keeping your Q2G2 igniters staying in place, here's a way to prevent them falling out.

The problem isn't the straw. It fits into the nozzle of the rocket motor just fine. The problem is that the igniter itself can pass too easily through the straw, slipping out before you press the launch button.

Here's what you do:

Cut a very small bit of masking tape.

Wrap the masking tape around the twisted part of the Q2G2 igniter. You don't want to cover the pyrogen head, obviously, and you want to leave the free ends of the igniter free to bend them in whatever direction you need to to hook the leads up to the launch controller.

You want just enough masking tape around the twisted part of the igniter so that it can still pass all the way through the straw and come into contact with the propellant, but that it will have enough of a friction fit that it won't fall out.

Now the igniter is securely installed. Don't worry - it isn't "stuck." When the motor ignites, it will eject the straw and the igniter. But it will ensure you get reliable ignition on as many motors you have in your cluster rocket!

Note: These pictures are for illustration only. You should not install the igniters in your rocket motors until you are on the flying field, preparing for launch!

Edit: As Rich Holmes correctly points out, it's fine to install an igniter at home. It won't fire unless the launch controller is hooked up to it. What I should have said is that you should install the motor in the rocket first, then install the igniter.

Myself, I wait to install igniters until I'm at the pad. I transport my rockets in a big box full of newspaper, and I figure some of the igniters will fall out if I install them at home.

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  1. I've used Q2G2s only once so I'm no expert... but the Quest instructions don't have you running the igniter through the straw. Instead they tell you to insert the igniter in the motor, and then wedge the straw in between the igniter leads and the nozzle, much like an Estes plug. I did that and it worked fine.

    I do sometimes prep my black powder motors with igniters the night before a launch. Composites, though, I'll do only on the field, and high power motors only right at the pad. Not sure of the logic there but it's according to advice I've heard.

  2. Hi Daniel,
    Rich is right, the plastic straw goes to the sides of the igniter wire.
    The straw holds the igniter in the nozzle, sort of a friction fit.

    Others have had problems using the Q2G2s. I did a blog post about forming the straw tip for easier insertion:

    1. What?? You mean I've been doing this wrong the whole time?

      Here I was thinking this was a pretty great idea for a blog post, and it turns out I simply failed to read the instructions correctly.

  3. Your method works too, or sometimes I just hold in igniters with tape and no straw. Now what you really need is a post describing how to hold igniters at the top of a 75mm motor :-)

  4. Used these igniters, they are very good.
    It is a problem however: instructions say that it is essential that the black head to contact the propellant, and it is important that the igniter to be fixed in place using that straw or whatever.
    Anyway, there is the chance, even small, that the motor won't ignite, not because of igniter but because other causes.
    Imagine a booster attached to a rocket. If the ejection is towards its back (the motor or motor pod is going backwards, dragging parachute with it), and if the engine doesn't start, the assembly will be simply pulled out from the body when the rocket is launched (the other engines ignited) as long as the igniter is fixed in the nozzle. Possible that the force necessary do extract the motor be smaller than the force needed to disconnect the igniter from clips/wiring. That can be a catastrophe.
    In this situation, the igniter shall not be fixed in nozzle, just inserted, with the straw all around, not lateral, as in first pictures above.
    It is not necessary for the top pf igniter to contact the propellant, the straw will create kind of "guide" for fire (= jet) into the propellant. Several grains of BP added on top will help.
    Will this reduce the chances of (simultaneous) ignition? Perhaps, at least theoretically.
    In fact, practically it didn't happen so far.
    Igniters can be kept in correct position with a special support, Just insert this support into the nozzles, one time for all engines.