So How Do You Get a G25 To Ignite?

[sandman]

I've heard a lot of comments on the G25 that it is "hard" to ignite.

OK, does anybody know how to get these things to fire?

I wasted 6 Copperheads yesterday and no ignition. I have some Quickburst "Twiggy" igniters but they don't seem to wanna go in more than 2" past the end of the nozzle. I don't think that's enough.

Any ideas?...could use a little help here! I can't get the motor out of the rocket so I have to fire it off.

OK I could get it out but I don't wanna...I wanna fire the rocket!

I have a small igniter about the size of the Quickburst Twiggy that won't go in more than 2" either.

I gently probed around inside the motor trying to "feel" the shape of the fuel grain but came up with no real answers.

Could I have something wrong with the motor? Could contiued trys at ignition only lead to a CATO?

sandman

 

[n3tjm]

As most of us have already figured out, G25 motors are notorious for being hard to ignite. It utilizes a moon grain core geometry, where it burns on the side of the motor. There is a small triangular ramp at the bottom of the core to “guide” the igniter into the slot on the side of the core. Since there is so little propellant surface area, and the fuel is White Lightning that has aged a bit, starting the G25 is a real chore. I personally started them with thin Magnelite igniters. The motor takes a while to start up, and makes a lot of noise. I have a video of rocket flown with a Magnelite started G25 on my November 3rd, 2001 video page (middle) that demonstrates this.

 

[sandman]

That is a strange configuration on the motor grain and my gentle probing confirms it.

Now just WHAT is a Magnelite Ignitor, and where do I get one?

sandman

 

[dluders]

Check out the Public Missiles Limited (PML) website for Magnelite Igniter Kits at
https://secure.consumersinterest.com/pml . Click on the "Igniters" link at the left side of that page.

PML has an online store. Their catalog says that "Once ignited, the pyrogen burns for approximately one second at a temperature around 6,400 degrees Fahrenheit!"

The 3/15/03 PML price list at https://secure.consumersinterest.com/pml/images/pmlprice.pdf lists the 12-wire ML-12 Magnelite Igniter Kit at $10.95. Check it out!

 

[n3tjm]

The Magnelite pyrogen itself is $22.95 from PML, and it lasts for ever. My current bottle that I use is over two years old. The ML-12 ($10.25 PML price) is the wires themselves. They come a dozzen per pack, and are worth the price. The wires are thin, and fit most composite motors (F20's and above), and have soldered bridge wires.

I also dip Crapperheads and Estes igniters in Magnelite pyrogen. This makes crapperheads more reliable, and Estes Igniters 100% reliable. I have also used those real thin wires from Firestar to make 100% reliable igniters for those small throat motors like D13's and F12's.

You can also buy them directly from Rocketflite, the manufacturer. They have great costumer service, and I have been buying from them for three years!

 

[rstaff3]

The Magnelite pyrogen works great on gapped wires dipped in conductive primer. One of the benefits here is you can make tiny ignitors.

You can also make your own bridge wires. In theory they should be soldered, but hand wire-wrapping works too.

 

[n3tjm]

I have an article on my website about igniters. I have included several interesting drawings and photographs. You may also be interested to see some videos of various igniters being fired.

 

[jflis]

For those of you who don't know what a "Moon Grain Core" or "Moon Burner" is, it is a grain design where the core is all the way on one side of the grain as opposed to the center.

The purpose of such a core is that, when burning from the edge in toward the center, the area of exposed, burning fuel (if it is designed properly) is constant throughout the entire burn. This has the effect of a very flat thrust curve.

See attached figure to see the progression of a moon burn (and you will see why it is called a "Moon Burner" or "Moon Grain".

A conventional core (hole through the center of the fuel) produces a continously climbing thrust ramp because as it burns from the inside out, the core is getting larger, resulting in a larger area of fuel buring, hence higher thrust.

ok, class is over, back to your regularly scheduled topic...

 

[rstaff3]

A true moon-burner is actiually regressive as you can see from the thrustcurve of the G25. C-slots are flatter, as are Bates grains.

 

[aadamson]

yea, least we educate the newcomers wrong...

The picture that is above is actually a C-Slot. A moon burner, would have a hole, with propellant all around it, like a bates grain or center core, but the hole would be towards the side and not in the center. It would run straight down the grain, it would just be drilled off center.

HOpe that helps,
Alan

I know of no AT reloads that are moon burners. All bates or c-slots.

 

[n3tjm]

Actually, I think Jim is right. Aerotech C4W, G25W, I65W, J90W, J125W, J180T*, J135W, K185W, and K250W are concidered by Aerotech to be Moon Grain motors. They are side burners, I don't think it is important how the core is made (round or square). What is important is all of these motors have the characteristic "Parabolic" thrust curve. C slots provide a "Half-Parabolic" thrust curve, Max thrust at begining.

* = I am not sure if the J180 is a moon grain or not.. I have never seen the instructions nor a reload for one.

 

[n3tjm]

Hmm...

I just looked at the thrust curve for a G25... it does look like a C-Slot curve. Core on the side, but still yeilds c-slot characteristics.

 

[rstaff3]

At least according to McCreary, the G25 actually looks like a moon-burner, not a c-slot. A c-slot ramps up as it burns, but not much. A moon-burner starts high and then ramps off, like the G25.

 

[KermieD]

In the Quickburst instructions that came with my stuff, they recommended slightly shaving the edges of the ignitor head to make it fit.

 

[LBarron]

Sandman,

I wish you had asked this question last year. I learned about the G-25's the hard way - months of work on a 1/70 scale Saturn V (see pic below) ended up in a pile when two of the three clustered motors misfired. A very sad day.

Good luck,
LB

 

[LBarron]

second try for the picture....

 

[sandman]

Man, I'm almost glad the pic didn't come out. I really don't wanna see a wrecked Saturn 1B!

I haven't built mine yet!

sandman

 

[LBarron]

Ok, the file is too big and I don't know how to adjust it so just pretend there's a 5 ft. Saturn V here.

Sorry.

 

[jflis]

LBarron,

Send the pix to me ([email protected]). I will reduce it and post it for you (or send it back for you to post). Photo evidence is **always** appreciated at TRF!

 

[jflis]

as for lighting a G25...

...seems to me a flare gun and a magnesium fire should do the trick...

 

[n3tjm]

Yeah... I bought one of Jim's G25's... I be practicing what I preach

 

[LBarron]

as for lighting a G25...

...seems to me a flare gun and a magnesium fire should do the trick...


__________________

now where was THAT info when i needed it!!

 

[LBarron]

here it is!

sorry, no crash pictures. didn't want to be reminded....