Ematch dipped in black powder or wrapped with cannon fuse?

[billdz]

At some launches I've seen an Aerotech igniter fail and the flyer did not have a spare igniter, but then he was able to launch the rocket by 1) dipping an ematch in glue and then rolling it in some black powder, or 2) wrapping some cannon fuse around the end of the ematch. Both techniques successfully launched the rockets I saw, but I'm wondering if these are good techniques. Wouldn't too much powder on the ematch potentially damage the motor?

 

[dhbarr]

You'd have to put a fair bit on to damage the motor. Many CTI loads, for instance, contain part of a small powder pellet in the top grain to help get things started.

 

[billdz]

You'd have to put a fair bit on to damage the motor. Many CTI loads, for instance, contain part of a small powder pellet in the top grain to help get things started.

How much powder, or what length of cannon fuse, would be recommended for an HPR motor?

My understanding is that CTI igniters (or at least most of them) are simply ematches, with the match igniting the powder pellet in the top grain, while Aerotech igniters cause the ignition themselves with their pyrogen coating.

The reason I'm asking about all this is that I have a cluster rocket with one 54mm hole and two 29mm. I have a CTI 54mm that I'd like to use along with two 29mm Aerotechs. I was thinking it would be better to use the same type of igniter in all 3 for a better chance of simultaneous ignition. Or doesn't it matter?

 

[mikec]

Mixing CTI and AT in a cluster may be problematic, because as a general rule CTI motors come up to pressure faster due to the BP pellet. Many people flying AT clusters use one of the dipped igniter products (e.g., Rocketflite ClusterFire) instead of the stock igniters, which require a fair amount of current. I haven't had much luck with ClusterFire myself for whatever reason (I think I have a hard time getting the consistency correct.)

Other options are pyrodex pellets, slivers of AT Blue Thunder propellant, etc.

The CTI stock igniter will almost certainly not ignite an AT motor, and using the AT igniter in a CTI motor won't help the problem.

 

[prfesser]

One possible solution would be to paint a stripe of pyrogen down the core of the topmost grain of the two 29mm motors. It could probably be a very simple pyrogen, i.e., a thick batter/thin paste of BP plus a little NC lacquer as is often used to boost Estes starters. With the pyrogen actually attached to the propellant, ignition is virtually assured as long as some part of the pyrogen ignites.

Or epoxy a strip (1/8" square x 1" long for 29 mm motors) of Blue Thunder or other easily-ignited propellant to the core of the top grain. One drop of epoxy on each end of the strip; we don't want the strip to fall off during ignition, nor do we want to coat the strip completely or it won't ignite.

 

[billdz]

Mixing CTI and AT in a cluster may be problematic, because as a general rule CTI motors come up to pressure faster due to the BP pellet. Many people flying AT clusters use one of the dipped igniter products (e.g., Rocketflite ClusterFire) instead of the stock igniters, which require a fair amount of current. I haven't had much luck with ClusterFire myself for whatever reason (I think I have a hard time getting the consistency correct.)

Other options are pyrodex pellets, slivers of AT Blue Thunder propellant, etc.

The CTI stock igniter will almost certainly not ignite an AT motor, and using the AT igniter in a CTI motor won't help the problem.

Good points. My particular CTI motor does not have a BP pellet, it has a pyrogen coated ematch. That's what led me to think about using a BP-dipped or cannon fused ematch for the Aerotech motors in the cluster, instead of the stock AT igniter, so that all 3 igniters would use ematch-based ignition.

 

[SharkWhisperer]

One possible solution would be to paint a stripe of pyrogen down the core of the topmost grain of the two 29mm motors. It could probably be a very simple pyrogen, i.e., a thick batter/thin paste of BP plus a little NC lacquer as is often used to boost Estes starters. With the pyrogen actually attached to the propellant, ignition is virtually assured as long as some part of the pyrogen ignites.

Or epoxy a strip (1/8" square x 1" long for 29 mm motors) of Blue Thunder or other easily-ignited propellant to the core of the top grain. One drop of epoxy on each end of the strip; we don't want the strip to fall off during ignition, nor do we want to coat the strip completely or it won't ignite.

Except a super hot FP-like pyrogen (which is absolutely suboptimal for motor grain ignition unless you like cracked propellant grains), if you've ever painted a typical NC lacquer/pyrogen mix in a stripe, even thickly, on a piece of foil or similar and ignited it after it dries, you will probably be surprised at precisely how slowly it burns in open air. And it by itself will generate little burn-rate-enhancing pressure even painted lengthwise inside the cored motor. Might start the motor, but not the way you're wanting to. NC films burn super slowly unless under high pressure (gun chamber pressures). BP will burn faster at either atmospheric pressure and noticeably faster at any pressure (hence utility as a fuel in lower pressure rocket motor tubes). Unless top-lighting, it's generally best to get a nice size of hot pyrogen in NC on igniter and ram it as far as possible upwards. If there's any question about igniter tip location, then drop some BP or perc-pyrogen (heated up with a little metal) up the core before inserting igniter. With enough amps and a suitable pyrogen, there's no reason why you can't coordinately fire-up clustered composites with similar timing reliability as with clustered BP motors. And apart from affording some protection in long-term storage, the pyro kits that use a plastic/acetone slurry instead of an NC/acetone slurry are in my opinion way inferior--the plastic coating actually inhibits flame transfer from they pyrogen and the containment can cause a potentially grain-splitting pop that is unnecessary with a super hot metal- and/or catalyst-enhanced pyrogen. I don't even bother as some do giving a final "protective" coating of NC lacquer alone. Though they'll work most of the time anyways if your pyrogen burns instantly and hot enough, those coatings and the associated "pop" from containment (and potential grain cracks) are not what you're aiming for. Unlike the ridiculous starter Estes setups (and silly plain-wire igniters), when I push that button, I expect immediate and efficient whole-core ignition. Simples.

 

[mikec]

FWIW, I've given up on clusters unless I can use all CTI motors with pellets, or use AT motors with pyrodex pellets, though many swear by various pyrogen mixtures. If you are using AT reloads you can at least get to the grain; it's tough to add something to a SU motor.

 

[cbrarick]

neither. Augmented igniters have little to do with cannon fuse or black powder. I like large 98 9 grain motors and have used several other augmentation strategies. Not certain this isn't EX domain forum, however.

 

[mikec]

i.e., a thick batter/thin paste of BP...

It's these food analogies that confused me with ClusterFire. The instructions say to make it the consistency of Hershey's Syrup, but even though I bought a small bottle of Hershey's to compare, I could never get the ClusterFire to match the thickness, and if it's too thick, it just pops and doesn't ignite (I guess.)

I never got consistent ignition on four-motor clusters of AT SU motors, but at least I had something to put on my ice cream.

 

[SharkWhisperer]

Unlike the unclear ClusterFire instructions regarding precisely when the acetone solvent is first introduced, if the two solid components are not intimately mixed before making a slurry, they certainly won't become intimately mixed afterwards afterwards. And settling metal (requiring continued remixing) is problematic with this concoction. This settling doesn't occur in a more appropriate lacquer/solvent, but that might entail more stringent shipping requirements, or a better "plasticizer". And it's the poorly-flammable "plastic" that makes it "pop". Although their metal selection does usually burn hot, I would use a much less reactive but super hot related metal alloy instead. The humidity restrictions are because acetone is very hygroscopic and will happily pull water from the atmosphere. Water can be problematic with their selected metal. And the plastic can trap that water inside the "dried" igniter comp. Water + oxidizer + metal = ?

This stuff sells for around $1/gram (citing 40g on package insert), when chem costs are about 3 cents per gram maximum, all-in (plus cost of plastic bottles and packaging). RocketFlite's got the right idea (as do several of their competitors), but that particular kit has material limitations.

And from a prior post, the idea of wrapping normal BP-based visco cannon fuse around an igniter will not be of any benefit in igniter "assistance", whatsoever. There exists a much faster white oxidizer-based grey visco fuse, too, but that would also need assistance to increase burn temperature and couldn't be used as suggested--trying to "wrap" it around an igniter would soon show itself to be an exercise in futility.

 

[billdz]

So gang, what's the verdict? Can I safely fly my rocket with the 54mm CTI motor (with pyrogen-coated ematch and no BP pellet) and 2 AT 29mm single use motors (with either the stock igniters, ematches dipped in black powder, or something else)?

Sounds like it would not help to substitute 29mm CTI motors, which would likely have the BP pellet.

 

[tfish]

are you igniting all the motors all at once on the ground?

If so, how does that rocket fly with just one of those 29mm motors? Once the first motor lites..the 54mm or one of the 29mm motors..the rocket might be head up and off the rail/rod. how long are your igniter leads.

I would not fly this combo without a intelligent flight computer. Ignite the center 54mm first and then bring on the 29mm motors.

Tony

 

[1MTRNTENF]

Exactly what motors are we talking about here? Most 54mm motors will take longer to come up to pressure than most 29mm motors.
The configuration of your cluster means that your rocket is at least 5" diameter. So will the 2 29's safely lift it?
It would be a much better bet if you had 4 or 6 29mm outboards. Then it wouldn't be an issue whether the 29's hit first or after the 54.
I agree with what tfish said.

 

[billdz]

OK, you've talked me out of trying this.

The rocket is a stock 5.5" LOC Magnum. I've always flown it with just one 54mm motor, with the two 29mm holes plugged. I wanted to fly it with a single CTI K160 54mm motor, but this is a long burn motor without sufficient initial thrust to get this rocket safely off the pad. So I had the idea of adding the two 29mm motors for additional boost at the start. But instead I'll just use the K160 with a lighter rocket.