New rocket ignition.

[Verge]

Hi everyone,

I recently got an idea of igniting a core rocket from the top.This should help get more thrust because the top ignites everything below it.I'm planning to plaster a wire in the top.I have to plaster since compacting a clay would make everything hard.When ready I hook up the ignition system.I have two questions.The first one is semi opinion based.Will I get more perform(faster lift off,etc.) doing this and how can I make the ignition system fall away reliably?

Edited July 14, 2011 by Vergeltungswaffe

[stckmndn]

Why not just run a fast paper fuse all the way up the core? It lights the whole core at once and gives a faster lift off. Easy peasy.

[TigerTail]

I think it should work the same even without fast paper fuse all the way up into the core. Fire travels up a core really very fast on its own. Also, whatever you plan to do from the top can simply be executed from the bottom, isn't it? Edited July 14, 2011 by TigerTail

[Verge]

I think it should work the same even without fast paper fuse all the way up into the core. Fire travels up a core really very fast. Also, whatever you plan to do from the top can simply be executed from the bottom, isn't it?

 

I was thinking since the thrust flows down faster than upwards it would burn more evenly.The paper fast fuse would also leave paper in the motor and therefore would not leave an even burn.Also at that moment I don't have paper fast fuse since I usually do everything elecltric.I recently made my first BM.

[TigerTail]

How about inserting an e-match all the way up into the core so it ignites the top first? But I still feel it shouldn't make any noticeable difference. I might be wrong.

[stckmndn]

I was thinking since the thrust flows down faster than upwards it would burn more evenly.The paper fast fuse would also leave paper in the motor and therefore would not leave an even burn.Also at that moment I don't have paper fast fuse since I usually do everything elecltric.I recently made my first BM.

 

A quick paper fuse (see Cannonfuse) burns at .50 seconds per foot. And it burns very hot and completely (no paper left). Your core will be lit in less than .25 seconds. Doubtful your method can improve upon that but give it a shot. Just seems like unnecessary work.

 

I light most of my 1 lb core burners with headers this way.

[Verge]

A quick paper fuse (see Cannonfuse) burns at .50 seconds per foot. And it burns very hot and completely (no paper left). Your core will be lit in less than .25 seconds. Doubtful your method can improve upon that but give it a shot. Just seems like unnecessary work.

 

I light most of my 1 lb core burners with headers this way.

 

Ok thx

[dagabu]

The time and trouble that it would take to top light a rocket motor with an embedded wire would undo any benefit. Quick paper fuse is fine as is an e-match, I top light with fast paper fuse (1/8" three stand type) that I run through a hand rolled tube to the top of the fuel grain.

 

Be careful as the initial thrust curve is significantly sharper then bottom lighting and can cause CATOs even in mild fueled motors. I am focusing on nozzleless motors now and find that a J hook with cheap green Chinese Visco works well as does a side wall piercing with the fuse just touching the end of the fuel grain. They sit and stew for a few seconds before lifting off, they are real pretty!

 

-dag

[stckmndn]

Yep, if the fuel is too hot this may not work. I've had a fuel so slow before, the rocket lifted about two feet and hovered for a second or two before taking off.

 

Right now I have 8 different motors with different fuel mixtures ready to test using both the J hooked fuse and the full core fuse. There should be a CATO or two in the bunch.

[dagabu]

Yep, if the fuel is too hot this may not work. I've had a fuel so slow before, the rocket lifted about two feet and hovered for a second or two before taking off.

 

Right now I have 8 different motors with different fuel mixtures ready to test using both the J hooked fuse and the full core fuse. There should be a CATO or two in the bunch.

 

Video? Please?

 

-dag

[stckmndn]

I'll see what I can do.

 

Dan

[r1dermon]

you should ignite your core burning rockets from the head end...the forward most part of the core. do not ignite your core burners at the nozzle end. if you are achieving success with this method, it's only because you're not using a very large header...your rocket motor is running very inefficiently and is wasting propellent. chances are good that your rocket motor could lift several times what it will when lit at the head end, as opposed to the nozzle end, as well as utilize more energy stored in your propellent rather than chuff them off.

 

if you consistently ignite your core burners from the head end, you'll notice a marked improvement over aft end ignition in regards to initial thrust, as well as total thrust. you'll lift higher payloads with the same amount of powder, and they'll travel further.

 

one other problem which occurs is your nozzle "choke" fails to occur, or occurs with less than adequite chamber pressure. when the motor pressure in the plenum reaches twice the ambient pressure (atmosphere, assuming you're burning your motor outside), the flow rate through the throat of the nozzle will accelerate to sonic velocity. mass flow through the divergent section is constant for a given chamber pressure. you can manipulate chamber pressure by changing your core:nozzle throat ratio. a larger core and a smaller nozzle throat=a higher chamber pressure.

 

anyway, hope this helps.

 

i wont get into expansion ratio's, since they're kind of impractical for fireworks use...basically when the ambient pressure is matched by the exit pressure, you achieve the highest thrust theoretically. you can manipulate this by tailoring your throat diameter and your exit size to a respective ratio which will allow you to match the parameters you're looking to. you can also calculate chamber pressure based on those numbers.

 

 

....anyway....

[dagabu]

That may be true of a slow fuel and a very strong tube but there is a very wide variety of tubes, fuels, missions that rockets may partake of.

 

Using a 3# rocket to lift a 4" shell, I want the height to not exceed 400" so I dump the fuel by end fusing and going nozzleless. Very pretty!

 

Using whistle fuel, you HAVE TO end light the fuel grain, there is no way you can fuse them differently without a CATO. They are known to travel well in excess of a mile, so much for having to use a nozzle.

 

Each fuel, each tube, each mission takes a different fusing method, there is simply no "one size fits all".

 

-dag

[stckmndn]

While clearly my method is the superior one, I too will try some tests lighting from the top of the core.

 

 

 

JUST A JOKE, GUYS.

[r1dermon]

that may be true, but that's indicative of an inefficient rocket motor. you could build a smaller motor and light it head end, for what you get with a larger motor lit near the nozzle. the reason your motor sits on the pad for a few seconds is because it takes a while for hot gasses to propogate forward through the core...lighting from the nozzle end is just inefficient. basically what im saying is that, if you're using a 1lb rocket to lift something 400', and it's a core burner, and you're lighting it at the nozzle end, you could actually make a smaller motor and use less propellent, but achieve the same or better results by lighting it at the head end. you'll also be able to lift much heavier payloads per gram of propellent, since it'll be achieving optimal efficiency. if your core burning rocket CATO's when lit "head end", the parameters need to be redesigned. it's not the ignition method that CATO's the rocket, its the surface area:nozzle throat diameter being too large...the point of me saying all this, is that while what your doing may work reliably...there is a more efficient way of doing it...but whatever works for you is good to go in my book. just realize that you could be lifting larger payloads by simply igniting your rockets from the head end, and if they CATO, by redesigning the core or nozzle. have a nice day.

 

and post some vids of your rockets!

[dagabu]

Have you considered holding a stick match to the top of the core? (A really bad joke)

 

-dag

[stckmndn]

You talkin' to me?

[r1dermon]

While clearly my method is the superior one, I too will try some tests lighting from the top of the core.

 

 

 

JUST A JOKE, GUYS.

 

if you could do some tests with both ignition methods, that'd be awesome. you can make a simple stand out of wood and place it on a scale...it's a crude way to measure thrust but it will give you a general idea. have fun!

[Verge]

Do you guys think it would make a difference lighting the farthest part of the core using electric or e-match? Edited July 14, 2011 by Vergeltungswaffe

[dagabu]

Yes, lighting the top of the core results in an immediate pressure spike and will result in a very fast lift off or a very short flight (BOOM!). E-match works well for lighting them, just take the shield off (pull it back) and tape the e-match to the launch tube, that way it cannot foul the hole.

 

-dag

[stckmndn]

if you could do some tests with both ignition methods, that'd be awesome. you can make a simple stand out of wood and place it on a scale...it's a crude way to measure thrust but it will give you a general idea. have fun!

 

No worries. My measurements will be crude. But what a fun topic.

 

Of course performance is relative to what one is trying to accomplish. Do you want the most thrust and height? Or do you want to deliver a payload on time every time to a certain height?

 

That's why I like to make "high performance" rockets aside from my payload lifters. I put a 10 gram salute on top, shorten the stick, and use hotter fuel. These are often the favorites of the kids.

[Verge]

Yes, lighting the top of the core results in an immediate pressure spike and will result in a very fast lift off or a very short flight (BOOM!). E-match works well for lighting them, just take the shield off (pull it back) and tape the e-match to the launch tube, that way it cannot foul the hole.

 

-dag

 

Do the matches have to be the red heads or can they be white?

[Verge]

No worries. My measurements will be crude. But what a fun topic.

 

Of course performance is relative to what one is trying to accomplish. Do you want the most thrust and height? Or do you want to deliver a payload on time every time to a certain height?

 

That's why I like to make "high performance" rockets aside from my payload lifters. I put a 10 gram salute on top, shorten the stick, and use hotter fuel. These are often the favorites of the kids.

 

Right now I'm focused on having the rockets go fast and high.I'm not trying to time anything.

[r1dermon]

Yes, lighting the top of the core results in an immediate pressure spike and will result in a very fast lift off or a very short flight (BOOM!). E-match works well for lighting them, just take the shield off (pull it back) and tape the e-match to the launch tube, that way it cannot foul the hole.

 

-dag

 

if your rocket CATO's, it needs a smaller core, or a larger nozzle throat. your efficiency is dramatically increased however. then when your 4" shell breaks at 800', you can reduce the size of your motor and save yourself a considerable amount of fuel.

[dagabu]

Do the matches have to be the red heads or can they be white?

 

The white "strike anywhere ones

 

-dag