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Talk to me about end burners

stckmndn

By stckmndn
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stckmndn Newbie

stckmndn

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Since I already have 1 lb tubes for my core burners - may as well look into some end burner tooling for variety.

 

Aside from girandolas and wheels what is the point of end burners? They're not really about lifting payloads, right?

 

Do they fly much higher than core burners?

 

 

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dagabu Newbie

dagabu

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Since I already have 1 lb tubes for my core burners - may as well look into some end burner tooling for variety.

 

Aside from girandolas and wheels what is the point of end burners? They're not really about lifting payloads, right?

 

Do they fly much higher than core burners?

 

 

 

Me and my boy just cam in from making 1/4" ID end burners 2" long and fused with a single strand of the blue quick match. It burned for about 5 seconds and went up about 300'. Almost silent in flight and with the huge heading of three dragon eggs, it made for a very pleasant afternoon distraction. I dont even go to the shop to make them, just an ounce of BP, hammer, tooling and some clay (and a green dragon egg dismantled from the fireworks stand) make about 6 of these little rockets. Also, I use the really thin skewers from the dollar store for sticks.

 

-dag

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stckmndn Newbie

stckmndn

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That's what I was looking for.

 

This is a pretty impractical hobby for me as far as lighting off shells and rockets with headers goes. But, it's pretty easy to fire off a rocket or two during the day without attracting much attention. And I get a kick out of it.

 

Recently MadMax put up some pictures in his gallery of his finned rockets and I'm very interested in looking into doing that. Check them out. They look awesome.

 

So, how high would a 1 lb "super bp design" end burner fly? And I would imagine a 10 gr salute wouldn't cause it much of a problem, would it?

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mabuse00 Newbie

mabuse00

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So, how high would a 1 lb "super bp design" end burner fly? And I would imagine a 10 gr salute wouldn't cause it much of a problem, would it?

Considering the weight of the motor alone 10g is nothing.

 

Do they fly much higher than core burners?

If you compare endburner and coreburner with an equal amount of fuel and payload I would assume that the endburner has a better range, as it is slower and thus suffers less from drag than the fast endburner.

If you drive a car with 80 km/h the range with a certain amount of fuel will be greater than with 200km/h.

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stckmndn Newbie

stckmndn

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You got me. It's Firesmith.

 

It uses the more aggressive De Laval nozzle geometry.

 

Would you be interested in making me a 1 lb set based on the NEPT tubes?

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dagabu Newbie

dagabu

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Sure, Brass, Stainless Steel or Aluminum spindle? Contact me off APC please, coldfire11@msn.com for pricing.

 

-dag

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drthrust Newbie

drthrust

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i know its all about increasing exhaust gas velocity for extra thrust, but is there much gain in such a small/simple motor by changing the nozzle design?

re: end burners v core burners , its all about the thrust babe!, end burners have an initial burst of power to get them off the pad ^_^ then a constant steady burn as only the end of the propellant grain is exposed to the flame front giving a longer burn time thus more height.

 

 

where your core burner is built for thrust babe!, now this is the fun bit, with the extra surface area of the propellant created by the core this = more fuel available which = more thrust, and as the motor burns the surface area of the core increases, exposing an even greater surface area of propellant so the motor throttles up throughout the burn!

so you only really need a core burner if your planning to carry heavy payloads, the heavier the payload the more thrust needed, my mate newton told me that

your finned rocket project sounds fun, good luck with it

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stckmndn Newbie

stckmndn

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Hi DrThrust,

 

The end burners are just for fun near town when I need to satisfy my rocket fix in a more discreet way.

 

My passion is core burners with payloads. :)

 

 

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dagabu Newbie

dagabu

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end burners have an initial burst of power to get them off the pad ^_^ then a constant steady burn as only the end of the propellant grain is exposed to the flame front giving a longer burn time thus more height.

 

Current endburner tooling has no or little throat and have no initial burst of power. The grain must burn a small conical space in the grain that allows for the initial thrust that gets the rocket off the pad. The thrust curve settles down some as the face (front) burns flatter and flatter as the burn progresses allowing for an extremely flat thrust curve about half way through the fuel grain.

 

i know its all about increasing exhaust gas velocity for extra thrust, but is there much gain in such a small/simple motor by changing the nozzle design?

 

Not really, the nozzle in the endburner will not take advantage of the de Laval design the way it is meant to be so actually in the role as an end burner, a modified de Laval straight walled design gives better performance then the actual bell shape of the de Laval design. The bell shape actually slows the rocket gasses as a greater back pressure is realized at the slower gas rate that occurs from endburner configurations.

"The aim of the De Laval nozzle is to produce supersonic flow by reducing the exit pressure well below . We consider a flow where the cross-sectional area changes slowly so that the flow can be considered one-dimensional."

-Landau & Lifshitz; Fluid Mechanics-

 

The amount of fuel dumped in such a short time as happens with core burning rocket motors like hybrid or whistle rockets seem to be the more likely rockets to see a huge thrust magnification from the use of the de Laval design.

 

-dag

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dan999ification Newbie

dan999ification

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if its a quick fix your after you cant go wrong with small endburners my 10mm id can take up 30g headers and one can be made in less than an hour with no real tooling, im working on 19mm id motors next and i think they should push 50-70g we'll see im also going to incorparate a de la val type nozzle on the inside not for performance but to spare the inner walls.

no real experience with the cored rockets but it's a fact you can lift bigger headers. the advantage of endburners for me is that i can adjust the burn time quite easilly 4.5g bp in 9 increments gives me about 2.5 seconds adding more fuel and increments would make it longer and theoretically higher until you reach the point of diminishing returns and you have lawn darts.

 

im still waiting to try finned endburners and my reckoning is that 10mm id will carry 40g without the stick, however may have trouble getting up off of the pad with the lower thrust as opposed to cored and finned.

 

dan.

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Adrenaline Newbie

Adrenaline

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I thought about buliding 19mm end burners with playload, too. It would be great if they could push 60g so one could use 2" can shells as a header.

Has anyone in here ever built end burners with such headers? ( My desired fuel would be sugar/KNO3 )

Some input would be great.

 

 

thanks,

Adrenaline

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stckmndn Newbie

stckmndn

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A few questions in anticipation of receiving the tooling. Wouldn't it be nice if my first end burner didn't CATO...

 

So I've read these use 75/15/10 milled meal dust. Check. My meal is very hot, as it should be. I've also read about people using 5" and 7.5" tubes. Is there any particular reason other than preference for this? For instance, I'll be using the thin walled NEPT tubes to begin with. Would using a shorter motor lessen the chances of burn through or CATO as opposed to using the 7.5" motor? Do these come down really hot?

 

And penultimately, the stick(s). Size and length? My core burners are using 3/8" sticks anywhere from 28" to 36" in length. What's a good size for an end burner? One stick or two smaller sticks?

 

Lastly, fusing. Just stick a piece of visco in it?

 

Thanks.

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dagabu Newbie

dagabu

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A few questions in anticipation of receiving the tooling. Wouldn't it be nice if my first end burner didn't CATO...

 

So I've read these use 75/15/10 milled meal dust. Check. My meal is very hot, as it should be. I've also read about people using 5" and 7.5" tubes. Is there any particular reason other than preference for this? For instance, I'll be using the thin walled NEPT tubes to begin with. Would using a shorter motor lessen the chances of burn through or CATO as opposed to using the 7.5" motor? Do these come down really hot?

 

And penultimately, the stick(s). Size and length? My core burners are using 3/8" sticks anywhere from 28" to 36" in length. What's a good size for an end burner? One stick or two smaller sticks?

 

Lastly, fusing. Just stick a piece of visco in it?

 

Thanks.

 

Yup, the longer the motor, the more likely that the tube will burn through. The same holds true with those that dont use convergence on their nozzle rammer. Use a stick long enough to stabilize the rocket in flight, some say a stick x6 longer then the motor and 1/2 the ID of the motor. I find that I can significantly reduce the stick length and/or use two short sticks to accomplish the same thing.

 

It will be tight to J hook a piece of visco but that is what i prefer for lighting rockets.

 

-dag

Edited by dagabu
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r1dermon Newbie

r1dermon

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Considering the weight of the motor alone 10g is nothing.

 

 

If you compare endburner and coreburner with an equal amount of fuel and payload I would assume that the endburner has a better range, as it is slower and thus suffers less from drag than the fast endburner.

If you drive a car with 80 km/h the range with a certain amount of fuel will be greater than with 200km/h.

 

true, however it is also slower off the pad, and much less efficient. a considerable amount of propellent is burned before even attaining stable flight speed, whereas with a core burner, it attains a stable flight speed much more rapidly given a rocket of the same weight. there's a happy medium between mass and average thrust, however, the most efficient altitude rockets i've found to be core burners with some mass to them. upon motor burnout, they continue climbing skyward due to their momentum. staying subsonic is also a factor in attaining maximum altitude per Ns of energy.

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stckmndn Newbie

stckmndn

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OK then. Would an end burner make a good second stage coming off a core burner rocket?

 

I hope to make some videos for comparison between the end burners and core burners. That is, once we get some rain. My 4th was much like Thunderboy's.

 

Also, if my 75/15/10 mix causes a CATO, how should it be dialed back?

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r1dermon Newbie

r1dermon

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it depends on the application. an end burner would make a fine rocket even off the pad, it's just not as efficient as a core burner, therefore, assuming optimal rocket design for either motor choice, the core burner rocket is going to actually go higher and use less propellant for it's given height. it's a matter of efficiency. it'd be like asking if a truck is better than a car...they both will work to get you from point A to point B, but one will get you to point B a lot more efficiently, and still have gas in the tank to go a bit further.
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dagabu Newbie

dagabu

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OK then. Would an end burner make a good second stage coming off a core burner rocket?

 

I hope to make some videos for comparison between the end burners and core burners. That is, once we get some rain. My 4th was much like Thunderboy's.

 

Also, if my 75/15/10 mix causes a CATO, how should it be dialed back?

 

Yes, an end burner is an excellent sustainer motor for dual stage rockets. They are hard to CATO and travel for quite a distance due to the initial speed that the booster rocket has reached. Go for it, you will have fun!

 

-dag

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