End Burner Problem

[Flaky234]

Hello,

 

I have a problem!

 

The nozzle of my end burners keeps blowing out.

 

I use standart 75/15/10 with willow charcoal and my nozzle mix is : 120g bentonite clay and 9g wax

 

I ramm everything with a small rubber mallet it weights: 350g

 

What is wrong with my set up??

 

The rocket has a 15mm id and the nozzle is 3-3.5mm wide! (commercial tooling)

 

I have ordered a 1.18kg wooden hammer, will this solve my problem and compact the clay better?

 

Thanks

[Bobosan]

Try again when you get your new hammer. Be sure to ram on a solid surface like concrete or solid post end.

 

The willow charcoal may be too hot. Try with commercial airfloat or hardwood charcoal.

 

If problems still occur, 60/30/10 is the normal rocket motor BP mix from what I read here on forum.

 

 

These are the initial steps I would take to isolate the problem you describe. Your new hammer will most likely be the cure.

Edited March 29, 2013 by Bobosan

[Flaky234]

Hi,

 

60/30/10 is for cored rockets not for end burners!

 

I just retry it with the new mallet and hope it works.... :/

[Mumbles]

It is essentially impossible to have BP too hot for an end burner. If someone tells you that theirs is, they're just not compressing it enough.

 

I'd think that the issue comes from the fact that your hammer is rubber and not heavy enough. They have too much bounce in my experience. I think all your problems will be solved with the new hammer.

[Flaky234]

Ok thanks!

 

Luckly this forum got an admin whichs knows what he is talking about^^

 

thx

[PyroCube]

Make shure that your tube isn`t too smooth on the inside. You better

make a rough surface on the nozzle part with a nail or something like this so the

bentonite plug doesn`t "slip" out.

 

 

Greets

[nater]

Is your nozzle flush with the end of the tube or recessed a little? When the nozzle is slightly recessed in the tube, it bulges the tube slightly, locking the nozzle in place.

 

Although, I am guessing your problems will stop with a heavier mallet. My issues with ramming motors were solved by a heavier mallet.

[Flaky234]

Hi,

 

No it doesn't has a bulge in it.....

Hopefully my rammer will solve the problem

 

Thanks for your answers!

[leedrill]

do you use a tube support

[Flaky234]

No

 

The tube is really strong ^^

[PyroCube]

I recently made a few new 24mm Endburners.

I use Alder Buckthorn charcoal, with 1/4 nozzle diameter,

I was able to lift 130g payload with ease. (3" ball shell)

Since I dont have a hydraulic press, I don`t think it`s a good idea

to go further down with the nozzle diameter, but I`m quite satisfied for now.

For heavier shells I will move to coerburning rockets.

 

Greets

[dagabu]

Just caught a breather so I will throw my hat in the ring for a go at this as well.

 

Great advice from nater and Mum but I don't agree with PyroCube about the scratching of the walls. There is no way that damaging the tube walls will give you better performance. The nozzle has immense pressure against it when the fuel burns and tries to push it out the back of the tube. Like Nater says, you need to move that nozzle end away from the tube end so that you have an ogival bulge in the tube. This shape allows for a permanent block of the tube causing an overpressure to break the tube wall before a nozzle failure takes place.

 

This is especially important to end burners where duration of the burn is as important as the fuel burn itself.

 

Use the very hottest black powder you can make but make sure your charcoal choice allows for compaction of the fuel or you will suffer pressure spikes that will burst your tube. The test for this is to use a sharpened brass or aluminum rod and scratch the surface of the last increment of fuel you pound in. If the fuel flakes off at all, you have one of three problems which have to be resolved or you will continue to have issues.

 

1.) More compaction/pressure

a.) This can be accomplished by using a heavier hammer, a press or use smaller increments.

b.) Use a binder with the fuel that will allow harder increments. Dextrin is helpful in this regard.

 

2.) The charcoal is to "airy" causing the charcoal to spring back after it has been compacted with the hammer.

 

3.) The rammer is bending, flexing or is too soft/long.

a.) Aluminum, stainless steel and brass are ideal metals for rammers, wood and plastics often will bounce when using soft face hammers allowing the fuel to flex back and causing small fissures in the fuel grain.

 

http://www.youtube.com/watch?v=9KL0VjCFWyk

[leedrill]

is that one of your rockets dag and can you give me answers

what fuel ratios where used in that rocket ?

and what where the dimensions ?

im currently working on my 3lb end burners am only on my 5th one now static looked good on the first and second had the same fuel 75/15/10 + 5 dextrin the second was launched and was sluggish on take off but after about 20m really got some speed going i dont think the ti grains in the head lit until about 3 to 400 m then i tried 77/15/8 + 4 dex and was a touch quicker out of the tube but i fear it wont lift much all bp was milled for about 12 hours and the for the 4th i milled for 24 hours i cant seem to get that initial punch on take off the one i pressed up today i plan on hand drilling a 7mm x 2.5mm core will make it easier to fuse with my 2.5mm visco but im not sure if its just my bp or wether to just use benzo lift or super whistle how do i get performance like that

[dagabu]

is that one of your rockets dag and can you give me answers

Yes, I would be glad to.

what fuel ratios where used in that rocket ?

​ 70 parts Potassium Perchlorate, 30 parts Potassium Benzoate, 1 part Red Iron Oxide, 1 part Mineral oil.

and what where the dimensions ?

#1 or 25mm ID by 7" or 175mm long.

im currently working on my 3lb end burners am only on my 5th one now static looked good on the first and second had the same fuel 75/15/10 + 5 dextrin the second was launched and was sluggish on take off but after about 20m really got some speed going i dont think the ti grains in the head lit until about 3 to 400 m then i tried 77/15/8 + 4 dex and was a touch quicker out of the tube but i fear it wont lift much all bp was milled for about 12 hours and the for the 4th i milled for 24 hours i cant seem to get that initial punch on take off the one i pressed up today i plan on hand drilling a 7mm x 2.5mm core will make it easier to fuse with my 2.5mm visco but im not sure if its just my bp or wether to just use benzo lift or super whistle how do i get performance like that

​IMHO, BP is not capable of carrying any significant load and whistle is not a whole lot better. About a 1:16 ratio is the max I would try to carry.

Edited April 6, 2013 by dagabu

[dagabu]

Ignore the "​", it's a program glitch.

[leedrill]

is this nozzleless or just a bigger hole than normal in the nozzle i have wolter tooling and am pretty sure the design will not take straight whistle and cheers for the response i know they wont lift much but 1/16 sounds good enough for me Edited April 6, 2013 by leedrill

[nater]

Endburners use nozzles. The surface area of the burning fuel is so small they do not build up as much pressure as a core burner. The sodium Benz whistle with mineral oil and iron oxide is a slower type of whistle mix too. Also Dag's 1:16 radio is total weight to thrust. If you measure 16 pounds od thrust, it should safely lift one pound of weight. This is including the weight of the completed motor, stick and headings. End burners are not meant to be heavy lifters. Their primary effect is the incredible long burn time. Some guys can get really nice tails arcing 1000 behind the rocket. Edited April 6, 2013 by nater

[leedrill]

cheers nater but im still at a loss as to wether my nozzle will be too small for even na benz i have a lot of bulk na sali but have the other 2 fuels as well, id really like to know the nozzle dimensions that you have for that rocket dag

[dagabu]

cheers nater but im still at a loss as to wether my nozzle will be too small for even na benz i have a lot of bulk na sali but have the other 2 fuels as well, id really like to know the nozzle dimensions that you have for that rocket dag

 

Listen to Nate, he knows his stuff. The standard nozzle opening is 1/4 that of the tube ID but your tooling will not mean anything if you are using clay. Clay swells, clay shrinks, clay relaxes and clay expands. If you are using a 1" (25mm) ID tube, you will want a 6mm drill bit in your hand with a few wraps of electrical tape to give your fingers some grip and hand drill out your nozzles PAST the end of the nozzle opening.

 

I cannot tell you haw many times this issue has come up over the years and still we keep blowing up rockets due to over pressure.

 

Look below and you will see that the nozzle tool starts at the base at 6.25mm and ends at 5.268mm which is WAY to tight and will lead to over pressure. Also look at the taper that the base of the spindle and the first rammer have, these help a lot in keeping the gasses from burning through the side walls. The spindle base also fits into the bottom of the tube a whole 10mm!

 

This allows for the nozzle to act as a plug and not be ejected while the motor is burning.

 

BTW- The drawing should say #3 rocket motor, gawd I hate pounds for rocket sizes...

 

Edited April 6, 2013 by dagabu

[leedrill]

thanks heaps both nater and dag i will post some vids for you to see of my first attempts tomorrow and get the verniers out and check how close that design is to wolters it seems close to identical from looking at the plans but could be a bit off but will make sure to keep a 6mm bit in my magazine. i really should succeed with the whistle comps with a bit of tweaking by the sounds of it and as long as im over 9000psi i assume, with my press i can get just above 11000psi on 1" id so i should be good once again thanks, you might hear from me in the next couple of days .

 

and sorry flaky234 for hijacking your thread i hope the questions ive asked help you in the future too

[Flaky234]

No problem Edited April 6, 2013 by Flaky234

[leedrill]

http://www.youtube.com/watch?v=dZehF4Jt5Gs

http://www.youtube.com/watch?v=0ymcaHDIow8

 

sorry about the crappy quality and yes my nozzle is 6mm and same divergent and convergent angles i made up .5kgs of the suggested whistle mix and will press the first up tonight or tomorrow will let you know how i go im thinking about putting a little meal in with the screened whistle but i might go with the usual approach of toning it done if it catos so i know redline on the first go i will try pressing to about 10 000 psi on 1" so i hope all goes well

 

ps the motor that was launched had about 5% ti in the last 0.8 of an inch the motor as you can see was way underpowered sluggishly leaving the ground it went behind a tree before i stopped filming and probably had about another 6 or 7 seconds of impulse and the ti looked amazing it went straight into the wind after going behind the trees and probably covered as much distance as it did height

 

hopefully the whistle mix does not do this

Edited April 9, 2013 by leedrill

[leedrill]

http://www.youtube.com/watch?v=7M0ERmsaBr0

 

cheers dag and nater successful flight yay

[dagabu]

Great job! Do you like the little ragged snort at the beginning?

[nater]

Congrats!