32 replies to this topic

[Pretty green flames]

Good evening all

I made my first end burner rocket tooling the other day and initial tests have been pretty much dissappointing. The rockets just CATO. Post mortem reveals that only the clay plugs were blown out.

I am using a 3.5mm nozzle on a 14mm ID tube, that's exactly 1/4 ID. I press these rockets under 2 tons of pressure so i'm guessing that insuficient packing was not the problem. Could it be the nozzle. Lancaster says that a 7mm nozzle should be used on a 24mm rocket, that's roughly 30%, should i enlarge the nozzle from the original 25 to 30% (4.2mm)? Also, how forgiving are these rockets in fuel terms, will different batches of BP seroiusly effect it's lifting capacity?

Thanks for your help.

[aquarius]

You might want to open up the nozzle a bit.
I use a 4 mm nozzleopening on 12 mm ID coreburners with great sucsess, but the corelength is critical.
All over 25 mm corelength invite CATO's. And that is with 70/20/10 homemade BP...

So I would advice to open up the nozzle. I suspect the blowout of the nozzle is due to one or more of these three things:

1: The nozzleopening is to small. Open up to 4 or even 5 mm. 1/3 is "usual" for coreburners.
2: The nozzle is not rammed hard, and/or it is to short.
3: Your BP is to fast. Slow it down with come coarse charcoal.

Remedy: Widen the nozzle to 4 mm, ram it as hard as you can and start with a very short core and hot BP.

[Pretty green flames]

Ok, i guess it was a typing mistake when you said core burner as i am experimenting with end burners. But yes, i will enlarge the nozzle to somewhere between 4.2mm and 4.5mm and see if i can get acceptble results.

Thanks for your help.

[StarScream]

While I'm certainly no expert, I've had really good luck with end burners... so far. Never had one fail yet, and I've made quite a few of them now. I'm not attaching headers to mine yet... just trying to establish some degree of consistency and predictability first. I still manually ram and drill the nozzles out by hand, because building a press & rocket tooling is still on my "To Do" list.

What are you using for your nozzles? If it's just cat litter/bentonite by itself you might want to try adding some grog and wax. Also, for end burners you need really fast propellant. I use 6:1:1 meal powder milled for 3 hours. Hot charcoal such as willow might help, although I only use my willow for lift. I use lump charcoal for everything else.

[aquarius]

No Pretty Green Flames, I meant coreburners.
My statement used is to clearify that a small nozzleopening and a long core will CATO (Obviously..). And if it CATO's, most of the time the endplug is blown out. ThereforeI opened up the nozzle on my rockets;-)

PS: Do you use a LaValle nozzle?

[Pretty green flames]

@Star scream, so you are using commercial lump wood charcoal in you rockets, what nozzle ID to rocket ID ratio do you use, how much do you drill into the propellant grain.

And i'll try the 6:1:1 formula, if i remember it is almost the same as the formulation that is used in all commercial model rocket engines.

[al93535]

I got your PM on the other board PGF, but decided to respond here.

I used a nozzle that was 1/5th the ID of my rockets. I had almost no core in these, at MOST 3/16" of an inch.
I used regular kitty litter as nozzle and plug. I rammed these pretty hard, and rammed in 1 ID thickness of clay for the nozzle. Then I rammed in my BP and then the top plug again, 1 ID thick. I used the hottest BP I could make, with willow charcaol. I drilled out the nozzle, my rockets were 5/8" ID and I used a 1/8" drill bit. I never had any cato's with these. And al of them worked excellent, well except one, but hat was not due to construction.

I must say, I was ramming my newer core burning rockets and had great reuslts. Then I began to press them, and low and behold cato's! I tried quite a few times and kept getting them. The problem? Not enough pressure! Ramming will consolidate the BP extremely well, where as pressing might not be! Unless you are sure you are getting 4,000 lbs of force, maybe even 5,000lbs, I would try ramming once and see if that is indeed the problem.

What I would do is:

Do not change your nozzle or formula. First try ramming. Make sure you are ramming that nozzle hard enough to slightly buldge the case. Unless you are using very think commercial tubes, in which case you can ram all day and you will not see it buldge! Then ram your BP and top plug.

Make sure your core is almost non existant. 1/8" or less is best.

As long as you are using the same charcoal, you should get pretty close to identical lifting capability between batches.

Oh by the way, I used 75/15/10 standard BP.

I hope this helps you!!!

Edited by al93535, 30 August 2006 - 10:12 AM.

[Pretty green flames]

Al, thank you for the response, i will try ramming first and if it doesn't work i shall switch to a slightly bigger spindle and see then how it works.

[seymour]

Do you add coarse clay, or add grog?

[Pretty green flames]

No, i just use kitty litter powder treated with 5% wax for better sticking properties. I hear grog seriously damages your tooling so i try not to use it. Course clay might be an idea though.

[StarScream]

@Star scream, so you are using commercial lump wood charcoal in you rockets, what nozzle ID to rocket ID ratio do you use, how much do you drill into the propellant grain.

And i'll try the 6:1:1 formula, if i remember it is almost the same as the formulation that is used in all commercial model rocket engines.

Yes, I have a large bag of "Royal Oak" brand lump charcoal that I use for virtually everything except lift pulverone. That's when I use my homemade willow. I drill the nozzle throat out to 25% of the tube ID, and I only drill into the BP a tiny amount. Maybe 1/16". A little further would give a higher initial kick of thrust, but I get a bit paranoid drilling into BP by hand!

The 6:1:1 seems to work quite well. In percentage form it works out to 75:12.5:12.5 which is pretty close to the Estes formula - 71.79:13.45:13.81 + 0.95 dextrin. I don't add any dextrin to my 6:1:1 propellant... I do it the messy way with meal squirting out of the tube everytime I insert the rammer!

[Pretty green flames]

Ok, i have made 6 rocket, 3 with a 3.5mm nozzle and 3 with a 4.25mm nozzle. All rocket were rammed extremely hard but still, every rocket CATO'd. This brings me to belive it's my fuel, i am using 75:15:10 which has been riced (no binder), could this be a problem.
Anyway, i am going to switch to something a little less fast.

[BrightStar]

I had some fun with end burners over the summer... Flights were as follows (all balanced with garden sticks attached and no headers)

1) 12mm ID * 80mm length with 3.5 mm clay nozzle, 75/15/10 willow meal hand rammed...

Result - CATO about 5m into the flight...

2) 12mm ID * 80mm, 3.8 mm clay nozzle, 75/15/10 formula with slow hard-wood charcoal...

Result - Smoke b**b... never left the pad...

3) 12mm ID * 80mm, 3.8 mm clay nozzle, RPH formula with willow charcoal...

see: http://www.creagan.n...mpositions.html

Result - successful flight but scarily came back down still under power (Dad's Army 'DONT PANIC!!!' moment for UK readers)

here's the vid (3gp mobile format, opens in Quicktime)

More work to be done here it seems...

Edited by BrightStar, 31 August 2006 - 10:53 PM.

[StarScream]

Ok, i have made 6 rocket, 3 with a 3.5mm nozzle and 3 with a 4.25mm nozzle. All rocket were rammed extremely hard but still, every rocket CATO'd. This brings me to belive it's my fuel, i am using 75:15:10 which has been riced (no binder), could this be a problem.
Anyway, i am going to switch to something a little less fast.

Are your end plugs still blowing out, or is the tube bursting when they CATO? How thick are your clay plugs? What kind of tubes are you using, commercial or homemade? What?s the tube wall thickness? My thinking here is that the problem may be in the construction, and not the fuel you?re using. 75:15:10 BP shouldn?t be too fast for an end burner? you need really fast propellant. I believe 6:1:1 is slightly faster than the standard 75:15:10 (15:3:2). Ricing then ramming could possibly introduce voids in the propellant grain, which would likely cause a CATO, but I know a lot of people do it that way successfully, so it's hard to say for sure.

[Pretty green flames]

The end bottom end plug blows out. I ram a 1ID plug out of clay (bottom and top), i have also reinforced the clay with some coarser mesh so it has better grip.

For the casing i am am hisong homemade tubes which have a wall thickness of 3.5mm.

Well, i think firstly i'm going to try reducing the milling time and see if it helps.