20 replies to this topic

[pritch]

Ok. So far I have had great success with a 3mm core width that is the same width as my fuse. So here's what im not sure about. If I increase my core width to 4 mm, will my 3 mm fuse still ignite it fast or should I add some bp to prime it. At the moment the fuse is in full contact with the walls of the core at 3mm. 4 mm and it will only be in contact at some points and it will mainly be sparks.

Im also creating my first 9 cm rocket today. Im not sure if fuse alone will be fast enough to ignite the whole core at the time of take off.

In case anyone is interested my motor specs are. 75, 15, 10 propellant, 15 mm id, 19 mm od, 9 cm length(was 10cm until I had to saw the ends off), 4mm core width, 60 mm core length, 3mm nozzle and about 10 mm overhang around the nozzle end to create a pocket.


UPDATE

Oh well. I just went ahead with my idea. 4 mm width core and i put a foil disk in to cover the bp while the nozzle made of all purpose filler drys. Im then adding a 3 mm throat through the cap. I also have a 1 cm overhang. I just wish I could film this.

Edited by pritch, 11 May 2004 - 07:04 PM.

[BurlHorse]

It'll Work, 1 MM Difference in the size of fuse in relation to the core, wont mean much, once the core ignites anywhere along it's length, the pressure and flame front should ignite the core as a whole within a matter of microseconds. I also believe you might be seting yourself up for more Cato's with a fuse exactly the same size as the core should anything not want to exit the nozzle.......Just a thought.

Regards,

Stay Green,

Bear

[pritch]

Thanks for that. It did work, pretty well but not as well as I had hoped. My mam got covered in the black waste it fired as well, something that concerns me because I thought it should have turned to vapour. Im not sure what has happened there. We were about 15 feet away from it but it was firing on a slight angle away from us, to make sure it landed safely in a field. Estes model rocket motors can launch rockets to several hundred feet and they are smaller than my rocket. Its hard to tell how high mine went but I doubt it made it over 150 feet.

Are these smaller estes motors that don't even have a core just incredibly well rammed bp or something?

It has to be either.

1. Their nozzle makes a big difference.
2. The propellant is much better rammed than mine.
3. The estes motor propellant mix makes a big difference.

or after hours of reading I have decided that meal may not be what estes use. I use straight mix out of my mill. I don't press and corn first. Something I have read has given me the impression that the model rocket motors may be using pressed and corned powder, which would explain how they get away with having no cores.


Ive just expected my launch site and i found my nozzle lying on the ground. It obviously shot off on launch and lots of fuel was pumelled out but it still made a good 150 feet
Thats great news. Means if I can just make sure its fixed next time it should go higher.

Edited by pritch, 12 May 2004 - 02:00 PM.

[chim-chim]

Estes model rocket motors can launch rockets to several hundred feet and they are smaller than my rocket. Its hard to tell how high mine went but I doubt it made it over 150 feet.

Are these smaller estes motors that don't even have a core just incredibly well rammed bp or something?

It has to be either.

1. Their nozzle makes a big difference.
2. The propellant is much better rammed than mine.
3. The estes motor propellant mix makes a big difference.

or after hours of reading I have decided that meal may not be what estes use. I use straight mix out of my mill. I don't press and corn first. Something I have read has given me the impression that the model rocket motors may be using pressed and corned powder, which would explain how they get away with having no cores.

The nozzle coming out was probably it but for your reference,

Estes uses:

KNO3 71.79
Sulfur 13.45
Charcoal 13.81
(150 mesh)
Dextrin 00.95

Pressed hard, really hard, not corned.

You might try adding some grog, sand or powdered glass to your nozzle mix to give it some bite on the sides.

Keep it up, it's a trial an error art and you're more than close.

Stay safe.

[BigG]

well, it's very nice to you to try and reach the estet quality of motors, but really you should not bother. First, the have purer matrials then you. Second, the have better milling facilities then you, third, they have better milling media then you, fourth, the probably mill for much longer then you, fifth, the compress the motors using industrial press, which is better then your press, sixth, the have 80 years of research into those motors - which is longer then you been alive.

In short, Estet motors should not be your bench mark. your bench mark should be the WOW factor your rockets produce, and then to try and make it even a better WOW.

Stay green.

[pritch]

Thanks for the advice guys. Im not aiming to make motors that are as high quality as theirs, more that I would like to do everything they do, to the best of my ability.

So the impression I am getting is they just mill the ingredients then press them into a very hard propellant. I will try it on my next batch. With my leftovers from my big rocket, i've pressed some small 15mm cakes in my vice. Gonna see how they dry up.

[chim-chim]

In short, Estet motors should not be your bench mark.

I meant to say that, but didn't know how to phrase it.
Thanks, BigG.

I've been reaching for the Estes level myself, not because I expect to make it, but because it's a quantifiable ideal. As BigG stated in another way, Estes is THE black powder motor manufacturer. If you were to get their level of performance without their level of control (as nearly perfectly consistant a process as possible), it likely wouldn't be safe. If your goal, like mine, is to launch an Estes rocket with your own motor, might I suggest either putting a 'D' (24mm) motor mount in an A-C (18mm) rocket or use the smallest 'D' rocket you can find. Getting 'B' performance from a 'D' sized case is a reasonble but not overly easy goal, and will lift a small 'D' or average 'A-C' rocket several hundred feet.

You may be able to get Estes performance from an Estes sized engine using a core-burning composite fuel, but that's a whole 'nother animal, with a lot less published help and experienced people to talk with. Model rocketry is very safe, high powered rocketry is rather safe, amatuer rocketry can be kept reasonbly safe (which I assume and hope you are), amatuer high-powered rocketry.....you get the trend.

Keep safe, keep it up, keep your goals reasonable, be patient with your progress, after all, this IS rocket science

P.S.- I havn't gotten an Estes rocket over 50 ft myself, but I'm making progress, and any flight is exciting. I've never been so happy to see an ejection charge on a rocket that has already crashed.

[pritch]

Yes I would love to launch a proper rocket using one of my motors. At the moment im just trying to perfect an engine design, which I test by launching on a stick.
Just to clarify this last point. Would it be pretty pointless for me to press some meal into a cake, then corn it into say 40 mesh(4fa) and then to press that powder into the rocket casing?
So im right in thinking estes don't do this?

I have read in another place they think estes do this. He also thought the mix was 60, 30, 10 though. He thought it was corned into 40 mesh and then poured into the tube all at once. Then pressed into one very hard mass.

[chim-chim]

Pressing the meal into a cake and corning it wouldn't be pointless.
Pressing it increases it's density, which will give you more power in a given volume of fuel, and corned powder is much easier/neater to work with, but grain size is likely irrelevant whereas you are going to go on to make one big grain out of it in the engine case.

60, 30, 10 is popular, workable amatuer mix, and you and I being amatuers.....
I just listed the Estes mix for reference, not a recommendation, sorry should have clearer

You may also need some manner of binder (probably dextrin), maybe not. The better the pressing, the less binder and solvent (water for dextrin) you'll need.

You will notice that the Estes mix and 60,30,10 both use less KNO3. 75,15,10 tends to be a little 'hot'. If your rocket flew after losing a nozzle, it likely would have CATO'd had it not. You'll probably have to tune down your powder when your nozzles start holding.

Which brings me to-

I posted-
'You might try adding some grog, sand or powdered glass to your nozzle mix to give it some bite on the sides.'

BigG has informed me that ground glass might not be a good idea. He feels the glass may increase sensitivity during pressing. I don't know, but why tempt fate. I haven't use glass myself, it was a second hand suggestion, I admit it , I've used a little grog to good effect, but BigG hasn't gotten back to me as to whether grog and sand have similar issues to glass (it hasn't been long, that's not a slam ). I've also cross drilled the tubes (four holes, evenly space, half way up the nozzle, 1/8" or so) and given them a wrap of cellophane tape before putting in the filler in to give the nozzle 'pins' into the case. It worked OK, but I wasn't comfortable with compromising the case. I finally settled with slightly longer nozzles for more surface area, which corrected any holding problems I've had. Which is what I probably should have suggested before. (would have saved a lot of typing )

I actually recommend ramming bentonite more than wet setting nozzles if only for speed and ease of use. If you are like me, drying time is like Christmas morning as a kid waiting for your parents to get up.

Most of my engines go up on sticks too, but once there consistant, you'll want to stick one in a rocket. You'll know you don't have the power yet, but you'll try it, you know you will.

[pritch]

Thanks for taking the time to type all that!

Right. Im guessing the estes mix can still afford to use allot of kno3 because it's only an end burner. I think for my next rocket. Im going to attempt to make high quality meal using around

KNO3 71.8 g
Sulfur 13.5 g
Charcoal 13.8 g
(150 mesh)
Dextrin 1 g

Then press it into cakes and let them dry for 24 - 48 hours

Then corn that into a fine powder just to make packing easier. Then ram some end burners using all my strength in my large vice, and an extra thick carboard tube that can have a few layers stripped off it after ramming.

I will let you know how I get on In fact I should have my digi cam back by then so I can film my launches.

I certainly will want to launch a comercial type rocket up as well. Stick a camera on there as well

I may have to buy a 2 ton jack. Start some serious pressing business!

[chim-chim]

Thanks for taking the time to type all that!

No problem, I'm at work. There paying me pretty good money to read posts and type to fellow pyros and rocketeers.

[Matt]

From what ive read 2 tonne isnt enough for most things... Might want to look into that to save buying a "weak" jack.

-Matt

[pritch]

Jesus. If 2 tonne isn't enough then me and my vice must just be a complete joke. I can get 4 tonne for a few extra pounds. I just thought 2 tonne would be tons!

I've just realized that there are both tons and tonnes. 1 ton is only 907.18474 kilograms and obviously a tonne is 1000 kg. Just some useless trivia

[BigG]

it depend on the size of your cake really, but 10-20 tons is more common in industrial use. For a good comet for example, of 2 inch, you already need to use around 6 tones. For 4 inch comet you will be lookking at 10-12 tons, so matt is quite correct. I use 12 ton press, and mine is not considered a big press.

[Phoenix]

I've been crawling by with my 1-1/2 ton press. I have used it to press a 37mm charcoal comet (in my BP die, which will do 50g of BP per go) which survived being dropped (unintentionally - I would have been pretty irritated if it hadn't) and that worked fine, though I would quite like a larger press.