16 replies to this topic

[knackers]

just curious more than anything else, i once read a reference to rocket ID sizes and lift potential and it classed a 3/4" ID as being a 1Lb rocket and a 1" ID as being a 3 Lber, my rockets are 38mm ( 1" 1/2 ) ID and i use pressed riced BP ( about 2-->4 ton ) and sometimes add Fe203 for tail effect, size is 5" long 38mm ID, 44mm OD and 4" x 1/2" core with a bentonite nozzle, i've been using 2 1/2"--4" shells with glitter stars, with mealed lawn seeds and about 5-->10g of 70:30 flash, shell weight somewhere in the vicinity of 100 -->400 grams, it uses a hell of alot of Bp and takes ages to get ready, Hence why i want to use mortars, my question is what potential is the payload of my rocket, " i only have a set of gun scales that go to 500g, so a test on scales is out of the question,

these rockets are very powerfull and just about send my shells into next week,

when i think of a 3LB rocket i visualise 3LBS of sugar riding on the top, ( thats pretty heavy )

[spanner]

The "weight" designation of BP rocket motors do not refer to the lifting ability of the rocket, it's just a size designation for the rocket's ID and length.

Common BP Rocket Engine Sizes (PASSFIRE)
Size..........I.D..........Length
2 oz..........3/8"..........2-3/4"
4 oz..........1/2"..........5"
8 oz..........5/8" .........6-1/4"
1 lb...........3/4"..........7-1/2"
2 lb...........7/8" .........10"
3 lb...........1" ............10"
4 lb...........1-1/4".......12"
6 lb...........1-1/2".......16"

Rocket size.........Payload
2 oz....................1/2 oz
4 oz................... 1 oz
8 oz....................2-3 oz
1 lb.....................4-6 oz
2 lb...................8-10 oz
3 lb..................12-14 oz
4 lb..................16 oz
6 lb..................18-24 oz
The above is a rather conservative estimate of the payload weight for a BP rocket. Properly tuned and optimized designs can exceed these estimates quite readily.

Edited by spanner, 26 January 2009 - 05:31 AM.

[knackers]

very good usefull information there spanner" that makes alot of sence,

i couldn't get my head around a 1" ID rocket about 7" long lifting 1.5kg of sugar ,

at that rate i could almost ride my own rocket and light the shell up there

[Mortartube]

Rocket grading is a bit odd.

The cardboard rocket tube used to be put into a metal tube to prevent the case splitting when it was charged and the grading is the weight of a lead ball that would just fit into the metal tube.

Now they generally just tend to be measured in fractions of a an inch or millimetres.


To reduce the amount of BP you use, you might want to try endburners. They are quicker to make and use a lot less powder.

The ones I have been working on are 18mm I.D and use a clay choke with a 3mm hole (yep 3mm is right), that just goes into the powder. The length of the powder increment inside is about 30mm and they reach about 60 metres or more. They burn for around 4 seconds and I have lifted 50 grammes with them. (still experimenting with max payload weight). The BP is straight homemade willow BP 75:15:10. It is not optimum BP for other uses but it works for this. If you try it and get CATO's either increase the size of the choke hole or add a little charcoal to tame the mix.

[spanner]

Rocket grading is a bit odd.

You got that right!

The question of rocket sizes was the very first question I asked on a forum, I believe it was the APC Forum.

In any event, here's a posts on the subject, sorry I cannot give proper credit, as I don't remember who posted it. Probably from rec.pyro Google group:

"The lead ball was the same as the OD of the case - the ID of the mould (sleeve) in which the case was held as it was rammed. The moulds were made by spill-boring and reaming, using the same techniques and tools as were used in making gun barrels. By the logic of the day it was perfectly reasonable to describe the diameter by the weight of a bore-fitting lead ball (as indeed we still do when speaking of a "12-bore shotgun," for example - having a calibre of 0.729", which is the diameter of a lead ball weighing 1/12 of a pound).

A lead ball of 4-oz. weight is 1.056" in diameter. Ordinarily the OD was assumed to be 1-1/2 times the ID, which would thus have been 0.704". In British practice, the designation 4-oz. was applied to a 3/4" ID rocket. See Kentish and Browne.

Somehow or other the American practice came to be to multiply the British designation by 4, so that a 3/4" ID rocket then became 1-lb. rather than 4-oz. I have heard several speculations about how this came to be, but the most likely explanation is good old-fashioned American hucksterism. One pound sounds more impressive than four ounces. The identification of a 3/4" ID rocket case as "1-lb." was in use as early as the date of Weingart's first edition (1930). He writes: "Of late, the diameters and lengths of Roman candles and rockets have been changed and reduced so often that no standard of sizes can be given, but the following will be found to be useful for average work..." (this text occurs in all editions, and may be found on p. 27 of the 1947 ed.)."
END

Indeed, end-burning rockets might be a solution. If you'd like to see a little more on the subject of 6 pound end-burners, take a look at:
http://fogoforum.us/rocket.php

[Arthur Brown]

Rockets will lift shells there were some nice flash burst 3in shells on rockets on the market until the flash = 1.3 problem.

The big problem is that as the shell gets bigger the rocket has to get bigger and the stick becomes a plank. Then you have to find somewhere to fire that can safely accept a 10 pound stick/javelin coming out of the sky in the dark.

[knackers]

through the necessity of hard to get items and time consuming tube rolling i use Al tubes i cut at work, and use a 9mm dowel 6' long, but i go to the waters edge of Port Phillip bay and fire my rockets there, i aim them over the water for 2 reasons, firstly and most obviously when gravity takes over nobody will get hurt and 2ndly and equally important its very dry here and a bush fire would probably be an outcome

[knackers]

i'm quite contented with the rockets i make and get right off on the awsome sound thay make at launch, and am very impressed with that monster end burner,
http://fogoforum.us/rocket.php,

and did i hear you corectly mortatube, " a 3mm choke" i'll have to give it a run, i've got some 4" x 1" tubes coming,

i went into passfire yesterday and was awe struck,, the tutorials are magnificent,, it would have taken me months if not years to find the treasure trove of info they have there, and still not found as much,,

i'm gunna be a busy boy for a while,, and just in the nick of time as i'm ready ( i think) to try my hand at some mortars and different shells,

[Mortartube]

You did hear me correctly 3mm.

With an endburner 1" I.D, the tube will only need to be about 2.5" long. They require much less length of propellent than a core burner.

As I mentioned before, mine have an 18mm I.D and a propellant length of around 30mm. So just less than twice the I.D.

If you can remove a bit from the length of the tube you can save a little weight and the stick can be marginally smaller too.

[dr thrust]

The "weight" designation of BP rocket motors do not refer to the lifting ability of the rocket, it's just a size designation for the rocket's ID and length.

Common BP Rocket Engine Sizes (PASSFIRE)
Size..........I.D..........Length
2 oz..........3/8"..........2-3/4"
4 oz..........1/2"..........5"
8 oz..........5/8" .........6-1/4"
1 lb...........3/4"..........7-1/2"
2 lb...........7/8" .........10"
3 lb...........1" ............10"
4 lb...........1-1/4".......12"
6 lb...........1-1/2".......16"

Rocket size.........Payload
2 oz....................1/2 oz
4 oz................... 1 oz
8 oz....................2-3 oz
1 lb.....................4-6 oz
2 lb...................8-10 oz
3 lb..................12-14 oz
4 lb..................16 oz
6 lb..................18-24 oz
The above is a rather conservative estimate of the payload weight for a BP rocket. Properly tuned and optimized designs can exceed these estimates quite readily.

"common" bp rocket sizes? there's nothing common about those larger sizes! the largest ive made was a 3lb, 1 id, 10 long with an 8 inch core, and it was jolly hard to get off the spindle i can tell you! how practical would it be to build a bp rocket 16" long?

[spanner]

"Common" is a relative term. Maybe common only in that tooling, tubing and comps for 6 lb. rockets are readily available.

Get your 6 lb. BP rocket tooling here: http://www.wolterpyr...catg&cat=rocket

If you wanted a 6 lb. BP rocket, but shorter- opt for a stinger or end burner. Or a whistle fueled rocket. More than one way to get it done.

[dr thrust]

agreed, whistle powered motors are a better option at a 6lb diameter, and indeed 95% of the large rockets Ive seen are whistle, i just cant see it being practical to make a 16" long motor, and thats why you just don't see them, and therefore there not "common".
yes the tooling is available( from another country) and pricey to $240! for £15's worth of ali!
i just don't think they would be worth the effort to make

Edited by chris m, 28 January 2009 - 09:24 PM.

[spanner]

It's likely geographical- here in the US they're more common. According to a trusted authority on the subject (LadyKate http://www.creagan.n...orks/index.html who doesn't build them, either), they're "the motor of choice in the large motor/rocket, level 4 classes" of competition. She goes on to say, "They take longer, have more to go wrong if something goes wrong, and use a lot of materials."

But some people just want to build the "biggest, baddest" of their ilk- practicality be damned.

While they do require a considerable commitment, it might be a mistake to judge the cost of the tooling solely on the amount of material contained- taken to an extreme, a person's worth maybe 2 quid- based on the raw chemicals contained therein! Time and labor for production as well as the testing/prototyping to perfect the design are all considerations.

The bottom line for me is: Vive la différence!

Edited by spanner, 29 January 2009 - 03:55 PM.

[pyrotrev]

very good usefull information there spanner" that makes alot of sence,

i couldn't get my head around a 1" ID rocket about 7" long lifting 1.5kg of sugar ,

at that rate i could almost ride my own rocket and light the shell up there

Not sure you could do that with BP, but a decent composite propellant motor of those dimensions ought to get it off thr ground.

[Mumbles]

The american designations, at least from what I've read, are different. They correspond to the mass of lead balls, having a diameter equal to the ID of the tube that will fill the tube. Generally, this is 10 balls, corresponding to the standard 10x ID length.