help in designing a rocket

[Zippiot]

my motor case is 7.75 inches long, 3/4 inch id, has a composite/cement nozzle and tube is made of copper pipe. fuel is rcandy, very p[owerful (enough to lift a cidnerblock that was holding it down).

i have made a nose cone out of fiberglass composite, it is going to be lathed thursday afternoon. right now it is 1.5 inches wide at the bottom and 4 inches long, but after lathing it will be shorter and thinner.

i have access to machining equipment fiberglass and some other materials, but no welder. does anyone have a good workign rocket design that will fit my motor and nose cone?

also any help with a parachute release would be much appreciated. i have reviewed many designs form the internet, all are some kind of explosion or computer chip, any mechanical versions out there?

[Zippiot]

so the part of the rocket that has to cut through the air the most has have consierably less drag...
got a pic sumwhere?

[Greg O'Bryant]

Zippiot:
When I used to want to test an engine without putting a rocket on the chopping block I would simply tape a stick on it and make a giant bottle rocket that you could lanch out of a pipe. You need to take care that the center of gravity is below the engine or it may shout towards you.

[Zippiot]

that is gonna be one big bottle rocket...

the motor is copper tube, im sure if i want it to not be hurt on impact ill have to wrap it in something...

[Jim Berquist]

:wink: Why do you want to use Copper?

There has to be about 20 better types of materials out there!

Composite, Aluminium, PVC, Card board Tube....Just to name a few!!!

Copper is just plain too heavy and sounds link a Bomb to me!!!

May I suggest a Hard Hat, Body Armer, Bunker, Maybe some First Aid Classes!

Why Copper????????????????????????????????????????????

Jim

[Jim Berquist]

My first rocket motor was a C02 cartridge, I opened the mouth of.

Then I filled it full of Match Heads.

Placed it six inches under ground with nossel up.

Placed fuse and Fired it up.....

I walked into the house with blood from nose to toes and after 35 years I still pick little bits of gravel out of my chest...

My dad forgave me for shot gunning the side of his truck , because I was alive and still had two eyes......

I guess I just don't want you to do the same DUMB things I did!!!

Think About It!!!! Jim

[Zippiot]

copper isnt very heavy, the metal is soft so when it flies away from me instead of bouncing everywhere it just kinda sticks to the ground. it is stronger and has better heat and pressure tolerances than pvc and is very easy to machine.

that and home depot didnt have any ss pipe, just copepr and galvanized.

[JetSet]

Couldnt you roll up some wallpaper paper with wallpaper paste to make cardboard tubes like the ameture firework dudes do? Paper will split when your rocket explodes... and paper will hurt a lot less than metal/PVC shrapnel too.

[Zippiot]

i was trying to go for something reusable, even if i only get a few launches out of it. this is my test motor actually, i have already began lathing a real nozzle for when i can find some stainless pipe.

is it worth it to fiberglass a body or just roll paper for the first few attempt rockets?

[Ray]

Steer clear of Stainless steel. Use aluminum. Its light, easy to machine, doesn't fragement to name of a few of its features.

Steer clear of composite, PVC and anything that fragments when it bursts.

Composite and PVC aren't visible on X-Ray, should it ever come to that.

Design so the motor fails longitudenaly (sp??)...that way there is less chance of fragmentation.

Above all, study this process, don't just go headlong into building without understanding what it is that you are doing. I get the feeling that you are so excited about building a rocket motor that you aren't getting into the nuts and bolts of understanding.

For example; can you tell me the burst pressure of your copper pipe? How about the safe operating pressure? How about the internal pressure your motor when it is operating? Three very basic values (among a miriad of others) you MUST know to make something safely.

STOP TESTING IN POPULATED AREAS!!!!!!!

All cliche's aside, this IS rocket science, and the most dangerous part of it. Education is the key. Richard Nakka has enough information on his website to get you to the point where you have a basic level of knowledge to do this safely, study, listen, learn.

[Zippiot]

i am currently working with a few friends (who happen to work at nasa or used to work at nasa).
i mentioned the copepr pipe which they did like. he said similar to aluminum copper wont fragment, it will bend and burn just like aluminum, although it is a softer metal. i have given him a sample of the kno3 sugar, prepared and cast. he said no doubt the copper pipe will be good for at least 10 firings, but wait until his word before preceding after 10.

i weighed it and the copper weighs just as much as sch 40 pvc, considering that the 3/4 id copepr pipe is about the same od as 1/2 inch pvc.

i gotta admitt i did jump into this a little, but i studied nakka and 3 other sites for about a week before i stuck any propellant into a close environment. for the first week i had fun making wut i call popsicles (check spelling). it is just a ball of the stuff stuck on the end of a bamboo skewer. as it burns down it does shoot off a few little pieces of propellant, but i do it into dirt gravel or a clay pot (clay pot breaks dont use them)

i have done 2 firings through the same section of pipe, 1 with a nozzle and 1 without. i suffered a cato of sorts on the firing with the nozzle. i was stupidly using a cork jammed in the back end as a stop, it popped out and the motor flew off. i found it about 800 feet down the street in my friends front yard, no dammage to proerty but i learned my lesson. i have since machined a removeable stop, made from leadalloy and fitted with an oring for proper sealing. i am yet to fit the quick release pin, so it is not in use yet.

i am taking my time on this project, mostly because a few of my other experiments blew up in my face, in my garage, in my room, in the backyard and in the front yard.

1 more question, the guy at nasa said that my copper motor tube would appear on their radar if the rocket goes past 1500 feet. now i do live only 4 miles from nasa ames at moffet field...do you really think that it will show? if so is that a problem, i know of many high powered rocketry groups in the area but i am not sure if any of them use metal tubes for motors...

[MJD]

If you get a rcandy 3/4" copper tube cased motor to go 1500 feet I will be totally amazed, esp. considering the descriptions of some of your other experiments. Copper isn't heavy? Copper has a specific gravity of 8.96! Al is only 2.7.

Also, and I say this from experience not hearsay, just because someone works at NASA doesn't mean they know anything about designing small solid rocket motors. What solid rocket motors has NASA designed and built lately?

One of the safest non-metallic materials for higher pressure motor cases is filament wound glass-epoxy tubing. It tends to accordion out rather than rupture, and more likely than not you will blow the closures not the tube anyway, esp. if you don't retain the closures effectively. Convolute wound is also pretty good - look at McMaster Carr under Garolite, G10 tubing. You can get 3/4" OD and 7/8" OD with 1/16" wall which is plently for sensible operating pressures.

Paper cases are also relatively safe, probably more so for this kind of stuff. In any case, if you are anywhere close enough to these motors when you ignite them to be at danger from shrapnel, no matter what your case material, then you have a big problem. And if you are anywhere near any other dwellings or people than youhave a bigger problem and really ought to think twice about what you are doing.

No insult intended, but what you are doing is cut-and-try. There is enough data available in the public domain to be far more methodical about your approach.

[Zippiot]

i meant copper isnt that heavy in the sense that it weighs just as much (about) as pvc pipe of equal id and length. the guy at nasa builds high powered model rockets, though his are nearly 10 feet tall. that isnt his job at nasa, not a clue wut he actually does, rocketry is his hobby.

i have fiberglass, but what i was looking for is a re-useable motor not a 1 time use then throw it out thing. i do admitt that strapping it to a cinderblock was a bad idea, from wut i had gathered from the int rcandy isnt very strong for its volume, but it is apparent that a chunk about 4 inches long at 3/4 diameter can move a cinderblock. lesson learned.

another guy at nasa (different person this one actually builds missles for the military...strange how nasa is doing defense stuff) told me that before i go and spend all my time building a rocket around a motor that i should grab an old rocket i had already built. modify the engine mount and such so that it accomodates the larger motor. he also said to attatch a streamer to it and remove the parachute assembly entirely. the streamer is to be strapped to each fin, and it should not be made of thin plastic but instead of high temp fabric (ill call a fabric store but i doubt they will take me seriously). he said the streamers will keep the center of gravity low and keep the rocket from going very high, it is more a test of how the propellant and motor assembly work while in flight.

anyone else heard of that?


and now that i see the dangers of the big motor i inted to scale thigns down, but i would still like a reusable case. i will start designing a reusable motor the size od an estes b motor (not a c, even though they have the same size case the c has much more propellant, and i intend to cap off an end with a removable piece, so it will be the same amount of propellant as a b). this way i will learn a lot more about how they all work before i try a larger scale flying bomb as it seems this current project will be...

[MJD]

The rules of model and high power rocketry are that reloadable motor cases are made of 6061-T6 aluminum, the rationale being that the ductility of the alloy pretty much prevents fragmentation. The additional rule is that the motor be designed to fail longitudinally - that can be done by ensuring that the tensile area at one or each end is reduced to a point where the tensile strength of the reduced cross-section area is lower than the burst pressure of the tube. The calculations are pretty rudimentary. For experimental motors the most common retention method is snap rings both ends.

Lastly, always put a barrier between yourself (and anything else of value like houses and people) and the motor. Dirt works. Distance is good too.

I can make a small, functional rocket airframe in 10 minutes out of spare parts, so for experimenting I would rather sacrifice something I throw together quickly like that, than an existing model.

But honestly, stick rockets are great for crude motor tests if you are in the boonies, which you should be anyways. For a "B" size motor casing use 3/16" - 1/4" square spruce or basswood or hard balsa and it will fly.

[Zippiot]

i have a few great open areas (school sports fields mostly, and 1 giant parking lot but its near an airport...) in my area, i have been shooting up to c sized motors there since i was a child. problem is, i always had a parachute, the rocket would float a little but it would still remain in the park. my only concern for the bottle rocket is if it comes down on an outlying house...

also i have machined a piece of aluminum (t6) that is the dimensions of an estes a-c motor. i drilled out 1/2 inch of the core, about the same as an estes motor. it is kinda heavy though and i fear it wont fly too well, how much thinner can the wall be to keep a good margin of safety?


all of my motor tests are completely encased in cinderblocks except on the top, so the flame can escape and multiple heavy duty straps are used to keep the motor in place.

would it be better to have a nozzle machiend into the motor tube itself and make the weak link at the top of the motor? this would make any failure not take off but instead blow out the walls of my rocket, which should be very replaceable compared to losing the entire thing... how about a cap that is the same width of the tube, and i lathe away and thread the outside of the tube so the cap fits. this will ensure that the tube at the top is weaker and also that the top is removeable?

most of my rockets sitting around are junk, too many crashes missing fins and smashed nose cones. losing one is a test firing of a motor isnt a huge deal