Pressurised aluminium body.

In a moment of stupidity I thought do do this, but I failed to find any simmilar madness by searching, so could I make a body tube by cutting out the parallel portions of several aluminium beer cans to make short tubes, then join them by expanding one end bigger using a die and gluing it over the next section etc etc. The ends could be sealed and the resultant tube pressurised, a bit like they did with the thin stainless fuel tank on the Blue Streak.

Should I just get back in my darkened room, lock the door and throw away the key!

Well.... the reason you didn't find anything is because aluminum beer cans aren't meant to be rocket motors.

If you want an aluminum tube for pressurizing, look at 6061-T6 aluminum tubing. If it overpressurizes, it will split down the side or spit the closure instead of exploding into a billion pieces.

Of course, I'm not a rocket scientist, so others may have a different explanation. But I say don't.

Not motor tube! Body tube! Rough figures would be :-

65.8 mm dia
.1mm (.004") thick
70 grams (2.3 oz) for 1 metre length *
125 grams (4.4 oz) for a 2 metre length *

* this includes 8 grams for a pair of end caps

If pressurised to a few PSI this should give a very rigid tube, if the joints can be sealed without getting a weight penalty. How heavy are the tube options avaliable in this sort of diameter at the moment per metre?

Fill your "tube" with two part expanding foam .

Eric

Won't the foam weigh shed loads more than the tube?
As an aside, the fuel tank of the blue streak missile held 30 tons of liquid fuel and had a wall thickness of .015" ( under .5 mm)

blackbrandt said:

If you want an aluminum tube for pressurizing, look at 6061-T6 aluminum tubing. If it overpressurizes, it will split down the side or spit the closure instead of exploding into a billion pieces.

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Well, this is hardly scientific but... having shot more than a few (cheap) beer and pop cans with a high powered rifle, I've never seen one shatter into pieces. It usually splits the can down one side. More of a tear than anything else.

W7AMI said:

Well, this is hardly scientific but... having shot more than a few (cheap) beer and pop cans with a high powered rifle, I've never seen one shatter into pieces. It usually splits the can down one side. More of a tear than anything else.

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After drinking the contents right?

rharshberger said:

After drinking the contents right?

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What? People actually drink Hamms Beer? It's actually more fun to shot the cans while they are still full and sealed.

Quite an unexpected post from a first timer. Late night at the pub, Roger?

If you want to discuss hobby rocketry, we're fine with it, but this question is off the wall and not what we do.

Bob Krech, TRF Administrator

If i get what your asking, a tube built this way would be lighter than an equivalent airframe tube of cardboard , you would still need the ability to mount recovery gear and motor and fins. More trouble than its probably worth. It also violates the "no substantial metal parts" of the model rocket safety code.

rharshberger said:

If i get what your asking, a tube built this way would be lighter than an equivalent airframe tube of cardboard , you would still need the ability to mount recovery gear and motor and fins. More trouble than its probably worth. It also violates the "no substantial metal parts" of the model rocket safety code.

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^^^^ This.

Plus time spent on cutting up beer cans and attaching them together takes away time available for the drinking of additional beer.

:y::y:

W7AMI said:

What? People actually drink Hamms Beer? It's actually more fun to shot the cans while they are still full and sealed.

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I remember the Hamm's bear from the commercials I saw growing up in Minnesota. They still make that stuff? Hamms I mean, I know they still make bears.

Evidently you can still buy it in a few markets. It is owned and produced now by Miller/Coors.

Rainier Beer used to have some great commercials too.

"Rainbeer Right Here!"! ..........Yuck!

Remember until about 1972-73 or thereabouts, pop and beer cans used to be much thicker/heavier -- I think maybe made of steel in some cases.

The reason I remember was I was a teenager in those years, I drank a lot of pop, and when I was 13-14 it took quite a bit of muscle power to crunch a pop can with your bare hand. But all of a sudden I was 15-16-17 and I was crushing pop cans like eggshells. I knew I was getting bigger and stronger and all that stuff, but mainly the difference was they started making the cans out of much lighter aluminum. So woo hoo for me, I guess.

I don't know how you'd seal/pressurize it, but it would be more worthwhile if you were talking at least twice the diameter of a beer can and metal the thickness of aluminum foil. That could also be filled with expanding foam.

With any "real" rocket the space would have to be filled with something useful, they don't have sections devoted to just making it look bigger!

In the "Bible of Modern Rocketry" by David Petry he made a rocket out of Mylar and pressurized it, don't remember the details and can't remember if he went into detail about recovery or not but it did have a chute. I am not sure why you would want it pressurized other than being able to say "Hey, I pressurized a model rocket made from aluminum cans." Which I suppose is reason enough in itself. Leave a section unpressurized for the chute and use a flight computer for deployment. Or leave the fin can unpressurized and have the chute rear eject from there. Epoxy will hold the cans together but not sure how good of a seal it would provide. Weather seal cement may work. It seals and glues. And is super messy BTW.

What constitutes being substantial? Would a few aluminum cans be considered substantial? The cans would collapse if crashed into something. I'm asking because I really don't know. Seems like an aluminum tip, aluminum bulkheads and minimum diameter mounts would be more substantial.

Mike

Mike:- sounds like you've got a good handle on the plan!
I am coming to the conclusion that it would be best to cut the tops off, and for the intermediate cans cut most of the bottom cap away as well except for the outer rim, as this thin rim adds a fair amount of strength working against the forces involved when you push the next can over it to make the join. The top can will be inverted to give a can base as the upper end cap.
Cans are lacquered inside and painted outside, but once that is carefully removed, special aluminium solder and flux will solder the cans together!!! Or as a glue would have to cope with flex, you could prime the surfaces and use automotive windshield adhesive, which would probably make lighter joint. (Flux and solder is on order, and I have some screen adhesive and primer at work)
The strength of the resultant body relies totally on getting pressurised to at least the pressure usually found in a full beer can, so as you say, hollow ends for chutes and stuff, none of which makes life easy.
But hey, Didn't some important guy once say "We're not doing it because it is easy, we are doing it because it is hard!" )
I am sure that a thin skin of light alloy does not constitute any danger as far as the rules are concerned and as a total novice it is my assumption that the no metal rule originated to stop fools launching steel conduit and scaffold poles rammed full of fuel, and also back then, peeps were using sheet and tubular aluminium rockets as there was not the composite options we have today, but who knows? Perhaps this suggestion is indeed breaking conventions, which is the whole point of posting this.
I was assuming this had been experimented with before, because let's face it, aluminium beer cans have been around for a while now and cost nothing! Perhaps I should find a Scotish or Yorkshire rocket club, and ask them !! (English joke)

bill_s :- The entire idea for this came from a real rocket! It was the UK rocket called the Blue Streak from the 60's. As I said above, it's entire body structure consisted of a wafer thin stainless steel fuel tank, 0.015" thick with 30 tons of kerosene inside. One of the few examples of these babies left is in a museum in Linconshire, and they have to keep the fuel tank pressurised to keep the thing standing, because without the pressure it is about as flimsy as .....err....an empty beer can!

Okay so you are gonna pressurize the thing so it will stand up. I see where you are going. The air gives it structural integrity just like a balloon. Very interesting indeed. I like the idea. Your are in for a time consuming project cutting all the cans and joining them. But that is part of the fun. My last scratch built was doomed from the start and I never finished it.

Soldering seems like it would add a lot of weight, but would surely add strength and seal it up well. Be sure to have the upper can slide over the lower can so you want have any edges sticking out there for air brakes. The rings left on the cans would add some structure like you say, like a zeppelin.

You need to think through the wall (TTW) fin mounting as well. I wouldn't trust the fins just attached to a flimsy beer can.

In your top section, or payload section, I would suggest putting a smaller diameter tube inside the main body tube. Just like a motor mount but up top. Foam around the inner tube. This would give some weight up top and add some strength for your ejection charge so it doesn't blow up your top section. Maybe use a red bull can to stick with your aluminum can theme. Of course, you would have to have a flight computer for that setup. Unless you used a stuffer tube running the length of the rocket and used motor eject. That would require even more sealing and what not though.

What length are you planning on making this rocket? I am thoroughly interested now.

Oh, I looked through the "Bible of Modern Rocketry" at that Mylar rocket. He just tells about it being launched and recovered. Not details on its construction other than mentioning having framework inside the rocket, which you shouldn't need.

JStarStar said:

Remember until about 1972-73 or thereabouts, pop and beer cans used to be much thicker/heavier -- I think maybe made of steel in some cases.

The reason I remember was I was a teenager in those years, I drank a lot of pop, and when I was 13-14 it took quite a bit of muscle power to crunch a pop can with your bare hand. But all of a sudden I was 15-16-17 and I was crushing pop cans like eggshells. I knew I was getting bigger and stronger and all that stuff, but mainly the difference was they started making the cans out of much lighter aluminum. So woo hoo for me, I guess.

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Yes. Some were steel. I can remember them rusting. We had some around my old place for a long time. Not sure where they ended up. And I believe they were steel even after 1972 and 1973 because I wasn't born until 1979. I do remember seeing steel cans though.

Mike

I will get the plan through the manufacturing of a test length before I worry about overall length. I was thinking to simplify things with some sort of motor mount with integral fins and then a chute at the motor end, and let the motor eject itself backwards with it's delay charge.
I was thinking of going down to red bull tins as the main body size, and with a load more complexity you could make a central core tube using cigar tubes, which are about 3/4" I think. Or just use a tiny motor and use cigar tubes as the body!! It gets sillier by the minute.
I will report back when I have soldered or glued some together.
Can someone report back with the weights per ft of commercial carbon body tube in these sizes please?

The inflatable rocket was the Dude by Estes.

[video=youtube;4oAPspH41i8]https://www.youtube.com/watch?v=4oAPspH41i8[/video]

A metal body tube does indeed violate the safety code.

If it comes in ballistic (arc over and streams in like a javelin with gravity or under power) and hits a human, the metal tube will slice into them and take a "core sample" of their head and brain (or whatever other body part you hit).

A cardboard tube will crumble if thin walled or it will be blunt if thicker walled.

Yes, generally a nose cone that is too hard or dense is a concern, but a metal tube is "primary structure". it is not a small part like a motor hook or screw eye.

This will violate National Fire Code and be illegal in most states.

If you injure or kill someone (other than yourself) you could be subject to criminal or civil prosecution.

Why not think up a more intelligent and safer project to challenge yourself?

Build and successfully launch and recover a boost glider.


Build and successfully launch and recover a helicopter recovery rocket.


Build and successfully launch and recover a scale model od something cool.

The Dude, that's the inflatable rocket. Didn't know it was Estes.

I am pretty sure the rocket the OP is talking about will have a nose cone thus it would not be a rocket powered core drill. The nose cone will still be what hits first and the body tube would likely rupture and crush. It's not aluminum conduit or a piece of drill stem. This rocket coming in ballistic will have less mass than an equal sized fiberglass rocket. A 3 lb fiberglass rocket with an aluminum tipped nose cone full of binary foam coming in ballistic, or under power, is pretty dangerous, can undoubtedly puncture car hoods and would be deadly. The foam would hold the nose cone together. I have seen a thick cardboard tube tossed (by an idiot mind ya) off of the roof of a paper machine building and it went through the windshield of our work truck. That was just chucked over the side and free fell. Had it hit someone, it would have been lights out. Fiberglass is more rigid than a few beer cans, even the thin wall stuff. If the cans were filled with foam, that would be quite different. But he is talking about pressurizing them with air. I am not arguing against that it could be dangerous but I don't think anymore so than a fiberglass one. Shoot, a CA impregnated balsa NC is pretty darn tough.

I am no expert when dealing with the rocketry safety codes or the National Fire Codes, so I did some reading to refresh my memory.
For a model rocket, such as what I build, the metal body tube certainly does violate the codes. Even the metal tip violates the model rocket safety code. But many NCs with metal tips are sold with kits advertised to be able fly on G motors, or smaller. I have stayed away from the metal tips in any case. I haven't stepped up to high power yet.
NFPA 1122 lists breakable plastic as an acceptable material. How breakable? Is thin wall fiberglass considered breakable? G12?
NFPA 1127 and NAR Safety Code for High Power Rockets both state that ductile metal can be used when necessary. Beer cans are made from a ductile metal. Is it necessary? Necessary, substantial and breakable are pretty vague since neither are clearly defined in the codes, that I can find.
What the heck is blue tube considered?

Not trying to start an argument on the codes. Like I say, I am no expert by far, nor am I rocket scientist. Just stating what I read.

Whether it is more dangerous than a standard fiberglass rocket or not, it DOES VIOLATE the codes for model rocketry. But is covered under the high powered codes. So.....yeah.

And as mentioned:

shreadvector said:

......
Build and successfully launch and recover a boost glider.


Build and successfully launch and recover a helicopter recovery rocket.


Build and successfully launch and recover a scale model od something cool....

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Great ideas. I have a V2 ready for launch, a heli recovery rocket on paper and a boost glider rattling around in my head.

Mike

It seems a crying shame that this lightweight tubeular material, that is free and abundant may get sidelined by a technicality in the rules.
If you take the time to quickly cut both ends off a beer can with the bread knife, you will see how light the tubular part is. It is only 4 thousandths thick, so hardly core drill status!
Please be assured that I won't be breaking any of the rules, and if I am told it is not a goer by my rocketry club then that will be it, but I will still make a test tube to try out the joining methods described.
Luckily I work with composites in my day job, so I will have to spiral wind something nice, and non metallic, but where's the fun in that!

Rog, Birmingham, UK.

Silverbrewer said:

...

Rog, Birmingham, UK.

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Wait a minute... you're in Blighty !!! While I suspect the U.K. has a similar definition for model rocket materials as the U.S. NFPA codes I don't know that for a fact. The NFPA codes are the basis for the insurance coverage offered by the NAR and Tripoli and separates what we do from amateur rocketry. Anyway I'd be interested to hear what the locals say about your project and if there is a venue where something like it could be flown legally and safely.

Samb:- I think our U.K. rules follow yours, but I have yet to go to my nearest launch sites to find out! Not much action from either of my club options at the moment because of crap weather etc. there is no where around here with good sounding names like Black rock desert, and every time you look up there is a bloody plane flying over! I think the launch ceiling around here is about 3000 ft, and most of you guys could piss that!
I did once have a hand making something that got launched from Woomera though, but did not manage to get myself on a jolly out to see it. (Google "Chevaline project") saw the bits when they got back from Australia though!! Totally knackered, cos they didn't bother with chutes!!!

Silverbrewer said:

It seems a crying shame that this lightweight tubeular material, that is free and abundant may get sidelined by a technicality in the rules.
If you take the time to quickly cut both ends off a beer can with the bread knife, you will see how light the tubular part is. It is only 4 thousandths thick, so hardly core drill status!
Please be assured that I won't be breaking any of the rules, and if I am told it is not a goer by my rocketry club then that will be it, but I will still make a test tube to try out the joining methods described.
Luckily I work with composites in my day job, so I will have to spiral wind something nice, and non metallic, but where's the fun in that!

Rog, Birmingham, UK.

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It's not a technicality in the rules. It's one of the fundamentals of rocketry as an amateur activity relatively safe from legal regulation and control.

In the very early days of model rocketry the "founding fathers" realized allowing metal parts in model rockets would drastically raise the danger factor. The "basement bomber" days of the 1950s and early 60s were rife with stories of kids blowing their fingers, hands, heads off when their pipe-bomb rockets went off in their faces.

Since then the rules in non professional rocketry have been pretty much inviolate. No metal parts for significant sections of the rocket body.

In the US in recent weeks we had a tragic incident in which a man was killed by a rocket. It is the first reliable report of a fatality resulting directly from hobby rocket flight in some 55 years. If we allowed metal bodies for rocket construction it would happen every two weeks. See Shreadvector's quite accurate description of the "core sample" phenomenon.

Forget it.

While I agree with the safety code as written, technology has certainly changed the nature of some model materials since it was created.

Ironically, a carbon fiber or even fiberglass model rocket legal in terms of the model rocket safety code could, under the right conditions, do exactly the sort of body part core sampling described in that earlier post.

By comparison, the beer can model might be safer.

Tab28682 and J starStar:- Yes it is indeed a quandary.

Getting away from aluminium for a moment, but sticking with micro thin body structures with contained pressurisation to give them the required strength, a micro thin carbon or Kevlar structure would probably do the same job, (at a cost) it would be legal and very very light. At this envisioned thickness it would not be reliably airtight, and I dare not say what I would consider using as an expandable inner air containment membrane, but any resultant sponsorship could raise an eyebrow!! Tubular Prophylactives don't sound like they can legally fly either, but they can

Back to aluminium.....As discussed, the rules are correct if you think of a metal tube as substantialy constructed sheet structure or normal wall thickness tube, but a bit over the top for a wafer thin, light alloy can with integral end caps. That does not make the rule incorrect, just perhaps in need of clarification or some leeway.

The same is true in my opinion regarding modern composite tubes which are ideally engineered to withstand immense compression forces, and if wafer thin, form a circular razor if you wish to describe them in a rather silly way. If those sensible forefathers had had composites on the table when formulating the rules they would not have viewed them lightly.

If, as a stupid example I suggested blowing a thin walled tube from molten glass and flying that, it would be legal! A carbon fibre tube is in effect a thin walled shatterable tube in much the same way as glass would be, and when mixed with Kevlar is a nearly impossible to shatter tube that happily transfers all its energy to its leading edge if called upon to do so. Not good.

Probably additional rules will need to address these immensely resilient tubes at some time in the future, with inbuilt crumple zones....oh wait a moment....that's almost exactly what an aluminium can behaves like! No inherrant compression strength whatsoever....so it crumples!

Well at the moment there is no easy answer to any of this, and the rules must be adhered to to keep insurance valid. I am not trying to annoy anyone or push any boundarys, just put the ideas out there and with a bit of (by the looks of it) , static testing, see if the resultant structures would cope with the stresses.

But all things considered, I know which I would prefer to be hit on the head by.....None of them.

rharshberger said:

If i get what your asking, a tube built this way would be lighter than an equivalent airframe tube of cardboard , you would still need the ability to mount recovery gear and motor and fins. More trouble than its probably worth. It also violates the "no substantial metal parts" of the model rocket safety code.

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Hmmm, for low power rockets the rule is:
1.Materials. I will use only lightweight, non-metal parts for the nose, body, and fins of my rocket.

The poster would undoubtably be violating the code since he is using it for the body.

Your comment " It also violates the "no substantial metal parts" of the model rocket safety code" seems a pretty sweeping generalization.

Actually the most dangerous piece of metal found in MANY rockets is, IMO, the engine hook. As provided it is a pointed and somewhat sharp edge small piece of metal which could certainly cause a gash if someone tries to catch the rocket on descent (or if accidentally hit by a rocket falling tail first, which is normal descent position.) Even a rocket coming down under an appropriately sized streamer could cause an injury. For this reason, I put an extra bend in the hook so the most tailward portion is rounded.

BTW, CATCHING a LOW power rocket is NOT a violation of the standard Model Rocket Safety Code. It IS a violation of the High Power Model rocket safety code:
13.Recovery Safety. I will not attempt to recover my rocket from power lines, tall trees, or other dangerous places, fly it under conditions where it is likely to recover in spectator areas or outside the launch site, nor attempt to catch it as it approaches the ground.

Of course, attempting to catch a high power rocket on descent may also be a qualification for the Darwin Awards, assuming the individual hasn't already reproduced.