what could go wrong?

Hi!
I'm new here, and I've been studying rockets for a couple months.
I'm aware I'm probably being naive here, but I'd like to understand why

I'm under the impression that making a big (solid fuel) rocket is not so hard.

For instance, let's assume I get a 20cm diameter x 200cm length PVC tube, fill it up with rocket candy, put some cardboard around it with a nice nose cone and adjust its CG and CP with a combination of mass on the top and fins on bottom. (I guess I need to consider how the CG moves while the fuel burns.)
Then I launch it on the simplest rocket launcher I can think of (something like 3 metal bars pointing up with the rocket between then), high enough for the rocket to get aerodynamic stability (I'd need to make some calculations).

Is there something else I would need to worry about? Otherwise model-rocket-science sounds kinda "trivial" (unless you start to play with liquid fuel/multi-staging or REALLY big (and expensive, and dangerous) rockets).

kavelot said:

Hi!
I'm new here, and I've been studying rockets for a couple months.
I'm aware I'm probably being naive here, but I'd like to understand why

I'm under the impression that making a big (solid fuel) rocket is not so hard.

For instance, let's assume I get a 20cm diameter x 200cm length PVC tube, fill it up with rocket candy, put some cardboard around it with a nice nose cone and adjust its CG and CP with a combination of mass on the top and fins on bottom. (I guess I need to consider how the CG moves while the fuel burns.)
Then I launch it on the simplest rocket launcher I can think of (something like 3 metal bars pointing up with the rocket between then), high enough for the rocket to get aerodynamic stability (I'd need to make some calculations).

Is there something else I would need to worry about? Otherwise model-rocket-science sounds kinda "trivial" (unless you start to play with liquid fuel/multi-staging or REALLY big (and expensive, and dangerous) rockets).

Click to expand...

Besides the PVC not being able to hold the pressure and becoming a burning mass about to land somewhere you have no control over...I think you have it covered.

Massive CATO with burning propellant spewing around, people getting hurt, property destroyed, out of control fires and the Feds arresting you? That seems within the realm of "what can go wrong" along with "what has gone wrong". Just saying.

I think the cardboard fins and nose cone give it a special touch...

Before anyone scares you off from Rocketry, there are several types. Most of us here are into High Power, Mid Power, and Model Rocketry aka Low Power and Research rocketry/Amateur rocketry. The Research section of which applies to the kind of rocketry you are asking about is off limits until certain conditions have been met. One of the conditions is iirc obtaining at least a Level 2 certification from the National Association of Rocketry or the Tripoli Rocketry Association. The reasons that section of the forums is off limits is that the information contained therein is dangerous in the hands of the inexperienced.

PVC imagine all of the above scenarios and add to the uh-ohs the fact that you put yourself and others in danger of flying shrapnel that is (I have heard) very difficult for doctors to see on X-rays. Our rockets are all made from cardboard, plywood, fiberglass, carbon fiber, very limited amounts and types of metal, and etc. Also they conform to the federal regualtions set forth in FAR 101, and several NFPA codes. Any rocket made from PVC is likely to be heavier than the somewhat unrestricted Class 1 rockets. Lots of people play around with PVC and "rocket candy", its far more dangerous than they think.

ok, that was the answers I was looking for

so, assuming I did this on a desert and didn't end up killing anyone or getting arrested

now I've wised up and learned I need to calculate the pressure the cylinder should be capable of holding
my next try would be to replace the PVC+cardboard with a aluminium/steel cylinder

this wouldn't be so easy to find, but other than that it seems trivial

don't get me wrong, I'm just trying to understand how HARD (not that it needs to be hard to be fun, but most people think it is) is launching a "big" rocket

kavelot said:

ok, that was the answers I was looking for

so, assuming I did this on a desert and didn't end up killing anyone or getting arrested

now I've wised up and learned I need to calculate the pressure the cylinder should be capable of holding
my next try would be to replace the PVC+cardboard with a aluminium/steel cylinder

this wouldn't be so easy to find, but other than that it seems trivial

don't get me wrong, I'm just trying to understand how HARD (not that it needs to be hard to be fun, but most people think it is) is launching a "big" rocket

Click to expand...

Launching one, not hard at all. Much cheaper to do it with premade motors and a few High Power rocket kits at NAR/TRA sanctioned club events. NAR/TRA clubs have people willing to work with you as mentors, to safely enjoy our hobby. The stuff we launch in High Power has more ISP per ounce than "rocket candy" (if IIRC again).

thanks for the answer
I live in south america, and apparently it's not easy to find people launching rockets around here
I just bought a 30cm rockets (and some A4 engines) to begin playing with, so I guess I'll start with that
but I actually don't plan on going bigger than D engines... I think I'll have more fun trying something like multi-stage after instead of growing bigger
I was just wondering how hard that actually is to make something really big

kavelot said:

thanks for the answer
I live in south america, and apparently it's not easy to find people launching rockets around here
I just bought a 30cm rockets (and some A4 engines) to begin playing with, so I guess I'll start with that
but I actually don't plan on going bigger than D engines... I think I'll have more fun trying something like multi-stage after instead of growing bigger
I was just wondering how hard that actually is to make something really big

Click to expand...

Definitely find out what the laws in your country are, there a quite a few "design considerations" when building large, heavy rockets. Fly lots of Low Power (LPR) then step up to MPR, and eventually HPR. That progression will give you all kinds of insight into the difficulties of building and flying larger more powerful rockets.

kavelot said:

thanks for the answer
I live in south america, and apparently it's not easy to find people launching rockets around here
I just bought a 30cm rockets (and some A4 engines) to begin playing with, so I guess I'll start with that
but I actually don't plan on going bigger than D engines... I think I'll have more fun trying something like multi-stage after instead of growing bigger
I was just wondering how hard that actually is to make something really big

Click to expand...

Now that sounds like a very good plan!

Many/most/pretty much all of us here started with small rockets and "grew up" from there. I still launch small rockets and enjoyed it from the very first day onward. I just told someone at the field this weekend that I'm in no hurry to get to the next level since I'm enjoying the experiences of where I am so much right now. Have fun and enjoy the trip!

kavelot said:

Hi!
I'm new here, and I've been studying rockets for a couple months.
I'm aware I'm probably being naive here, but I'd like to understand why

I'm under the impression that making a big (solid fuel) rocket is not so hard.

For instance, let's assume I get a 20cm diameter x 200cm length PVC tube, fill it up with rocket candy, put some cardboard around it with a nice nose cone and adjust its CG and CP with a combination of mass on the top and fins on bottom. (I guess I need to consider how the CG moves while the fuel burns.)
Then I launch it on the simplest rocket launcher I can think of (something like 3 metal bars pointing up with the rocket between then), high enough for the rocket to get aerodynamic stability (I'd need to make some calculations).

Is there something else I would need to worry about? Otherwise model-rocket-science sounds kinda "trivial" (unless you start to play with liquid fuel/multi-staging or REALLY big (and expensive, and dangerous) rockets).

Click to expand...

Having learned through model rocketry and now struggling to progress to high power I'm still a relative beginner.

So far my experience has been trouble free but only thanks to the advice of others, particularly on this forum.

I think your question should not be phrased "what could go wrong" with an implication that it seems easy, but more so, "it seems easy so what have I missed".
My experience of web sites and books on the subject tend to tell you "how" but rarely "why". I've found that nothing is easy with rocketry components until you understand why. Then it's "flaming obvious". To a beginner no question is naive or stupid. Not asking the question is both of those things however.

As I move into HPR my limited advice would be:

1. Safety is paramount - your own and that of others.

2. Design to the nth degree. Keep your tolerances as small as possible and use proven components.

3. Test, test, and test again.

4. Ask "stupid questions" and question stupid answers (you will get some).

5. If you want to push your limits do it in very small and controllable steps.

Above all, enjoy what you are doing and challenge yourself to improve with each flight.
From a beginner onwards, rocketry can be a real challenge. Not only to your design and build skills but also to your humility.

"How easy can it be"? Very easy. If it wasn't for the air, balance, finding somewhere to fly, ejection timing, power to weight ratios, flying clubs, safety rules, demands on your wallet, hang gliders, dry crops, industry suppliers, recovery, electronic reliability, etc. etc. etc. ........

But keep going because the satisfaction of a perfect design is worthwhile when it flies exactly to plan - on any motor and rocket size.

SO.

There are two really good books (in English, don't know about translations but seems your English is pretty good) that explain everything you need to know in much detail.

Handbook of Model Rocketry by G. Harry Stine

Modern High Power Rocketry 2 by Mark Canepa

Between these two books you can learn everything there is to know about rocketry; however, experience is the best teacher. The books help you be safe and get ideas, and experience solidifies those ideas into fun practice.

Rocketry, like anything, needs to be "learned along the way." If you want to ride a motorcycle, start with a tricycle, then a bicycle with training wheels, then a bicycle without training wheels, then a moped, then a motorcycle. Make sense?

Thanks for all the hints guys!
I found the "Handbook of Model Rocketry" to buy here. I didn't find the other one, but I guess this is enough to begina

Space Oddity said:

I think your question should not be phrased "what could go wrong" with an implication that it seems easy, but more so, "it seems easy so what have I missed".

Click to expand...

yeah, I tried to say that with "I'm aware I'm probably being naive here, but I'd like to understand why", but I admit this wasn't a good title

kavelot said:

Hi!
I'm new here, and I've been studying rockets for a couple months.
I'm aware I'm probably being naive here, but I'd like to understand why

I'm under the impression that making a big (solid fuel) rocket is not so hard.

For instance, let's assume I get a 20cm diameter x 200cm length PVC tube, fill it up with rocket candy, put some cardboard around it with a nice nose cone and adjust its CG and CP with a combination of mass on the top and fins on bottom. (I guess I need to consider how the CG moves while the fuel burns.)
Then I launch it on the simplest rocket launcher I can think of (something like 3 metal bars pointing up with the rocket between then), high enough for the rocket to get aerodynamic stability (I'd need to make some calculations).

Is there something else I would need to worry about? Otherwise model-rocket-science sounds kinda "trivial" (unless you start to play with liquid fuel/multi-staging or REALLY big (and expensive, and dangerous) rockets).

Click to expand...

It's a really big rocket motor..... Making a rocket motor of this size successfully is not easy, especially a sugar motor.....and you will need written permission of your national aviation control authority to launch it, regardless of your country.

kavelot said:

ok, that was the answers I was looking for

so, assuming I did this on a desert and didn't end up killing anyone or getting arrested

now I've wised up and learned I need to calculate the pressure the cylinder should be capable of holding
my next try would be to replace the PVC+cardboard with a aluminium/steel cylinder

this wouldn't be so easy to find, but other than that it seems trivial

don't get me wrong, I'm just trying to understand how HARD (not that it needs to be hard to be fun, but most people think it is) is launching a "big" rocket

Click to expand...

It is not trivial to make large sugar motors. Sugar Shot 2 Space started 10 years ago and has still not successfully launched a 150 mm sugar motor AFAIK.

kavelot said:

thanks for the answer
I live in south america, and apparently it's not easy to find people launching rockets around here
I just bought a 30cm rockets (and some A4 engines) to begin playing with, so I guess I'll start with that
but I actually don't plan on going bigger than D engines... I think I'll have more fun trying something like multi-stage after instead of growing bigger
I was just wondering how hard that actually is to make something really big

Click to expand...

We do not know the laws in your country. Make sure you do or you could get into serious trouble.

Internationally however the laws are fairly uniform for sending objects into controlled airspace. For all but the smallest rocket you will require the approval of your national aviation authority (In the US it's the FAA and you need a "waiver" of the rules which do no allow the activity.) before you launch.

kavelot said:

Thanks for all the hints guys!
I found the "Handbook of Model Rocketry" to buy here. I didn't find the other one, but I guess this is enough to begina

yeah, I tried to say that with "I'm aware I'm probably being naive here, but I'd like to understand why", but I admit this wasn't a good title

Click to expand...

Amazon is your friend. You can purchase almost any book there....

Bob

You haven't mentioned how you expect to get the rocket back to the ground, presumably in one piece. That's an art in itself...