Amateur Rocketry

[Opus_723]

Is anyone around here experienced in hobby rocketry?

I've been thinking it would be a lot of fun, but I have very little expendable income for hobbies right now and it seems like a spendy one. I saw that one amateur group actually managed to build a suborbital rocket, which was really inspiring! But I'm stuck with match rockets for now I think.

Does anyone who launches rockets have any good stories have any good stories or advice to newbies who are interested?

Edited July 25, 2018 by Opus_723

[Cunjo Carl]

Oh, I used to do a lot of amateur rocketry with my folks. For what it's worth, it's a very fun hobby.

If you have funds to build from a kit, the 1-2ft (~30-60cm) -ish sized rockets launched with engines at the low end of their range tended to be the best experience for value. Loading higher power motors into a rocket make it go higher and faster, which mean you get to see it for less long, and it drifts on its parachute dramatically farther away. Most rockets that are lost are lost to parachuting into distant trees! Since they go pretty high, there can definitely be stiff breezes up above that you don't feel on the ground. It's not a big deal, and chasing after them is part of the fun! But if you're going on a budget, losing a rocket to the wind is pretty obnoxious. When you use a bigger rocket with a smaller engine, it's helpful to get a shorter-end delay for the parachute charge so the chute will still pop at the rocket's apex. Most kits will provide recommendations.

Choosing your motors can be hard at first. Fortunately, experience in KSP will make it a lot more intuitive! Another bit of good news is there's some very common and standard sizes. Most rocket engines are Estes brand, or atleast conform to their standards. The way they're designated is by a letter and 2 numbers. From a super simple perspective, the letter tells you how high the rocket will go (total impulse), and the first number tells you how fast (roughly proportional to thrust within a given letter). The second number tells you how much delay there will be between the engine burning out, and the parachute-popping charge from firing. All of the common starter engines (1/2A , A , B , C) are the same diameter, which gives you a good degree of flexibility. Naturally, choosing an engine too 'small' causes the rocket not to lift and too large causes... more exciting problems! Here's a list of some favorites for comparison: http://www2.estesrockets.com/pdf/Estes_Engine_Chart.pdf

When you glue together rockets, proper glue choice is important! For a first rocket, I'd recommend 5min epoxy. It has its own troubles, but they're less than that of the cyanoacrylates (crazy glue), the urethanes (rubber cement) or the longer cure epoxies (which are a better choice in the long run). I wonder if anyone has experience with gorilla glue? It came out after my time.

Packing chutes is really an art form. Most rockets will have instructions, but the one thing I'll add is that a light dusting of baby powder really helps them open up consistently. If you do a smaller rocket with a streamer, powder up that thing too!

Nothing beats the smell of burning gun powder SRBs in the morning! If you do decide to give it a try, I hope you have fun, @Opus_723.

As for stories, I once had a tiny rocket named the minnow (or perhaps the mosquito?) Anyways, it was a tiny thing that was barely large enough to contain its engine. My family and I were out in the desert, and figured if we were ever going to try overpowering it, this was the day! So we loaded the poor 1/2A rocket with a high thrust A, and hit the ignition! There was a faint "zwip" noise and the thing simply disappeared! No smoke trail, nothing. A good half hour of searching lead us to find it a hundred yards away, but it was a good lesson in F=ma!

Edited July 25, 2018 by Cunjo Carl

[sevenperforce]

I used to build my own rockets out of sugar, stump remover, and PVC. Safe enough as long as you use packed clay rather than metal for the nozzle and endcap. Better isp than black powder and lots of fun.

[Cunjo Carl]

17 minutes ago, sevenperforce said:

I used to build my own rockets out of sugar, stump remover, and PVC. Safe enough as long as you use packed clay rather than metal for the nozzle and endcap. Better isp than black powder and lots of fun.

I also used to build rockets and out of more garden variety materials, but for someone starting off rocket candy is a little bit of... well trial by fire. Good for those that have a lot of non-burnable space and eyebrows to spare!

I think a happy in between for cheap home built rockets are water rockets (which can apparently get pretty powerful if taken seriously), and alcohol rockets. I'll never forget my first water rocket. That thing... uh... really moved! I live in a safety culture, so "Wear eye and ear protection, and operate in a safe, open environment with responsible adult supervision." If you're an irresponsible adult, goodness help you I suppose!

How high did you get with those rockets @sevenperforce? Did the mixtures treat you well? I like the choice of PVC, by the way!

[Bill Phil]

I remember someone in my high school attempting a two stage water rocket. Troube was... the pressure came from the launcher. It can't really be two stages. I'm sure it can be done, just not with that setup.

[sevenperforce]

On 7/25/2018 at 7:52 PM, Cunjo Carl said:

I also used to build rockets and out of more garden variety materials, but for someone starting off rocket candy is a little bit of... well trial by fire. Good for those that have a lot of non-burnable space and eyebrows to spare! How high did you get with those rockets @sevenperforce? Did the mixtures treat you well? I like the choice of PVC, by the way!

The 1" sugar candy rockets I built had a TWR of around 10 but only about 5-6 seconds of burn time. Nice red exhaust plume, too.

PVC wasn't actually a reactant; the purpose of the PVC was to allow me to use a hand press to pack the plug, propellants, and nozzle. PVC will hold the pressure nicely. I cannot stress this enough, though: do NOT use a metal nozzle or cap with a PVC rocket. You MUST use a substance (like clay) with a lower burst pressure than PVC. Otherwise you stand a very, very good chance of creating a pipe bomb. PVC shrapnel is lethal.

Another option is to create your own COPV by wrapping a paper tube in narrow, helical layers of duct tape under tension. If you get it right, that will have enough strength to allow you to pack propellants, and you can use a cast clay nozzle or something even sturdier, since the burst mode of a duct-tape COPV is benign. It will have a better mass ratio than a PVC option.

Otherwise you have to melt and cast the rocket candy, which is inherently really dangerous.

Quote

I think a happy in between for cheap home built rockets are water rockets (which can apparently get pretty powerful if taken seriously), and alcohol rockets. I'll never forget my first water rocket. That thing... uh... really moved! I live in a safety culture, so "Wear eye and ear protection, and operate in a safe, open environment with responsible adult supervision." If you're an irresponsible adult, goodness help you I suppose!

The alcohol bottle rocket is neat...basically making a liquid fuel-air bomb inside a bottle, and then opening one end.

On 7/26/2018 at 3:27 AM, Bill Phil said:

I remember someone in my high school attempting a two stage water rocket. Troube was... the pressure came from the launcher. It can't really be two stages. I'm sure it can be done, just not with that setup.

You could do parallel staging easier than you could do serial staging.

Edited July 27, 2018 by sevenperforce

[wumpus]

3 hours ago, sevenperforce said:

You could do parallel staging easier than you could do serial staging.

Does that rely on fins/spin stablization?  I've always wondered just how exact the burn lengths on parallel staging had to be, and suspected that would be a problem.

It also just hit me that I think I had a water rocket that was designed to accept the "standard" water rocket as a top stage.  My neighbor had a "standard" rocket, and I'm wondering if we could have put them together...  This was way back in the 1970s so my memory is rather iffy.  I'd be that the upper stage would drift waaaaay further off course than we'd ever expect, and our favorite launch site wasn't all that big.

[sevenperforce]

40 minutes ago, wumpus said:

Does that rely on fins/spin stablization?  I've always wondered just how exact the burn lengths on parallel staging had to be, and suspected that would be a problem.

It also just hit me that I think I had a water rocket that was designed to accept the "standard" water rocket as a top stage.  My neighbor had a "standard" rocket, and I'm wondering if we could have put them together...  This was way back in the 1970s so my memory is rather iffy.  I'd be that the upper stage would drift waaaaay further off course than we'd ever expect, and our favorite launch site wasn't all that big.

Parallel staging is rather challenging with hobby rockets because thrust and burn duration have to be exactly the same, and combustion instabilities usually preclude that. But with water rockets you can make the two boosters 100% identical and verify in advance that they're going to have exactly the same thrust and "burn" length. 

Probably best to set it up like an Atlas, with the parallel boosters on a jettisonable skirt that simply drops away as soon as the side boosters run out of water. Sustainer in the middle.

[Cunjo Carl]

5 hours ago, sevenperforce said:

PVC wasn't actually a reactant; the purpose of the PVC was to allow me to use a hand press to pack the plug, propellants, and nozzle. PVC will hold the pressure nicely. I cannot stress this enough, though: do NOT use a metal nozzle or cap with a PVC rocket. You MUST use a substance (like clay) with a lower burst pressure than PVC. Otherwise you stand a very, very good chance of creating a pipe bomb. PVC shrapnel is lethal.

Oh, I was assuming it was your fuselage choice, but it sounds like it was also your engine housing? When I was younger we also used PVC for a bunch of medium pressure applications. It's tough, cheap, mildly fire resistant (though not terribly heat resistant), and can withstand a good range of chemicals and solvents, so we were always finding creative applications. We'd never considered using it for a fuselage or a rocket motor. I just liked the idea! I'll actually be using clear PVC soon to make a prototype vacuum 'distillation' reflux extractor unit a family friend wanted.... it's really versatile stuff.

 

[sevenperforce]

15 hours ago, Cunjo Carl said:

Oh, I was assuming it was your fuselage choice, but it sounds like it was also your engine housing? When I was younger we also used PVC for a bunch of medium pressure applications. It's tough, cheap, mildly fire resistant (though not terribly heat resistant), and can withstand a good range of chemicals and solvents, so we were always finding creative applications. We'd never considered using it for a fuselage or a rocket motor. I just liked the idea! I'll actually be using clear PVC soon to make a prototype vacuum 'distillation' reflux extractor unit a family friend wanted.... it's really versatile stuff.

Yeah, I would use cardboard for a fuselage, for sure. PVC has really good behavior under tensile load so it will retain (and return to) its shape under most circumstances. Although I did have a time that I was trying to do a static fire, and strapped the PVC to the test stand with a little too much tape, and so when the motor fired the heat weakened the PVC, heated the tape, and squeezed the casing shut in the center like a cardboard tube. That was quite a bang.

It's possible to build a hybrid rocket using PVC as combined fuel + casing; you just have to abrade the inner surface to expose a lot of surface area and then hook it up.

[Gargamel]

Oddly enough, when introducing my nephew to my old hobby of rocketry, I had hard time finding any nice 3d printed launch pads.  So I designed and printed my own. 

Feel free to download and print if you have access to a printer:

 

https://www.thingiverse.com/thing:588121

Edited July 30, 2018 by Gargamel

[Gargamel]

Oh, and a cool little program I found a while back that helps in designing rockets from scratch, us KSP'ers should love this app, even if you never build one, as it will do full flight sims too:

 

http://openrocket.info/

On 7/25/2018 at 5:58 PM, Cunjo Carl said:

I wonder if anyone has experience with gorilla glue? It came out after my time.

Gorilla glue has the habit of expanding a bit into a foam like material.  Which has it's plusses and minuses.  It is also water accelerated when curing.  For woodworking projects, I would wet down one piece with a damp rag, and apply the glue to the other piece.  The expansion can be good for slight gap filling when that gap is not a structural element, as the 'foam' is not very strong.  

[Zeiss Ikon]

During my adult model rocketry period (late 1990s), I demonstrated that, at least with plywood and paper as the materials (sufficient for supersonic flights with the correct choice of engines), ordinary white glue (aka Elmer's) is more than strong enough, and there's no reason to use anything else unless you're in too much of a hurry to wait for it to dry (additional advantage: unlike epoxy or cyanoacrylate, about 60% of the mass of white glue applied evaporates by the time it's fully hardened).  Using double glue joints (an old, old technique that originated no later than the 19th century, used for furniture construction) and self-bracing construction (fins through the body tube, bonded to the motor tube and centering rings), I flew my NAR HPR Level 1 certification (in 1999) with a rocket in which the structure was bonded solely with Elmer's White Glue.  The engine was an Aerotech H128 (29 mm reloadable), rocket kit was a Thug (don't now recall the kit maker).

The bond created by double gluing with Elmer's is stronger than the base material -- plywood/plywood bonds will break in the wood when tested to destruction.  There is no bond you can make with any adhesive that's stronger than "stronger than the base material."  To improve on that construction you'd need to either coat the entire structure in a composite (fiberglass in resin or epoxy, for instance) or change to stronger material.

[Cheif Operations Director]

On 7/25/2018 at 3:30 PM, Opus_723 said:

Is anyone around here experienced in hobby rocketry?

I've been thinking it would be a lot of fun, but I have very little expendable income for hobbies right now and it seems like a spendy one. I saw that one amateur group actually managed to build a suborbital rocket, which was really inspiring! But I'm stuck with match rockets for now I think.

Does anyone who launches rockets have any good stories have any good stories or advice to newbies who are interested?

Sort of dreaming/designing a liquid fuelled rocket.

[Gargamel]

7 hours ago, Zeiss Ikon said:

ordinary white glue (aka Elmer's) is more than strong enough,

White glue is really good.   Yellow wood glues (PVA), depending on the type you get and it's intended purpose, have very similar properties.   The problem, in particular with anything outdoors, is that most Whites and some PVA's can reabsorb moisture from water contact, and become solvent again.  So crashing a rocket into a puddle, the glue might come undone.   Anything I need to get glued in up in a hurry for woodworking, I use a white glue called Assembly 8, has about 5 minutes of open time, and about 15 for a working cure time. 

I've done a lot of research into glue types for a variety of purposes, but I've never considered wet mass vs dry mass.   I'll have to look into that for some applications. 

7 hours ago, Zeiss Ikon said:

Using double glue joints (an old, old technique that originated no later than the 19th century, used for furniture construction)

I've built furniture professionally and as a hobbyist, never heard of this.  Care to share some links or something for further research? 

Edited August 3, 2018 by Gargamel

[sevenperforce]

5 hours ago, Gargamel said:

White glue is really good.   Yellow wood glues (PVA), depending on the type you get and it's intended purpose, have very similar properties.   The problem, in particular with anything outdoors, is that most Whites and some PVA's can reabsorb moisture from water contact, and become solvent again.  So crashing a rocket into a puddle, the glue might come undone.   Anything I need to get glued in up in a hurry for woodworking, I use a white glue called Assembly 8, has about 5 minutes of open time, and about 15 for a working cure time. 

I've done a lot of research into glue types for a variety of purposes, but I've never considered wet mass vs dry mass.   I'll have to look into that for some applications. 

I've built furniture professionally and as a hobbyist, never heard of this.  Care to share some links or something for further research? 

It just means that you apply a double layer of glue -- first, a layer on both surfaces to be joined (which you then allow to air-dry), and then a wet layer on one of the surfaces before joining and clamping. 

[Zeiss Ikon]

7 hours ago, sevenperforce said:

It just means that you apply a double layer of glue -- first, a layer on both surfaces to be joined (which you then allow to air-dry), and then a wet layer on one of the surfaces before joining and clamping. 

Exactly.  I first ran across the technique, specific to model building, almost fifty years ago in Keith Laumer's book, How to Design and Build Flying Models, but I've seen it touted by G. Harry Stine (one of the fathers of model rocketry) as well.  I got the impression it was an old technique, dating back to the invention of water soluble glues (casein glue was the first Elmers, introduced in 1947 by Borden -- mainly known for their milk products -- but the production and use of casein glue goes back to Egyptian times).  Modern white glue is polyvinyl acetate in water, and has as its main advantage over casein glue that it won't spoil in the bottle (casein glue is still sold in powder form, used mainly for sizing artist canvas).

The way I learned it was to rub the first layer of glue well down into the wood grain or paper surface, then when it was just barely still tacky, make the second application and join the parts.  Aside from overall joint strength, the other advantage is that the glue grabs very quickly when applied this way -- plain Elmer's will tack hold in ten or fifteen seconds from joining the parts, a process that takes up to a half hour if you apply the same total amount of glue and immediately join the parts.  Clamping can almost be eliminated for model construction purposes, total glue amount applied can be reduced (which, once again, helps with finished frame weight), and the finished joint is stronger than balsa, spruce, light-ply, and most hardwood ply.

[Gargamel]

11 hours ago, sevenperforce said:

It just means that you apply a double layer of glue -- first, a layer on both surfaces to be joined (which you then allow to air-dry), and then a wet layer on one of the surfaces before joining and clamping. 

Oh, yeah I've seen that.  Numerous tests have shown this to be slightly weaker than one layer of glue.   The first layer of glue soaks into the surface and starts to cure, and the second layer doesn't stick tho the first as well.      As well as the first layer still being wet.    Letting the first layer cure a bit weakens the bond some, but if it's still fresh, it'll have soaked in but will still bond better with the second layer.    Not saying it won't work, just that it's slightly weaker than both being wet. 

But this two layer technique is really only necessary for porous surfaces, like the end grain of wood, where the material itself would absorb so much of the adhesive, that the joint itself would be starved of glue. 

[Adstri]

I used to make bottle rockets. I would design and test them, And launch. It was basically my own space program.

Might get back into it!

Edited September 18, 2018 by Adstriduum