an explantion of rockets please

[jack_h]

i dont quite get the idea of rockets yet. i know you need two fuels, i think, then i know you have a combustion chamber and a nozel. what i dont get is the fuels and how much and what part you need. as soon as i can find on that i can make one, right.


And if any one has plans or detailed picture that would be a great help.

[BigtonyICU]

Let me give you a quick breakdown on rockets... I know where you can get plans but with you lack of info from you previous post I refuse to give those links to you (you'll kill yourself).

Yes you need fuel... but fuel doesn't burn in a rocket engine (combustion chamber) because there's no Air… well more prissily Oxygen. So you need to supply it with Oxygen or a strong oxidizer (IE. oxygen donor ex: Liquid N2O / Solids like KNO3, CLO4, NH4ClO4) you need depending on you fuel and oxidizer as much 80% oxidizer to 20% fuel ratio is required. As the combustion takes place the gasses expand, they are accelerated and ejected through the nozzle. As per Neuton 3rd law, every action has an equal and opposite reaction, the gases are push pushed down so the rocket is pushed up.

That's the easy explanation... but then you get in to lovely stuff like material tensile strength combustion temperature, softening of components due to elevated temperature. If you're using liquid fuel and oxidizer you need a way to pump those fuel (IE turbo pumps), cooling system to keep your combustion chamber from melting...shall I go on, and that's only for engine then you need to build the rocket... (okay building the rocket is easy work designing it is a hole different story) calculation Center of Pressure, center of gravity, Aerodynamic drag, stabilizing fin dimensions... well I think by now you get the idea

My suggestion is start small, really small (like pre-made solid rocket motor) start with models... then design the rocket around a pre-made motor, (you might want to know that you can get pretty impressive results by clustering and staging those engines (several 1000s of feet).

But most importantly they are SAFE (okay I say safe in relative terms don't go hold one in your hand and light it). And quite honestly you’re not going to save any money making them your self till you get in to large engines F-N class... I'll Quote Richard Nakka's saying... "Model rocketry is the art of making rocket fly; Amateur rocketry is the dream of making rocket fly"

If you go on and decided to build your own engines expect allot of set back. For every rocket that goes up 10 are going to stay on the ground and blow up. (I might sound pessimistic but that reality...)

If your young pay a lot of attention in science class (especially physics and chemistry) if you decide you want to go on get a BA in engineering...

I’m not trying to discourage you,… keep trying, get a good book and who knows

[jack_h]

thanks for that. im acctulay looking at liquid rockets one to for fun then hopefully one for a go kart. iv seen this plan on the web have a look and tell me what you think.

http://www.gramlich.net/projects/rocket/

[El-Kablooey]

If you want to make rockets, start wit solid fuels. They are easy and cheap to make! Google Rcandy, you'll find plenty of instructions for making rocket engines using sugar and potassium nitrate for fuel. I have made several dozen Rcandy engines and never had one blow up, it is not that difficult at all. Liquid fueled rockets may be a different story,, I have never tried but I don't see any reason that it would be all that difficult.

[jack_h]

howfun are these little solid fuel rockets.

just thinking would nos Nitros Oxide work because it has a fuel and an oxidizer for a liquid rocket.
http://www.gramlich.net/projects/rocket/

[El-Kablooey]

Who said they have to be little???? I have made some as big around as a coke can! NOS can be used as an oxidiser, in liquid fueled rockets, and in some solid fuel fockets like those packed with asphalt for fuel. The asphalt rockets do look extremely simple to build...

[larry cottrill]

Who said they have to be little???? I have made some as big around as a coke can! NOS can be used as an oxidiser, in liquid fueled rockets, and in some solid fuel fockets like those packed with asphalt for fuel. The asphalt rockets do look extremely simple to build...

jack h -

Though I have never flown rockets, I have also fired a few sugar and saltpeter engines, and one of the size El-K is talking about (actually, my younger some made and fired that engine, with my guidance) and it worked marvelously. It was a shaving cream can about 2/3 full of the melted sugar mixture. There are a lot of good safety rules about making such engines, but I think the most important are:

1. Work OUTDOORS
2. After you get the fuel grain poured (the slug of solidified fuel in the engine is called the 'grain'), handle the engine with care - do not let it get banged around or dropped before you fire it
3. Get plenty of distance between you and the engine before igniting - the bigger the engine, the greater the distance you need!

I think any solid fuel engine is potentially explosive if the fuel grain gets cracked, or if there is separation of the grain from the engine wall. Even sugar rocket grains are brittle enough to crack if badly handled. I wouldn't be surprised if practically all solid fuel engine explosions could be traced to a cracked fuel grain (maybe the real rocket experts will correct me if I'm exaggerating this). When we did our shaving cream can engine, we buried it in the ground (sandy soil) right up to the "nozzle" (the 1-inch diameter top rim) to absorb the energy of a possible explosion. But, we had handled our engine carefully and it ran great!

The ideal firing is to have a perfectly uniform progression from the rear end forward with constant surface area burning throughout the run, providing constant exhaust gas pressure in the chamber. If the surface area of the burn suddenly increases (as when encountering a large void or crack running through the grain), explosion is practically inevitable.

The great advantage of solid fuel rockets is simplicity. The great disadvantage is lack of control once firing starts - they are all or nothing, once you have ignition, until the grain is consumed. Solid fuel rockets are ideal for learning the basics of rocketry, and even small rockets can be pretty exciting to use. The simplicity of solid fueling also minimizes expense and greatly reduces the need for mechanical skills and precision tooling.

Again, the experts are free to correct anything I've said that might be misleading. I am out of my depth in this area.

L Cottrill

[El-Kablooey]

I'm definately no expert, but you sound right on the money to me, Larry. Rcandy burns pretty slow, but a crack greatly inreases the surface area, and could easily increase the burn rate enough to cause a cato.

[Ray]

I wouldn't be surprised if practically all solid fuel engine explosions could be traced to a cracked fuel grain

Not to pick nits...but to pick nits :)

Rocket motors don't typically explode. They over-pressurize. There is a significant difference, both in perception and in reality.

You are right on some fronts on the cracked grains causing problems. Sugar motors are more prone to this and need to be carefully handled as a result. AP/rubber motors almost never crack a grain, they are flexible enough to take some pretty rough handleing.

I have built quite a few AP motors and been around a LOT of home made motors both in flight and static testing. Most of the overpressurizations resulted from either erosive burning, nozzle throat too small, propellent mixed wrong, or propellent not characterized fully.

Usually (not always) when a motor lets go, the sudden change in pressure snuffs the fire inside...so most of the propellent goes unburned.

[BigtonyICU]

Sorry for taking so long to reply (I’ve been on a business trip for the past few days). I've build A liquid rocket engine several years ago using the cal off the page you gave (I have the book)... it works great... but definitely not for beginners.... the power is high very very high... my 9 inch diameter x 12 long combustion chamber put out 750lb of thrust for 8 seconds end drops rapidly due to nozzle erosion... if you decide to ignore everyone’s advice... and still build a liquid engine take my advice ... graphite nozzle or graphite insert nozzle and the more cooling you give the better... on my second try I use 5000PSI Nitrogen to drive the kerosene pump, I then routed the exhaust (around 700PSI) around the combustion chamber in and interlace spiral with the oxidizer.... I also used a graphite insert nozzle I managed to get 28 seconds of burn before CATO... (and you want to but this on a cart...not a wise idea the LAB O2 canister was punctured by shrapnel for the combustion camber with turned it in to a missile right thought the kerosene = 1 Big MF Bomb...) there was nothing resembling and engine or a test stand ... I was glad 2 b 250 feet away..) Putting it on a kart is a death wish...

Even using CRandy put a nice piece of 1" ply between you and the engine. Even with it behind you the shock wave will break you back if you get a cracked grain that ends up over pressurizing the engine.

N2O haze the safety (well I guess as safe as 2-1000 rocket of thrust might be) of being throtelable (u know what I mean). But the amount of working parts just means there's that much more parts that can break...Get a defective regulator and well I don't care how much plywood and steal is between you and the combustion chamber... your a goner (or a crippled in the best of cases). Theses aren't toys...