Homemade model rocket fuel

[sevenperforce]

Thinking about making my own rocket motors for hobby rockets. However, my chemistry is not nearly as good as my physics, so I'm a touch uncertain as to what fuel+oxidizer combinations would be best.

I can get finely powdered potassium nitrate easily enough for the oxidizer. Mixing it with confectioner's sugar would make classic R-candy. But what about making a paste out of the potassium nitrate and something like mineral oil? Would it not produce a good burn surface? What about a mixture of sugar, mineral oil, and the K nitrate?

Interested in specific impulse, probable TWR ratios, general safety, and ease of handling.

[lajoswinkler]

Rocket candy must never ever be made without dissolving the sugar, and I don't mean melting it (extremely high probability of ignition and the mixture isn't homogeneous because the salt won't dissolve in molten sucrose) but dissolving in a solvent that dissolves both it and potassium nitrate. The cheapest solvent that does it is distilled water (avoid tap water because of limescale).

Usual mixture is sucrose:KNO₃=40:60 with a pinch of iron(III) oxide. It simply has to be dissolved in warm water and then evaporated and stirred constantly on a hot plate. When enough water evaporates, the procedure gets dangerous because hotspots can occur. Also, the mixing must not be such that it introduces air bubbles because those will quite possibly cause the engine to explode when the reaction front reaches them.

The end result has to be a hot plasticine-like mass that still has some water in it and needs to be either immediately ram-packed into the engine or made into little cylinders and sealed in plastic baggies because it's deliquescent.

 

It takes a lot of practice and the consequences can be disastrous if you don't know what you're doing. Always assume it will ignite and take proper measures. Rcandy is very stable and not subjectible to usual dangers but be careful.

Edited July 1, 2016 by lajoswinkler

[Streetwind]

My first stop on a quest to find performance data on various home-grown fuels would be your national amateur rocketry organization. They will have forums where such things are probably discussed at length.

And who knows, there might just be a subreddit on the topic...