oxidizer. The propellant can be divided into three groups of components: the fuel, the oxidizer, and the (optional) additive(s). In the past, sucrose was most commonly used as fuel. Modern formulations most commonly use sorbitol for its ease of production. The most common oxidizer is potassium nitrate (KNO3). Potassium nitrate is most commonly found in tree stump remover. Additives can be many different substances, and either act as catalysts or enhance the aesthetics of the liftoff or flight. A traditional sugar propellant formulation is typically prepared in a 65:35 (13:7) oxidizer to fuel ratio.[1]
There are many different methods for preparation of a sugar-based rocket propellant. Dry compression does not require heating; it only requires grinding the components and then packing them into the motor. However, this method is not recommended for serious experimenting.[why?] Dry heating does not actually melt the KNO3, but it melts the sugar and then the KNO3 grains become suspended in the sugar. Alternatively, the method dissolving and heating involves both elements being dissolved in water and then combined by boiling the water off, creating a better mixture.[2]
The specific impulse, total impulse, and thrust are generally lower for the same amount of fuel than other composite model rocket fuels, but rocket candy is significantly cheaper.
In the United States, rocket candy motors are legal to make, but illegal to transport without a low explosives users permit.[3][4]
Since they count as
FAA
flight waiver.
Components
Rocket candy can be broken down into three major groups of components:
oxidizers
, and additives. The fuel is the substance that burns, releasing rapidly expanding gases that provide thrust as they exit the nozzle. The oxidizer provides oxygen, which is required for the burning process. The additives can be catalysts, to speed up or make the burning more efficient. However, some additives are more aesthetic, and can add sparks and flames to liftoff, or add smoke for ease of following the rocket in the air.
Fuels
Many different sugars are used as the fuel for rocket candy. The most common fuel is typically sucrose, however, glucose and fructose are sometimes used. As an alternative, sorbitol, a sugar alcohol commonly used as a sweetener in food, produces a propellant with a slower burn rate and is less brittle when made into propellant grains.[5] Sugars with a double bonded oxygen, such as fructose and glucose, are less thermally stable and tend to caramelize when overheated.[6] Sugars that only have alcohol groups, like sorbitol, are much less prone to this decomposition. Some other commonly used sugars include erythritol, xylitol, lactitol, maltitol, or mannitol.
Oxidizers
The oxidizer most often used in the preparation of sugar motors is potassium nitrate (KNO3). Other oxidizers can be used as well, such as sodium and calcium nitrates as well as mixtures of sodium and potassium nitrate.[7] KNO3 can be acquired through purchasing a granular "stump remover" from stores that carry garden supplies. Other rarely used oxidizers are ammonium and potassium perchlorate.
Two main issues need to be addressed with respect to the oxidizer if one is using potassium nitrate. The most important issue is the purity of the material. If a purchased material does not perform satisfactorily it may be necessary to recrystallize the KNO3. The second important issue with respect to the oxidizer portion of a propellant is its particle size. Most propellant makers prefer their KNO3 ground to a small particle size, such as 100 mesh (about 150 μm) or smaller.[2] This can be done using a coffee grinder. Rock-tumblers can also be used to mill into a fine grained well mixed powder.