Black Powder Motor Components
Black powder motors consist of four primary components, all of them non reusable.  The case is, almost always, wound paper.  Paper has good coefficent of expansion at standard storage temperatures when loaded with black powder, an item important when you don't want your grain to seperate from the liner.  It also ablates well with the bare flame present in the end burn BP motor.  Clay is used for the nozzle, due to its low cost and its low ablative properties with BP's consistent pressure and burning properties.  A delay/smoke column similar to composite motor delays is placed at the top of the grain.  The final item is the loose black powder ejection charge, which is sealed with either a thin layer of clay or a paper cap.

Black Powder Motor Manufacture
Black powder motors are manufactured with specialized hydraulic pressing machines which have precise controls to press black powder into the  casings.  Black Powder has a fine line between compression and self ignition, pressures up to 900 to 1000 psi. are typical pressures for pressing but a slight increase in this pressure can lead to combustion.  The rear section of the motor then gets a clay nozzle, the forward end of the motor gets the delay and smoke generator charge followed by the ejection charge and charge cap.


Grain Types
There are two types of black powder motor configurations.  These are "end burners", grains that burn from the end face of the grain and "port burners" grains that had a small drilled or molded core hole in the end of the grain, usually around 1/4 to 1/2 inch deep.  This is not to be confused with the standard end burner port (less than 1/8" deep hole used to enhance ignition).  End burner BP motors are always "flat curve" motors exhibiting a true "top hat" curve with a slight peak at ignition (from that small port).  Port burners had a large spike at the start of the burn that gradually regressed to the same level as as a standard end burner, but of course it would lead to a shorter burn.  Port Burners (B14 or B8 for example) are not being manufactured by the known BP motor manufacturers at this time.


Thrust Classes
Black Powder cannot be easily modulated or enhanced by additives as easily as composite propellants, other than "effects" additives such as titanium or other metals for spark effects.  This means the only way to produce different thrust motors is to change the diameter of the grain face (average thrust) or lengthen the grain (total thrust).


Cons on BP motors
The two primary disadvantages to using black powder motors are black powders low ISP (ability to lift its own weight) and storage sensitivity.  Black powder has a low power ratio, the bigger the motor, the larger the case to contain it, which equals more weight, requiring a longer, heavier rocket to fly it in.  There are currently no commercial motors being built any higher than the E thrust class although in the past BP motors up to H class were made.  Sensitivity to storage is  the other problem with BP motors.  The larger the grain there is a problem with  temperature cycling on the grain.  The pressed black powder grain exhibits the same tendencies of a large crystal, any temperature changes can cause fractures in that "crystal" and any cracks present during the thrust cycle could cause a large pressure spike possibly causing failure of the nozzle,  The larger the grain the larger the possible cracks.


Summary
Black Powder Motors are easy motors to use and very stable especially when new.  They can be cheaper than composite motors and are more easily available as well in a lot more locations than higher power composite propellant.  They are good motors for contest and sport use due to the standard thrust characteristics from lot to lot.


*Original picture used by prior permission from the Kloudbusters prefecture website.