BLACK POWDER SOLID PROPELANTS
Solid propellants of the composite type contain separate fuel (or reducer, chemically) and oxidiser (in a separate compound) intimately mixed. While generally not considered as composite, black powder was in fact the oldest composite propellant. Before 1940 black powder, in common use, was nearly synonymous with the words ‘rocket motor’.
Black powder technically should not be called gunpowder because its use in rockets preceded that in guns. The ingredients are charcoal, sulphur, and saltpetre (potassium nitrate). These three ingredients were known in China for many centuries, however, before they were combined into black powder. Charcoal was known from the earliest times, and sulphur and saltpetre at least since the sixth century AD, and probably as far back as the first century BC That the saltpetre is definitely of Chinese origin is indicated by the names given to this material by the Arabs, who called it “Chinese snow”, and the Persians, who called it “salt from China”.
By 1045, just twenty-one years before William the Conqueror invaded Saxon England, the Chinese were well acquainted with black powder. The Wu-ching Tsung-yao (Complete Compendium of Military Classics) published that year, contained many references to the subject.
In black powder, saltpetre (potassium nitrate- KNO3) is the oxidiser, while sulphur (S), and charcoal (mainly carbon- C) are the fuel. But, depending on the percentage of each ingredient, sulphur may also act as an oxidiser for potassium in the reaction: 2KNO3 + S + 3C = K2S + N2 + 3CO2.
Some early black powder formulae:
- Saltpetre + sulphur + acacia seeds.
- 1 chin 14 ounces of sulphur, together with 2 1/2 chin of saltpetre, 5 ounces of charcoal, 2 1/2 ounces of pitch, and 2 1/2 ounces of dried varnish are powdered and mixed. Next, 2 ounces of dried plant material, 5 ounces of tung oil, and 2 1/2 ounces of wax are also mixed to form a paste. Then these ingredients are all mixed together, and slowly stirred, The mixture is then wrapped in a parcel with five layers of paper, which is fastened with hempen thread, and some melted pitch and wax and is put on the surface.
It was in the early thirteenth century that man turned toy fireworks into weapons of war. The first recorded use of rockets as military weapons was in defence of Kai Fung Fu, China, in 1232. The Chinese “arrows of fire” were fired from a sort of crude rack-type launcher. The black powder was packed in a closed tube (probably bamboo) that had a hole in one end for the escaping hot gases, and a long stick as an elementary guidance (or stabilisation) system.
Black powder had a very low specific impulse. About 1280 AD, Arab military men, referring to the propulsive ability of black powder, suggested improvements over the simple Chinese skyrocket. One interesting innovation was what might be best described as an air squid or travelling land mine; it could scurry across land in the manner of a squid through water.
By about 1400 when rocketry became of commercial importance throughout Europe and especially in Italy- where perhaps the greatest designers of pyrotechnics were found. The use of fireworks for all sorts of celebrations created a major market for the manufacture of large quantities of rockets. This spread throughout Europe and reached its zenith during the middle of the eighteenth century.
One of the earliest technical publication on rocketry, the Treatise Upon Several Kinds of War-Fireworks, appeared in France in 1561. The treatise made a critical analysis of the rockets used in earlier military campaigns. A recommendation was made to substitute varnished leather cases for the commonly accepted paper and bamboo ones. There is no evidence that this suggestion was followed by later rocketeers.
Refinements in rocket design came faster over the next few hundred years, at least on paper. In 1591, some three hundred years before Goddard, a Belgian, Jean Beavie, described and sketched the important idea of multistage rockets. Multistaging, placing two or more pockets in line and firing them in step fashion, is the practical answer to the problem of escaping earth’s gravitational attraction. An even earlier forerunner was Conrad Haas, chief of the artillery arsenal in Sibiu, Romania, between 1529 and 1569.
By 1600, rockets were being used in various parts of Europe against cavalry, foreshadowing the modern antitank hand weapon, the bazooka of World War II and Korean fame. Later, in 1630, a paper was written describing exploding aerial rockets which created an effect similar to that of the twentieth-century shrapnel shell. By 1688, rockets weighing over 120 pounds had been built and fired with success in Germany. These German rockets, carrying 16- pound warheads, used wooden powder cases reinforced with linen.
Toward the end of the eighteenth century a London lawyer, Sir William Congreve, became fascinated by the challenge of improving rockets. He made extensive experimentation with propellants and case design. His systematic approach to the problem resulted in improved range, guidance (stabilisation), and incendiary capabilities. The British armed forces used Congreve’s new rockets to great advantage during the Napoleonic Wars.
When Congreve died in 1828, his applied engineering and dedication had already resulted in several technological advances. In addition to fortified cases, new propellants, and incendiaries, Congreve developed stabilising fins that provided rocketeer with effective stabilised rockets. Congreve rockets were built in weights of 18, 24, 32, 42, 100, and 300 pounds (8, 11, 15, 19, 45, and 136 kg).
In 1906, Alfred Maul successfully took aerial photographs by attaching a camera to a black powder rocket (thereby creating the first instrumented sounding rocket).
During World War I, Le Prieur black powder rockets were sometimes fired from French and British biplanes or from the ground against German captive balloons. Otherwise, military rockets could not compete in range or accuracy with artillery of the day.
In United States, beginning in 1915, many tests were conducted, by Goddard, with rockets using black powder.
In early June 1927, rocket and space enthusiasts in Germany founded the Verein fuer Raumschiffahrt (Society for Space Travel). Some members experimented with black powder rockets.
Automobile manufacturer Fritz von Opel piloted his own rocket glider, Opel Rak.2, in tests near Frankfurt on 30 September 1928. Its 16 rockets, each producing 50 pounds of thrust, were build by Friedrich Sander a pyrotechnics specialist. The propulsion system combining high-thrust, fast-burning powder rockets for initial acceleration with lower-thrust, slower-burning rockets to sustain velocity.
Opel approached Alexander M. Lippisch, a young designer working at the Rhon-Rossitten-Gesellschaft, who had already displayed a penchant for the unorthodox in airplane configuration, with the proposal that he, too, design a glider for rocket power.
Max Valier and Alexander Sander also succeeded in arousing enthusiasm for rocket propulsion in a twenty- seven-year-old aircraft designer, Gottlop Espenlaub. His E 15 tail-less design was of interest as a rocketplane.
On 11 June, Fritz Stamer effected the first rocket- propelled flight in Lippish’s glider. The glider had been dubbed Ente, or Duck. That lead later to the Lippish’s Komet – the Messerschmitt Me 163, liquid rocket manned interceptor.
Reinhold Tiling launched a black-powder rocket from Osnabruck in 1931. It rose to a height of 2.5 miles.
Gerhard Zucker envisioned rocket mail service across the English Channel. The longest shot he attempted was from Harris to Scarp, in western Scotland, on 31 July 1934. But the rocket blew up before takeoff.
In 1939 researchers at the California Institute of Technology in California, seeking to develop a high performance solid rocket motor to assist aircraft takeoff, combined black powder with common road asphalt to produce the first true composite motor. This was the birth of the true composite motor and marked the end of the use of black powder in major rocketry applications.
credit © Mark Wade http://www.astronautix.com/