I wuld like to ad some thawts of my own on this;
Solid propellants of the composite type, containing separate fuel (or reducer, chemically) and oxidiser (in a separate compound) intimately mixed, replaced the simple double-base propellants to a considerable extent, especially for large non-military motors. The organic fuel material is initially in a liquid or semi-liquid form that can set to a solid (binder). Among the earliest substances used were asphalt and various synthetic rubbers. 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' .
While working on the theory of rocket propulsion for his doctoral thesis in 1937, Frank Malina mentioned to Fritz Zwicky of Caltech some difficulties he was having in his study. Zwicky exploded with the opinion that Malina was wasting his time on an impossible subject. For, he said, Malina must realise that a rocket could not operate in space as it required the atmosphere to push against to provide thrust! By 1940 he realised that he was mistaken.
At Guggenheim Aeronautical Laboratory, California Institute of Technology (GALCIT),in 1939, one of the first objectives was to develop a solid propellant rocket unit capable of delivering a constant thrust on the order of 1000 pounds for a period of 10 to 30 seconds. As far as is known, no black powder or smokeless powder rocket had ever been constructed to meet these specifications of thrust and duration. Experts consulted by Malina, John Parsons, and Forman were very dubious about the possibility of doing so.
Preliminary experiments made by Parson and Forman with pressed solid propellant charges restricted to burn cigarette-fashion appeared to support this view. It was generally believed that the combustion chamber pressure of a restricted burning solid rocket unit would continue to rise from the moment of ignition until any combustion chamber of reasonable weight would burst. In other words, it was thought that such combustion was inherently unstable.
The GALCIT group's mentor, Professor Theodore von Karman, in the spring of 1940, had to listen to both the opinions of the experts and to the explosions of Parson's rockets. One evening at home Von Karman wrote down four differential equations describing the operation of an ideal restricted burning motor, and asked Malina to solve them. It was found that, theoretically, a restricted burning unit would maintain a constant chamber pressure as long as the ratio of the area of the throat of the exhaust nozzle to the burning area of the propellant charge remained constant, that is, the process was stable. Experimental verification of the theory was soon obtained.
Although there have been centuries of experiments with black powder rocket, and several investigators used smokeless powder and Ballistite in rockets between about 1918 and 1939, none of these rockets had the thrust and duration required for the aircraft "super-performance" applications. Parsons and Forman in 1938 built and tested a smokeless powder constant-volume combustion motor similar to the one that had been used by Goddard. They concluded after these tests that the mechanical complications of constructing an engine using successive impulses to obtain thrust durations of over 10 seconds was impractical. Upon Parson's recommendation, they concentrated their efforts on the development of a motor provided with a restricted burning powder charge that would burn at one end only at constant pressure to provide a constant thrust.
Parsons started with the traditional sky rocket. This type of pyrotechnic device was propelled by a black powder charge pressed into a cardboard combustion chamber with a conical hole in its centre. The gases escaped through a rounded clay orifice. Its efficiency was very, very low, but it was reliable. The conical hole in the charge was believed to be the secret that kept the charge from burning down the sides of the container or to produce chamber pressures that would burst the container. The longest duration of thrust of this motor did not exceed about 1 second.
During 1939 and 1940, various mixtures based on black powder and mixtures of black powder with smokeless powder were tested in 1 in. and 3 in. diameter chambers. The charge for the 3 in. chamber was made up of 6 in. long pellets compressed at around 6,500 psi., and coated with various substances to form a solid or liquid seal between the charge and the walls of the chamber. The charge of the 1 in. chamber was pressed directly into the chamber in small increments at pressures between 7,700 and 12,000 psi. Most of the tests of these charges ended in an explosion.
Mechanical causes for failures, such as burning of the charge on the surface next to the wall because of leakage, transfer of heat down the walls sufficient to ignite the sides of the charge, and cracking of the charge under combustion pressure, were suspected. However, there were those who were convinced that the combustion process of a restricted burning charge in a rocket motor was basically unstable. Only after von Karman and Malina proved the process was stable in their analysis of the characteristics of the ideal solid propellant rocket motor in the spring of 1940 was a concentrated effort was made to study the mechanical causes of failure.
Hundred of tests were then made with different powder mixtures, using black powder as the basic ingredient, with various loading techniques and various motor designs. The dependence of chamber pressure on the ratio of chamber cross section area to nozzle throat area was determined for each specific powder mixture.
By the spring of 1941 the results were sufficiently encouraging to schedule flight tests of an aircraft equipped with solid propellant rockets specially designed for it. The propellant charge used in the Ercoupe motor was a type of amide black powder designated as GALCIT 27 (amide: organic compound containing carbon, hydrogen, oxygen, and nitrogen. Some examples: HCONH2, CH3CONH2, C6H13CONH2). The 2 lb. charge was pressed into the combustion chamber, which had a blotting paper liner, in 22 increments by a plunger with a conical nose shape at a pressure of 18 tons. The diameter of the charge was 1.75 in. and its length varied between 10 and 11 in. The motor was designed to deliver about 28 lb. thrust for about 12 seconds.
Eighteen rocket motors were delivered every other day for the first tests at March Field, California, about an hour's drive from the project. During the first phase of the flight tests one motor failed explosively in a static test and one while Ercoupe was in level flight. Thereafter, 152 motors were used in succession without explosive failure. The motors were prepared by Parsons, Forman, and Fred Miller.
On August 16, 1941, Boushey made the first take-off of the Ercoupe with six JATOs firing. The first American manned flight of an aircraft propelled by rocket thrust alone was made by Boushey on August 23, 1941. The propeller of the Ercoupe was removed and 12 JATO units installed, of which only 11 functioned. The Ercoupe was pulled by a truck to a speed of about 25 m.p.h. before the JATOs were ignited. The airplane left the ground and reached an altitude of about 20 ft. This flight was not originally scheduled but the group could not resist the opportunity to make the improvised demonstration of the future possibility of rocket propulsion.
Frank Malina noted that it was most fortunate that the flight tests were carried out close to the location of the project, which permitted the rocket motors to be fired within a few days from the time they were charged with propellant. Following the flight tests, it was found that after the motors were exposed to simulated storage and temperature conditions over several days they exploded in most cases. It was evident that either the blotting paper liner or the mechanical characteristics of the propellant were unsatisfactory.
But the Navy Department regarded the successful Ercoupe tests with much interest from the point of view of application of rockets for assisted take-off of aircraft from aircraft carriers. Upon the urging of Lt. C.F. Fischer of the Bureau of Aeronautics, who had witnessed the tests, a contract was placed by the Navy with the Project in early 1942 for the development of a 200 lb. thrust, 8 second unit. The unit was designated by the acronym JATO for Jet Assisted Take-Off (sometime RATO), and this designation is still used.
This Navy contract came in the midst of the explosive failure of the JATO unit developed for the Ercoupe tests. All efforts to improve the amide-black powder propellant and loading techniques of the motor developed for Ercoupe tests failed to meet specified storage conditions ranging from Alaska to Africa. Investigations of motors using Ballistite also proved negative, mainly because of its ambient temperature sensitivity (variation of its rate of burning and thrust with ambient temperature).
hope my thoughts here helps you fellers understnad rokkets
