Plasma Wind: A Brief History of ATR Development: The Early Years 1900-1945

The history of Air Turbo Rocket development is surprisingly long, beginning early in the twentieth century. In significant ways, it parallels both the development of rocket engines, and that of turbojet engines as well. Similar thinking as to the motivations for development and the solution to technical problems are found in all three of these of propulsion development trajectories.

The fact that rocket propulsion proceeded turbojet propulsion by centuries has significant bearing on the development of the ATR. Motivated by the desire to improve rocket engine performance, especially at low speeds and low altitudes where most rocket vehicles start their journey, early developers looked for ways to utilize some portion of the available atmosphere in order to increase the effective thrust per unit mass flow rate of on-board propellant usage. We know this metric today as the specific impulse.

During the period of time from the beginning of the twentieth century to the start of World War II, the development history of the ATR is almost completely dominated by the work of one man: Robert Hutching Goddard. It is likely that other ATR development work on-going during this period, however Goddard’s work remains the most significant, and has had the most overall influence on the resulting development trajectory of the ATR.

Few propulsion workers have been as prescient or innovative as Dr. Goddard, the man who designed, built, and tested the world’s first liquid bi-propellant rocket engine. As early as 1930, and probably earlier, Dr. Goddard recognized that rocket propulsion was very inefficient at low speeds and at low altitudes, but if some use of the available atmosphere could be made, such as by the incorporation of propellers or fans, then the overall propulsion efficiency could be improved. It was at this time that Dr. Goddard first conceptualized the integration of a turbine and fan with a rocket motor. The design that he proposed is, in fact, the first Air Turbo Rocket engine ever conceived. He described his design, its applications, and the motivations for developing such an engine in an article he wrote in the March 1932 issue of Scientific American: “A New Turbine Rocket Plane for the Upper Atmosphere”.

In Goddard’s configuration, rocket motors impinge against turbine blades which jut into the rocket’s exhaust. The blades are affixed on the outer circumference of a larger fan. The rocket exhaust causes the fan the spin, producing additional thrust by the fan’s reaction against atmospheric air. In this manner, the rocket can produce significantly more thrust while still in the sensible atmosphere, as it climbs up and out. There are two turbine-fan assemblies, configured such that these assemblies could be translated laterally in and out of the rocket exhaust. Turbine blade rows on each fan assembly were staggered such that they could interdigitate within the rocket exhaust, providing a multi-stage turbine expansion process. He called his new engine concept the “rocket turbine”.

Goddard continued to develop his ideas on the rocket turbine engine concept. Goddard was unique in many ways from his contemporaries and predecessors, in that he actually designed, built, and tested what he conceived of. Dreams, Ideas, and notional concepts are, by comparison, easy to come up with. But actually fashioning them out of materials, and then testing them, is much more difficult and time-consuming. The development of the rocket turbine engine was no exception to Dr. Goddard’s approach. During the period of approximately 1930 through the start of WWII, Goddard designed and built a number of sub-scale rocket turbine test bed engines, as well as all sorts of other amazing technical innovations, such as turbopump systems for liquid rocket engines, gyroscopic-based guidance, navigation, and control systems for rocket vehicles and aircraft, and the development and testing of ion propulsion.

Much of Dr. Goddard’s later work took place in Roswell, New Mexico, where he maintained his household, a large test range, launch tower, and shop. He was active in the Roswell Rotary Club, and in the Roswell community in general. After Dr. Goddard's passing in 1945, his wife Esther began donating his rocket materials to the Roswell Museum and Art Center (RMAC), beginning in about 1949. In 1969 the RMAC dedicated the Robert H. Goddard Wing of the museum. The RMAC has perhaps the finest collection of Goddard Artifacts in the world, and includes a recreation of his workshop in the Robert H. Goddard Collection of Liquid-Propellant Rocketry, as well as the actual launch tower from which he flew many of his rocket vehicles.

In 2003, my good friend and colleague, John Bergmans (of Bergmans Mechatronics fame), visited the RMAC, and the Goddard Exhibition. He took many pictures, and was kind enough to share them. Shown below are two pictures of the reproduction of Goddard’s workshop.

These photos are strongly evocative of images we’ve seen before, of Dr. Goddard in his shop, toiling away on a rocket vehicle laying on its side. Outside the museum, Goddard's actual launch tower is displayed:

A commemorative plaque rests at the base of the launch tower:

However, the most astounding discovery at the RMAC were some of the artifacts shown in the museum. To his surprise and astonishment, John Bergmans recognized that some of the artifacts displayed were actually sub-scale prototypes of the rocket turbine engine concept Dr. Goddard has proposed in the 1930's. Due to the very small number of workers in the ATR field, John was very likely one of the first people to recognize these engines for what they were: the earliest working prototypes of an ATR engine. Shown below are some of John’s photographs of the prototype.

As can be seen, the turbine/fan assembly is made from a single sheet of metal, cut and folded to produce the fan blades, and also the turbine blades. The tan cylinder on the lower left is the rocket motor which produces the hot gas to drive the turbine/fan assembly. It is likely that this rocket motor used a solid propellant, as Goddard had done a great deal of development of solid rocket motors, and would possibly have had solid propellant materials at hand.

A close up of the turbine blade assembly shows a re-entry turbine passage, making the turbine portion of this engine a partial-admission, re-entry turbine configuration.

The rocket turbine concept was later featured in a number of popular magazines of the time, including the December 1931 issue of Popular Science , and the December 1932 issue of Modern Mechanics and Inventions, the cover of which is shown below:

Although these articles help popularize the rocket turbine concept, they did not always provide an accurate depiction of what Goddard actually had in mind, and often were more or less simply the creation of whatever graphic artist the magazine had assigned to doll up the story.

Nevertheless, Goddard continued development work on the rocket turbine concept, as well as many other propulsion-related projects, until his death in 1945. Goddard was granted patent number 2,286,908 for his rocket turbine engine concept in June of 1942.

Goddard never saw any further development or utilization of his rocket turbine concept beyond what he had conceived of in his lifetime. Yet today, we must be amazed at how truly visionary Goddard was. In the decades that have followed, the same motivations for propulsion improvements which drove Dr. Goddard, drive the development of the Air Turbo Rocket which exists today.

Comments

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I had no idea that the tip turbine concept went back that far. My first though was, "turn the turbine blades on their sides and it becomes my cagejet concept". From before my parents were born.

Posted by: john hare | October 06, 2009 at 01:41 PM

John,
It is indeed pretty amazing.
Steam turbine technology goes back to early in the 19th century. There might be examples even earlier, but the development of better turbine technology had to wait until the thermodynamics of the gas expansion process was better understood and quantified.

Posted by: John Bossard | October 06, 2009 at 01:54 PM

To "brief" want more... Now... quit reading and start writing... why are you still here... Get to work...

Seriously; insitefull, informative, and interesting. As usual you have the "3-I's" covered perfectly :o)

Randy

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