Rolls-Royce Heritage Trust
Technical Series Reviews - Page 01
Rolls-Royce and the Rateau Patents
Softbound, 208mm x 148mm x 4mm, 43 pages
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Reviewed by Kimble D. McCutcheon
In 1960 the French company Socété Rateau sued Rolls-Royce in France and the United Kingdom for patent infringement, Rolls-Royce having supplied engines with axial-flow compressors for French, British and American aircraft. The two patents in question, filed in the name of M. René Anxionnaz in 1939, appeared at first inspection to apply to all jet propulsion using axial-flow compressors.
Harry Pearson, a Rolls-Royce engineering manager, became involved with the litigation when his careful reading of the patents exposed a fundamental flaw — that they were based on a false claim. Pearson first had to convince the Rolls-Royce solicitors, and then Rolls-Royce counsel that his views were correct and that the patents should be attacked.
The Rateau patents showed remarkable foresight and ingenuity for 1939, but they were based on the claim that a divergent inlet can slow air velocity from flight speed to a speed that when compounded with compressor blade tip speed, will remain below the speed of sound, and indeed can be tuned to provide any predetermined velocity into the compressor. This claim was proved false.
Pearson spent the next six years helping prepare technical evidence for the cases and enlisting the testimony several expert witnesses, including Sir Frank Whittle. Rateau had asked that in the event of successful action that it be compensated for engines already built, that further manufacture of offending engines should cease, and that Rolls-Royce should deliver to them all parts, materials and complete engines. Clearly the stakes were very high.
Rolls-Royce mounted several challenges to the validity of the patents:
The French suit was tried first. To its surprise, Rolls-Royce won.
The English suit started on 1 November 1966 and ended on 8 February 1967, the second longest patent suite up to that point. The judgment was read on 26 April 1967. All of Rolls-Royce's challenges were upheld except for point 4. Rolls-Royce and Rateau reached an agreement to settle the costs, and the matter ended.
By the time the suits were settled Anxionnaz had retired. Pearson expressed sorrow that such ingenuity that was shown in the 1939 patents could not have been put to better use.
This is the first book in the Rolls-Royce Heritage Trust Technical Series. Though neither Pearson's narrative nor the patents (which are reproduced in appendices) are highly technical, this work provides insight into a very crucial point in Rolls-Royce gas turbine history.
The Vital Spark!
Softbound, 208mm x 148mm x 5mm, 59 pages
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Reviewed by James A. King, Jr.
One can learn much from Keith Gough's short book and enjoy the process.
Aircraft piston engine enthusiasts who track increases in engine performance tend to overlook the contributions of improved fuels and sparking plugs. Gough covers the many problems and solutions required from the very first plugs (French) through those for the highest-performing aircraft engines — ones operating from maximum take-off and climb to extended slow cruise on very long missions, at extreme boost, with fuels rich in tetraethyl lead. The plugs discussed range from those marginally capable of surviving a single mission to those operating quite satisfactorily untouched for the full engine lifetime. Also covered are igniters for gas turbines.
The Vital Spark! , Number 2 in the Rolls-Royce Heritage Trust Technical Series, is a most informative, interesting, to-the-point, entertaining and enjoyable short read.
The Performance of a
Softbound, 208mm x 148mm x 6mm, 89 pages
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Critical Analysis by Robert Raymond
Rolls-Royce Heritage Trust Technical Series No. 3
Aside from laying the ground work for extremely impressive performance improvements, this effort by Rolls-Royce probably was a watershed in engine performance testing and analysis at that time. The report itself is remarkably clear and comprehensive for an internal company document. Reading reports in the engineering literature from that era and before, one senses that most engine development was not as insightful or far-sighted as their work. The adoption of dimensional analysis in supercharger testing illustrates this change.
The best that could be hoped for in the years leading up to World War II was a test where only one variable was changed at a time. Even in the work described here the analysis of the pumping loop was not thermodynamically rigorous but this oversight did not impact their results. They knew what needed to be varied and what held constant to make their technique work. Reading Schlaifer’s account of supercharger development in the 1930s gives one a sense of the crudeness that was prevalent throughout the industry. Some rigor was introduced by the NACA and their academic affiliates but the people that built and used the machines were mostly of the “cut and try” school of engineering.
This is not to denigrate these organizations, “cut and try” is an art form in itself, one in which Rolls-Royce also excelled and cannot be replaced by any analytical techniques in engine design and development even today.
Flow Matching the Stages
Softbound, 208mm x 148mm x 6mm, 77 pages
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Reviewed by Charlie Cravens
Rolls-Royce Heritage Trust Technical Series No. 4
Upon retirement from his senior engineering job at Rolls-Royce, author Geoffrey Wilde became a visiting professor at the local university where he taught a course in gas turbine design. In this course, students were required to complete the aerodynamic design of an engine, to power a specific airplane, given its mission requirements.
In the design of such an engine, the compressor is crucial to its success, including not only its performance but also what is called "handling". This refers to starting and smooth response to throttle inputs. An improperly designed compressor can result in failure to reach idle on starting, a stall or a surge resulting from throttle movement.
The blades and vanes in an axial compressor are airfoils, and as such are subject to stall when the angle of incidence is too great. Stall is cleared by reducing the angle of incidence; adding power is not an option within the engine, and in fact the stall reduces pressure and airflow to the turbine and therefore reduces the power available to the compressor.
If the stall is a major event, it can cause compressor surge. When surge occurs, static pressure in the front part of the compressor drops drastically, and an instantaneous flow reversal will come from the downstream part of the engine. Normal flow will be re-established; however, these events are violent and startling.
Note: I have seen high speed photos of a JT9D inlet taken during a surge event, and fire from the combustor was clearly visible.
In an axial compressor, the exit conditions from each airfoil row must match the required inlet conditions of the row behind it. If there is a mismatch, stall/surge may result.
Flow area at the compressor exit is a function of the total flow required by the turbine at its design point. Upstream geometry is designed to match, insofar as possible. However, correct match cannot be achieved for all conditions (static and transient), and optimal angle of incidence is achieved by use of movable stator vanes.
Mr. Wilde's book is based on a lesson plan used for his third year engineering students, and describes the design of the R-R Avon engine's compressor. Supplementary text describing some of his experiences at R-R is also provided.
The result is a combination of interesting anecdotes and complex mathematics. The mathematics deals with the vector analysis process used for the compressor design. Although the Greek letters and fancy algebra may put the reader off, the underlying process is actually rather simple. The key to understanding it is to follow the vectors from stage to stage. You won't be able to design a compressor, but you will understand how it is done.
Vector analysis is also used to design turbines so you'll understand that too.
The mathematics is necessary to determine temperatures, pressures, flow rates, and efficiencies within the machine.
The Avon dates from the 1950-1960 time frame, and employed a 12-stage compressor with a 6.5:1 pressure ratio. Present day technology is represented by the majority of civil turbofan engines which have pressure ratios of around 25:1, with the GE90 operating at 40:1 and the R-R Trent at 50:1. No doubt further improvement will be made.
It is interesting to compare these numbers with typical compression ratios for modern gasoline engines (9:1) and diesels (20:1).
Although design of a modern axial compressor is a far more complex process than is described in this book, it is still based on a vector analysis.
To summarize, this book is a worthwhile read for gearheads wanting to introduce themselves to gas turbines. It illustrates the inherent complexity that underlies the basic simplicity of the turbines. As technology has advanced, however, the basic simplicity of the turbine engine has been mostly lost.
Gearheads should treat these engines with respect because of the kinetic energy in the rotating parts. Failures tend to be spectacular, and can originate from seemingly trivial issues.
Softbound, 295mm x 210mm x 10mm, 148 pages
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Reviewed by Graham White
Number 5 in the Rolls-Royce Heritage Trust Technical Series, Fast Jets is a must read for folks who enjoy high performance gas turbines. The mention of Derby in the title refers to Derby England where Rolls-Royce aircraft engines have been developed since this famous company got involved in aircraft engine development in 1914. Consequently, this book only covers those reheat applications developed at this location.
Like me, you probably thought that afterburning, or reheat in English speak, was simply a question of dumping a bunch of kerosene in the tail pipe of a jet. Think again. But it must be added that even Lord Hives had the same though I had. Reheat development took an inordinate amount of painful effort with almost the same number of problems one would associate with engine development. Rolls-Royce entered the traitorous field of gas turbines with the Derwent. It should be noted that all Rolls-Royce gas turbines were and are, named after rivers, the Derwent being a river situated in the midlands of England. Entering production in 1944, the Derwent powered the Gloster Meteor. As always in military power plants, too much power is just enough, in other words there is never enough. So experiments were conducted with injecting fuel into the tail pipe. From these beginning stages, Rolls-Royce went on to develop many reheat designs for military applications. Of course, describing engine development has to go hand in hand with aircraft development. By the jet age, more and more emphasis was placed upon the power plant, how it was mounted and catering to all its needs.
This book is strictly for those who enjoy the technical aspects of gas turbines, no wimps allowed. Obviously, it is focused on reheat but don't be fooled into thinking there is not much to it. To emphasize that point, this book should receive an honorable mention in the Guinness Book of Records for having the largest fold-outs of any book in print. Some of the fold out measure a staggering 60 inches wide - and this just illustrates the reheat part of the engine. These massive fold-outs, many of which are in color, need some studying to figure out what's going on but after a while it's possible to understand the myriad schematics illustrating fuel, hydraulics, compressed air, electrical systems, etc. Although the illustrations fall in roughly the appropriate part of the text, it would have been helpful to the reader if the illustrations had been referenced in the text. Nevertheless, the photographs and illustrations are absolutely first class.
Author Elliot goes through the various developments that took place in Derby chronologically. He covers all the gas turbine developments up to the Spey, used in the F4 Phantom. The F4K Phantom has been described (not in this book I might add) as being the slowest, heaviest and thirstiest of all the Phantoms. However, when you look at the task facing Rolls-Royce engineers, it was a miracle it was even pulled off. Even so, excellent insight is offered in the horrendous design and engineering problems that had to be overcome in shoe-horning a Spey into a Phantom airframe. After the Phantom episode, author Elliot was reassigned and the text is picked up by John Goodwin who takes us through the Adour development phase and its numerous sub types powering the Jaguar.
A nice Appendix One lists all the Rolls-Royce reheat engines including performance and applications. Appendix Two, put together by Dave Birch who also edits the Rolls-Royce Heritage Trust Derby Branch magazine, Archive, describes all the aircraft test flown by Rolls-Royce in reheat development.
Again, this is a must-buy for those interested in gas turbines. The fold-outs alone are well worth the incredibly low price.