Helicopter Theory

Rating:
Summary: Excellent job
Review: I picked up this book with the intent of getting some ideas for physics demonstrations that illustrate the physics of helicopter flight. Also, I was curious as to why helicopters are not made that are three, four, or perhaps ten times the size that they are now, and if chaotic dynamics could be present in helicopters. Over a thousand pages long, this book gave me what I needed and much more. Written for design and mechanical engineers who are involved in helicopter manufacturing, the book could be read profitably by anyone who is curious about the physical principles behind helicopters.

In the introduction to the book, the author defines a helicopter as an aircraft that uses rotating wings to provide lift, propulsion, and control. He then discusses briefly the basic physical principles that a helicopter needs in order to sustain vertical lift, as well as to move translationally. The design engineer must then weigh the factors that enable the helicopter to move against the maintenance and human factors involved in the use of the helicopter for transportation. The rest of the book is then an extremely detailed and fascinating account of the engineering analysis that goes into the design of a succesful helicopter. The author also overviews the history behind the helicopter, beginning with the Chinese rotor, circa 400 B.C. and with the first succesful flight with one passenger, and one meter above the ground, for about one minute, by Breguet-Richet of France in 1907. The author remarks that helicopter engineering currently emphasizes research and development than with invention. This is especially true in the military environment, with the Apache helicopter being a superb example of just how sophisticated a helicopter can be. It will be interesting to see how the technology and design of helicopters will change in the decades ahead. The trend might be towards pilotless flight for delivering military supplies or manufactured goods from one point to another, or perhaps helicopters that can morph into completely vertical or horizontal aircraft as the need arises.

The physics behind vertical flight is described by the author as 'momentum theory', which was developed for marine propellors in the late nineteenth century. As the name implies, this is just an application of the principle of conservation of momentum. The rotor disk of the helicopter feels a thrust created by the action of the air on the helicopter blades. It must therefore exert an equal and opposite force on the air. This forces the velocity of the air in the rotor wake to be opposite in direction to the direction of the thrust. Momentum conservation, energy conservation, and mass conservation then give a relation between the induced power loss and the rotor thrust. The author also gives details on the 'vortex theory', which is based more on fluid dynamical laws of the flow field of the rotor wake. Emphasizing the local aspects, it reduces to momentum theory in appropriate limits. The author also shows how momentum theory applies to the forward flight of the helicopter.

The author also treats helicopter performance analysis, which boils down to determining the power required and available for a range of flight conditions. The rotor forces and power must be calculated, and the author details two methods to do this: the 'force balance method' and the 'energy balance method'. The use of the computer has made this analysis considerably easier for the design engineer of course. The author gives a very interesting overview of helicopter speed limitations and how the helicopter could be landed safely after an engine failure, all of this being analyzed from a physics perspective.

The mathematics of rotating systems is included in the book, along with the differential equations of motion for the rotor blade. The motion of the blade is expanded into a normal mode representation and analyzed using Sturm-Liouville theory. The author though outlines other approaches to the blade dynamics, such as the Lagrangian formulation and the Galerkin method. And also, in spite of the ability of computers to solve for the aeroelastic equations of motion, the author considers their analytical solution for the cases where such solutions can be obtained. One very interesting part of this discussion was that of 'ground resonance', which is a dynamic instability involving the the coupling of the blade lag motion with the in-plane motion of the rotor hub. There is then a resonance between the frequency of the rotor lag motion and the natural frequency of the structure supporting the rotor.

Rating:
Summary: Essential resource for Helicopter Engineering
Review: Looking for information on how to fly a helicopter? Look elsewhere. Trying to design and build your own helicopter? Yeah, right, how about performing a quadruple bypass on your own heart? But if you are an aerospace engineer interested in helicopters, or if you are studying to become one (an engineer, not a helicopter), this is a must-have book.

This *is* an advanced textbook, which will take you from the fundamentals of helicopter aerodynamics, dynamics, and flight dynamics, all the way to the advanced topics. The book came out in 1980, and helicopter engineering has made a lot of progress since then. However, much of what is in the book remains current. The extensive bibliography gives a comprehensive picture of the state of the art until 1980.

Want some bedtime reading? Get Patricia Cornwell. Want to read stories about airplanes and military hi-tech? Read Dale Brown or Tom Clancy. Serious about learning helicopter engineering? Get this book.

Rating:
Summary: Helicopter Theory
Review: OK for a reference book, but much too bulky for any classroom. Mr. Johnson would do well to write an abridged addition. There does not appear to be any attempt to start with basic concepts and proceed to more difficult ones. Try to get a copy to review before buying it.

Rating:
Summary: Advanced concepts
Review: This book is quite difficult to understand and the concepts contained in it are quite complicated. With that in mind, and the fact that I did not understand most of it, I can't fairly rate it. I will however warn any potential buyer that a thorough knowledge of Calculus and Matrix Algebra is required to fully understand the text.