It is an historical fact that the Rotol Airscrew Co was formed in the late 1930s specifically to manufacture variable pitch propellers. It would not be unnatural, therefore, to think that the development, in 1975, of a propeller for a crop spraying aircraft would be a routine matter for a company with nearly 40 years experience in the business. To some extent it was, but in other ways it proved to be an interesting and exciting challenge. Perhaps this was partly due to the fact that it was a new type and new types of aircraft or engine or major accessories are something special these days. But the main reason was that some fairly radical changes in design philosophy to those which the Company was accustomed were employed and these provided the major source of development activity.

‘Testing distribution equipment’ is a simple enough tide, deceptively so, and the superficial simplicity of our subject has in my view been misleading and somewhat detrimental to agricultural aviation development. With this remark made, I will now try to justify it and explain why I think that testing is in fact reasonably complex, even though, because the physical mechanisms are usually straightforward, the subject appears to be more simple than it really is.

Firstly, I would like to take a moment to consider the meaning of the two words ‘distribution’ and ‘testing’.

This paper has been written at rather short notice, which has prevented me from going into statistics and detailed figures, as I would have wished. It is therefore given fairly broad brush treatment and concentrates mainly on the larger types of crop-spraying aircraft in the category of around 6/7000 lb all up weight. This is where the engine situation is most critical and the need for a satisfactory powerplant which the operator can afford is most needed.

My only claim to be able to offer ideas or suggestions and perhaps some prognostications for the future is by associating with a number of Ag operators over the last four years, mainly in the States and particularly at the last four National Agricultural Aircraft Conventions in Florida and at Las Vegas; I have therefore no intention of being pontifical. Another reason for caution is because most of my past experience with engine installations has been with sophisticated aircraft, such as jet fighters, where I have had the good fortune to be supported by a team of technical experts and colleagues.

Over the 40-year evolution of the helicopter, man's understanding of vibration control techniques has greatly increased. However, with the performance of helicopters also increasing, the extent of their vibration problems has not diminished. Crew vibration therefore remains a significant factor in the design of all current helicopters. With more complex and critical demands being placed on aircrews it becomes more important that vibration should not impair their performance. Thus, as man's greater understanding of vibration control techniques provides the ability to constrain the vibration the definition of appropriate vibration limits becomes both more necessary and more useful.

Throughout the aviation industry the term ‘third level operation’ has many different definitions, ranging from ‘an operator whose aircraft have 12 seats or less’, the definition used in the Edwards Report, to the more general interpretation used in the United States, where the concept is normally that of either a small regional air carrier, operator of feeder liner services, or commuter services.