The College of Aeronautics performs an annual group project as a major part of its Aircraft Design MSc programme. Projects are chosen to be representative of current areas of interest and the programme carried out in a manner which is as close as possible to that of aircraft manufacturers.

The chosen projects alternate annually between civil and military types to give breadth to the course. It was decided that an executive jet would be a suitable subject for examination and a market study was performed. The small capacity end of the market was served by such aircraft as Learjets and medium capacity by BAe 125s and Citations. The top end of the market was of more interest because suitable aircraft could also perform other roles. The main reason for this was that market pressure for unrestricted headroom pointed towards larger diameter fuselages which could also be used for commuter aircraft.

I would in the first place express my appreciation of the honour conferred upon me by the invitation to deliver the J. D. North memorial lecture, on a subject with which I have been engaged for the past 37 years.

The subject is very wide, covering many types of pumps, and to do it full justice would require far more space and time than can be covered in a single paper. I have therefore attempted to bring out the reasons why we followed certain paths and the problems which caused significant design changes. If I appear to have given undue prominence to the work of the Lucas team, and made insufficient mention of the work of others, I would ask their forgiveness. The pumps used for reheat have been omitted as they are in a field of their own. The future may see a drawing together of the engine and reheat pump practices, although it is too soon to make a meaningful presentation, an indication of the most likely path is shown.

It is not always possible for a designer to accommodate a conical diffuser giving the greatest possible pressure recovery for a given area ratio because this usually involves a long version with a total conical angle of about 7 degrees. Considerable efforts have therefore been made to improve the performance of diffusers with total conical angles up to at least 30 degrees by adopting various techniques listed in Ref. 1. One suggestion was the addition of whirl to the flow in the inlet pipe; that is, to superimpose a vortex coaxial with the pipe and diffuser axis. However, Refs. 1 and 2 show the amount of published research on this topic to have been meagre.

A previous paper has dealt with the case of adding a forced vortex whirl velocity distribution to the incoming flow and showed that improvements were possible, certainly in static pressure recovery and even in so-called efficiency, using a restricted definition of the latter. Because of mechanical vibration problems, the maximum swirl angle that could be added to the flow was about 15 degrees, corresponding to a forced vortex rotation rate of about 28 rad/s. This led to a beneficial redistribution of axial velocity components and a diminished tendency for flow separation from the walls.

It is envisaged that future earth resources satellites will be required to perform frequent attitude manoeuvres and also to maintain a given orientation to within a few seconds of arc. These requirements place a severe demand on the attitude measurement and control systems used, and this, demand is increased when the satellite needs to carry large flexible solar arrays.

By combining inertial and optical measurements using an optimal filter, an attitude estimate can be obtained for which the error components are minimised over a wide frequency band. Jude, used intermittent star sensor readings to update the attitude and gyroscope drift estimates from an optimal filter and he noted that it would be useful to study the effect of mismatch between actual sensor models and those assumed in the computation of the optimal filter. Jude's recommendation is investigated in this paper.

Wind energy has long been recognised as a potentially abundant source of clean and renewable mechanical and electrical power. History records that wind energy has been harnessed by man since about the year 2000 BC when windmills were used for energy production in Babylon and China. An ancient Persian vertical-axis windmill of about 7th century vintage is shown in Fig. 1. Windmills appeared in Europe in the 12th century and flourished until the 19th century as one of the few forms of rotary mechanical power. The Dutch windmill achieved lasting fame as the subject of paintings and etchings by the Dutch Masters including Rembrandt and van Ruisdael. Rembrandt's etching ‘The Windmill’ shows the fine detail of a 17th century windmill in Amsterdam.

The final versions of Dutch and English windmills were relatively sophisticated machines, well suited to the tasks of grinding grain and other materials, pumping water and sawing wood. Steam power came to displace wind power in the 18th century, and windmill numbers diminished rapidly during the late 19th and early 20th centuries. Nevertheless, working examples of traditional windmills can still be seen in Holland, England and on the Greek islands.