When in 1937, I last had the privilege of lecturing to the Royal Aeronautical Society on the subject, the automatic pilot was still in its infancy. The automatic pilot then described was known as the Mark IA. It may now be revealed that it had developed out of researches at the Royal Aircraft Establishment in the field that came to be known during the Second World War as Special Weapons. The Royal Navy had been backing the work, primarily with the object of developing a pilotless target aeroplane.

Under the guidance of R. McKinnon Wood, at that time in charge of the Aerodynamics Department of the R.A.E., the World's first successful pilotless aeroplane was developed as an anti-aircraft target in 1925, after a series of abortive attempts in which failure was due primarily to instability arising from the unsuspected coupling between the yawing and rolling motions caused by downward tilt, in relation to the flight path, of the rotor axis of the azimuth gyroscope used to control the rudder.

Apart from its normal functions in aviation the applications of radar have been few. In the post-war period T.R.E., in conjunction with the Meteorological Office, have been making a study of possible uses of radar to the science of meteorology and the results of these investigations are described in this paper.

1. In the experimental work radar has been used to: —

2. (a) investigate precipitation,

3. (b) detect clouds dangerous to flying,

4. (c) measure cloud height, and

5. (d) measure wind speed and direction.

An account is given of how radar may be used to measure the density of the atmosphere at altitudes up to many tens of miles and of some problems still to be solved in the design of a radar sonde system for measuring pressure, temperature and humidity profiles.

It is concluded that radar will become an established meteorological tool and some possible profitable future lines of research are indicated.

From the start of the development of helicopters at the Bristol Aeroplane Company the necessity was appreciated of providing means of testing, independently of the aircraft, rotor hubs and blades. The usual method of testing on the helicopter suffers from several disadvantages, the most important being that proximity of the ground beneath the rotor greatly affects the flow through it and makes such performance figures as can be obtained unrepresentative. Others are the probable inconvenience of having to wait for the completion of the aircraft before rotor-testing can start, the comparative difficulty of instrumentation, and the risk of damage to the aircraft by failure or misbehaviour of the rotor.

Parts 1 to 5 of this paper (February, September and November 1947 issues of the JOURNAL) investigated the stresses and deformations of closed tubes in which the thicknesses were governed by the ts* and t* laws. In the present part, the analysis is extended to multi-cell tubes with openings, open tubes with or without St. Venant torsional stiffness, and to tubes formed by joining elements of different cross-sections. To illustrate the theory a numerical example of the stressing of a four-boom wing consisting of seven joined elements is fully worked out. Finally, an appendix gives practical methods of dealing with tubes which do not conform to the ts* and t* laws, and of finding approximate solutions for four-boom tubes with direct stress carrying covers.