Until the past few years inertia navigation has been a little known subject due to a cloak of security; but recently a number of informative reports and articles have been published, notably those by Adams, Schnerb, and Klass, all published during 1956. Moreover, many of the components of inertial systems have emerged from the early development stage, during which they were largely monitored by military agencies, and may now be purchased with a guaranteed performance specification.

An appreciation is made of recent experimental and project work of relevance to the design of a very light weight aircraft capable of being taken off and flown by two men. The emphasis is on the aerodynamic problems involved. It is concluded that, although there are many difficulties still needing attention, all the information supports previous assertions that flight by muscular power alone is possible. The merits and de-merits of a particular projected design are studied, and its performance and stability assessed.

A number of airlines throughout the world will, in the near future, be reconditioning and testing Dart engines from Viscount, Friendship and Herald aircraft. In most cases the testing will employ a technique which has been in use at the Rolls-Royce Australian overhaul base at Sydney, N.S.W., since August 1954. This is based on the torque reaction of the engine to the propeller and is suitable for testing any comparable engine.

The so-called ejector nozzle has received a large amount of experimental study as a means for achieving efficient supersonic expansion of the main jet without the difficulties of a mechanically variable convergentdivergent nozzle. No satisfactory theory for the calculation of its performance has yet been put forward and it is the object of this paper partly to remedy this defect.

It is Sometimes required to find the maximum amplitudes of vibration attained and the speeds at which they occur when a machine is run through its critical speed with different accelerations. The solution of this problem for single degree of freedom systems has been obtained by Lewis and by Ellington and McCallion for mechanical vibrations and by Hok for the equivalent electrical case. These solutions require higher mathematics (contour integration, Fresnel's integrals or series solutions leading to Bessel functions). The purpose of this note is to show how, by using simple integration only, an alternative method of solution can be obtained for both zero and small values of damping.

MR. Harpur's interesting and stimulating paper (page 363, May 1958 Journal) is obviously of great importance to all who have to face the problem of fatigue strength of aircraft. These comments all refer to Section 3—Design Loads. Mr. Harpur's conclusions are based on analysis of a typical flight plan of a medium haul civil transport, and are formulated as a proposal for two fail-safe design requirements.