Unlike the motor-car engine, which is generally designed, built and tested in association with the vehicle which it eventually propels, the aero engine is often designed and built with little or no knowledge of the types of aircraft in which it will be employed. The remainder of the power plant, fuel, water and oil systems of the car are also designed at the same time and to suit the chassis, but the aero engine, in the various types of aircraft, is likely to be coupled to many different forms of these systems, and consequently numerous problems arise between the completion of the acceptance tests of an engine and the final approval of an aircraft power plant for flight tests.

Ever since I first began to study Aeronautics I have been annoyed by the vast gap which has existed between the power actually expended on mechanical flight and the power ultimately necessary for flight in a correctly shaped aeroplane. Every year, during my summer holiday, this annoyance is aggravated by contemplating the effortless flight of the sea birds and the correlated phenomenon of the beauty and grace of their forms.

It may be of interest to give a resume of the Cirrus engine from the time of its conception up to the present period. The main idea actuating the designer was to produce an engine whose features would be reliability, low maintenance costs, and capacity to run for long periods with little more attention than a motorist gives to his car engine, and also so constructed that the average owner driver or motor mechanic could readily understand it and maintain it in perfect running order. The first Cirrus type engine was completed in May, 1925, and was submitted to the 100-hour Air Ministry type tests. These tests were successfully passed. The series of tests laid down by the Air Ministry Form A. P. 840 are of a most exacting nature.

It is my privilege to speak to you to-night on some aspect of the work of testing experimental aircraft, and in order to present my subject to you in as lucid a manner as possible, I am going to ask you to consider that we actually have a machine before us waiting for its first test.