Airscrew development has proceeded along four main lines :–

1. (1) Aerodynamic design.

2. (2) Materials.

3. (3) Adaptation to engine and aircraft.

4. (4) Fans for cooling and ventilating purposes.

Section (4) I have omitted. It may form the subject of a paper elsewhere. Section (1) I have barely outlined. It is of great interest, but I have concentrated on Sections (2) and (3) as being of immediate practical concern.

When the Royal Aeronautical Society did me the honour several weeks ago of asking me to give a lecture on sound-proofing of aircraft, I hoped to be able to prepare a formal paper and read it to you. I did not realise at that time, however, that my temporary duties as consulting engineer to the civil aircraft division of the French Air Ministry would take practically all my time. So I arrived in London with only the scantiest notes and shall be obliged to talk more or less extemporaneously on the broader subject of comfort in air travel. I hope that I may have the opportunity to supplement this lecture by a more elaborate paper at a later time.

In the design of a fan drive regard should be had to possible critical or resonant speeds which may result in failure of the system. It is not sufficient to arrange for the ordinary whirling speed to be well above the maximum running speed. In whirling the forced vibration arises from static or dynamic unbalance of fan and/or its shaft and the frequency of the forced vibration is the frequency of revolution of the fan shaft. Other important forced vibrations may however be set up.