SECTIONAL TRANSACTIONS.—G. 511 
AFTERNOON. 
Visit to works of Messrs. Taylor, Taylor & Hobson. 
Friday, September 8. 
Mr, R. S. Capon.—The reduction of aircraft noise (10.0). 
Audiometer measurements have been made of aircraft noise in flight, and 
of the noise of airscrews and engines on the ground. The experiments are 
described and deductions are made as to the means by which the noise may 
be reduced. 
It is shown that the airscrew noise depends primarily on the speed of the 
tips of the blades: lower tip speeds are therefore required for quietness. 
The improvement obtainable in this way is limited by the engine exhaust 
noise, which is about 80 decibels in cruising flight. Effective exhaust 
silencers of the baffle type can be made, but they may involve some increase 
of fire risk in the event of an accident. It is estimated that the noise level 
in a single-engined aircraft might be reduced to rather less than 70 decibels 
(approximately that in a train with open windows) by the use of an exhaust 
silencer and a low-speed airscrew. 
Reduction of noise in cabins by sound-proofing the walls is briefly 
considered, and some reference is made to the reduction of aircraft noise 
heard on the ground. 
DIscussION (10.30). 
The film in engineering—Opening Statement by Mr. H. E. Wimprris, 
C.B.E. (11.0). 
Cinemaphotography is found to be an increasingly useful tool in scientific 
and technical investigations. It may be used in three quite different ways. 
The simplest of all is its use to record the rapidly changing indications on the 
dials of instruments in cases where it is impossible to have an observer, or 
where, if there were one, he could not make and record his observations 
quickly enough ; an example is the ‘ automatic observer ’ used in the testing 
of single-seater aircraft. 
Another use lies in the ability of the cinema camera to make at any desired 
speed a record of the position or attitude of some moving body, the films 
being afterwards measured up under a microscope. An example of this, 
again drawn from aeronautical engineering, is the study of the motion of the 
spin of a free flying model ; another the study of the full scale motion of 
porpoising in a flying-boat. 
The third method of using the film is to take slow-motion pictures of 
rapid movements so that they are easily followed by the eye, thus enabling 
the quality of the action to be studied or demonstrated—e.g., the study of 
the launching of an airplane from a catapult. 
A series of short films prepared by the Empire Marketing Board are 
shown to illustrate some of the methods employed in aeronautical research, 
together with another Empire Marketing Board film illustrating the technical 
development of a motor transport train to open up undeveloped territories 
in Africa. 
Examples : 
Mr. H. E. Wimperis, C.B.E.—Aeronautical research (11.10). 
