THE AIRWAY

Sun (Auckland), Volume III, Issue 824, 19 November 1929, Page 7

THE AIRWAY

(By

THE ROCR

Problems in Speed Planes IT is hard tor the lay mind to appreciate the many problems that arise in the designing of aircraft for high speed purposes. It is not generally known, for instance, thai without an intricately designed cooling system the ordinary (piantity of water in the racing engine of the Gloster seaplane in the Schneider Cup would be brought to boiling--1 point after one minute at full throttle.

The problem of cooling is extremely difficult, because ordinary radiators, standing out in the air. are incompatible with the general streamlining of design. The designers, therefore, ingeniously circulate the water for ( ooling the machine under the actual skin of the wings, thus making the air not only lift the airplane, but in rushing past extract the heat from the water. which would otherwise quickly reach boiling point in the water jackets around the cylinders. The designer finds it extremely ditli- < ult to strike a balance between the lirst three essentials of low bead resistance. perfect shape and high power, without giving weight to any one consideration at the cost of the others. He is brought up immediately against two solid facts. The fuselage must he large enough to hold a mail, its frontal area cannot be less than that of the engine, and the weight of the two. plus fuel needed, will govern the final size of the complete aircraft. Therefore, the designer literally fits the man to the machine, and urges the i name-maker to produce for him as small an engine as is humanly possible with exceptionally low weight for whatever power it develops. The result of this combination means a general rigidity of the machine and the consequent saving of weight devoted to stiffening parts not on the centre of the machine’s mass—the vines have less to lift and ill turn become smaller. When if is stated that the sheer dead weight of these racers necessitates floats almost two-thirds the size of tiie fuselage above, holding man and engine, the immense importance of saving every pound of weight will become clear. Also the wings themselves offer a resistance to the air. and it is important to reduce this resistance to a minimum. ' Then of course, another complication worries the designer. The smaller the wings the higher the speed obtainable. but unfortunately those win -s must travel faster through the air before they will exert enough lift to take the seaplane out of the water. The designer must then ask himself the question how high dare the speed be raised with safety to the Pilot riid-1’ average water conditions. Hie racers in the Schneider Cup Glided probably two miles or more at something more than I‘>o rti.ph. before they settled on the water. >et

; the pilots became so accustomed to these speeds that this year it was possible to make the landing speed even higher. VERTICAL BANK DIFFICULTY The greatest difficulty of all to be met by the designer arises from the i necessity of making vertical bankI turns at frequent intervals along the course. No pilot can stand the enormous forces temporarily imposed upon both man and machine when a sudden vertical bank is attempted at anything like | the extreme speed of which the machine is capable. There is in- | deed very little difficulty in travelling at 300 miles an hour, or even more on a straight course, provided ‘ the acceleration or deceleration is gentle; but when a pilot suddenly changes course a new set of forces i comes into operation. Here we have ! in a very acute form the unpleasant \ sensation experienced in a lift which suddenly ascends or descends. A simple illustration of the increased gravity strain on man and machine is possible from a gauge of the varying pressure in the fuel quantity which is carried, in the case of the seaplanes, in the floats. Assuming for the sake of argument that the pressure of the petrol on the bottom of the float tank is 1001 b. and the machine, travelling at 300 miles an hour, suddenly changes direction, the fuel weight might be temporarily increased as much as 4001 b. and the fuel tends to push its, way through the bottom of the float. Should the i turn be sharp enough, the pressure ; might rise to about 6001 b. This is ' what is known as subjecting something to a force of four or six times gravity, and the same laws are applicable to the pilot. The force that is normally responsible for the pumping of the blood to the pilot's brain is in abeyance, and the blood tends to be drained away from the brain into the body. TC he attempts to turn too sharply, everything will momentarily go black before his eyes. The number of times a man can withstand the force of gravity thus imposed is of vital importance not only to him personally, but also to the designer, who must eventually build aircraft that will withstand weight, for the reasons already given. The human element may be hard to gauge, as it varies from time to time, and with

different pilots, and i$ probably the most difficult factor to cope with in the high-speed aircraft construction. The effect of this increased gravity does not end with the pilot, but the mechanical heart of the engine also feels the strain. The petrol in a vertical bank tenefs to run away from the carburettor and the engine, and if not fed by an extremely strong force, will tend to cut out. The motorist, accustomed to run something like 25 miles to the gallon. will be startled to learn that the Schneider Trophy engines may consume as much as two gallons of fuel a minute, and the heat units absorbed by the lubricating oil alone, if translated into terms of power, would exceed the highest power of an}’- car on the road today. Oil does not part with its heat quickly, and so it is that an elaborate system of oil coolers is necessary. The supermarine seaplane actually pumps the lubricating oil from the engine in the nose to the hollow fm at the tail, where it is sprayed against the thin metal surface in order to reduce its temperature. while the Gloster racer uses the- skin of the fuselage by the cockpit, the float struts, and even the surface of the floats themselves, to keep the oil from losing its properties from over-heating.