Safety of Air Travel - Aeroplane or Airplane

SAFETY OF AIR TRAVEL - AEROPLANE or AIRPLANE.

One reason why air travel is not more common is a general public apprehension of the risks involved. These risks are asso ciated with the following causes: (I) physical failure of the pilot, ( 2) fire when in flight, (3) collision when in flight, (4) breakage of the structure, (5) forced landing. Dangers of the first four types are not peculiar to aircraft and the precautions they involve are common to transport by road, rail and sea. The measures adopted in air transport have practically eliminated them. It is mainly the dangers which may arise when an aeroplane is forced to land that loom large in the minds of those who might other wise travel by air. While it cannot be said that these fears are entirely unwarranted, yet in so far as the design of aircraft is in volved the position is rapidly improving.

Forced Landings.

Forced landings may be necessitated by engine trouble, structural failure, fuel shortage, weather, ice form ing on the aeroplane or loss of knowledge by the pilot of location. A well qualified pilot with a properly equipped aeroplane should not experience forced landings caused by loss of bearings, and should never experience fuel shortage. Forced landings caused by weather, while annoying, are not dangerous in a country well equipped with emergency landing fields. Structural failures are extremely rare in normal flight. Ice forming on the wings and propellers is a serious problem. The danger of ice is two-fold. It adds considerable weight to the structure and at the same time decreases the normal efficiency thereof by spoiling the lifting qualities of the wings and the traction qualities of the propellers. Some trouble has also been experienced by ice forming in car burettors and reducing engine power output. However, invention as well as the development of efficient meteorological services and weather broadcasting systems has largely if not completely met the situation. It would be a rare phenomenon if ice form ing conditions existed throughout the altitude range of the aero plane. Altitudes for flight should be sought which do not favour icing. To arrive at such altitudes, however, it may be necessary to pass through icing layers. Since clear ice, under severe condi tions, can form at the rate of 3 inches per minute, it is an important problem which has given much cause for thought and experimentation. Its importance has been more keenly felt in recent years since the development of instrument flying. For merly little cloud flying was attempted but with modern methods cloud flying is nearer the rule than the exception.

To prevent ice from forming in carburettors, heaters are in stalled to warm the incoming air. There has recently been devised a de-icer for propellers. It consists of a container holding sev eral gallons of a mixture of alcohol and glycerine. This is fed by gravity into a rotating slinger ring and thence to absorbent pads at the blade roots. The solution moistens the surface of the blade and prevents adhesion of ice thereto.

Various systems of preventing ice from forming on wings and struts have been used. The one which appears at present to have most promise is that of using vibrating rubber pads in the leading edge. The vibration cracks the ice and it is carried off by the air.

Aeroplane engines are at present remarkably reliable and forced landings due to this cause are infrequent. With the use of two or more engines in aeroplanes, capable of sustention with one engine dead, an immediate forced landing due to engine failure is, al though not altogether impossible, worthy of little consideration and no apprehension. Instruments usually give some indication of impending engine failure and thus permit the pilot to land and correct the difficulty before complete loss of power results.

From the height of about 3,00o feet approximately four min utes are available in which the pilot may choose a landing place. If the failure occurs before the aeroplane has reached its cruising altitude, the time and the corresponding area of ground in which this landing place is to be found are reduced in proportion. These considerations unfortunately may result in the pilot having to execute somewhat sharp turns in order to place the aeroplane correctly, and it is during these that the controllability of the machine is most severely tested. The ultimate danger lies in the fact that the speed of horizontal travel at the moment of landing cannot possibly be less than the stalling speed. In practice with a typical commercial aeroplane it will be between 55 and 70 miles per hour. The pilot, therefore, endeavours to make the most of what space is available. This consideration, combined with the psychological effect of the apparent increase in the aeroplane's speed as the ground is approached' may lead an inexperienced pilot to carry out manoeuvres at a low speed, where the inherent characteristics of the aeroplane are least favourable and the con trols least effective. (See above §7.)