RADIO ALTIMETER

Evening Star, Issue 23699, 5 October 1940, Page 4

RADIO ALTIMETER

INVALUABLE TO AVIATION GIVES ACTUAL HEIGHT FROM LAND BAROMETRIC TYPE WORKS ON SEA-LEVEL Last year n group of America’s leading radio and aeronautical engineers wiU.cssed a successful trial of a new instrument to aviation. This instrument, the terrain clearance meter, or the radio altimeter, is claimed to be the first practical instrument for telling the exact height a plane is above _ the ground. The radio altimeter promises to eliminate one of the greatest hazards of present-day flying—that of running into a mountain in a fog. The radio altimeter would give the pilot plenty of warning as to the condition of the ground underneath so as to be able to gain enough height to cross the mountain or other obstacles. The • radio altimeter consists of a transmitter and a receiver in the wings of the plane. The transmitter directs radio waves to the earth, and the receiver picks up the reflected waves. A timing device in the pilot’s _ control cabin is sensitive .enough to register the infinitesimal fraction of a second that the wave takes to travel the distance. This fraction of a second is translated into thousands nr hundreds of feet. A switch on the instrument board enables a fine or a rough reading to be taken. This switch adjusts the altimeter to either 5,000 ft or to a scale in hundreds of feet. In addition to the meter a tell-tale light may be fitted to flash on when the plane is below a determined height. The principle is the same as that used in the echo sounder for shipboard use, giving depths on a chart forming a profile view of the sea bottom.

The height above sea level can be found only with the standard altimeter of the barometric type which responds to the diminishing air pressure, but this varies greatly from actual height from the nearest land point. To find the real height above any particular point on his chart a pilot must take into consideration the known height of that point. If he is uncertain of his position he may misjudge the safety of altitude; some of the worst air crashes have been traced to this cause.

The new instrument mounted on the side with a standard altimeter in the cabin of an aeroplane gave observers the comparison that shows the use of radio altimeter. While flying over the skyscrapers of New York the standard altimeter remained perfectly steady, but the hand of the radio altimeter was jumping . “ all over the dial.”

The radio altimeter was actually registering the distance from the plane to the tops of the skyscrapers below. During the landing the radio altimeter registered the descent, while the barometric one was still Jagging behind after the t plane had landed.

The experimental model described was manufactured by two of America’s largest laobratories.. It employed a 5-watt transmitter operating from the plane’s generator, and produced radio waves of 500,000,000 million _ cycles. This ultra-high frequency is said to be free from static. Many air litters in the United States have now been equipped with the radio altimeter.

Americans go to a lot of trouble to entertain their audiences. Spectacular travelling by the WLW “ Boone County. Jamboree,” a radio and personal appearance entertainment organisation, has been revealed. Figures show that members of the “ Jamboree ” units, touring to cities of all sizes in the mid-west, covered approximately 480,000 miles in a year. The average personal appearance trip is 150 miles, and the performer is on the road five days a week, 40 weeks a year. Playing fairs demands a good deal of stamina on the part of the stars, who must get back to the studios for their other programmes daily after playing in some town. For example, some girls hurried 250 miles for a broadcast next morning. After the broadcast they wore off to another town 60 miles away. They returned to Cincinnati that night for another broadcast, then made a 175mile trip for afternoon and evening performances.