North Cape

For the next year, Teleman got to know the A-17 better than he had ever known any other aircraft. Under the supervision of the design engineers, he took apart and reassembled the aircraft. Then he took the A-17 up for hours on end, always flying the same tight pattern at one hundred thousand feet, well above the allowable levels for commercial planes. Gradually, as he came to know exactly what the airplane would do, flight altitudes and speeds were increased until he was flying routinely at Mach 5 and two hundred thousand feet.

Now he was nearly on his own. He spent so many hours in the aircraft that without the log he would have lost all count. Of the hours spent cramped in the cockpit, sitting in the closely guarded hangar flying computer-devised emergency conditions, he did lose track. At the end of the year he came to feel that the A-17 was an extension of himself. And then the medical people moved in to make it so.

It had been recognized when the A-n cum SR-7i. was completed that man had just about reached his limits in controlling his own aircraft. The A-n was capable of Mach 3 and nearly Mach 4 by the time the Pratt & Whitney J-58 engines had been up-rated to their fullest extent. The A-11. was only marginally effective as an interceptor aircraft. At Mach 3, fifty miles was needed to complete a 180° turn. Almost go percent of the aircraft was composed' of fuel tanks and her cruising range was severely limited at speeds above Mach 1.5, allowing little or no loiter time to contact a target. Because of the immense fuel load needed to keep her in the air, her reconnaissance payload, and therefore her cameras and other sensors, were severely limited also. In effect, and compared to the A-17, she was little help to the satellite surveillance system. Some stopgap measure was needed so that aircraft could spend time over enemy territory without being detected and could gather the smallest details necessary until large, manned satellites could be placed in orbit — still four years in the future.

For nearly ten years the X-15 series of rocket craft had been providing behavior and engineering data on hypersonic aircraft. The X-15 was used as the basic design for the A-17. The X-15 was rocket-powered, and this provided the tremendous speeds necessary — but powered flight time was limited to a few minutes duration. The A-17 needed days of flight time.

The turbojet engine is the most efficient of all propulsion systems' for speeds between Mach .9 and Mach 2.5, where fuel load, speed, range, and weight are the critical factors. Beyond Mach 2.5 and one hundred thousand feet, the ramjet becomes the most efficient Beyond 120,000 feet, where the air is too thin to support even the ramjet, the rocket engine, with its self-contained oxidizer, becomes the most efficient. To avoid Soviet antiaircraft missiles, the A-17 needed an altitude greater than 125,000 feet. Since the late 195os, a combination of the three types of propulsive systems had been the research goal of aeronautical research laboratories all across the world. The approach finally adapted to the A-17 was the U. S. Air Force concept called the TURBO-RAM-ROCKET. Below eighty thousand feet and Mach 2.5, the twin power plants in the A-17 functioned as turbojets — air sucked in through the inlet and forced into a combustion chamber, where it mixed with fuel, burned fiercely and the hot gas was forced past a turbine and expelled from the nozzle. The turbine was in turn coupled to the compressor behind the air inlet to compress air and force it into the combustion chamber. An improvement was made on the basic system by adding another stage in front of the compressor assembly called a fan. The fan was just that. Huge blades, coupled to and spun by the turbine, pulled in far more air than the combustion process needed. The excess air was ducted out the side of the engine casing to add as much as 30 percent more thrust.

The turbofan, as it was properly called, was capable of pushing the A-17 to speeds above Mach 2.5. Depending upon the altitude and various atmospheric conditions that necessitated the change — somewhere above Mach 2.5 to 3 — the engine switched from the turbojet mode to ramjet. It was in this versatility that the twin engines differed radically from earlier jet aircraft engines. These assemblies are composed of a thick disk of high-strength steel alloy upon which are mounted cambered blades. The blades are twisted to assume an airfoil shape. In the usual turbojet engine, these blades are mounted rigidly. The turbine assembly is constructed the same way and the blades are made of various materials, selected to withstand temperatures in excess of 1600° F as the hot gases exit from the burner chamber. As a rule of thumb, Teleman had been taught, the hotter the temperature of the gases leaving the burner — the Turbine Inlet Temperature (TIT) — the greater the thrust developed by the engine. The A-17 's TIT was in excess of 3200 degrees.