Marrying airframes and engines in ground test facilities - An evolutionary revolution

Abstract

HEN I was offered the honor of presenting this 58th AIAA Wright Brothers lecture, I was asked to address the role of ground test facilities in the integration process for airframes and jet engines. This topic is especially appropriate for this lecture series. Wilbur and Orville Wright, for whom this lecture is named, were, by definition, the first successful practitioners of the art and science of airframe-engi ne integration for propellerdriven aircraft. History also confirms that the Wright Brothers utilized ground test facilities to support their airframe and engine integration process.1 Further, although the Wright Brothers' engine was inferior to the engine of at least one unsuccessful competitor, their integration of the propulsion system (engine and propeller) and airframe was superior to that of their competitors. Their integration approach provided the winning edge in areas such as two propellers turning in opposite directions, pusher propeller configuration, substantially higher propeller efficiency, and chain drives to the remotely mounted propellers.1'2 Successful integration of airframes and engines has remained a major engineering and management challenge ever since the Wright Brothers' triumph in 1903. From a historical point of view, the last 50 years of aircraft development can be characterized as the jet propulsion era. The scope of this paper is restricted to the marriage of jet engines and airframes during this half-century period, with primary emphasis on turbine engines and a secondary emphasis on ramjet engines. By all measures the increases in aircraft capabilities during this period have been awesome. Aircraft parameters such as range, speed, altitude, payload, all-weather capability, maneuverability, durability, and reliability have all increased by large factors. Many of these increases in aircraft capabilities have been enabled by advances in technology and engineering for aerodynamics, thermodynamics, structures, and materials. Another key enabler has been the large increases in net propulsive thrust and thermal and propulsive efficiencies available to the integrated airframe-engine combination. These improvements in propulsion system performance were made possible not only by increased net thrust per unit engine weight and decreased fuel burned per unit thrust, but also because of improvements in the airframe and engine control systems. In addition, improvements in the propulsion system tolerance of adverse weather, i.e., rain, snow, hail, and ice, supported some of the major advances in aircraft capability. Concurrent with these advances in integrated propulsion system capability, other mission-critical improvements in propulsion systems related to environmental factors such as smoke, chemical emissions, noise, and electromagnetic emissions have been developed and qualified.