A New Look at High-Altitude Turbulence

Abstract

Reconnaissance by aircraft from high altitudes remains an important priority for the Department of Defense. Aircraft at these altitudes experience both traditional mechanical turbulence as well as oscillatory fluctuations of temperature and horizontal and vertical wind speeds, which are attributed to gravity (also called buoyancy) waves. This paper investigates the effects of wavelike behavior on high-flying aircraft, finding high aircraft loads at certain frequencies. Aircraft are most susceptible to problems at the upper range of altitudes. This analysis shows that autopilots based on maintaining a constant Mach number and an indicated airspeed are both susceptible to temperature fluctuations. In addition, temperature changes shift the flight envelope, creating potentially dangerous stall or overspeeding conditions. The absence of temperature variation requirements in current aviation continuous gust load specifications along with a possible deficiency in gust magnitude design requirements at high altitude lead to a recommendation for revisiting high-altitude turbulence requirements and investigating the vulnerabilities of high-altitude unmanned aircraft.