Adaptive aerostructures: the first decade of flight on uninhabited aerial vehicles

Abstract

Although many subscale aircraft regularly fly with adaptive materials in sensors and small components in secondary subsystems, only a handful have flown with adaptive aerostructures as flight critical, enabling components. This paper reviews several families of adaptive aerostructures which have enabled or significantly enhanced flightworthy uninhabited aerial vehicles (UAVs), including rotary and fixed wing aircraft, missiles and munitions. More than 40 adaptive aerostructures programs which have had a direct connection to flight test and/or production UAVs, ranging from hover through hypersonic, sea-level to exo-stratospheric are examined. Adaptive material type, design Mach range, test methods, aircraft configuration and performance of each of the designs are presented. An historical analysis shows the evolution of flightworthy adaptive aerostructures from the earliest staggering flights in 1994 to modern adaptive UAVs supporting live-fire exercises in harsh military environments. Because there are profound differences between bench test, wind tunnel test, flight test and military grade flightworthy adaptive aerostructures, some of the most mature industrial design and fabrication techniques in use today will be outlined. The paper concludes with an example of the useful load and performance expansions which are seen on an industrial, military-grade UAV through the use of properly designed, flight-hardened adaptive aerostructures.

Advanced control techniques for post-buckled precompressed (PBP) flight control actuators

“…This was followed by the first rotorcraft, Gamara, in December 1996, the first VTOL MicroAerial Vehicle (MAV) in September 1997 and a number of missile and munition flight control surfaces through the late 1990's. [2]- [8] These actuators generated significant deflections as seen in Figure 1. In addition to possessing high deflection capability, they also possessed high bandwidth and very low power consumption through the entire speed range.…”

“…Because the flight control systems were both aerodynamically and inertially balanced, no flutter tendencies were ever observed in any wind tunnel or flight test. [8] However, their "soft spring" deflection properties at the limits of their stroke meant that buffet and stall loads simply could not be resisted. Figure 2 shows the typical actuator moment generation decay with increasing deflection which is a hallmark of early piezoceramic actuator elements.…”

“…In addition to possessing high deflection capability, they also possessed high bandwidth and very low power consumption through the entire speed range. [1]- [8] Although these flight control systems worked well, they employed piezoceramic actuators which experienced a linear decay in moment and force generation capability with increasing deflections. Because the flight control systems were both aerodynamically and inertially balanced, no flutter tendencies were ever observed in any wind tunnel or flight test.…”

Post-buckled precompressed elements: a new class of control actuators for morphing wing UAVs

“…In 1996 a rotary wing UAV showed that flight control weight could be cut by 40% while decreasing both power consumption and drag simultaneously [8,9]. In 2000 it was shown that by using shape-memory-alloy filaments the pitch of the individual wings could be altered, thereby generating large control forces [10]. An important disadvantage however, was the increase in power consumption by a factor of two compared to conventional electromechanical actuators.…”

Solid State Adaptive Rotor Using Postbuckled Precompressed, Bending-Twist Coupled Piezoelectric Actuator Elements

“…These overview papers described many approaches and listed several different techniques and approaches for achieving flight control. One of the later overview papers summarized not only rotorcraft, but missile, munition, and UAV successes which were numerous by 2004 [32].…”