Aerospace structures research at the University of Kansas comprises fundamental and applied research in support of transportation, defense, airborne remote sensing and energy.
In addition to advancing the state-of-the-art in adaptive and/or multifunctional structures, students, faculty and staff design, analyze, fabricate, ground test, flight test and field custom aircraft, sensors and other aerospace systems to enable interdisciplinary scientific discovery. For instance, primary funded research addresses ice-penetrating radar that can assist CReSIS researchers in the quest to capture data and create accurate 3-D maps of ice sheets all the way to the bedrock. Airborne sensor suites have also been developed for fine scale measurements of terrestrial ecosystem structure and biomass. Past projects include small and large unmanned aircraft, radar arrays and fairings, wind turbine blades, telescopes and fuel containment devices.
In support of the NASA ICEbridge campaign, University of Kansas and DARCorporation researchers equipped the NASA Dryden DC8 and the NASA Wallops P3 with extensive radar arrays comprising accumulation, snow, KU-band, and the multi-channel coherent radar depth sounder (Mcords) antennas. Again, the use of composite structures is required to tailor the distribution of relative permittivity for radar performance, as well as to ensure structural, aerodynamic and aircraft performance requirements are met.
The NASA DC-8 is a turbojet aircraft capable of up to 12-hours of flight endurance at high altitudes, though it can also support low-altitude operation. Typical airspeeds range between 218 and 252 m/s. One of the major requirements for the aircraft structures housing the antennas is that they should not reduce aircraft range by more than 2.5%. This requirement was imposed to maximize data collection time over target areas. The two main design drivers for the fairing were preventing shockwave formation and minimizing aerodynamic loads on the fairing. Due to the transonic flight regime of the DC-8 much care was given to the external shape of the fairing to prevent shocks from forming, and the resulting shapes lend themselves to composite manufacturing. In addition, the size of the fairing was kept as small as possible to minimize the aerodynamic loads on the fairing and to eliminate a possible ground strike during the takeoff rotation. Since the fairing was limited in mounting to a nadir viewport frame and surrounding aircraft longerons, aerodynamic loads had to be minimized to meet conservative NASA structural requirements. Structural elements above the radiating antennas are electrically conductive, while those below and parallel to the radiating antennas have low relative permittivity. To the best of our knowledge this is the first radar sounder/imager flown successfully over the polar ice sheets on a turbojet aircraft and from high altitude.
The NASA P-3B is a four-engine turboprop aircraft that is well suited for low altitude airborne science missions of long duration (8-12 hrs). The nominal cruise speed of this platform is 124 m/s, although speeds up to 205 m/s can be reached. Analyses were completed not only to determine the range reduction of the aircraft and the aerodynamic loads used for structural sizing of the fairing, but also to determine the effects of the presence of the fairing on the stability and control of the aircraft. The size of the wing-mounted fairing was limited due to the need for adequate separation between the fairings, the propellers, and the wing tips. The turbulent flow behind the propeller (prop wash) and from wing tip vortices can increase the drag of the fairing and potentially fatigue the structure due to the series of impinging pressure waves. The fairing was made as large as possible without infringing in these turbulent flow regions. In this case the lower surface of the wing is used as the reflective ground plane, and so structural elements above, below and parallel to the radiating antennas have low relative permittivity. Thicknesses of composite structures are tailored to the local frequencies of the radiating antenna elements. To the best of our knowledge this is the largest ice radar sounder/imager array flown successfully over the polar ice sheets.
Each of these installations involved high-fidelity, physics-based, interdisciplinary simulations for geometry, aerodynamic loads, aircraft performance, static and dynamic structural response, and radar performance. In each case the design and fabrication of the antennas and the aircraft integration structures were undertaken by the researchers at the University of Kansas with significant involvement of graduate and undergraduate students in Aerospace and Electrical Engineering. To date, these aircraft and these instruments have flown more than 48 science flights, totaling more than 440 hours in Greenland and Antarctica, massing in excess of 150,000 flight nm and enabling collection of over 235TB of unique data for ice bed topography and internal layering. We continue to develop new sensors and platforms, and to operate these platforms to develop unique data sets for the broad scientific community.
COMPOSITE MATERIALS LABORATORY
The Composite Materials Laboratory addresses applied and developmental research in environmental remote sensing, energy and transportation. This laboratory supports researchers to design and construct aircraft, sensors and systems to enable airborne environmental remote sensing, with the primary funded research addressing ice-penetrating radar that can assist CReSIS researchers in the quest to capture data and create accurate 3-D maps of ice sheets all the way to the bedrock. Sensor suites have also been developed for fine scale measurements of terrestrial ecosystem structure and biomass. Past projects include small and large unmanned aircraft, radar arrays and fairings, wind turbine blades, telescopes and fuel containment devices. Teams of faculty, staff and students in recent years have designed, fabricated and flight-tested unmanned aircraft and manned aircraft sensor suites, predominantly for remote sensing in Greenland and Antarctica.
The composite lay-up facility is a 59 m2 “clean” room with a 6.7 m2 lay-up table and 24.3 m3 of –30° C material storage. The composite tooling and processing laboratory encompasses 128.4 m2, and contains a radial diamond saw, 17.8 cm diamond blade precision sectioning saw, 22.9 cm abrasive cutter, two hydraulic specimen mounting presses, orbital and vibrating polishers and a microhardness tester. Sample inspection and documentation is aided with a Nikon Epiphot inverted reflected light photomicroscope capable of magnification to 1000X, with Polaroid and 35mm film or digital video capture. The composite curing facility encompasses 66.3 m2 and includes an autoclave for curing thermoset and thermoplastic composite materials, 107kN and 667 kN electrically heated water cooled platen presses, and electronically controlled ovens. The autoclave is rated to 2.4 MPa and 370° C and has a usable space of 30x30x91 cm. The smallest oven is rated to 370° C and has a usable space of 51x51x46 cm. and the intermediate oven is rated to 370C and has a usable space of 1.5m x 1 m x .8m. The composite materials laboratory also houses an electronically controlled walk-in curing oven capable of 260° C, with a usable space of 2.1 x 2 x 6.1 m.