Aeroelastic Response and Stability of Highly Flexible Aircraft

Student : Ben Hallissy

Sponsor : AFRL/RB


Summary:

High Altitude, Long Endurance (HALE) aircraft have become popular for dull, dirty, and dangerous missions.  Long on-station times require high L/D ratios, high aspect ratios, high fuel fractions, and low structural weight – which all lead to increased flexibility.  HALE aircraft are often subjected to nonlinear aerodynamics (shocks) and large, geometrically nonlinear deflections.  Nonlinearities are also present in kinematic relations, because of time varying inertia properties. This work focuses on simulating the free-flight behavior of highly-flexible HALE aircraft.

  • Integrate high – fidelity Euler/NS fluid solver with in-house UM/NLABS structural solver to determine nonlinear aeroelastic response.  CFRDC/MDICE is used as the communication and interpolation interface between the fluid and structural solvers

  • Develop 6-DOF flight dynamics module to enable pitch-plunge and free-flight time simulations of highly flexible aircraft. Use this to characterize interaction between flight dynamics and control system

  • Validate this simulation with flight test data from X – HALE design, then investigate compressibility effects on aeroelastic response

NASA/AeroVironment Helios
Source: NASA
Static deflection of cantilevered wing. Flight speed: 25 m/s
Multidisciplinary Computing Environment (MDICE) screen shot
High-Fidelity Very Flexible Aircraft (HiFi – VFA) simulation flow chart

Post-critical aeroelastic response of a representative very flexible aircraft wing. M=0.5 @ 20km.

Post-critical aeroelastic response of a representative very flexible aircraft wing. Cross-sectional view at 75% span. M=0.5 @ 20km