The feasibility of a composite tailored wing for a high-speed civil tiltrotor is addressed using existing analytical methods. Composite tailoring is utilized to increase the proprotor aeroelastic stability margins for a thin wing (18% t/c) designed to improve high speed performance and productivity. Structural tailoring concepts are applied to the wing alone to improve the stability of the symmetric wing beamwise bending mode and the symmetric wing chordwise bending mode, which are the two most critical modes of instability. Skin laminate tailoring is shown to favorably influence the wing pitch/bending coupling and improve the stability of the wing beamwise mode. The wing chordwise mode stability is reduced by skin laminate tailoring due to a decrease in wing stiffness, but by tailoring the distribution of stringer and spar cap areas, the wing chord mode stability can be recovered. Parametric studies show that the overall stability gains from composite tailoring can be limited because of conflicting structural design requirements imposed by the two critical modes of instability, and the necessity to balance the stability boundaries for both modes. The parametric studies are used to define an 18% t/c tailored wing configuration that meets the stability goals with a minimum weight penalty.
I ~-_j An aeroelastic stability analysis has been developed for predicting flutter instabilities on vertical axis wind turbines. This report describes the analytical model and mathematical formulation of the problem as well as the physical mechanism that creates flutter in Darrieus turbines. Theoretical results are compared with measured experimental data from flutter tests of the Sandia 2 Meter turbine. Based on this comparison, the analysis appears to be an adequate design evaluation tool.
ABSTRACThelicopters because of the limitations imposed by aerodynamic physics, there is hope that tiltrotor topend and The requirements for increased speed and productiv-cruise speeds may increase further with improved engiity for tiltrotors has spawned several investigations asso-i n current limitations on speed for the V-22 tiltrociated with proprotor aeroelastic stability augmentation tor are associated with control loads, control margins, and and aerodynamic performance enhancements. Included power, while the tiltrotor is power limited. The among these investigations is a focus on passive aeroe-aeroelastic stability of tiltrotor systems is also an imporlastic tailoring concepts which exploit the anisotropic ca-tant concern, as the stability margins associated with curpabilities of fiber composite materials. Researchers at rent tiltrotors are not far beyond the speed limitations set Langley Research Center and Helicopte~ have de-by loads and power today. It is anticipated that the u p voted considerable effort to assess the potential for using per velocity limit for future high-speed tiltrotors may be these materials to obtain aeroelastic responses which are set by both loads and aeroelastic stability considerations. beneficial to the important stability and performance con-To achieve higher speeds for tiltrotors, structural tailoring siderations of tiltrotors. Both experimental and analyt-of blades and wings using advanced composite ical studies have been completed to examine aeroelastic has been considered in several past investigations. tailoring concepts for the tiltrotor, applied either to the wing or to the rotor blades. This paper reviews some of the results obtained in these aeroelastic tailoring investigations and discusses the relative merits associated with Researchers at Lagley Research Center and Bell Helithese approaches.copter have devoted considerable effort to assess the potential for using composite materials to obtain aeroelastic responses which are beneficial to the important stability INTRODUCTION and performance considerations of tiltrotors. Both experimental and analytical studies have been completed qytrotor aircraft have advantages over conventional he-which examine aeroelastic tailoring concepts for the tiltrolicopters with respect to speed and range. While a heli-tor, applied either to the wing or to the rotor blades. copter is limited at high speeds by compressibility This paper reviews some of the results obtained in these on the rotor advancing side and stall on the rotor retreat-aer0elaStic tailoring investigations and discusses the reling side, a tiltrotor converts from a helicopter mode to ative merits associated with these approaches. While an airplane mode for high speed flight is less re-the material presented in this report focuses on activi-
Rofur-L)y,zamics U.S. Artfly Vehicle Sfrrrctares r)irecto,nte Bell Helicopter Texfro~r, hic., For1 W0rtI1, TX NASA Lar~gley Research Genre,; Hnnrprorr, VA A composite tailored tiltrotor wing was designed and tested on a US-scale semispan aeroelastic model to demonstrate that composite tailoring techniques can be used to improve pmprotor stability. Structural tailoring of the model-scale wing torque box is acconlplished by using unbalanced composite laminates to modify wing bending torsion coupling, which is shown analytically to improve proprotor stahility in high-speed airplane mode flight. The analytical methodologies used to develop the math models and predict the improved aeroelastic stahility characteristics of the conlposite tailored wing are discussed. The frequency and damping characteristics of the critical wing beam and wing chord modes were measured during wind tunnel tests performed in airplane mode. The structural modes mere excited a t their natural frequencies and the damping values were measured from the time history decays following the excitations. The composite tailored wing aeroelastic stahility boundary is compared to the stahility boundary of a baseline untailored wing configuration. Finally, the modal damping and measured instabilities are then compared to analytical predictions for both the baseline and tailored wing configurations.
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