3.5 Challenges in modern aerostructures

3.5.1 Sandwich structures and composite materials

NASA Pubic Domain

  • High stiffness with low weight material configuration
  • Core carries the shear load which the face sheets carry the tensile and compressive loads associated with bending
  • Early example of sandwich structure was De Havilland Mosquito which had balsa core sandwiched between spruce face sheets
  • Carbon and boron fibers are commonly used face sheets due to high specific stiffness and specific strength
  • Core is often constructed of foam with high compressive strength
  • Core and face can be adhesively bonded or molded in place
  • Other cores are corrugated metals or metallic foams
  • Early composite aircraft was the Raytheon/Beach Starship 2000 (1986)

Metalic foams permit shear loads to be carried by a low density (porous) structure.

Blanchet matthieu, CCSA3.0, 2012

It also may serve multiple functions, ie, cooling

Jean-Michel Hugo, CCSA3.0, 2012

3.5.2 Tailored stiffness–composite materials

  • Aeroelastic tailoring: use of directional differences in properties to carry load and cause intentional deformations that have aeroelastic advantages (stiffer in one mode of deformation than another)

NASA

  • Grumman X-29A–Forward swept wing with aeroelastic tailoring.
    • The advantage is that the wing tips stall last instead of first, allowing greater control
    • Downside is that the aeroelastic deformation causes positive feedback on wing loading (wing loading drives higher angles of attack, drives higher wing loading)–Divergence
  • Bend/twist coupling allows minimization of divergence effects

3.5.3 Wing warping

@TAMU2014

@TAMU2014

Challenges

  • Maintain structural integrity during large changes in configuration
  • Control