Aeroelasticity (made simple) Terry A Weisshaar Purdue University weisshaar@purdue.edu Armstrong Hall 3329 765-494-5975 Purdue Details i Class in ARMS 1021 Purdue Grading - Tests and Homework i i i Homework is assigned on Fridays and is handed in at the beginning of each class the following Friday Homework counts 30% of final grade score Two tests (two hours long) – each 35% of final grade score – One test the week before Spring Break – covers static aeroelasticity – Second exam during Finals Week – covers dynamic aeroelasticity Course materials i Text distributed free – Reading assignments for each lecture – Help me edit i Notes, homework and supplemental material available on the AAE website – Look under AAE556 Restricted folder i Reading for Wednesday – Chapter – Chapter 2, sections 2.1-2.5 Purdue Aeroelasticity What’s it all about? i i i i What is aeroelasticity? Why is it important? When is it important? Key features of aeroelastic response UAV flutter.mp4 Purdue Aeroelasticity definition & effects A eroelasticity is a design activity concerned with interactions between aerodynamic forces and structural deformation, both static and dynamic, and the influence of these interactions on aircraft performance • Aerodynamic load and structural deflection interaction • Static stability • Control surface effectiveness • Flutter and dynamic response Purdue Classical aeroelastic problems i Static aeroelasticity – wing divergence , aero/structure stiffness – load redistribution - drag, stresses change – aileron reversal, lack of control – lift ineffectiveness, vertical tail yaw control i Flutter and dynamic response – self-excited wing vibration/destruction – self-excited panel vibration, LCO Purdue Venn diagram showing interactions Aerodynamic forces L=qSCL Dynamic Static stability aeroelasticity Flutter Elastic Forces F=kx Purdue Vibrations Inertial Forces F=ma Flutter at a glance Purdue Early history- static aeroelasticity Elastic Forces F=kx Purdue Aerodynamic forces L=qSCL Static aeroelasticity Swept wing load redistribution 1.0 Total lift is the same spanwise center of pressure moves inboard to reduce root bending moment Elastic Forces F=kx Purdue Aerodynamic forces L=qSCL Static aeroelasticity Forward swept wings X-29 began as a Ph.D dissertation topic in 1972 Purdue Aeroelastic tailoring Intentional use of directional stiffness and load interaction to create beneficial performance Purdue Flutter and dynamic response Aerodynamic forces L=qSCL Dynamic Static stability aeroelasticity Flutter Inertial Elastic Forces Forces Vibrations F=ma F=kx Purdue Heinkel flutter Purdue Flutter in practice Purdue Classical Flutter aileron frequency & motion Purdue wing bending and torsion Glider flutter Purdue Engines and under-wing stores Purdue Supersonic and hypersonic flight Purdue Panel flutter – going into space Frequency merging – amplitude limited by nonlinear effects - creates noise and fatigue Supersonic flow Dead air Purdue 28 Body-freedom flutter Purdue Aeroelasticity regulations i i i i Civil aviation - FAR 23 and FAR 25 Military - Navy MIL-A8870C Air Force - AFGS-8722 Joint Services Guide Specification, Aircraft Structures Purdue Military Specification Airplane strength and rigidity vibration, flutter and divergence i i i i Prevent flutter, divergence and other dynamic and static instabilities Control structural vibrations Prevent fatigue failure Prescribe structural dynamic analyses, laboratory and ground tests, flight tests required to demonstrate compliance with design requirements Purdue The future … new configurations, old and new problems Purdue Aeroelasticity