Aeroelasticity (made simple) Terry A. Weisshaar Purdue University weisshaar@purdue.edu Armstrong Hall 3329 765-494-5975 Purdue Aeroelasticity

Purdue Aeroelasticity Details Class in ARMS 1021 Purdue Aeroelasticity

Grading - Tests and Homework 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 AAE556 – Spring 2008

Course materials Text distributed free Reading assignments for each lecture Help me edit Notes, homework and supplemental material available on the AAE website Look under AAE556 Restricted folder Reading for Wednesday Chapter 1 Chapter 2, sections 2.1-2.5 Purdue Aeroelasticity

Purdue Aeroelasticity What’s it all about? What is aeroelasticity? Why is it important? When is it important? Key features of aeroelastic response Purdue Aeroelasticity

Aeroelasticity definition & effects Aeroelasticity 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 Aeroelasticity

Classical aeroelastic problems Static aeroelasticity wing divergence , aero/structure stiffness load redistribution - drag, stresses change aileron reversal, lack of control lift ineffectiveness, vertical tail yaw control Flutter and dynamic response self-excited wing vibration/destruction self-excited panel vibration, LCO Purdue Aeroelasticity

Venn diagram showing interactions Aerodynamic forces L=qSCL Inertial Forces F=ma Elastic F=kx Vibrations Static aeroelasticity Dynamic stability Flutter Purdue Aeroelasticity

Purdue Aeroelasticity Flutter at a glance Purdue Aeroelasticity

Early history- static aeroelasticity Aerodynamic forces L=qSCL Elastic Forces F=kx Static aeroelasticity Purdue Aeroelasticity

Aeroelasticity changes history and puts the hex on monoplanes Langley Wright Bleriot Purdue Aeroelasticity

Samuel Langley well financed, doomed to failure Excessive wing twist caused by too much wing camber Before After “almost everything unexpected during the development process is bad” Purdue Aeroelasticity

The Wright Stuff innovation in action Wing morphing (warping) in action Wing warping Purdue Aeroelasticity

Griffith Brewer weighs in on aeroelasticity – sort of … Purdue Aeroelasticity

Bleriot XI - monoplane wing warping England here we come! Purdue Aeroelasticity

Purdue Aeroelasticity John B. Moissant 1868-1910 Moissant in Bleriot airplane airplane Cross-Channel flight 1910 Moissant all-aluminum airplane 1910 The end of the trail-Dec. 31, 1910 1910 Purdue Aeroelasticity

Control effectiveness Reduced ability, or loss of ability, to roll or turn quickly aileron reversal Purdue Aeroelasticity

Swept wing load redistribution 1.0 Total lift is the same spanwise center of pressure moves inboard to reduce root bending moment Aerodynamic forces L=qSCL Elastic Forces F=kx Static aeroelasticity Purdue Aeroelasticity

Purdue Aeroelasticity Forward swept wings X-29 began as a Ph.D. dissertation topic in 1972 Purdue Aeroelasticity

Aeroelastic tailoring Intentional use of directional stiffness and load interaction to create beneficial performance Purdue Aeroelasticity

Flutter and dynamic response Aerodynamic forces L=qSCL Inertial Forces F=ma Elastic F=kx Vibrations Static aeroelasticity Dynamic stability Flutter Purdue Aeroelasticity

Purdue Aeroelasticity Heinkel flutter Purdue Aeroelasticity

Purdue Aeroelasticity Flutter in practice Purdue Aeroelasticity

Purdue Aeroelasticity Classical Flutter frequency airspeed wing bending and torsion aileron frequency & motion Purdue Aeroelasticity

Purdue Aeroelasticity Glider flutter Purdue Aeroelasticity

Engines and under-wing stores Purdue Aeroelasticity

Supersonic and hypersonic flight Purdue Aeroelasticity

Panel flutter – going into space Frequency merging – amplitude limited by nonlinear effects - creates noise and fatigue Supersonic flow Dead air Purdue Aeroelasticity

Purdue Aeroelasticity Body-freedom flutter Purdue Aeroelasticity

Aeroelasticity regulations Civil aviation - FAR 23 and FAR 25 Military - Navy MIL-A-8870C Air Force - AFGS-8722 Joint Services Guide Specification, Aircraft Structures Purdue Aeroelasticity

Purdue Aeroelasticity Military Specification Airplane strength and rigidity vibration, flutter and divergence 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 Aeroelasticity

The future … new configurations, old and new problems Purdue Aeroelasticity