Aeroelasticity made simple Terry A Weisshaar Purdue University

Aeroelasticity (made simple) Terry A. Weisshaar Purdue University weisshaar@purdue. edu Armstrong Hall 3329 765 -494 -5975 Purdue Aeroelasticity 1

Details i Class in ARMS 1021 Purdue Aeroelasticity 2

Grading - Tests and Homework is assigned on Fridays and is handed in at the beginning of each class the following Friday. i Homework counts 30% of final grade score i 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 AAE 556 – Spring 2008

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 AAE 556 Restricted folder i Reading for Wednesday – Chapter 1 – Chapter 2, sections 2. 1 -2. 5 Purdue Aeroelasticity 4

What’s it all about? i What is aeroelasticity? i Why is it important? i When is it important? i Key features of aeroelastic response Purdue Aeroelasticity 5

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 6

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 Aeroelasticity 7

Venn diagram showing interactions Aerodynamic forces L=q. SCL Dynamic Static stability aeroelasticity Flutter Elastic Forces F=kx Vibrations Purdue Aeroelasticity Inertial Forces F=ma 8

Flutter at a glance Purdue Aeroelasticity 9

Early history- static aeroelasticity Elastic Forces F=kx Aerodynamic forces L=q. SCL Static aeroelasticity Purdue Aeroelasticity 10

Aeroelasticity changes history and puts the hex on monoplanes Langley Wright Bleriot Purdue Aeroelasticity 11

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 12

The Wright Stuff innovation in action Wing morphing (warping) in action Wing warping Purdue Aeroelasticity 13

Griffith Brewer weighs in on aeroelasticity – sort of … Purdue Aeroelasticity 14

Bleriot XI - monoplane wing warping England here we come! Purdue Aeroelasticity 15

John B. Moissant 1868 -1910 Moissant in Bleriot airplane Cross-Channel flight 1910 Moissant all-aluminum airplane 1910 The end of the trail-Dec. 31, 1910 Purdue Aeroelasticity 16

Control effectiveness Reduced ability, or loss of ability, to roll or turn quickly aileron reversal Purdue Aeroelasticity 17

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 Aerodynamic forces L=q. SCL Static aeroelasticity Purdue Aeroelasticity 18

Forward swept wings X-29 began as a Ph. D. dissertation topic in 1972 Purdue Aeroelasticity 19

Aeroelastic tailoring Intentional use of directional stiffness and load interaction to create beneficial performance Purdue Aeroelasticity 20

Flutter and dynamic response Aerodynamic forces L=q. SCL Dynamic Static stability aeroelasticity Flutter Inertial Elastic Forces Vibrations F=ma F=kx Purdue Aeroelasticity 21

Heinkel flutter Purdue Aeroelasticity 22

Flutter in practice Purdue Aeroelasticity 23

Classical Flutter ed pe rs ai aileron frequency & motion freq y uenc wing bending and torsion Purdue Aeroelasticity 24

Glider flutter Purdue Aeroelasticity 25

Engines and under-wing stores Purdue Aeroelasticity 26

Supersonic and hypersonic flight Purdue Aeroelasticity 27

Panel flutter – going into space Frequency merging – amplitude limited by nonlinear effects - creates noise and fatigue Supersonic flow Dead air Purdue Aeroelasticity 28

Body-freedom flutter Purdue Aeroelasticity 29

Aeroelasticity regulations i Civil aviation - FAR 23 and FAR 25 i Military - Navy MIL-A 8870 C i Air Force - AFGS 8722 i Joint Services Guide Specification, Aircraft Structures Purdue Aeroelasticity 30

Military Specification Airplane strength and rigidity vibration, flutter and divergence 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 Aeroelasticity 31

The future … new configurations, old and new problems Purdue Aeroelasticity 32