The flutter analysis of the JS1 glider

Pieter S. Rossouw

Master’s Degree Student

Supervisor: Mr. Attie S. Jonker

North-West University (Potchefstroom)

Slide 2 © CSIR 2006 www.csir.co.za

Introduction

• New composite glider: JS1 Revelation• 18 meter wingspan• Maximum speed:

290 km/h (Vne)

• Designed by Attie Jonker & team

• Certify new aircraft• Design diving speed (VD)• 1.2VD = 388.8 km/h

= 209.9 knots

Slide 3 © CSIR 2006 www.csir.co.za

Problem definition/statement

• What is flutter?• Flutter analysis main steps

• Modal analysis• Flutter prediction• Flutter flight test

• Modal analysis done by• Finite element software • Ground vibration test

• JS1 flutter analysis steps:• Modal analysis• Flutter prediction

Slide 4 © CSIR 2006 www.csir.co.za

Modal analysis

• Ground vibration test @ CSIR• Two glider configurations• Simulate free condition• Excitation with electrodynamic shaker• Response measurement with sensors• Dynamic characteristics are

• Natural frequency• Mode shape• Modal damping

• What is a mode?• Wing, fin and tailplane modes found

Slide 5 © CSIR 2006 www.csir.co.za

Modal analysis (continued)

Slide 6 © CSIR 2006 www.csir.co.za

Modal analysis (continued)

• 2nd symmetric wing bending @ 7.34 Hz

Slide 7 © CSIR 2006 www.csir.co.za

Flutter prediction

• Use modal data in flutter code• Flutter code utilizes

• Doublet lattice method• p-k method

• Flutter results• Damping vs. airspeed• Frequency vs. airspeed

• Altitudes up to 8000 meters• One indication of flutter: 430 knots• Results above 210 knots – no concern

Slide 8 © CSIR 2006 www.csir.co.za

Flutter prediction (continued)Configuration 1: Symmetric wing modes

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0 100 200 300 400 500 600 700

Equivalent Velocity (knots)

Da

mp

ing

1st wing bending

in-plane bending

2nd wing bending3rd wing bending

torsion

210 knots(1.2VD)

Slide 9 © CSIR 2006 www.csir.co.za

Conclusion

• Modal analysis done by• Ground vibration test

• Flutter analysis done for• Speeds up to 388.8 km/h

(210 knots)• Altitudes up to 8000 meters

• For all modes found• Stability for

JS1 design envelope