AGARD R-800 - FTP Directory Listing - Nato

SUMMARY
A review of two different landing gear shimmy
mathematical models is presented. One model uses
the Moreland tire model and the other model uses the
Von Schlippe-Dietrich tire model. The results of a
parametric study using these models is presented
indicating the sensitivity of various parameters to
numerical variation. An identification of stability
critical parameters in the models is given. Three
different aircraft landing gear shimmy data sets are
reviewed and model stability predictions are
discussed. A comparison is made with actual
experimental results. One of these data sets indicates
the nonlinear variation of various input parameters as
a function of strut stroke. In the course of the
presentation some design rules and cautions are
- suggested.
LIST OF SYMBOLS
A REVIEW OF AIRCRAFT LANDING GEAR DYNAMICS
The definitions of the various parameters used in
the mathematical models are defined below. Except
as noted, the parameters are used in both the
Moreland and the Von Schlippe-Dietrich models.
C - Tire Yaw Coefficient (radllb)
(Moreland Model Only)
C, - Moreland Tire Time Constant (sec)
(Moreland Model Only)
h - Half Length of the Tire Ground Contact Patch
(in) (Von Schlippe-Dietrich Model Only)
L,
- Tire Relaxation Length (in)
(Von Schlippe-Dietrich Model Only)
C, - Structural Rotation Damping Coefficient
(Rotation of Mass about the Trail Arm Axis)
(in-lb-sechad)
C,
- Tire Lateral Damping Coefficient (lb-sedin)
WILLIAM E. KRABACHER
WL/FIVMA Building 45
WRIGHT LABORATORY
WRIGHT PATTERSON AFB
2130 Eighth Street, Suite 1
Ohio 45433-7542, USA
C,
- Structural Lateral Damping Coefficient
(lb-sec/in)
CT - Rotational Velocity Squared Damping
Coefficient (Rotation about the Strut Vertical
Axis) (in-lb-sec2/rad2) OR Linear Viscous
Damping Coefficient (in-lb-sechad)
CFl - Friction Torque (in-lb)
CF2 - Coefficient of Friction Torque as a Function
of Side Load at the Ground (in-lbAb)
FP - Peak to Peak Torsional Freeplay of the Gear
about the Strut Vertical Axis (rad)
I - Mass Moment of Inertia of the Rotating Parts
about the Axle (in-lb-sec*/rad)
I,
I,
- Equivalent Mass Moment of Inertia of the
Lumped Mass System about the Trail Arm
Axis (in-lb-sec*/rad)
2- 1
- Equivalent Mass Moment of Inertia of the
Lumped Mass System about the Strut Vertical
Axis (in-lb-sec*/rad)
K, - Rotational Spring Rate about the Trail Arm
Axis Measured at the Wheel/Axle Centerline
(in-lb/rad)
K,
K,
K,
KT
- Cross Coupled Spring Rate (lb)
- Tire Lateral Spring Rate (lb/in)
- Lateral Spring Rate of the Structure at the
Trail Arm and Strut Vertical Centerline
Intersection (Ib/in)
- Torsional Spring Rate of the Structure about
the Strut Vertical Centerline with the
Damper Locked (in-lb/rad)
Paper presented ut the 8lst Meeting of the AGARD SMP Panel on “The Design, Qualification and Maintenance
of Vibration-Free Landing Gear”, held in Ban8 Canada from 4-5 October 1995, and published in R-800.