OS-V: 1305 Flutter Analysis of a Generic Transport Aircraft Model

Flutter analysis of a Generic Transport Aircraft (GTA) model is performed using the KE method.

The results are validated against a publication from the AIAA Journal1.

Benchmark Model

Figure 1. GTA model
Dimension details of the model:
Value (mm)
Wing Span
Uniform Chord Length
Length of Aircraft
Height of Aircraft
The model is symmetric about the X-Z plane and the structural domain consists of a stick model with CBAR and CELAS2 elements. Flutter analysis is performed for a Mach number of 0.3, density ratio of 1.0, and equally spaced reduced frequencies in the range [0.50, 1.50] Hz. Unit of output velocity is defined in knots using PARAM, VREF.


From the .flt file, the flutter point (where damping changes sign) corresponding to the lowest mode is identified as the 7th mode (flutter point A) with a velocity between 308.698 knots to 343.006 knots.
Note: By definition, instability (flutter or divergence) occurs when the damping values are zero. At this point, if the frequency is zero, then the instability is due to divergence. Otherwise, the instability is due to flutter.

Figure 2. Flutter analysis summary from the .flt file
Plotting the v-g curve, the velocity at this flutter point is 327.668 knots. This is the most critical flutter point that needs to be avoided.

Figure 3. Identify the flutter points. The flutter point corresponding to the lowest velocity is also visually identified.

Figure 4. Identify the frequency value at the critical flutter point from the v-f curve.
Plotting the v-f plot for the 7th mode (corresponding to the critical flutter point), the frequency value for 7th mode at a velocity of 327.668 knots is determined as 13.334 Hz.
Flutter Speed
Approximately 300 knots
327.668 knots
The results from the OptiStruct flutter analysis are verified.
Note: The slight difference in flutter speed may be attributed to:
  • Uncertainties in the model. The precise geometry, damping, and other data used in the reference are not known and may differ from what was used in OptiStruct1.
  • The order approximation for the DLM kernel. The order used in the reference is not known and may differ from what was used in OptiStruct1.

Model Files

Refer to Access the Model Files to download the required model file(s).

The model files used in this problem include:
  • aeroelasiticity_flutter_GTA_model.fem


1 M. Karpel, A. Shousterman, C. Maderuelo, and H. Climent,“Dynamic Aeroservoelastic Response with Nonlinear Structural Elements,” in AIAA Journal, 2015, vol. 52, no. 11, pp. 3233–3239. doi: 10.2514/1.J053550.