Definition of P.S.D.-design loads for nonlinear aircraft

Definition of P.S.D.-design loads for nonlinear aircraft

Noback, R.

National Aerospace Laboratory NLR

1989-01-17

The Power Spectral Density (P.S.D.)-method is used to define design loads due to atmospheric turbulence. The design loads are calculated using linear transfer functions. These methods can not be used if the equations describing the behaviour of the aircraft are nonlinear. One method to define design loads for a nonlinear aircraft is by means of computer simulation. The definition for the design loads as used in the P.S.D.-method are inadequate in this case. This report deals with the necessary changes in the definitions of the design loads for a Design Envelope Analysis and a Mission Analysis. In the D.E.A. the probability that the load exceeds the design load is used as a criterion. The proposed definitions are based on the use of a representative value of the standard deviation of the input and on the use of an approximation of the integrand representing the contribution of the input level to the probability of exceedance or the number of level crossings. The correlation between loads is also discussed. The methods are illustrated with an example consisting of a simple mathematical aircraft model with load alleviation system with limited controls.

atmospheric turbulence
statistical analysis
expectancy hypothesis
aircraft design
structural design criteria
nonlinear systems
design analysis
power spectra
computerized simulation
gust loads
gust alleviators

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Nationaal Lucht- en Ruimtevaartlaboratorium

Campus only

NLR Technical Publication TP 890016 U

Aerospace Engineering Reports

report

(c) 1989 National Aerospace Laboratory NLR