Evaluation of strip theory and doublet-lattice aerodynamics

In this report, a comparison is made between Doublet-Lattice and strip theory aerodynamics in symmetrical conditions of a Fokker-100-like aircraft model with rigid and flexible degrees of freedom. The generalized aerodynamic force matrices that result from the two methods show some resemblance, but this does not yield much physical insight in the aerodynamic force distributions. A comparison of aircraft stability derivatives that result from the two methods with data of the NLR simulator model shows that both methods will result in reasonably correct aircraft rigid body motions at low frequencies. The influence of flexibility of the aircraft structure on stabihty derivatives is roughly the same for both methods. The aerodynamic load distributions over wing and horizontal tail plane have a more realistic profile when Doublet-Lattice is used (the three-dimensional effect of finite span width is represented), but strip theory coefficients can be adapted easily to experimental data in symmetrical conditions. The Doublet-Lattice and strip theory lift distributions on wing and stabilizer due to the plunge motion do not differ much at (very) low frequencies. At a higher frequency of 19.1 rad/s, more significant differences are observed in the amplitude and the phase angle of the lift distributions.