# Estimation of Stability Parameters for Wide Body Aircraft Using Computational Techniques
## 2 US DATCOM  
DATCOM is a computer algorithm that is used to estimate the aerodynamic properties, i.e., stability and control coefficients of fixed-wing aircraft either by extrapolation or interpolation of information available in a database [43]. The computer program was modified into commercial software that has been extensively used in academia as one of the reliable tools for the stability and control of an aircraft. The software now is in the public domain and has been replaced in the aerospace industry by newer computational analysis options [44; 45]. It is a combination of theoretical and experimental procedures that are required to analyze aerodynamic stability and control parameters. DATCOM can be used for the autonomous design of the flight control system for a fixed/blended wing aircraft [46]. Aerodynamic parameters are generally obtained from wind tunnel testing, computational fluid dynamics, or flight tests; however, dimensionless aerodynamic stability (static/dynamic) derivatives can be directly estimated using DATCOM [47]. The inputs required in DATCOM are only physical dimensions and flight conditions, but the output can be varied according to the requirements. Not only can the coefficients of the entire aircraft be obtained, but individual surfaces or a combination can also be produced as an output. Additional output configurations include wing, horizontal tail, wing-tail, and wing-fuselage-horizontal tail configurations. In DATCOM, forward lift surfaces are always treated as wing and the aft lift surface is considered as a tail [48]. The analysis gives meaningful results for the estimation of a complete set of longitudinal stability and control coefficients for lifting, stability, and control surfaces. Aircraft model simulation can also be obtained to visually check the various surfaces. Figure 3 shows the Boeing 737 model obtained from DATCOM based upon geometric parameters. The output can further be utilized to evaluate the flight dynamics characteristics. Aircraft control surface deflections and aerodynamic data at various Mach number regimes can also be computed [49].  
The characteristics based on body aerodynamics and subsonic longitudinal data can be obtained at different Mach numbers for rotational and cambered bodies having arbitrary cross-sectional areas [50]. Moreover, the trim output can also be computed by the manipulation of stability and control characteristics. The trim mode includes a horizontal tail or wing coupled with a trim control mechanism and longitudinal aerodynamic characteristics, and deflection angles required to trim are obtained as outputs. Some special control procedures, i.e., hypersonic flap methods related to controllability and stability for high-speed operating devices, are also incorporated in DATCOM. The initial sizing procedure of 2D transverse jet controls for an aft-end located nozzle operating at a high Mach number can be obtained from this technique. Moreover, the interaction of the local flow field and transverse jet can also be evaluated. The output from DATCOM can be imported into MATLAB through the MathWorks Aerospace Toolbox where stati  
Figure 3: Boeing 737 model, as prepared using US DATCOM in this research.  
and control derivatives can be stored in arrays that can be further used in the Simulink block for stability analysis.