The United States Air Force Stability and Control Digital DATCOM is a computer program that implements the methods contained in the USAF Stability and Control DATCOM to calculate the static stability, control and dynamic derivative characteristics of fixed-wing aircraft. Digital DATCOM requires an input file containing a geometric description of an aircraft, and outputs its corresponding dimensionless stability derivatives according to the specified flight conditions. The values obtained can be used to calculate meaningful aspects of flight dynamics.
History In February 1976, work commenced to automate the methods contained in the USAF Stability and Control DATCOM, specifically those contained in sections 4, 5, 6 and 7. The work was performed by the McDonnell Douglas Corporation under contract with the United States Air Force in conjunction with engineers at the Air Force Flight Dynamics Laboratory in Wright-Patterson Air Force Base. Implementation of the Digital DATCOM concluded in November 1978. The program is written in FORTRAN IV and has since been updated; however, the core of the program remains the same. A report was published, separated into three volumes, which explains the use of Digital DATCOM. The report consists of
Volume I, User's Manual Volume II, Implementation of DATCOM Methods Volume III, Plot Module
Inputs Section 3 of the USAF Digital DATCOM Manual Volume I defines the inputs available for modeling an aircraft. The inputs are categorized by namelists to facilitate reading the file into FORTRAN.
Flight conditions and options The FLTCON Namelist describes the flight conditions for the case. A maximum of 400 Mach-altitude combinations can be run at once, with up to 20 angles of attack for each combination. The user can specify whether the Mach number and altitude varies together, the Mach number varies at a constant altitude, or the altitude varies at a constant Mach number. Both subsonic and supersonic analysis can be run in Digital DATCOM. The OPTINS Namelist defines the reference parameters for the aircraft. The theoretical wing area, mean aerodynamic chord, and wing span are input along with a parameter defining the surface roughness of the aircraft.
Synthesis parameters The SYNTHS Namelist allows the user to define the positions of the center of gravity and apexes of the wings. The X- and Z- coordinates are needed for the wing, horizontal tail, and vertical tail in order for the aircraft to be synthesized correctly. DATCOM does not require that the origin for the aircraft has to be the nose of the aircraft; any arbitrary point will do, but all of the dimensions need to be referenced from that point. Incidence angles can also be added to the wing and horizontal tail.
Body parameters The BODY Namelist defines the shape of the body. Digital DATCOM assumes an axisymmetrical shape for the body. Up to 20 stations can be specified with the fuselage half-width, upper coordinate and lower coordinate being defined at each station. For supersonic analysis, additional parameters can be input.
Wing, Horizontal and Vertical Tail parameters The WGPLNF, HTPLNF and VTPLNF Namelists define the wing, horizontal tail and vertical tail, respectively. The basic parameters such as root chord, tip chord, half-span, twist, dihedral and sweep are input. Digital DATCOM also accepts wing planforms which change geometry along the span such as the F4 Phantom II which had 15 degrees of outboard dihedral. Canards can also be analyzed in Digital DATCOM. The canard must be specified as the forward lifting surface (i.e. wing) and the wing as the aft lift surface. For airfoil designations, most traditional NACA 4-, 5-, and 6- airfoils can be specified in Digital DATCOM. Additionally, custom airfoils can be input using the appropriate namelists. Also, twin vertical tails can be designated in Digital DATCOM, but not twin booms.
High Lift and Control Devices Using the SYMFLP and ASYFLP Namelists, flaps, elevators, and ailerons can be defined. Digital DATCOM allows a multitude of flap types including plain, single-slotted, and fowler flaps. Up to 9 flap deflections can be analyzed at each Mach-altitude combination. Unfortunately, the rudder is not implemented in Digital DATCOM. Digital DATCOM also offers an automated aircraft TRIM function which calculates elevator deflections needed to trim the aircraft.
Other Inputs Other Digital DATCOM inputs include power effects (propeller and jet), ground effects, trim tabs, and experimental data. The EXPRXX Namelist allows a user to use experimental data (such as coefficient of lift, coefficient of drag, etc.) in lieu of the data Digital DATCOM produces in the intermediate steps of its component build-up. All dimensions are taken in feet and degrees unless specified otherwise. Digital DATCOM provides commands for outputting the dynamic derivatives (DAMP) as well as the stability coefficients of each components (BUILD).
Output Digital DATCOM produces a copious amount of data for the relatively small amount of inputs it requires. By default, only the data for the aircraft is output, but additional configurations can be output:
Body alone Wing alone Horizontal tail alone Vertical tail alone Wing-Body Configuration Body-Horizontal Tail Configuration Body-Vertical Tail Configuration Wing-Body-Horizontal Tail Configuration Wing-Body-Vertical Tail Configuration Wing-Body-Horizontal Tail-Vertical Tail Configuration For each configuration, stability coefficients and derivatives are output at each angle of attack specified. The details of this output are defined in Section 6 of the USAF Digital DATCOM Manual Volume I. The basic output includes:
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