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Experimental aerodynamic investigations were conducted on a stingmounted 0.0405-scale representation of the 140A/B space shuttle orbiter in a 7.75 by 11-Foot low speed wind tunnel from April 24 to April 26, 1974. Differential inboard/outboard elevon panel deflections with the 6-inch gap were investigated to determine outboard panel aileron effectiveness. The elevons were deflected from +20 degrees to -40 degrees in various combinations. Aerodynamic force and moment data for the orbiter were measured in the body axis system by an internally mounted, six-component strain gage balance. The model was sting mounted with the center of rotation located at F.S. 60.172. The angle of attack range was from -10 degrees to +24 degrees.
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A change in the wind vector over a short distance along the flight path (wind gradient) has caused several severe airplane accidents during take-off and landing. Results of a previous study showed that, in descending flight, a positive wind gradient (decreasing head wind) caused severe divergent motion and a negative wind gradient (decreasing tail wind) caused oscillatory motion which should not create a control problem. The results obtained when the same method of analysis was applied to climbing and to straight and level flight are reported. In straight and level flight, a wind gradient was found to cause effects similar to those found in descending flight. In climbing flight, it was found that a negative wind gradient caused a slightly divergent oscillation that presented no control problems and a positive wind gradient caused oscillatory divergence. Results of motion studies indicated that adequate control of the airplane motions can be provided by automatic control systems.
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Inviscid and viscous CFD codes have been applied to a modified Space Shuttle orbiter geometry to investigate differences between preflight aerodynamic predictions and aerodynamic data from hypersonic reentry flight. Flow field solutions were obtained for wind tunnel conditions and flight conditions to assess Mach number, real-gas, and viscous effects on the reentry aerodynamics of the orbiter. Based on the CFD studies, a methodology model has been developed to (1) extrapolate wind tunnel data to flight conditions and (2) calculate a DCM for use with the Aerodynamic Design Data Book. Comparisons are made with selected flight data. Results of the study indicate that the differences between flight and pre-STS-1 predictions of hypersonic pitching moment are primarily due the to Mach number and real-gas effects.
An exploratory low-speed investigation of a 70 deg/46 deg cranked-wing planform was undertaken to evaluate two vortex-control concepts aimed at alleviating a severe pitch up which limits the usable lift well below the C(sub L,max) of the basic wing. One concept was a strake-like extension introduced across the wing crank, whose vortex helps to stabilize the outer-wing flow and alleviate tip stall. The other was a lower-surface cavity flap employed to trap a vortex just beneath the inboard leading edge, resulting in reduced vortex lift over the inner-wing panel. Each of these concepts was shown to eliminate the high-alpha pitch up, potentially raising the maximum usable lift of the cranked wing practically to its C(sub L,max) value.
The literature available on high aspect ratio canard configurations shows them to have some unique stability characteristics. Using a generic canard-wing model, the effects of canard-wing flow-field interactions on stability were investigated in the NASA Langley Twelve-Foot Low-Speed Wind Tunnel. Results for the attached flow regime indicate linear interactions shift the neutral point of a canard configuration forward, but the effect of a canard on a wing can change significantly when the flow over the surface begins to separate, even several degrees below stall. The asymmetry of the canard downwash in a sideslip condition can result in an increment in effective dihedral roughly proportional to canard lift coefficient. At very high angles of attack the presence of a wing can cause an incremental normal force on a canard, contributing to the possibility of a deep-stall trim point. This effect is greater for a high canard and less for a low one.
In the present analytical treatment of the cruising flight stability of an aerospacecraft in nearly circular orbit, on the basis of a thrust law which arbitrarily depends on altitude, speed, and angle of attack, attention is given to thrust law effects on the translational (height and phugoid) and rotational (angle of attack) modes. The partial derivatives of the propulsive forces in conjunction with the aerodynamic forces, with respect to speed and altitude, are noted to exert a major influence on the stability of translational dynamics; the partial derivative of the component of propulsive and aerodynamic forces which is perpendicular to vehicle velocity (with respect to the angle of attack) is a primary determinant of the damping of angle-of-attack oscillations, while the partial derivative of the sum about the center of mass of aerodynamic and propulsive pitching moments, with respect to the angle of attack, determines the corresponding period.
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