Colin P. Britcher

Interference-Free Measurements of the Subsonic Aerodynamics of Slanted-Base Ogive Cylinders

Drag, lift, pitching moment, and base-pressure measurements have been made, free of support interference, on a range of slanted-base ogive cylinders, using the NASA Langley Research Center 13-in. magnetic suspension and balance system. Test Mach numbers were in the range 0.04-0.2. Two types of wake flow were observed, a quasisymmetric turbulent closure or a longitudinal vortex flow. Aerodynamic characteristics differ dramatically between the two wake types. Drag measurements are shown to be in agreement with previous tests. A hysteretic behavior of the wake with varying Reynolds number has been discovered for the 45-deg base. An interaction between forebody boundary-layer state and wake flow and base pressures has been detected for higher slant angles. CL CD CM ReD SCR Nomenclature = lift coefficient, based on frontal area = drag coefficient, based on frontal area = pitching moment coefficient, based on frontal area and half length of 0-deg base model = Reynolds number, based on model diameter = silicon controlled rectifier

A flying superconducting magnet and cryostat for magnetic suspension of wind-tunnel models

Abstract The quality of aerodynamic tests on aircraft or missile models in wind tunnels is improved by magnetically suspending these models, thus avoiding the intrusion of mechanical supports. The size of the electromagnet array required for this task may be prohibitive at large scales but can be reduced by increasing the magnetic moment of the models internal magnetic core. This article describes a new approach, in which a superconducting solenoid is carried within the model in place of the conventional ferromagnetic core. The potential advantages, the philosophy and details of the design of a prototype, and some experiences in its use are outlined.

A High Performance Aircraft Wind Tunnel Test using Response Surface Methodologies

A Response Surface Methodology (RSM) approach to wind tunnel testing of high performance aircraft is being investigated at the Langley Full-Scale Tunnel (LFST). In an effort to better characterize an aircrafts aerodynamic behavior as a function of attitude and control inputs, and also decrease testing time required, an exploratory study was completed using RSM on a 19 percent scale modified X-31 model. The X-31 model was chosen based on its non-linear aerodynamic behavior at high angle of attack that is representative of modern fighter design and a substantial pre-esisting data base. A five-level nested fractional factorial design, augmented with center points and axial points, produced regression models including pure cubic terms for the characteristic aerodynamic forces and moments over a cuboidal design space as a function of model attitude and control surface inputs. Model adequacy and uncertainty levels were described using robust statistical methods inherent to RSM practice. Comparisons to baseline data and sample lateral-directional and longitudinal aerodynamic characteristic are given.

Experimental Geometry Optimization Techniques for Multi-Element Airfoils

Experimental geometry optimization techniques for high-lift airfoils are reported. A modern three-element airfoil model with a remotely actuated flap was designed, tested, and used in low-speed wind-tunnel experiments to investigate optimum flap positioning based on lift. Detailed results for lift coefficient vs flap vertical and horizontal position are presented for two airfoil angles of attack, 8 and 14 deg. Two automated optimization simulations, the method of steepest ascent and a sequential simplex method, were demonstrated using experimental data. A simple online optimizer was successfully demonstrated with the wind-tunnel model that automatically seeks the optimum lift as a function of flap position. Hysteresis in lift as a function of flap position was discovered when tests were conducted using continuous flow conditions

A Magnetic Suspension System With a Large Angular Range

In order to explore and develop technology required for the magnetic suspension of objects over large ranges of orientation, a small‐scale laboratory system, the large‐angle magnetic suspension test fixture (LAMSTF) has been constructed at NASA Langley Research Center. This apparatus falls into the category of large‐gap, actively stabilized magnetic levitation systems. The hardware comprises five conventional electromagnets in a circular arrangement, each driven from a separate bipolar power amplifier. Electromagnet currents are commanded by a digital control system, implemented on a microcomputer, which in turn derives the position and attitude of the suspended element from an infrared optical system. The suspended element is a cylindrical, axially magnetized, permanent magnet core, within an aluminum tube. The element is ‘‘levitated’’ by repulsive forces, with its axis horizontal, 0.1 m above the top plane of the electromagnet conductor. The element is stabilized in five degrees‐of‐freedom, with rotatio...

A description of a laboratory model magnetic suspension test fixture with large angular capability

The Large-Angle Magnetic Suspension Test Fixture (LAMSTF) research project is reviewed. In the LAMSTF, a cylindrical element containing a permanent magnet core is levitated above a planar array of electromagnets, permitting demonstration of stability and control in five degrees of freedom, and of controlled rotation of the model in one degree of freedom over a range of 360 degrees. The air-gap is around 0.1 m. The objectives of the research effort and the hardware involved are reviewed, and the control problem and the approaches used are described. Two mathematical models have been developed to assist in the design and evaluation of controllers, a linearized and a full nonlinear model. Control approaches demonstrated so fast have included analog and digital phase-advance compensators with static decoupling and a digital linear-quadratic regulator. A digital linear-quadratic-Gaussian controller is under development.<<ETX>>

Progress toward magnetic suspension and balance systems for large wind tunnels

Recent developments and current research efforts leading toward realization of a large-scale production wind tunnel magnetic suspension and balance facility are reviewed. Progress has been made in the areas of model roll control, high-angle-of-attack testing, digital system control, calibration techniques, high magnetic moment superconducting solenoid model cores, and system failure tolerance. Formal design studies have confirmed the engineering feasibility of large-scale facilities.

Experimental investigation of multielement airfoil lift hysteresis due to flap rigging

A study is reported on a particular type of lift hysteresis discovered while developing experimental geometry optimization techniques for high-lift airfoils. A modern three-element airfoil model with a remotely actuated e ap wasdesigned, tested, and used in low-speed wind tunnel experimentsto investigate optimum e ap positioning based on lift. Hysteresis in lift as a function of e ap position was discovered when tests were conducted using continuous e ow conditions. It was shown that optimum or near-optimum lift coefe cients determined using continuous e ow conditions exist over an extended range of e ap positions when compared to those determined using traditional intermittent conditions.

A STUDY OF GROUND SIMULATION FOR WIND TUNNEL TESTING OF FULL-SCALE NASCAR's

A road simulation system has been developed at the Langley Full-Scale Tunnel (LFST) to support the aerodynamic testing of road vehicles, particularly NASCARclass race cars. The leading edge of the existing ground board was recontoured to alleviate a separation bubble and an active suction boundary layer control system, incorporating a bleed slot and axial flow blower, has been implemented. Performance evaluations include boundary layer surveys at various locations in the vicinity of the car balance with the empty tunnel as well as force measurements with a representative vehicle both with and without the boundary layer control system operating.

Superconducting electromagnets for large wind tunnel magnetic suspension and balance systems

This paper presents a new design study of a Magnetic Suspension and Balance System (MSBS) for airplane models in a large 8 ft × 8 ft wind tunnel. New developments in the design include: use of a superconducting solenoid as a model core instead of magnetized iron; combination of permanent magnet material in the model wings along with four racetrack coils to produce the required roll torque; and mounting of all the magnets in an integral cold structure instead of in separate cryostats. Design of superconducting solenoid model cores and practical experience with a small-scale prototype are discussed.