Static and dynamic testing of the NASA 0.7 percent scale Hybrid Wing Body (HWB) configuration was conducted in the Rolling Hills Research Corporation water tunnel to investigate aerodynamic behavior over a large range of angle-of-attack and to develop models that can predict aircraft response in nonlinear unsteady flight regimes. This paper reports primarily on the longitudinal axis results. Flow visualization tests were also performed. These tests provide additional static data and new dynamic data that complement tests conducted at NASA Langley 14- by 22-Foot Subsonic Tunnel. HWB was developed to support the NASA Environmentally Responsible Aviation Project goals of lower noise, emissions, and fuel burn. This study also supports the NASA Aviation Safety Program efforts to model and control advanced transport configurations in loss-of-control conditions.

The players' ability to achieve the greatest distance in kicking is determined by their efficiency in transferring kinetic energy from the body to the ball. The purpose of this study was to compare the kinetics and kinematics of the plant leg position between male and female collegiate soccer players during instep kicking. Twenty-three soccer players (11 males and 12 females) were filmed in both the sagittal and posterior views while performing a maximal instep kick. Plant leg kinetic data were also collected using an AMTI 1000 force platform. There were no significant differences between the sexes in plant leg position, but females had significantly greater trunk lean, plant leg angle, and medial-lateral ground reaction force than the males. Males showed higher vertical ground reaction forces at ball contact, but there were no significant differences in ball speed at take-off between the sexes. Ball speed at take-off was inversely related to peak anterior-posterior ground reaction force (-0.65). The anatomical differences between the sexes were reflected in greater trunk lean and lower leg angle in the females.

The purpose of this study was to determine if patterns in vertical ground reaction forces resulted in differences in hip, knee and trunk angular velocity and efficiency of the open kinetic chain. 20 subjects performed a maximal in-step kick while ground reaction forces of the plant leg, as well as angular, approach and ball velocities were recorded. Although approach and ball velocity did not change between groups, the decreasing vertical force group had significantly higher initial peak vertical ground reaction forces and angular hip velocities than subjects with a double vertical peak pattern. There was a significant relationship between approach velocity and ball velocity, as well as a negative relationship between posterior lean on contact and leg angular velocity. It seems that the pattern of vertical force with the plant leg is not a key factor in ball velocity.

The objective of this study is to determine the effectiveness of using an active sensor/suction technique to identify and remove low-speed streaks from a turbulent boundary layer in order to reduce skin friction. An experimental investigation was conducted in both water and wind tunnel facilities to visualize streak development and removal and also to obtain preliminary quantitative drag reductions of an active sensor/suction system. Flush mount hot-film sensors were used with a detection algorithm to identify lowspeed streaks and activate suction ports to remove the streaks in their growth phase. Suction coefficients ranged from 0.0005 to 0.015. Hot-wire boundary-layer measurements were used to determine skin friction drag. The preliminary results show significant skin friction reductions are possible using low suction rates and reduced mass flows.

A new technique for reducing the drag of existing aircraft configurations was investigated. Heating the surface under a turbulent boundary layer reduces the turbulent skin friction. An experimental program was conducted to determine the feasability of applying this technology to military and commercial aircraft. Three different experimental investigations were conducted to measure the extent of the drag reduction. The first experiment was a low speed wind tunnel test. Very significant drag reduction was measured while only heating the forward portion of the wind tunnel model. In order to determine the effects of higher Mach and Reynolds number, a flight test program was conducted using the NASA Dryden F-15B Flight Test Fixture. The experiment measured the skin friction over a flat plate using a momentum deficit technique. The magnitude of the drag reduction was less than measured in the wind tunnel, but showed a trend of increasing effectiveness with decreasing Reynolds number. The third experiment confirmed the overall drag reduction on a business jet class aircraft. This work has shown that significant drag savings can be achieved using boundary layer heating. NOMENCLATURE a Local speed of sound, ft/sec Cf Friction coefficient Df Drag due to skin friction γ Specific heat ratio g Acceleration of gravity, ft/s KT Total temperature correction factor μ Dynamic viscosity, lb-sec/ft M Mach number PT Total pressure, lb/ft P Static pressure, lb/ft ρ Density, slugs/ft R Gas constant, air, 53.3 ft-lbf/(lbm-°R) θ Momentum thickness, ft T Static temperature, deg. Rankine TR Temperature ratio TT Total temperature, deg. Rankine u Local velocity, ft/sec U Free stream velocity, ft/sec x Axial location, ft y Boundary layer height, ft INTRODUCTION The benefits of reducing the drag of either a new or existing aircraft configuration are obvious. An aircraft’s endurance is directly proportional to its lift to drag ratio. Decreased drag also translates into faster top speed, quicker acceleration, shorter take-off distances and lower direct operating costs in the form of fuel savings. In order to project military air power, or on the commercial side, receive better range and fuel economy, reducing drag during the cruise portion of a flight is critical. * Director, Advanced Technology Development. Senior Member AIAA † Chief Scientist. Senior Member AIAA ‡ Engineering Specialist. § Aerospace Engineer ¶ Aerospace Engineer. Member AIAA # Professor. Senior Member AIAA Copyright © 1998 by the Eidetics Corporation. Published by the American Institute of Aeronautics and Astronautics, Inc. with permission. During cruise, the drag of the aircraft primarily comes from profile drag (skin friction), induced drag (drag due to lift), compressibility drag, separation drag and interference drag. Of these, skin friction (from the “wetted” elements of the aircraft) typically accounts for more than 50% of the total. In order to decrease the skin friction of an aircraft, many methods have been successfully employed that delay the transition of the 1 American Institute of Aeronautics and Astronautics boundary layer from laminar to turbulent. These methods fall into three categories: Natural Laminar Flow (NLF), Laminar Flow Control (LFC), and a combination of the two referred to as Hybrid Laminar Flow Control (HLFC). A major drawback to this approach to drag reduction, is the extreme difficulty in retrofitting an existing aircraft to incorporate these drag reducing techniques. There are also many maintainability issues concerning bug / bird strikes and general contamination of the surface. This approach is also only effective on wing and tail surfaces because the length of most (particularly transport) aircraft fuselages cause the Reynolds number to be far too great (can be over 300 million) to maintain laminar flow. Another approach to reducing the total aircraft drag is to reduce the existing turbulent skin friction drag. A well-known method for doing this is with riblets. Riblets are very small v-shaped grooves that are attached to, or manufactured into, the aircraft’s skin, and are aligned in the direction of the flow. Riblets have the advantage of providing significant drag reduction (≈4%) while being simple to apply to an existing aircraft as well as a new design. Perhaps the greatest single reason that riblets have not found wide spread acceptance in commercial aviation is the issue of maintainability. In order to function correctly, the grooves in the riblet material must be kept clean. This could be a real problem for aircraft that spend most of their flight time at lower altitudes. The current research uses active surface heating in the turbulent regions of the aircraft’s boundary layer. When heat is added to the turbulent boundary layer, the skin friction is reduced roughly as a function of the ratio of the skin temperature to the ambient temperature. The benefit of wall heating on the skin friction drag, which is caused by the difference in viscosity and density of a fluid when it is heated, can easily be seen with a simple calculation of skin friction as a function of temperature:             ∝ 6 5 6 1 ρ μ f D define temperature ratio as: