Ground effect (aerodynamics)

About: Ground effect (aerodynamics) is a research topic. Over the lifetime, 1818 publications have been published within this topic receiving 19304 citations.

Predictions of vortex-lift characteristics based on a leading-edge suction analogy.

Abstract: Leading edge suction analogy for predicting low speed lift and drag-due-to-lift characteristics of sharp edge delta and related wing planforms

Mechanics of Flight

Abstract: Preface. Acknowledgments. 1. Overview of Aerodynamics. 1.1. Introduction and Notation. 1.2. Fluid Statics and the Atmosphere. 1.3. The Boundary Layer Concept. 1.4. Inviscid Aerodynamics. 1.5. Review of Elementary Potential Flows. 1.6. Incompressible Flow over Airfoils. 1.7. Trailing-Edge Flaps and Section Flap Effectiveness. 1.8. Incompressible Flow over Finite Wings. 1.9. Flow over Multiple Lifting Surfaces. 1.10. Wing Stall and Maximum Lift Coefficient. 1.11. Wing Aerodynamic Center and Pitching Moment. 1.12. Inviscid Compressible Aerodynamics. 1.13. Compressible Subsonic Flow. 1.14. Supersonic Flow. 1.15. Problems. 2. Overview of Propulsion. 2.1. Introduction. 2.2. The Propeller. 2.3. Propeller Blade Theory. 2.4. Propeller Momentum Theory. 2.5. Off-Axis Forces and Moments Developed by a Propeller. 2.6. Turbojet Engines: The Thrust Equation. 2.7. Turbojet Engines: Cycle Analysis. 2.8. The Turbojet Engine with Afterburner. 2.9. Turbofan Engines. 2.10. Concluding Remarks. 2.11. Problems. 3. Aircraft Performance. 3.1. Introduction. 3.2. Thrust Required. 3.3. Power Required. 3.4. Rate of Climb and Power Available. 3.5. Fuel Consumption and Endurance. 3.6. Fuel Consumption and Range. 3.7. Power Failure and Gliding Flight. 3.8. Airspeed, Wing Loading, and Stall. 3.9. The Steady Coordinated Turn. 3.10. Takeoff and Landing Performance. 3.11. Accelerating Climb and Balanced Field Length. 3.12. Problems. 4. Longitudinal Static Stability and Trim. 4.1. Fundamentals of Static Equilibrium and Stability. 4.2. Pitch Stability of a Cambered Wing. 4.3. Simplified Pitch Stability Analysis for a Wing-Tail Combination. 4.4. Stick-Fixed Neutral Point and Static Margin. 4.5. Estimating the Downwash Angle on an Aft Tail. 4.6. Simplified Pitch Stability Analysis for a Wing-Canard Combination. 4.7. Effects of Drag and Vertical Offset. 4.8. Effects of Nonlinearities on the Aerodynamic Center. 4.9. Effect of the Fuselage, Nacelles, and External Stores. 4.10. Contribution of Running Propellers. 4.11. Contribution of Jet Engines. 4.12. Problems. 5. Lateral Static Stability and Trim. 5.1. Introduction. 5.2. Yaw Stability and Trim. 5.3. Estimating the Sidewash Gradient on a Vertical Tail. 5.4. Estimating the Lift Slope for a Vertical Tail. 5.5. Effects of Tail Dihedral on Yaw Stability. 5.6. Roll Stability and Dihedral Effect. 5.7. Roll Control and Trim Requirements. 5.8. The Generalized Small-Angle Lateral Trim Requirements. 5.9. Steady-Heading Sideslip. 5.10. Engine Failure and Minimum-Control Airspeed. 5.11. Longitudinal-Lateral Coupling. 5.12. Control Surface Sign Conventions. 5.13. Problems. 6. Aircraft Controls and Maneuverability. 6.1. Longitudinal Control and Maneuverability. 6.2. Effects of Structural Flexibility. 6.3. Control Force and Trim Tabs. 6.4. Stick-Free Neutral and Maneuver Points. 6.5. Ground Effect, Elevator Sizing, and CG Limits. 6.6. Stall Recovery. 6.7. Lateral Control and Maneuverability. 6.8. Aileron Reversal. 6.9. Other Control Surface Configurations. 6.10. Airplane Spin. 6.11. Problems. 7. Aircraft Equations of Motion. 7.1. Introduction. 7.2. Newton's Second Law for Rigid-Body Dynamics. 7.3. Position and Orientation: The Euler Angle Formulation. 7.4. Rigid-Body 6-DOF Equations of Motion. 7.5. Linearized Equations of Motion. 7.6. Force and Moment Derivatives. 7.7. Nondimensional Linearized Equations of Motion. 7.8. Transformation of Stability Axes. 7.9. Inertial and Gyroscopic Coupling. 7.10. Problems. 8. Linearized Longitudinal Dynamics. 8.1. Fundamentals of Dynamics: Eigenproblems. 8.2. Longitudinal Motion: The Linearized Coupled Equations. 8.3. Short-Period Approximation. 8.4. Long-Period Approximation. 8.5. Pure Pitching Motion. 8.6. Summary. 8.7. Problems. 9. Linearized Lateral Dynamics. 9.1. Introduction. 9.2. Lateral Motion: The Linearized Coupled Equations. 9.3. Roll Approximation. 9.4. Spiral Approximation. 9.5. Dutch Roll Approximation. 9.6. Pure Rolling Motion. 9.7. Pure Yawing Motion. 9.8. Longitudinal-Lateral Coupling. 9.9. Nonlinear Effects. 9.10. Summary. 9.11. Problems. 10. Aircraft Handling Qualities and Control Response. 10.1. Introduction. 10.2. Pilot Opinion. 10.3. Dynamic Handling Quality Prediction. 10.4. Response to Control Inputs. 10.5. Nonlinear Effects and Longitudinal-Lateral Coupling. 10.6. Problems. 11. Aircraft Flight Simulation. 11.1. Introduction. 11.2. Euler Angle Formulations. 11.3. Direction-Cosine Formulation. 11.4. Euler Axis Formulation. 11.5. The Euler-Rodrigues Quaternion Formulation. 11.6. Quaternion Algebra. 11.7. Relations between the Quaternion and Other Attitude Descriptors. 11.8. Applying Rotational Constraints to the Quaternion Formulation. 11.9. Closed-Form Quaternion Solution for Constant Rotation. 11.10. Numerical Integration of the Quaternion Formulation. 11.11. Summary of the Flat-Earth Quaternion Formulation. 11.12. Aircraft Position in Geographic Coordinates. 11.13. Problems. Bibliography. Appendixes. A Standard Atmosphere, SI Units. B Standard Atmosphere, English Units. C Aircraft Moments of Inertia. Nomenclature. Index.

Biology and physics of locust flight. III. The aerodynamics of locust flight

Abstract: A proper understanding of how locusts fly must be based upon knowledge of how the wings are moved. A desert locust was suspended from a balance and placed in an air stream so that it flew under nearly the same conditions as during natural forward flight. Four stroboscopic slow-motion films were selected for measurement. The movements of the wings, i.e. their positions, velocities and accelerations, were then calculated in sufficient detail to show how these quantities vary with time during one complete wing stroke. The aerodynamic lift and drag of the entire natural wing were measured in a wind tunnel with the wing arranged in different positions relative to the flow. By placing it in the boundary layer of the tunnel, the wind speed was graded from tip to base in approximately the same way as during the actual flight. There is therefore no error due to scale effect or to the induced drag. In most respects the wings resemble ordinary, slightly cambered airfoils. Their characteristics are given as polar diagrams. The kinematic and aerodynamic analyses make it possible to calculate the forces which act upon the locust at any instant of time. It is here necessary to presuppose that the non-stationary flight situations are essentially similar to a sequence of stationary situations. For locusts, this presupposition is justified: (i) from theoretical estimates of the quantitative effect of non-stationary flow; and (ii) from control measurements of the average thrust and lift produced during flight. It was found that the calculated vertical force, when averaged over an entire wing stroke, equalled the average reduction in body weight, as measured directly on the flight balance. Similarly, the average thrust of the wings corresponded to the drag of the body. The analysis shows how the aerodynamic forces vary during the wing stroke. The hindwings are responsible for about 70 % of the total lift and thrust. About 80 % of the lift is produced during the downstroke. During flight at normal lift the angles of attack (middle part of wing) are small during the upstroke and vary between 10 and 15° during the downstroke. When the lift was larger or smaller than the body weight these figures increased or decreased respectively. The forewings are peculiar in two ways: (i) during the middle part of the downstroke a true flap (the vannus) is put into action; (ii) during the upstroke the proximal part has a Z-shaped cross-section and gives but little lift and drag. The hindwings are characteristic in that the posterior part (vannus) is flexible and becomes moulded by the wind, increasing the angle of attack at which stalling occurs to about 25°. Since both the movements of the wings relative to the body and the aerodynamic forces are known at any instant, the exchange of power with the surrounding air can be calculated. The moments of inertia of the wing mass being known, the power for accelerating the wings can also be estimated. The sum of these contributions is the power which passes the wing fulcrum; this estimate is used in a later paper (part IX) where the energetics of flight is discussed in detail. The diagrams are correct to scale. The restriction of freedom caused by the suspension is discussed, together with the possible errors of a stationary analysis.

Dragonfly flight. I. Gliding flight and steady-state aerodynamic forces.

Abstract: The free gliding flight of the dragonfly Sympetrum sanguineum was filmed in a large flight enclosure. Reconstruction of the glide paths showed the flights to involve accelerations. Where the acceleration could be considered constant, the lift and drag forces acting on the dragonfly were calculated. The maximum lift coefficient (CL) recorded from these glides was 0.93; however, this is not necessarily the maximum possible from the wings. Lift and drag forces were additionally measured from isolated wings and bodies of S. sanguineum and the damselfly Calopteryx splendens in a steady air flow at Reynolds numbers of 700-2400 for the wings and 2500-15 000 for the bodies. The maximum lift coefficients (CL,max) were 1.07 for S. sanguineum and 1.15 for C. splendens, which are greater than those recorded for all other insects except the locust. The drag coefficient at zero angle of attack ranged between 0.07 and 0.14, being little more than the Blassius value predicted for flat plates. Dragonfly wings thus show exceptional steady-state aerodynamic properties in comparison with the wings of other insects. A resolved-flow model was tested on the body drag data. The parasite drag is significantly affected by viscous forces normal to the longitudinal body axis. The linear dependence of drag on velocity must thus be included in models to predict the parasite drag on dragonflies at non-zero body angles.