Ground Effect on the Longitudinal Stability of an Unmanned Airplane

AIAA Atmospheric Flight Mechanics Conference

Quijada

Cárdenas

2016

A numerical investigation has been developed to evaluate the influence of dynamic ground effect on the aerodynamic coefficients of a wing using a panel method. This simulates unsteady flow by the time-marching method with a deformable free wake. The image method is used to model ground effect. Lift, induced drag, and pitching moment coefficients were obtained considering fixed height above the ground (static ground effect) and the wing in sink and flare maneuvers (dynamic ground effect). The results at static ground effect were compared with analytical and numerical results in order to verify and validate the created panel code, and they are acceptable. Lift and the absolute value of the pitching moment coefficients increase and the induced drag coefficient decreases as the height diminishes. Although the trends in static and dynamic ground effect are similar, the aerodynamic coefficients achieved in static ground effect are less affected than those ones calculated by simulations of the wing approaching the ground. Linear models of the wing in ground effect were developed by using the data of constant rate of descent and flare maneuvers. The sink rate produces significant variations in the aerodynamic coefficients of a wing. Nomenclature b= wingspan CL, CD, CM = lift, drag, and pitching moment coefficients CL0, CD0, CM0 = lift, drag, and pitching moment coefficients at zero angle of attack CLq, CDq, CMq = variation of lift, drag, and pitching moment coefficients with pitch rate CLh, CDh, CMh = variation of lift, drag, and pitching moment coefficients with c H CLα, CDα, CMα = lift, drag, and pitching moment slopes

Section: Resultsmentioning

confidence: 94%

Section: Resultsmentioning

confidence: 99%

Dynamic Ground Effect on the Aerodynamic Coefficients of a Wing using a Panel Method

AIAA Atmospheric Flight Mechanics Conference

Quijada

Cárdenas

2016

“…(18) and (19), respectively, and the values obtained using ATHENA, PAN AIR and CMARC presented in Ref. [12]. Figure 4 represents the induced drag factor as a function of a non-dimension height (h∕b).…”

Section: Case Studymentioning

confidence: 97%

“…This wing was selected because previous numerical data had been published in Ref. [12] in static ground effect and in free flight. The wing is tested at different heights in order to verify the code solutions in static ground effect.…”

Section: Case Studymentioning

confidence: 99%

Linear Computational Fluid Dynamic Analysis of Dynamic Ground Effect of a Wing in Sink and Flare Maneuvers

Quijada

AIAA Atmospheric Flight Mechanics Conference

2015

A numerical investigation has been conducted to analyze the influence of the dynamic ground effect on the aerodynamic characteristics of a rectangular wing. The numerical model is based on a three-dimensional panel method and the ground effect is analyzed using the method of images. Before simulating the wing approaching the ground, the model developed was tested assuming fixed height and the results were examined by comparison to analytical and numerical results showing a good agreement. Then, the dynamic ground effect was investigated for two flight conditions: constant rate of descent and varying rate of descent. The results obtained by dynamic ground effect and those ones computed using static ground effect were compared evidencing that the static ground effect underpredicts the lift coefficient and overpredicts the induced drag coefficient. In addition, for these flight conditions, the lift coefficient increases when non-dimensional height decreases observing that it is more significant for a constant value of rate of descent, and the induced drag coefficient decreases while non-dimensional height reduces evidencing a significant decrease for a varying rate of descent. Finally, the effect of the flight path angle was evaluated demonstrating that the lift and the induced drag coefficients decrease with more negative flight path.

“…Also, lift and drag coefficients decrease as the flight path angle reduces. 13 Boschetti and Cárdenas 14 established that the h derivatives have a strong influence in the longitudinal stability of airplanes, and then Boschetti, Quijada, and Cárdenas 15 concluded that the sink rate produces significant variations on the aerodynamic coefficients of a wing, also proving that different models must be created to simulate different flight paths. The h derivatives define the variation of the aerodynamic coefficients as functions of height.…”

Section: Introductionmentioning

confidence: 99%

Dependence of the Flight-path on the Aerodynamic Characteristics of Rectangular Wings due to Dynamic Ground Effect

Merkl

AIAA Scitech 2019 Forum

Cárdenas

2019

The objective of this paper is to evaluate the dependence of the flight-path when height changes as function of time on the aerodynamic characteristics of single rectangular wings with aspect ratios between 4 and 12 due to dynamic ground effect using an unsteady vortexring panel code, which uses a time-stepping method and the image method to simulate climb and sink maneuvers with a free wake. It is observed that each maneuver has different effects on lift, drag, and pitching moment coefficients. For a constant rate of descent and climb maneuvers, the flight path angle has an important impact over the results increasing the lift and induced drag coefficients and decreasing the pitching moment coefficient as the flight path angle decreases because the flight path angle is linked to the effective angle of attack. In contrast, no evident relation is appreciated between the static and dynamic ground effect in flare. Lift and induced drag spanwise distributions are also considerably affected by the specific maneuver. Finally, the nondimensional h derivatives are related to the flight path of the wing in ground effect. Nomenclature b = wingspan CL, CD, CM = lift, drag, and pitching moment coefficients CL0, CD0, CM0 = lift, drag, and pitching moment coefficients at zero angle of attack CLq, CDq, CMq = variation of lift, drag, and pitching moment coefficients with pitch rate CLh, CDh, CMh = variation of lift, drag, and pitching moment coefficients with nondimensional height CLα, CDα, CMα = lift, drag, and pitching moment slopes