Aerodynamics DGCA Mod 8

Cheatsheet Content

### Fundamentals of Aerodynamics - **Atmospheric Properties:** - **Standard Atmosphere:** ISA (International Standard Atmosphere) defines standard values for temperature, pressure, and density at various altitudes. - **Pressure ($P$):** Force per unit area. Decreases with altitude. - **Density ($\rho$):** Mass per unit volume. Decreases with altitude. - **Temperature ($T$):** Decreases with altitude in the troposphere (lapse rate $\approx 6.5^\circ C/1000m$). - **Airflow Concepts:** - **Streamline:** Path traced by a massless particle in a fluid flow. - **Streamtube:** Bundle of streamlines. - **Steady Flow:** Flow properties at any point do not change with time. - **Incompressible Flow:** Density remains constant (valid for low speeds, typically below Mach 0.3). - **Compressible Flow:** Density changes significantly (at higher speeds). ### Aerodynamic Forces - **Lift ($L$):** Force perpendicular to the relative airflow, opposing weight. - **Formula:** $L = \frac{1}{2}\rho V^2 S C_L$ - **Factors affecting Lift:** Air density ($\rho$), True Airspeed ($V$), Wing Area ($S$), Coefficient of Lift ($C_L$). - **Drag ($D$):** Force parallel to the relative airflow, opposing thrust. - **Formula:** $D = \frac{1}{2}\rho V^2 S C_D$ - **Types of Drag:** - **Parasite Drag:** - **Form Drag (Pressure Drag):** Due to the shape of the object. - **Skin Friction Drag:** Due to the viscosity of the air. - **Interference Drag:** From the intersection of airflows around different components. - **Induced Drag:** Inherent consequence of producing lift. Decreases with speed, increases with Angle of Attack (AoA). - **Wave Drag:** Significant at transonic and supersonic speeds. - **Thrust ($T$):** Forward force produced by the engine. - **Weight ($W$):** Gravitational force acting on the aircraft. ### Airfoils and Wings - **Airfoil Terminology:** - **Leading Edge:** Front edge of the airfoil. - **Trailing Edge:** Rear edge of the airfoil. - **Chord Line:** Straight line connecting leading and trailing edges. - **Mean Camber Line:** Line equidistant from the upper and lower surfaces. - **Camber:** Curvature of the mean camber line. - **Thickness:** Maximum distance between upper and lower surfaces. - **Angle of Attack (AoA or $\alpha$):** Angle between the chord line and the relative airflow. - **Angle of Incidence:** Angle between the wing chord line and the longitudinal axis of the aircraft. - **Stall:** Occurs when the critical Angle of Attack is exceeded, leading to a sudden loss of lift. - **Wing Planforms:** - **Rectangular:** Simple, good stall characteristics. - **Tapered:** More efficient, better lift distribution. - **Elliptical:** Ideal lift distribution, but complex to manufacture. - **Swept:** Delays Mach effects, good for high-speed flight. - **Delta:** Used in supersonic aircraft. - **Aspect Ratio (AR):** Span squared divided by wing area ($AR = b^2/S$). High AR reduces induced drag. ### High-Speed Flight - **Mach Number ($M$):** Ratio of aircraft speed to the speed of sound. - $M 1.2$: Supersonic - **Critical Mach Number ($M_{crit}$):** Lowest Mach number at which airflow over some part of the aircraft reaches Mach 1. - **Shock Waves:** Form when airflow exceeds local speed of sound, causing sudden pressure and temperature changes, and wave drag. - **Area Rule:** Aircraft designed to have a smooth cross-sectional area distribution to reduce wave drag in transonic flight. ### Stability and Control - **Stability:** Tendency of an aircraft to return to its original flight path after a disturbance. - **Static Stability:** Initial tendency to return. - **Dynamic Stability:** Oscillation characteristics over time. - **Axes of Flight:** - **Longitudinal (Roll):** Controlled by Ailerons. - **Lateral (Pitch):** Controlled by Elevator. - **Vertical (Yaw):** Controlled by Rudder. - **Control Surfaces:** - **Ailerons:** Control roll. - **Elevator (or Stabilator):** Controls pitch. - **Rudder:** Controls yaw. - **Flaps:** Increase lift and drag for takeoff and landing. - **Slats:** Extend the leading edge, increasing lift and delaying stall. - **Spoilers:** Increase drag, reduce lift. - **Trim Tabs:** Reduce control forces. ### Aircraft Performance - **Thrust vs. Drag:** - **Max Speed:** Where thrust available equals drag, and thrust available is maximum. - **Min Drag Speed ($V_{MD}$):** Speed at which total drag is minimized, also best glide speed. - **Max Endurance Speed:** Speed for minimum fuel flow (often near $V_{MD}$). - **Max Range Speed:** Speed for maximum distance covered per unit of fuel (typically slightly faster than $V_{MD}$). - **Climb Performance:** - **Rate of Climb (RoC):** Vertical speed. - **Angle of Climb (AoC):** Steepness of climb path. - **Takeoff and Landing Performance:** Affected by weight, runway condition, wind, temperature, and altitude. - **Load Factor ($n$):** Ratio of lift to weight ($n = L/W$). Increases in turns and maneuvers. - **V-g Diagram:** Plots load factor against airspeed, showing structural limits. ### Special Topics - **Ground Effect:** Reduced induced drag when flying close to the ground. - **Vortex Generators:** Small vanes to re-energize boundary layer and delay flow separation. - **Boundary Layer:** Thin layer of air adjacent to the surface of an object, where viscous effects are significant. - **Laminar Flow:** Smooth, orderly flow. - **Turbulent Flow:** Disordered, chaotic flow. - **Stalling Speed ($V_S$):** Minimum speed at which an aircraft can maintain level flight, typically at $C_{Lmax}$. - **Wake Turbulence:** Vortices generated by wingtips, especially dangerous behind heavy, slow aircraft.