Basic Aerodynamics - Jeremy&Kilo Aviation

Understanding Aerodynamics

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The Four Forces of Flight

Every aircraft in flight is affected by four fundamental forces. Understanding how these forces interact is essential for safe and efficient flying. These forces are defined by the FAA as:

Lift
The upward acting force created by the wing airfoil as it moves through the air. Lift opposes the downward force of weight and acts perpendicular to the flight path and to the lateral axis of the aircraft.
Weight
The downward acting force caused by gravity. Weight always acts toward the center of the Earth. The CG (center of gravity) is the point where the total weight of the aircraft is considered to be concentrated.
Thrust
The forward acting force produced by the powerplant/propeller combination. Thrust opposes drag and acts parallel to the longitudinal axis of the aircraft.
Drag
The rearward acting force caused by disruption of airflow by the aircraft. Drag opposes thrust and acts rearward, parallel to the relative wind.
Steady-State Flight: LIFT = WEIGHT | THRUST = DRAG
FAA Definition: In steady-state flight (constant airspeed and altitude), the opposing forces are in equilibrium. This is also called unaccelerated flight.

Forces in Climbs & Descents

Straight and Level Flight

Straight and Level Flight

In straight and level unaccelerated flight, all four forces are in equilibrium. Airspeed and altitude remain constant.

Key Concept

Weight always points directly toward the Earth's center, regardless of aircraft attitude. This is a critical concept for understanding climbs and descents.

Climbing Flight

Climbing Flight

In a climb, the aircraft's longitudinal axis is inclined upward relative to the flight path.

What Happens in a Climb?

  1. Weight Vector Movement: As the aircraft pitches up, weight continues pointing straight down. Relative to the aircraft, weight appears to move backward.
  2. Increased Drag Effect: This rearward component of weight now acts in the same direction as drag, creating additional resistance to forward motion.
  3. Thrust Requirement: To maintain airspeed during a climb, thrust must be increased to overcome both drag AND the rearward component of weight.
Remember: If you enter a climb without adding power, the aircraft will slow down because drag effectively increases due to the rearward component of weight.

Descending Flight

Descending Flight

In a descent, the aircraft's longitudinal axis is inclined downward relative to the flight path.

What Happens in a Descent?

  1. Weight Vector Movement: As the aircraft pitches down, weight continues pointing straight down. Relative to the aircraft, weight appears to move forward.
  2. Added Thrust Effect: This forward component of weight now acts in the same direction as thrust, effectively adding to the propulsive force.
  3. Speed Control: To maintain constant airspeed during a descent, thrust must be reduced (or drag increased) to compensate for the forward component of weight.
Remember: If you enter a descent without reducing power, the aircraft will accelerate because thrust is effectively increased by the forward component of weight.

Aerodynamics of Turning Flight

Understanding Lift Components in a Turn

Turning Flight

When an aircraft banks, total lift is divided into vertical and horizontal components.

No Lift Turn Demonstration

Without increasing lift in a turn, the aircraft will lose altitude.

Increased Lift Turn

Increasing lift allows the aircraft to maintain altitude in the turn.

Lift Division in a Banked Turn

When you bank the aircraft, the total lift vector tilts with the aircraft. This lift is now divided into:

  • Vertical Component of Lift (VCL): Opposes weight and maintains altitude
  • Horizontal Component of Lift (HCL): Provides the centripetal force needed to turn the aircraft
Critical Concept: As bank angle increases, more lift is directed horizontally for the turn, leaving less lift available to oppose weight. This is why back pressure is required to maintain altitude in a turn.

Why Back Pressure is Required

Maintaining Altitude in a Turn

  1. Initial Bank: When you roll into a bank without adding back pressure, the total lift tilts but its magnitude stays the same.
  2. Reduced Vertical Lift: With the lift vector tilted, the vertical component is now less than the aircraft's weight.
  3. Altitude Loss: Since weight exceeds the vertical component of lift, the aircraft begins to descend.
  4. Adding Back Pressure: By increasing the angle of attack with elevator, you increase total lift. This increases the vertical component back to equal weight, maintaining altitude.
Level Coordinated Turn: VCL = WEIGHT | HCL = CENTRIFUGAL FORCE
FAA Note on Load Factor: In a turn, total lift must increase. This increased load is measured as "load factor" (G-force). A 60° bank requires 2Gs - the wings must produce twice the lift needed in level flight.

Coordinated vs. Uncoordinated Turns

Coordinated Turn

BALANCED
Coordinated Turn

Characteristics:

  • HCL = Centrifugal Force
  • Ball centered in turn coordinator
  • No side slip or skid
  • Proper bank angle for rate of turn

✓ This is what we aim for in every turn

Slipping Turn

TOO MUCH BANK
Slipping Turn

Characteristics:

  • HCL > Centrifugal Force
  • Rate of turn too slow for bank angle
  • Aircraft yaws toward outside of turn
  • Ball deflects to outside of turn

Correction:

  • Decrease bank angle, OR
  • Increase rate of turn (add rudder)

Skidding Turn

TOO MUCH RUDDER
Skidding Turn

Characteristics:

  • Centrifugal Force > HCL
  • Rate of turn too fast for bank angle
  • Aircraft yaws toward inside of turn
  • Ball deflects to inside of turn

Correction:

  • Reduce rudder input, OR
  • Increase bank angle
Safety Note: Skidding turns are particularly dangerous at low altitude (e.g., in the traffic pattern) as they can lead to a spin if a stall occurs. Always maintain coordinated flight, especially when slow and low.

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