PHAK Chapter 5 Aerodynamics of Flight Flashcards
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Questions and Answers

What are the forces acting on aircraft in flight?

  • Weight (correct)
  • Drag (correct)
  • Thrust (correct)
  • Lift (correct)

What is thrust?

Forward force produced by the powerplant/propeller or rotor.

What is drag?

Rearward, retarding force caused by disruption of airflow by the wing, rotor, fuselage, and other protruding objects.

How does thrust act?

<p>Parallel to the longitudinal axis.</p> Signup and view all the answers

How does drag act?

<p>Rearward parallel to the relative wind.</p> Signup and view all the answers

What is lift?

<p>A force that is produced by the dynamic effect of the air acting on the airfoil.</p> Signup and view all the answers

How does lift act?

<p>Perpendicular to the flight path through the center of lift (CL) and perpendicular to the lateral axis.</p> Signup and view all the answers

What is weight?

<p>The combined load of the aircraft itself, crew, fuel, and cargo.</p> Signup and view all the answers

How does weight act?

<p>Vertically downward through the aircraft's center of gravity.</p> Signup and view all the answers

What is Angle of Attack (AOA)?

<p>Defined as the acute angle between the chord line of the airfoil and the direction of the relative wind.</p> Signup and view all the answers

Density is affected by?

<p>Pressure, temperature, and humidity.</p> Signup and view all the answers

What is the lift-to-drag ratio (L/D)?

<p>The amount of lift generated by a wing or airfoil compared to its drag.</p> Signup and view all the answers

What happens if the aircraft is operated in steady flight at L/Dmax?

<p>Total drag is at a minimum.</p> Signup and view all the answers

What are the two types of drag?

<p>Parasite and induced.</p> Signup and view all the answers

What is parasite drag?

<p>All the forces that work to slow an aircraft's movement.</p> Signup and view all the answers

What are the 3 types of parasite drag?

<p>Form, interference, and skin friction.</p> Signup and view all the answers

What is form drag?

<p>The portion of parasite drag generated by the aircraft due to its shape and airflow around it.</p> Signup and view all the answers

What is interference drag?

<p>Arises from the intersection of airstreams that creates eddy currents, turbulence, or restricts smooth airflow.</p> Signup and view all the answers

What is skin friction drag?

<p>The aerodynamic resistance due to the contact of moving air with the surface of an aircraft.</p> Signup and view all the answers

What is downwash?

<p>When air and vortices roll off the back of your wing, they angle down.</p> Signup and view all the answers

When are wingtip vortices the greatest?

<p>When the generating aircraft is 'heavy, clean, and slow.'</p> Signup and view all the answers

What is a 'moment'?

<p>Mathematical measure of an aircraft's tendency to rotate about its center of gravity (CG).</p> Signup and view all the answers

What is stability?

<p>The reaction of any body when its equilibrium is disturbed.</p> Signup and view all the answers

What are the two types of stability?

<p>Static and dynamic.</p> Signup and view all the answers

What is static stability?

<p>The initial tendency, or direction of movement, back to equilibrium.</p> Signup and view all the answers

What is positive static stability?

<p>The initial tendency of the aircraft to return to the original state of equilibrium after being disturbed.</p> Signup and view all the answers

What is neutral static stability?

<p>The initial tendency of the aircraft to remain in a new condition after its equilibrium has been disturbed.</p> Signup and view all the answers

What is negative static stability?

<p>The initial tendency of the aircraft to continue away from the original state of equilibrium after being disturbed.</p> Signup and view all the answers

What is dynamic stability?

<p>Refers to the aircraft response over time when disturbed from a given pitch, yaw, or bank.</p> Signup and view all the answers

Stability affects which two areas?

<p>Maneuverability and controllability.</p> Signup and view all the answers

What is Longitudinal Stability?

<p>Lateral axis, pitching as the aircraft's nose moves up and down in flight.</p> Signup and view all the answers

What is Lateral Stability?

<p>Stability about the aircraft's longitudinal axis, nose of aircraft to tail.</p> Signup and view all the answers

What are the four main design factors that make an aircraft laterally stable?

<p>Dihedral, sweepback, keel effect, and weight distribution.</p> Signup and view all the answers

What is dihedral?

<p>Outer tips of wings are higher than the wing roots, forming an upward angle.</p> Signup and view all the answers

What is the Keel Effect?

<p>A high wing aircraft always has the tendency to turn the longitudinal axis of the aircraft into the relative wind.</p> Signup and view all the answers

What is yawing or directional stability?

<p>Stability about the aircraft's vertical axis (the sideways moment).</p> Signup and view all the answers

What is Dutch roll?

<p>A coupled lateral/directional oscillation that is usually dynamically stable but is unsafe in an aircraft due to its oscillatory nature.</p> Signup and view all the answers

What are the factors in planform design?

<p>Aspect ratio, taper ratio, and sweepback.</p> Signup and view all the answers

What is aspect ratio?

<p>Ratio of wing span to wing chord.</p> Signup and view all the answers

What is taper ratio?

<p>Planform or thickness or both, is a decrease from wing root to wingtip in wing chord or wing thickness.</p> Signup and view all the answers

What is sweepback?

<p>Rearward slant of a wing, horizontal tail, or other airfoil surface.</p> Signup and view all the answers

What is Newton's First Law of Motion?

<p>Law of Inertia, states that an object at rest or moving in a straight line remains at rest or continues to move in a straight line until acted on by some other force.</p> Signup and view all the answers

What must happen in constant altitude turns to maintain altitude?

<p>Vertical component of lift must be equal to the weight.</p> Signup and view all the answers

What are the four elements of Torque (left turning tendency)?

<ol> <li>Torque reaction from engine and propeller, 2. Corkscrewing effect of the slipstream, 3. Gyroscopic action of the propeller, 4. Asymmetric loading of the propeller (P-factor).</li> </ol> Signup and view all the answers

What is precession?

<p>The resultant action, or deflection, of a spinning rotor when a deflecting force is applied to its rim.</p> Signup and view all the answers

What results in a pitching moment?

<p>Any yawing around the vertical axis.</p> Signup and view all the answers

What results in a yawing moment?

<p>Any pitching around the lateral axis.</p> Signup and view all the answers

What is P-Factor?

<p>Asymmetric loading; 'bite' of the downward moving blade is greater than the 'bite' of the upward moving blade.</p> Signup and view all the answers

What are load factors important for?

<ol> <li>It is possible for a pilot to impose a dangerous overload on aircraft structures. 2. Increased load factor increases stalling speed and makes stalls possible at seemingly safe flight speeds.</li> </ol> Signup and view all the answers

What is a 1.5 load limit factor called?

<p>Factor of safety.</p> Signup and view all the answers

During a constant altitude, coordinated turn in any aircraft, what is the load factor the result of?

<p>Centrifugal force and weight.</p> Signup and view all the answers

What is 'design maneuvering speed' (VA)?

<p>Speed below which you can move a single flight control, one time, to its full deflection, for one axis of airplane rotation only (pitch, roll or yaw), in smooth air, without risk of damage to the airplane.</p> Signup and view all the answers

What are the effects of Forward CG?

<p>Stalls at a higher speed, higher elevator control forces, increases the need for greater back elevator pressure.</p> Signup and view all the answers

What are the effects of Aft CG?

<p>Cruises faster, less stable, decrease in Angle of Attack (AOA).</p> Signup and view all the answers

What are the two different types of boundary layer flow?

<p>Laminar and turbulent.</p> Signup and view all the answers

What is a shock or 'compression' wave?

<p>The boundary between the undisturbed air and the region of compressed air.</p> Signup and view all the answers

What is 'force divergence'?

<p>The Mach number that produces a sharp change in coefficient of drag.</p> Signup and view all the answers

Study Notes

Forces Acting on Aircraft in Flight

  • Four fundamental forces: Thrust, Drag, Lift, and Weight.
  • Thrust: Forward force generated by the engine, propeller, or rotor.
  • Drag: Retarding force arising from airflow disruption due to the aircraft structure.

Characteristics of Forces

  • Thrust Direction: Acts parallel to the longitudinal axis of the aircraft.
  • Drag Direction: Acts rearward, parallel to the direction of relative wind.
  • Lift: Dynamic force generated by airflow over the airfoil, acting perpendicular to the flight path at the center of lift (CL).
  • Weight: Combined mass of the aircraft, crew, fuel, and cargo, acting vertically downward through the center of gravity.

Aerodynamic Concepts

  • Angle of Attack (AOA): Acute angle between the airfoil's chord line and the direction of relative wind.
  • Density: Influenced by pressure, temperature, and humidity.
  • Lift-to-Drag Ratio (L/D): Measure of lift generated compared to drag; maximized (L/Dmax) for efficient flight.
  • Types of Drag: Includes parasite drag (slows movement) and induced drag (caused by lift generation).

Parasite Drag Types

  • Form Drag: Related to the shape and airflow around the aircraft.
  • Interference Drag: Results from the interaction of different airstreams, causing turbulence.
  • Skin Friction Drag: Caused by aerodynamic resistance from airflow contact with the aircraft surface.

Stability and Control

  • Stability: Reaction of an aircraft when equilibrium is disturbed; includes static and dynamic stability.
  • Static Stability Types:
    • Positive: Tendency to return to equilibrium.
    • Neutral: Tendency to stay in new positions.
    • Negative: Tendency to move away from equilibrium.
  • Dynamic Stability: Long-term response to disturbances in pitch, yaw, or bank.
  • Affects Maneuverability and Controllability.

Types of Stability

  • Longitudinal Stability: Stability around the lateral axis, affecting pitch movements.
  • Lateral Stability: Stability along the longitudinal axis, influencing roll behavior.
  • Key design factors for lateral stability: Dihedral, Sweepback, Keel Effect, and Weight Distribution.

Design and Performance Factors

  • Aspect Ratio: Ratio of wingspan to wing chord, influencing lift and efficiency.
  • Taper Ratio: Reduction in wing thickness or chord from root to tip.
  • Sweepback: Rearward slanting of wings, which affects aerodynamics.

Aircraft Dynamics

  • Newton’s First Law: An object in motion remains in motion until acted upon by another force.
  • Load Factor Importance: Can create dangerous overloads, increases stalling speeds.
  • Design Maneuvering Speed (VA): Speed for full deflection of one flight control without risk of aircraft damage.

Center of Gravity Effects

  • Forward CG: Results in higher stalling speeds and increased elevator control forces.
  • Aft CG: Offers faster cruising but less stability; reduction in angle of attack (AOA).

Boundary Layer Flow and Shock Waves

  • Two types of boundary layer flow: laminar (smooth) and turbulent (chaotic).
  • Shock Wave: Formation at the transition from undisturbed to compressed air, impacting drag significantly.

Additional Concepts

  • Precession: Movement of a spinning rotor in response to deflecting forces.
  • P-Factor: Asymmetric loading of the propeller blade affects yaw and performance.
  • Dutch Roll: A lateral and directional oscillation that introduces potential instability in flight.

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Test your knowledge with these flashcards from PHAK Chapter 5, which covers the essential forces acting on aircraft in flight. Understand the concepts of thrust, drag, lift, and weight, and how they interact during flight. Perfect for students and aviation enthusiasts alike!

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