PHAK 5 Flashcards
What are the four forces acting on an aircraft in flight?
- Thrust
- Drag
- Lift
- Weight
What is the relationship of forces in steady flight?
The sum of opposing forces is zero:
- Upward forces equal downward forces.
- Forward forces equal backward forces.
Define angle of attack (AOA).
The acute angle between the chord line of the airfoil and the direction of the relative wind.
Name the three types of parasite drag.
- Form drag
- Interference drag
- Skin friction drag
What is induced drag?
Drag caused by the creation of lift, proportional to the pressure difference between the upper and lower airfoil surfaces.
What is the purpose of winglets?
Reduce wingtip vortices and improve lift efficiency.
What is ground effect?
A phenomenon where airflow around the wing is altered by proximity to the ground, reducing induced drag.
What are the three axes of an aircraft?
- Longitudinal axis (roll)
- Lateral axis (pitch)
- Vertical axis (yaw)
Define static stability.
The initial tendency of an aircraft to return to equilibrium after being disturbed.
Define dynamic stability.
The overall tendency of an aircraft to return to equilibrium over time after being disturbed.
What is the critical angle of attack?
The angle at which the wing produces maximum lift before stalling.
What is the lift-to-drag ratio (L/D)?
The efficiency of an airfoil, calculated as lift divided by drag. Maximum efficiency occurs at L/DMAX.
What are the effects of high aspect ratio on wing performance?
- Decreased drag
- Improved climb performance
- Increased structural weight
What causes Dutch roll?
Coupled oscillation of roll and yaw, typically corrected with yaw dampers in modern aircraft.
What is the role of dihedral in lateral stability?
Provides stability by increasing lift on the lower wing during a sideslip.
What is the relationship between thrust and drag during constant airspeed?
Thrust equals drag.
What is parasite drag?
Drag that does not contribute to lift, including form drag, interference drag, and skin friction drag.
What factors increase induced drag?
- High angle of attack
- Low airspeed
Define wingtip vortices.
Rotating airflows created by the pressure difference at wingtips as lift is produced.
How can wake turbulence be avoided?
- Avoid flight paths below and behind larger aircraft.
- Take off before or land after their rotation points.
What is the effect of ground effect on induced drag?
Reduces induced drag significantly when close to the ground.
What are the three motions of an aircraft and their corresponding axes?
- Roll - Longitudinal axis
- Pitch - Lateral axis
- Yaw - Vertical axis
What is the function of ailerons, elevators, and rudders?
Ailerons: Control roll
Elevators: Control pitch
Rudders: Control yaw
What is the center of gravity (CG)?
The point where the total weight of the aircraft is concentrated.
What happens if the CG is forward of the center of pressure (CP)?
The aircraft tends to pitch nose-down, requiring tail force to balance.
What is dihedral?
The upward angle of wings from horizontal, providing lateral stability.
How does sweepback contribute to stability?
Increases lift on the lower wing during yaw, restoring directional stability.
What is Dutch roll?
A coupled oscillation in roll and yaw, typically seen in swept-wing aircraft.
What is spiral instability?
A condition where strong directional stability and weak lateral stability cause a steep spiral descent.
What is the impact of a high aspect ratio on wing performance?
Decreases drag, improves climb efficiency, and increases structural weight.
Define the critical angle of attack.
The angle at which maximum lift occurs before the wing stalls.
What is L/DMAX?
The angle of attack at which the lift-to-drag ratio is maximized, representing maximum efficiency.
What are the two types of stability?
- Static stability (initial response)
- Dynamic stability (long-term response)
What are the effects of forward and rearward CG locations?
Forward CG: Increases stability, decreases maneuverability.
Rearward CG: Decreases stability, increases maneuverability.
What are the three types of static stability?
- Positive: Returns to equilibrium
- Neutral: Maintains new state
- Negative: Diverges from equilibrium.
