aerodynamics Flashcards
(19 cards)
load factors
four forces of flight
thrust, weight, drag, lift
thrust
the forward force produced by the powerplant/ prop. it overcomes the force of drag. typically parallel to the longitudinal axis
drag
drag opposes thrust, and acts as a rearward parallel to the relative wind. is a rearward force caused by the wing, rotor, fuselage, and other protruding objects
lift
is a force that is produced by the dynamic effect of the air acting on the airfoil and acts perpendicular to the flight path through the center of lift and perpendicular to the lateral axis. in level flight, lift opposes the downward force of flight.
AOA
the acute angle between the chord line of the airfoil and the direction of the relative wind
lift/ drag ratio
the amount of lift generated by a wing compared to its drag. aircraft with higher L/D ratios are more efficient than those with lower L/D ratios.
parasite drag
is comprised of all the forces that work to slow an aircraft’s movement. it is the drag not associated with the production of lift.
types of parasite drag
form, interference, and skin fraction
form drag
generated by the aircraft due to its shape and airflow around it.
when air has to separate to move around a moving aircraft and its components, it eventually rejoins after passing the body. how quickly and smoothly it rejoins is representative of the resistance that it creates, which requires additional force to overcome.
interference drag
come from the intersection of airstreams that create eddy currents, turbulence, or restrict smooth airflow.
the most interference drag is found when two surfaces meet at perpendicular angles. ex. where airflows around the fuselage and collides with airflowing around the wing.
skin friction drag
resistance due to the contact of moving air with the surface of an aircraft. every surface no matter how smooth has a rough ragged surface.
the air molecules that come in direct contact with the surface of the wing are virtually motionless, each layer of molecules above the surface moves slightly faster until the molecules are moving at the velocity of the air moving around the aircraft.
induced drag
wings produce lift but this is at the expense of induced drag. this kind of drag is inherent whenever an airfoil is producing lift.
wingtip vortices
when an airfoil is flown at a positive AOA a pressure differential exists between the upper and lower surfaces of the aircraft. the pressure above the wing is less than atmospheric pressure and the pressure below the wind is equal to or greater than the atmospheric pressure. air always moves from high pressure to low pressure and the path of resistance is toward the airplane’s tips, there is a spanwise movement of air from the bottom of the airfoil outward from the fuselage around the tips. this flow results in spillage over the tips, creating a vortex.
whenever a plane is producing lift, induced drag occurs and wingtip vortices are created.
when are wingtip vortices the greatest?
when the aircraft is heavy, clean, and slow. most common in approaches and departures, because the aircraft AOA is at the highest to produce the lift necessary to land or takeoff.
how do you avoid wing tip vortices/ wake turbulence
avoid flying through another aircraft’s flight path, and rotate prior to the point where the other aircraft rotated, avoid following aircraft on a similar flight path at an altitude within 1,000 ft, go above the other aircraft’s flight path/ touch down after the point at which the other aircraft wheels contacted the runway.
ground effect
the air trapped between the wing and the landing surface acts as a cushion.
moment arm
is the distance from a datum to the applied force
