ch 4 aerodynamics Flashcards
describe parasite drag
is composed of all the forces drag that work to slow an aircraft’s movement
-that includes all the forms:
form (shape of the airplane)
interference (b/w surfaces wing, joint anf fuselage)
leakage (high pressure air leaking to the outside of the
aircraft from door seals
cooling (air diverted into the engine compartment in resipicating engines
Explain form drag
form drag is the portion of parasite drag generated by the aircraft due to its shape and airflow around it. examples of factors contributing to form drag include the engine cowling, antennas, and the aerodynamic shape of other components
What is interference drag and how can it be reduced in aircraft design?
Interference drag comes from the intersection of airstreams that creates eddy currents of turbulence, or restricts smooth airflow
Explain skin friction drag
The air molecules on the surface of an aircraft have zero velocity in relation to the surface, but the layer above moves over the stagnant surface molecules because it is pulled along by the third layer. The velocities of the layers increase as the distance from the surface is increased until free stream velocity is reached.
Describe cooling and leakage drag
cooling drag refers to the air diverted into the engine compartment in reciprocating engines. (Engine) cooling drag has the characteristics of both form drag and skin drag. It is difficult to estimate and reduce. Leakage drag refers to the air that is dumped out of the outflow valves in pressurized aircraft. Leakage drag is impossible to control and insignificant.
what is air circulation above the wing called
When a wing is producing lift, there is a static pressure differential created across the wing, with pressure well below atmospheric on most of the top surface and slightly below atmospheric on most of the bottom surface. The pressure differential induces a circulation flow to the top surface of the wing, or to the low-pressure area.
what is induced AOA
As the pressure differential increases (increasing AOA) the downwash increases, which increases the induced angle of attack. The result is a greater angle between the lift and resultant force vectors and therefore, an increase in the induced drag.
explain induced drag and how the pilot changes it during flight
induced drag is the byproduct of lift. The pilot can change the amount of induced drag the wing is producing by changing the AOA
what aerodynamic factors affect induced drag?
the most significant factors are weight, velocity and wingspan
list three factors that affect total drag
weight, configuration, and altitude
how can interference be reduced on the aircraft design?
the rounder the objects at the intersections, the better off you are. having a fuselage and the wing at 90 degrees not good, but if you put a fairing you can smooth things over reducing interference.
Explain skin friction drag in terms of the air over the wing
first airflow completely stopped
airflow above it moves further and further along the wing.
until the free stream is unimpeded below
induced drag
the rear tilting of the vertical lift component
2 ways to create lift
speed and angle of attack
velocity affects both induced and parasite drag
what happens induced drag as velocity increases or decreases?
what happens to parasite drag as velocity increases or decreases?
induced drag decreases with speed, varying inversely as the square of the velocity and increases linear as air density increases …….
As velocity increases parasite drag increases
why does the weight affect the total drag?
the heavier the aircraft, the higher angle of attack in order to support the aircrafts weight and hold altitude.
the heavier you are the higher induced drag will be
with velocity affect the total drag , is AOA higher or lower?
the faster you go the lower AOA.
with the wingspan affecting total drag, deals with the aspect ratio of the wing
the lower the aspect ratio which is between the wingspan and cord line, the lower induced drag will be
induce drag is ___ proportional to the aspect ratio
inversely proportional to the aspect ratio.
drag acts parallel and opposite to the
flightpath
different type of drag
interference, skin and form
definition of parasite drag
is composed of all the forces that work to slow an aircrafts movement
induced drag
the portion of the total force that is due to the production of the lift force. induced as the win develops lift.
relation between speed verses drag.
which one changes with changes in speed (induced, parasite)
parasite drag increases at the square of increasing airspeed and decreases linearly as air density decreases
what is the boundary layer?
Covering the entire “wetted surface” of the aircraft is a thin layer of air called the boundary layer or the total distance between the surface and the point where the free stream is reached,
total drag
parasite and induced. it is the sum of the induced drag and parasite drag , which results in a curve characterized by a decrease and then an increase in drag as the velocity of the airplane increases (assuming level flight and constant weight, configuration, and altitude.)
difference between finite and infinite wing
finite has wing tip
finite and infinite wing, which one will prevent wing tip vortices?
infinite
what are wing tip vortices?
as the wing nove through the air mass, the air trying to flow around the wingtip causes a vortex behind the wing tip. the wing tip vortex induces a spanwise flow and creates vortices along the trailing edge of the wing.
what percentage of the downwash is the rear tilting?
50%
when is ground effect come into play?
1 wing span
what is eliminated in ground effect?
induced
True/False
drag tends to retard motion and increase fuel consumption affect performance such as range, endurance, and maximum velocity
true
What are two ways to minimize drag?
retracting landing gear and flaps
True/ false Parasite drag aids flight
false
true/ false Induced drag is a result of an airfoil developing lift
true
True false parasite drag is associated with lift
false
what type of drag contributes to engine cowlings, antennas?
form drag
interference drag
come from the intersection of airstreams that creates eddy currents or turbulence , or restricts smooth airflow.
True/ false the most interference drag is observed when two surfaces meet at acute and perpendicular angles
true
what is the purpose of a fairing?
to reduce interference drag by allow the air steams to meet gradually from air flowing over the body and the wing
The various layers of air within the boundary layer are sliding over one another and creating a force that retards motion, or a drag force, due to the viscosity of the air is known to be what type of drag?
skin friction drag
how to reduce skin friction drag?
flesh mounted rivet and removing irregularities that protrude above the wing surface. smooth and glossy finish
What are two important properties of the air when determining skin friction?
viscosity (or stickiness) and the compressibility (springiness).
Reynolds number?
displacement thickness depends on the Reynolds number.
reynolds is the ratio of inertial (resistant to change or motion) forces to viscous (Heavy gluey) forces
boundary layer can be ___ or ___ depending on the reynolds number?
laminar (layered), or turbulent (disordered)
no down wash occurs at the aerodynamic center
true
bound vortex
circulation about the wing
true/false the trailing edge edge vortices are strongest at the tips and diminish in intensity progressing toward the centerline of the wing
true
no trailing edge vortices exist at the centerline of the aircraft because in looking forward, the right wing vortices revolve counterclockwise and the left wing vortices revolve clockwise
true
as AOA increases the pressure differential __.
this ___ the down wash, which ___ the induced AOA
as a result there is a ___angle between the lift and resultant force vectors and there force, and ___ induced drag
increased increases increases greater increase
is AOA directly related to the induced drag?
yes
swept wing have ___ induced drag at slower speeds
more
