Avit 323 Block 10 Exam Lents
the motion:
-Dp increases as the square of velocity -Di decreases as the square of velocity -inclination determines the varying shape -boundary layer: "viscous drag"
thrust
-must be generated to overcome the natural resistance of drag -newton's third law : "for every action there is an equal and opposite reaction"
wing tip vortex
-one part of induced drag -loss of kinectic energy
reciprocating aircraft engine
-power producing machine -fuel flow directly proportional to power output
propeller: thrust available
-propeller is an airfoil -not 100% efficient -produces induced and parasite drag -affected by airflow disturbed by other blade
effect of boundary layer: laminar flow
-reduced skin friction drag (effective shape is smaller) -increased pressure drag when operated at high AOA
the object:
-size, shape, streamlining determine form (pressure) drag -lift determines induced drag -surface roughness and surface area determines skin friction (viscous or boundary layer) drag
types of parasite drag
-skin friction -form -profile -interference -cooling -leakage
slipstream effects
-small trim tab attached to rudder, adjustable only on the ground -cant the engine, offset the thrust centerline -these corrections are for normal cruise flight only
skin friction drag
-the aerodynamic resistance due to the contact of moving air with the surface of the aircraft -no matter how smooth a surface appears, every surface has rough and ragged surface when viewed under a microscope -paint leaves molecular ridges causing drag
what determines induced drag?
-velocity -air density -lift required -charactersitic of wing
three elements that change total drag the most
-weight -configuration -altitude
factors that influence skin friction
-wetted surface -amount of viscous drag in the boundry layer -velocity -*speed
Finite Wing
-wing tip vorticies -downwash -induced drag -must operate at higher velocity to produce same lift as infinate wing -less lift at the same velocity as infinate wing
What is the highest value of e, the Oswald Efficiency Factor?
1
more efficient the wing the number is closer to
1
propeller rotates clockwise
-airplane tends to twist/turn left -noticable on the ground, more friction on the left wheel during the takeoff roll
increase in forward velocity
-angle of attack of blade decreases -thrust decreases
elliptical wing
-area matches lift distribution -airfoil sections work equally
drag "bucket"
-as long as the aircraft operates at low angles of attack, the coefficient of drag is greatly reduced -higher angles of attack produce seperation and increase the coefficient of drag
endplates
-block airflow around tip -more parasite drag -tiptanks shaped like wings or torpedoes
geometric pitch
-built in angle of incidence, path the blade would take in a static condition -measure of it's path of rotation
characteristic of wing
-coefficient of lift -aspect ratio -wing planform
laminar flow airfoil
-delays the transition to turbulent flow -reduces the coefficient of drag
droop tips
-downward deflection of spanwise flow -vortex forms farther away -only efficient to a certain point
parasite drag
-drag that is NOT associated with the production of lift -the result of displacement of air by the aircraft
interference drag definition
-drag that is the result of two airstreams that intersect, creating turbulence and restricting smooth airflow -merging air currents create more drag when combined than when seperated
reducing skin friction
-flush mounted rivets -smooth finish -remove dirt and keep waxed (section 8 POH)
the fixed pitch propeller is only efficient at one particular speed range
-for takeoff and climb: low pitch, which results in high RPM and high power -for cruise: high pitch, which results in low RPM and efficient cruise
wing tip vorticies
-free stream air -spanwise (root to tip) flow
turbulent boundary layer
-high viscous drag -seperation occurs later
effect of boundary layer: turbulent flow
-increased skin friction drag (effective shape is bigger) -reduced pressure drag when operated at high AOA
air density
-induced drag decreases with greater density >increasing pressure >lower altitude >colder temperature
span efficiency factor
-induced drag decreases with more efficient wings -elliptical = 1 -others = .85 to .95
velocity
-induced drag decreases with the square of velocity -big factor
wing span
-induced drag decreases with the square of wing span -big factor
weight
-induced drag increases with the square of weight -big factor
constant speed propeller
-it's like being able to shift gears in an airplane -balance between centrifugal force and oil pressure >pressure maintained by governor
Laminar boundary layer
-low viscous drag -seperations occurs earlier especially with curved or round objects
constant speed prop
-more blade settings -greater range of efficiency
winglets
-most effective at low speed and/or high angle of attack
non-geared, direct drive engine
BHP = SHP
When you change power/ thrust what two things could happen?
1. climb 2.
As weight increases, which direction does the Total drag curve move?
Shifts Up because induced drag is increased the most
unaccelerated
means the airplane neither speeds up or slows down, but remains at a constant velocity
elicipitcal plan form is
most efficient
When a wing is within 1/10 of its span to the surface, its induced drag is reduced
by nearly half
thrust equation
newton's second law of motion f=ma & a = a change in velocity divided by a change in time
coefficient of induced drag
non-dimensional and efficiency of wing
wing tip vortex creates what kind of air component?
downward component to air
downwash
downward deflection of air and increases magnius effect
induced drag definition
drag that results from the production of lift
loss of lift at wing tips
due to span wise flow and what span wise flow does to angle of attack
torque effects
caused by the propeller -slipstream effects -equal and opposite reaction -p-factor -precession
drag
a result of the interaction and contact of a solid body with a fluid (liquid or gas)
power =
force x velocity
Which type of drag is also known as pressure drag?
form drag
Propeller efficiency
always less than 100%
infinite wing
an airfoil in a wind tunnel spanning from one wall to the other experiences no spanwise flow, and produces the same amount of upwash and downwash from chordwise flow, which cancel eachother out and do not affect lift at all. -no wing tip vorticies -no down wash -no induced drag
form drag reminder
anytime airflow must change direction energy is required (drag)
rectangular wing
area does not match lift distribution -root works hardest: higher local -tip works least: lowest local
speed fairings
help to streamline and reduce form drag
fixed pitch propellers: cruise
higher pitch, lower RPM, and thus less horsepower produced
Efficiency
how much BHP the propeller converts to THP
f or Equivalent Flat Plate Area, is important in calculating what kind of drag?
parasite drag
fixed pitch prop
peak efficiency at one airspeed
span efficiency factor
depends on wing planform -elliptical=1 -other planforms between = .85 to .95
accelerating
if thrust is greater than drag, the speed would increase - as speed increases so does drag - it will build until it equals the new drag and we will once again be unaccelerated
changing weight
increase weight= up on curve decrease weight= down on curve
deceleration
initially drag is greater than thrust (speed), but as we slow drag decreases until it reaches equilibrium with thrust
What happens to induced drag as speed increases?
it decreases exponentially
What happens to parasite drag as speed increases?
it increases exponentially ie. weight squared
what are the two types of boundary layers?
laminar and turbulent
propeller driven airplanes
large mass of air accelerated to relatively low final velocity
better efficiency =
least amount of drag
high aspect ratio
longer wings
fixed pitch propellers: climb
lower pitch, higher RPM and thus more horsepower developed
form drag definition
portion of drag which is generated by the shape of the aircraft and its components
wetted area
portion of the aircraft that is in direct contact with the atmosphere
thrust horsepower
power that is imparted by the propeller to the air
induced drag
pressure difference between upper and lower wing surfaces
Which type of drag is a combination of skin friction and form drag?
profile drag
changing speed
puts you along the curve
Drag is
resistance to airflow & forward motion
shockwave drag
result of shockwave formations at high speeds
profile drag definition
result of the skin friction and form drag that an airfoil creates
reducing form drag
stream lining -reduces form drag -increases skin friction
propellers: rotating airfoil
subject to stalls, induced drag, and other troubles that affect airfoils
drag definition
the component of aerodynamic force that is parallel to the relative wind and retards the forward motion of the aircraft
induced drag
the portion of drag which is caused by the production of lift
total drag
total drag of airplane total = parasite + induced
Which of these factors affects induced drag the most?
weight
form drag
when airflow is caused to seperate, a net force develops which opposes the flight path
wake turbulence
wing tip vorticies -weight -span -velocity
effective pitch
actual path the propeller is taking in the air at any particular time
laminar flow airfoil maximum camber is moved
aft (60% chord line) to delay the transition to turbulent air flow
what is the boundary layer?
airflow which shows local reduction in airflow due to viscosity
Output Power of an Engine: PLANK
P-indicated effective pressure (psi) L-length of stroke in ft or fractions of ft A-area of the cylinder (sq. in.) N-number of power strokes per min K-number of cylinders
gas turbine engine airplanes
small mass of air accelerated to a relatively high final velocity
low aspect ratio
shorter wings
