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