8.2 aerodynamics Flashcards
kinetic energy =
KE = 1/2 p x V2. p = local air density V = is speed in m/s. KE = joules
principle of continuity
energy and mass can neither be created or destroyed. they can only be changed from one form to another
smooth regular airflow patterns around an object are called
laminar flow
turbulent airflow is
when air is disturbed and separates from the surface of a moving body .
a flying body does not attain the speeds necessary to compess air in what region
subsonic region
the speed of airflow is inversely proportional to the area of the cross-section of the tube if the density remains constant.
V1 x A1 = V2 x A2
Principal of continuity
diffuser outlet means
when the diameter increases and the speed decreases
jet outlet means
when the diameter decreases and speed increases
in bernoulis principle using a valve what happens to the pressures
as valve is opened, static press decreases whilst dynamic press increases. the total press is always unchanged.
dynamic pressure =
total pressure - static pressure
dynamic pressure expressed mathematically is
q = 1/2 p x V2
dynamic pressure increases sixteen times if speed increases by how much
4 times
dynamic pressure is indicated to the pilot as
the Indicated Air Speed (IAS)
at the point of stagnation…
the speed of the airflow falls to zero and static press equals total press.if there is no dynamic press, there is no flow
the difference in static pressure acts on the surface to create what force
lift
the boundary layer is
the layer of fluid in the immediate area of a surface
no slip condition is
when air flows over a wing, the fluid at the surface are stationary, as molecules at the surface are brought to rest by friction
after the boundary layer what happens
layers bind to each other but shear slightly relative to the layer beneath them until a layer reaches the velocity of the free stream
the fixed boundary is
where the layer close to the skin of the wing has zero velocity
the moving boundary is
the point where the air has met free air stream velocity
the region between the fixed boundary and moving boundary is called the
boundary layer
if the aircraft velocity is increased what happens to the boundary layer
it becomes thinner
if fluid viscosity is decreased or fluid density is increased what happens to the boundary layer
it becomes thinner
laminar flow is
smooth flow parallel to one another. stream lines not crossing eachother.
what can affect laminar flow
rivets and other protruding objects
laminar flow over a wing is desirable because
it gives high lift and low skin friction drag
at sufficinent distance where air is unaffected by the aircraft moving through it, it is considered to be what
free stream velocity
relative airflow is the direction of the airflow with respect to the object moving through it
in level flight - the aircraft is flying directly into the wind
nose up attitude - the wind would appear to come from below.
a region of space around the aircraft where the velocity of the relative airflow is zero
stagnation point
common location for stagnation points on an aircraft is
leading edges on wings and it results in a local increase in static pressure compared to the surrounding fluid.
if the angle of attack is increased, what happens to the transition point
it moves closer to the leading edge and the adverse pressure gradient becomes stronger.
advantages of laminar flow
low fuel usage
greater range
faster top speed
glide further
disadvantage of laminar flow
due to lower kinetic energy contained, its easier for flow separation to occur.
this results in easier stalling at lower AOA
upwash is
as air flows towards a wing, it will be turned towards the low-pressure region of the upper surface of the aerofoil.
downwash is
as the air flows back over the aerofoil it will tend to slow down and returns to its original state
vortices are
circular patterns of rotating air formed behind a wing or control surface as it generates lift or force from the pressure differential
vortices rotate which way
in a conventional view from behind
clockwise - left wing tip
anti-clockwise - right wing tip
camber is
mean camber line is a line drawn of equal distance between the upper and lower surfaces of the profile.
chord is
chord line is a straight line connecting the leading edge and trailing edge. the chord is the distance between leading and trailing edges.