Define Rectilinear - ANS-Consisting of straight lines
Define wave drag - ANS-Component of aerodynamic drag on every part of an aircraft due to the
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of shock waves
Why do ICBM's have a blunt nose instead of an aerodynamically favorable pointy nose? - ANS-Although a
slender nose would reduce wave drag, it creates more skin friction heating as air molecules are able to
directly contact the tip of the missile as it travels at very high speeds (Mach 25). To reduce the amount of
heat on the missile from air friction, a blunt nose design is implemented which creates a bow shockwave
that consumes some of this frictional heating and transfers it into the air instead of onto the aerodynamic
body.
What is the critical Reynold's number? What is its value? - ANS-This describes the value at which flow
transitions from a laminar flow regime to a turbulent flow regime. This number varies for certain
aerodynamic shapes.
(10^3 - 2x10^5) for most airfoils. Rex(trans) in x/c, measured with respect to the chord length of airfoil.
What flow properties is Reynold's number comparing? What is the equation for Reynold's number? - ANSReynold's number is the comparison of inertial to viscous forces in a given flow.
Re = inertial forces/viscous forces
Re = (rho*v*L)/mu
-rho = density (kg/m^3) or (slug/ft^3)
-v = velocity (m/s) or (ft/s)
-L = Characteristic length (length of body in direction of flow) (m) or (ft)
-mu = absolute (dynamic) viscosity (Pa*s)
Which has less skin friction drag: laminar or turbulent flow? - ANS-Laminar
What is the equation for local skin friction coefficient? - ANS-cf = shear stress/dynamic pressure (Pa/Pa)
What is the equation for the wall shear stress on an airfoil? - ANS-tau = mu(dv/dy) @y=0
-mu = dynamic viscosity
-(dv/dy) = velocity gradient
Define parasitic drag. Which type of flow greatly reduces parasitic drag? - ANS-Drag induced by an object
moving through a fluid.
Laminar flow
Define shockwave - ANS-A strong pressure wave in a elastic medium like air. Propagates faster than the
speed of sound...
How does air flow speed effect boundary layer thickness? - ANS-Greater air flow speed causes a thinner
boundary layer.
What is boundary layer thickness? - ANS-The distance traveled normal to a surface to go from v=0 (no slip
condition) at surface to v=v∞ or freestream velocity at 𝛿 height.
Define nacelle - ANS-A streamlined body sized to what it contains i.e. engine nacelle
Define fairing. Name 2 types of fairings. - ANS-Streamline body on aircraft to reduce drag at transition
points
Wing root fairing, flap track fairing
What are the 2 primary sources of all aerodynamic forces and moments? - ANS-Pressure distributions over
body surface and shear stress distributions over body surface.
What is angle of attack measuring? -
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