Lift and drag are defined w.r.t
Free stream flow
Normal and axial force are defined w.r.t
The chord
N cos a - A sin a
L = lift
N sin a + A cos a
D = drag
L cos a + D sin a
N = normal force
D cos a - L sin a
A = Axial force
Explain what it is and the formula
Reynolds Numbers
Re = ρVc/μ
Is a dimensionless number that relates the flow regime of a given object/shape against a stream
μ = viscosity
c = chord
V = velocity
ρ = density
How do trailing vortices reduce the effective angle of attack?
Vortices cause local downwash near the wing, adding a vertical velocity component that shifts the velocity vector downwards by an angle α.i. This makes the effective angle of attack smaller than the geometric angle of attack
Effective angle of attack formula
α.eff = α - α.i
What causes induced drag?
The reduced angle of attack from downwash-induced shift in air velocity near the wing
What is parasite drag?
Parasite drag, ( a.k.a Zero-lift Drag (C.d0) ) is the drag not associated with Lift. It grows with speed
Components of Parasite Drag:
- Profile drag
- Form/Pressure drag (due to flow separation)
- Skin-friction drag (from viscous shear forces at the
surface) - Interference drag (from junctions such as wing-fuselage, struts, etc.)
What are the effects of velocity on drag?
Higher velocity:
Decreases induced drag
Increases profile drag
What are the effects of Aspect Ratio on Lift and Drag?
Lift:
A lower Aspect Ratio decreases the C.lmax as well as the slope of the lift curve.
Drag:
A higher aspect ratio decreases C.di
Induced Drag Coefficient Formula
C.di = C.l² / (pi A e)
e = Oswal Efficiency Factor
Total Drag
C.d = C.d0 + C.di
What are the definitions and relationships between flight path angle, pitch angle and angle of attack?
Pitch angle θ: Angle between the nose of the aircraft and the moving earth axis horizontal
Flight path angle γ: Angle between the velocity vector of the aircraft and the moving earth axis horizontal
Angle of attack α: Angle between the pitch angle and the velocity vector of the aircraft
α = θ - γ
Steady Climbing Flight Equilibrium Equations
T - D - W sin γ = 0
- L + W cos γ = 0
Steady Gliding Flight Equilibrium Equations
L = W cos γ
D = W sin γ
Glide Ratio
In unpowered descent:
L/D = 1/tan(γ) = cot(γ) = C.L/D.L
Steady Gliding Flight Performance based on Glide Ratio
h/R = tan(γ)
R = h/tan(γ)
R = h * (C.L/D.L)
R = h * Glide ratio
h = Altitude
R = Distance travelled per altitude lost
