The Four Forces Acting On An Aircraft Flashcards
Where does the weight force on the aircraft act through ?
Centre of gravity
Where does thrust vector act along?
Force parallel to the longitudinal axis of the aircraft.
Where does lift force act through?
Centre of pressure, perpendicular to the relative airflow.
What is the total reaction?
Sum of the lift and drag forces that act through the centre of pressure on the wing.
What direction does drag act through?
- Parallel to the relative airflow.
- Acts through the centre of pressure
What is the lift equation?
L = 0.5 x rho x V^2 x Cl x S
Within the lift formula , what can the pilot change?
- Altering the Cl by changing the AOA or configuration
- Altering velocity
- Altering wing area by using Fowler flaps
What is the boundary layer?
Layer of air closest to the aero foil that is affected by friction from the wing.
What is laminar flow?
Smooth flow over the wing
What is the adverse pressure gradient? Where does it start on the wing? What is this point called?
- As flow starts to slow down it will encounter an adverse pressure gradient
- This starts after the transition point
- This occurs at the point of maximum thickness/chamber of the aerofoil.
What is the separation point?
Point where flow will not be able to overcome the adverse pressure gradient and will separate from the surface of the aerofoil
How do Cp, transition point and separation point move with increasing angle of attack?
Move closer to the leading edge of the wing.
Where are the two stagnation points on the aerofoil? Are these greater than static freestream velocity?
- Leading edge and trailing edge
- yes
Which angle of attack is the point of maximum lift achieved on the aerofoil?
Just before stall angle.
How does lift dependent drag vary with the speed?
Decreases with the square of the speed.
Does lowering the flaps increase or decrease the critical angle of attack?
Decrease.
What occurs to the critical angle of attack with slats it leading edge devices?
Increases the critical angle of attack.
What occurs to critical angle of attack when wing trailing edge and leading edge flaps/slats are deployed?
Increases critical angle of attack
What is the drag equation?
Drag = Cd x 0.5 x rho x V^2 x A
What are the two main drag effects?
- Lift dependent drag
- Zero lift drag
What are the three components to zero lift drag?
1) Skin friction
2) Form drag
3) Interference drag
What causes wingtip vortices?
Spanwise flow on top and bottom of wing that collided at trailing edge and forms vortices.
What is the cause of lift dependent drag?
Wingtip vortices.
What part of the wig are wingtip vortices the strongest ?
Wingtip
