SM2 Flashcards
Why is air considered an ideal fluid.
Since air has a veery low internal friction.
What is streamline or free stream flow.
When particles of a fluid move move in an orderly manner and maintain relative positions in successive cross sections.
Laminer flow is the same.
Continuity equation.
States that the speed of the airflow is inversely proportional to the area of the cross-section of the tube if density remains the same.
Therefore:
V1 x A1 = V2 x A2
Equation for dynamic pressure
Dynamic pressure is directly proportional to density and to the square of relative velocity.
Q = 1/2 x p x V^2
Indicated to piolet by the indicated air speed.
What creates lift.
The difference in static pressure
Boundry layer
Layer of air in the immediate vicinity of the wing.
The fluid on the surface can be said to be stationary. As molecules bought to rest by friction.
The next layer of molecules binds to the first but tends to shear slightly relative to the layer beneath them.
What happens to the boundry layer when the velocity of an aircraft increases, fluid viscocity is decreased, or density is increased?
It becomes thinner
Why is laminar flow desirable?
It is desirable bc it gives rise to high lift and low skin friction drag.
Why does flow separation happen?
Bc laminar flow is easier to achieve with a positive pressure gradient (high to low).
The pressure gradient from the thickest part of the wing to the trailing edge is a negative pressure gradient (low to high).
Therefore if energy is insufficient, it will detach from the surface.
Lift decreases and pressure drag increases.
Why can turbulent flow be a good thing
The air can have high energy allowing the boundry layer to remain in tact
Why do we deliberately causse turbulent flow on the rear pert of a wing.
A trade of betweeen drag and preventing a stall
Why are ailerons and controlling surfaces positioned towards the wing tip
So that control surfaces can still function during a root stall.
Equation for aspect ratio
Length of wing / width of wing.
Or
Wingspan^2 / wing area
What effects induced drag
Aspect ratio
Wingtip design
Aircraft speed
What does wash in refer to?
An angle of incidence that is greater towards the wing tips
