Basic Aerodynamics + IR

Question 1

What causes ground effect?

Answer 1

1. The upwash in front of the wings, and the downwash behind the wings are substantially modified when the aircraft is in close proximity to the ground, about one wingspan length. The effect is even more noticeable when below 1/2 the wingspan length.

Question 2

The 4 prominent effects of ground effect

Answer 2

1. The pressure distribution around the wing is substantially altered by the modified upwash and downwash in front and behind the wing, this increases the effective angle of attack of the wing and the coefficient of lift, which affects the lifting capability at any given angle of attack and reduces the minimum speed of the aeroplane. As a result, the airplane will still at a lower angle of attack.
2. This increase in the effective angle of attack and increase coefficient of lift is felt by the pilot as a floating sensation.
3. The reduction in wing tip vortices translates into a reduction of induced drag which, results in an increased float distance which is not ideal for short runways.
4. A nose down pitching moment may exist during the ground effect, the altered downwash and upwash increases the angle of attack of the tailplane.
5. When leaving the ground, and exiting the ground effect zone, a decrease in coefficient of lift and a decrease in effective angle of attack will be felt. Also induced drag will be increased. Thus, the danger is that you might be able to fly close to the ground but not able to climb.

Question 3

The angle between the chord line and the relative airflow -

Answer 3

Angle of Attack

Question 4

A straight line that joins the centre of curvature of the leading edge and the trailing edge

Answer 4

The chord line

Question 5

Camber is measured as the maximum distance between the -

Answer 5

camber line and the chord line

Question 6

stalling angle of attack value is -

Note: this point is where maximum coefficient of lift is achieved, a further increase in AoA will result in a drop of lift.

Answer 6

15 degrees

Question 7

CL max is achieved at what angle of attack?

Answer 7

15 degrees

Question 8

Profile drag:

This is also referred to as zero lift drag or parasite drag and may be subdivided into the following:

Answer 8

1. Form drag

2. Skin friction

Question 9

Ground effect modifies the upwash and downwash when in close proximity of the ground, specifically when it is within -

Answer 9

one wingspan distance from the surface and more noticeable at or below 1/2 wingspan distance from the surface

Question 10

Ground effect increases the effective AoA and the wings coefficient of lift which will reduce the -

Answer 10

minimum speed of the aeroplane. I.E, the aeroplane will stall at a lower angle of attack.