Gliding and Soaring

Question 1

How does gliding differ from parachuting

Answer 1

the angle of descent for gliding is less than 45 degrees

the angle of descent for parachuting is more than 45 degrees

Question 2

Based on energy conversion what is the principle behind gliding

Answer 2

gliders convert potential energy into kinetic energy (trade altitude for forward motion and lift)

Question 3

Why can’t gliders maintain a horizontal gliding position if the wind is directly blowing on it

Answer 3

because there would be no thrust force that could be generated so even though there is a lift force there is a drag force as a result of the oncoming wind which would result in the lost of airspeed

Question 4

how do gliders glide?

Answer 4

a positive glide angle is adopted

lift tilts forward to provide a force to balance rearward drag. . the resultant force equals the weight

Question 5

How do gliders choose their glide angle

Answer 5

Glide angle is chosen based on the lift to drag ratio.
a low L/D ratio means a steep glide angle
a high L/D means a shallow glide angle

Question 6

How do we calculate the lift to drag ratio

Answer 6

distance travelled/ height lost =lift/ drag = Cl/Cd = 1/tan(theta)

Question 7

What affects the speed of the glide?

Answer 7

the weight of the object , heavier glides travel faster along the same path as a lighter one, because more lift needs to be produced to offset the weight and drag .

Question 8

What sets the
a. glide angle
b speed

Answer 8

a. glide angle determined by L/D ratio

b. speed is set by the weight

Question 9

What is represented in a glide polar plot?

Answer 9

sinking speed over the airspeed

Question 10

What are the factors that can alter a glider’s air speed and sink speed

Answer 10

1. vary angle of attack
2. vary the wing camber ( curvature of the wing)
3. vary the wingspan

Question 11

On a graph polar identify where the optimum air speed for maximum distance , and where is the optimum airspeed for maximum time aloft

Answer 11

L20 slide 24

Question 12

What are the constraints when gliding with a high L/D ratio

Answer 12

shallow glide angles

Question 13

How can we reduce induced drag ?

Answer 13

have a high aspect ratio by Having long thin wings

Question 14

What are the 3 most important points on a glide polar plot - identify them on the glide polar plot

Answer 14

1. minimum sink speed: maximizes time spent in air
2. maximum distance speed: airspeed needed to maximize distance travelled in the air
3. minimum airspeed: the slowest speed that can produce lift without stalling the aerofoil

Question 15

Objects with a high L/D ratio cannot ascend quickly, how can an object ascend quickly if it has a high L/D ratio?

Answer 15

1. use of air brakes increase the drag without increasing the lift. to maintain airspeed the glider tilts forward and increase its glide angle. can vary the glide ratio
2. birds use their feet and stick out their neck – produces controllable amount of drag,
3. steepen your glide angle to hasten your descent

Question 16

What happens to the glide polar when you increase the weight of the glider

Answer 16

1. increase in wing loading
2. glide polar is shifted to the downward right because more airspeed and sinking speed is needed (as well as the min. airspeed before stalling)
3. higher speeds increase the lift needed to balance the increase in weight