Gliding and Soaring Flashcards

1
Q

How does gliding differ from parachuting

A

the angle of descent for gliding is less than 45 degrees

the angle of descent for parachuting is more than 45 degrees

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2
Q

Based on energy conversion what is the principle behind gliding

A

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

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3
Q

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

A

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

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4
Q

how do gliders glide?

A

a positive glide angle is adopted

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

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5
Q

How do gliders choose their glide angle

A

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

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6
Q

How do we calculate the lift to drag ratio

A

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

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7
Q

What affects the speed of the glide?

A

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 .

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8
Q

What sets the
a. glide angle
b speed

A

a. glide angle determined by L/D ratio

b. speed is set by the weight

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9
Q

What is represented in a glide polar plot?

A

sinking speed over the airspeed

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10
Q

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

A
  1. vary angle of attack
  2. vary the wing camber ( curvature of the wing)
  3. vary the wingspan
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11
Q

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

A

L20 slide 24

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12
Q

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

A

shallow glide angles

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13
Q

How can we reduce induced drag ?

A

have a high aspect ratio by Having long thin wings

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14
Q

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

A
  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
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15
Q

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

A
  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
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16
Q

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

A
  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