Chapter 5 Glider Performance

Question 1

What 4 factors affect glider performance?

Answer 1

Glider design, Density, Weight, Wind

Question 2

How does Density Altitude affect glider performance?

Answer 2

High Altitude Density decreases lift and therefore increases take-off distance and decreases climb.rate.

Question 3

3 types of Wind?

Answer 3

Headwind, Tailwind, crosswind. If headwind and tailwind are not direct, they will have crosswind components to them.

Question 4

Tailwind increases?

Answer 4

Ground roll on take-off and landing.

Question 5

Headwind increases/decreases slope of landing and take-off.

Answer 5

Increases. Steeper

Question 6

Does headwind or tailwind increase sink rate?

Answer 6

Neither. Sink rate is independent of wind.

Question 7

How is a glider affected by an obstacle at the beginning of a runway with a tailwind?

Answer 7

Tailwind will create a sink zone downstream of the obstacle. A headwind will create lift.

Question 8

What is wind gradient?

Answer 8

Wind speed aloft is usually higher than wind close to the ground.

Question 9

What speed to fly when landing into a headwind?

Answer 9

Landing speed plus 1/2 of the wind speed.

Question 10

What speed to fly when landing into a headwind with gusts?

Answer 10

Landing speed + 1/2 wind speed + 1/2 of difference between wind speed and gust speed.
LS = 55 Headwind = 10 Gust = 30
55 + .5(10) + .5(30 - 10)
30 - 10 = Gust Factor

Question 11

The closer to the ground, the more/less uniformity in the wind speed?

Answer 11

Less uniformity close to the ground.

Question 12

Additional weight causes the stall speed to (increase/decrease.

Answer 12

Increase

Question 13

How much does the stall speed increase with additional weight?

Answer 13

Stall speed increases as the square root of the weight increase.
150% of normal weight = Sq Rt of 1.5 = 122% of normal stall speed.

Question 14

What is the relationship between bank angle, load factor , and stall speed?

Answer 14

Stall speed increases as the Sq Rt of the Load Factor increase.
Angle Load Factor Stall Speed
30 120% 110%
45 140% 120%
60 200% 141%

Question 15

How does weight affect turn radius?

Answer 15

Additional weight requires higher speed. Higher speed at same bank angle means larger turn radius.

Question 16

What is plotted on the X & Y axies of a Polar Graph?

Answer 16

X-axis = Airspeed knots
Y-axis = Sink Rate knots

Question 17

Where is min sink rate found on the Polar?

Answer 17

The highest point of the curve. Min sink speed corresponds to the speed at this point.

Question 18

Where is the best L/D speed found on the curve?

Answer 18

Draw a line from the origin to a tangent point on the curve. Airspeed at this point is Best L/D speed.

Question 19

How does the polar curve shift with a heavier glider?

Answer 19

For added weight it moves the curve down and to the right. Min sink increases. Min sink speed increases. Best L/D speed increases.

Question 20

Which speed is higher Min Sink or Best L/D?

Answer 20

Best L/D speed is always higher than Min Sink speed.

Question 21

How do you adjust the Polar for a headwind?

Answer 21

Move the origin to the right on the X-axis by the amount of the headwind. Draw a line from the new origin to the tangent point.

Question 22

How do you adjust the Polar for a tailwind?

Answer 22

Move the origin to the left on the x-axis by the amount of the tailwind. Draw a line to the tangent point. But do not fly lower than Min Sink speed.

Question 23

How is the Polar adjusted for flying sinking air?

Answer 23

To find best L/D speed in sink, move the origin up on the Y-axis by the sink rate. Drawi tangent line to curve.

Question 24

What is the best speed to fly in lift?

Answer 24

Min sink speed.

Question 25

Increasing the wingspan will shift the curve up/down.

Answer 25

Longer wings moves the curve up and reduces the sink rate and best L/D.

Question 26

Setting flaps to a negative setting does what?

Answer 26

It reduces drag and increases the best L/D speed. It also slightly reduces sink rate. It moves the curve to the right.

Question 27

What are typical climb rates for winch launch? Motorized glider?

Answer 27

Winch = 2000 ft/min. Motorized glider = 200 - 800 ft/min.

Question 28

What is equation used to find Cg of glider?

Answer 28

(moment of mass1 + moment of mass2 …) / total weight. Moment = mass x distance from ref point.

Question 29

Where are ballast tanks?

Answer 29

Usually wings. Sometimes in vertical stabilizer.

Question 30

When should ballast tanks be drained?

Answer 30

Prior to landing pattern. 3-5 minutes to drain.

Question 31

What should be a concern when carrying ballast?

Answer 31

Possibility of freezing at high altitudes. Or freezing of drain valve.

Question 32

What is the purpose of ballast?

Answer 32

1. Increase best L/D speed to minimize time between thermals.
2. Adjust Cg. Weighted seat cushions or bolted on weights.

Question 33

What are the effects of ballast in wings?

Answer 33

Reduced response of ailerons due to inertia increase.
Increased ground roll on take off.
Increased stall speed.
Reduced ground acceleration.