Chapter 5 Glider Performance Flashcards

1
Q

What 4 factors affect glider performance?

A

Glider design, Density, Weight, Wind

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2
Q

How does Density Altitude affect glider performance?

A

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

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3
Q

3 types of Wind?

A

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

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4
Q

Tailwind increases?

A

Ground roll on take-off and landing.

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5
Q

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

A

Increases. Steeper

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6
Q

Does headwind or tailwind increase sink rate?

A

Neither. Sink rate is independent of wind.

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7
Q

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

A

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

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8
Q

What is wind gradient?

A

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

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9
Q

What speed to fly when landing into a headwind?

A

Landing speed plus 1/2 of the wind speed.

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10
Q

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

A

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

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11
Q

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

A

Less uniformity close to the ground.

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12
Q

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

A

Increase

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13
Q

How much does the stall speed increase with additional weight?

A

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.

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14
Q

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

A

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%

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15
Q

How does weight affect turn radius?

A

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

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16
Q

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

A

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

17
Q

Where is min sink rate found on the Polar?

A

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

18
Q

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

A

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

19
Q

How does the polar curve shift with a heavier glider?

A

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

20
Q

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

A

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

21
Q

How do you adjust the Polar for a headwind?

A

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.

22
Q

How do you adjust the Polar for a tailwind?

A

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.

23
Q

How is the Polar adjusted for flying sinking air?

A

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.

24
Q

What is the best speed to fly in lift?

A

Min sink speed.

25
Q

Increasing the wingspan will shift the curve up/down.

A

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

26
Q

Setting flaps to a negative setting does what?

A

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

27
Q

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

A

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

28
Q

What is equation used to find Cg of glider?

A

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

29
Q

Where are ballast tanks?

A

Usually wings. Sometimes in vertical stabilizer.

30
Q

When should ballast tanks be drained?

A

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

31
Q

What should be a concern when carrying ballast?

A

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

32
Q

What is the purpose of ballast?

A
  1. Increase best L/D speed to minimize time between thermals.
  2. Adjust Cg. Weighted seat cushions or bolted on weights.
33
Q

What are the effects of ballast in wings?

A

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