XC 2: Flying Further and Faster

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XC 2 Flying Further and Faster
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The Plan

• The polar curve and performance
• Flying Further maximising the glide
• Flying faster in theory
• In practice rules of thumb
• Final glides
• Technology

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Performance
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Polar Curve
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Different Gliders
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Flying Further
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Glide Ratio at max LD
49/1.62 30.3
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20 kt Headwind
34/1.85 18.4
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15 kt Tailwind
62/1.55 40.0
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2 kts Sink
60/4.2 14.3
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6 kts Sink 30 kt Headwind
57/11.2 5.1
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Flying Faster
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Assumptions Climb by circling i.e. cover no
distance while climbing. Thermal strength is
constant with altitude. Thermal strength is
known in advance (!)
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x
Caution Algebra Ahead
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V Airspeed S Rate of Sink (negative) C Rate
of Climb (positive) During the glide we fly
distance e with loss of height h in time t1 We
then climb h in time t2 (1) Total time, t t1
t2 (2) Average speed, Vav e/t (3) Altitude loss
in glide, -h S t1 (4) Altitude gained while
climbing, h Ct2 (5) Gliding time, t1 e/V (6)
Combining 3 and 4 t2 t1(-S/C) (7) Substitute
for t2 from (1) t - t1 t1(-S/C) (8) Substitute
for t1 from (5) t (e/V)(1- S/C) (9) Substitute
for t from (2) e/Vav (e/V)(1- S/C) gt
Vav/V C/(C - S)
h
e
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Climb of 2kts
Vav/V C/(C - S)
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As our expected rate of climb increases we fly
faster.
But how much faster?
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Climb or Glide?
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Climb of 2kts
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2 Kt
2 Kt
2 Kt
6 Kt
1819
730
1520
1321
14.49
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So much for Theory...
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Rules of Thumb

• Final Climb Speed Ring Initial Climb
  (Reichmann/Comté)
• Do I have enough height to get to a (probably)
  better climb yet? (Chris Rollings)
• MIAROC Minimum Instantaneous Acceptable Rate of
  Climb (Platypus)

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A Typical Flight
4 Kt
5 Kt
4 Kt
3 Kt
6 Kt
5 Kt
4 Kt
5 Kt
3 Kt
4 Kt
5 Kt
5 Kt
4 Kt
4 Kt
5 Kt
4 Kt
3 Kt
4 Kt
4 Kt
4 Kt
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A Typical BRITISH Flight
5 Kt
0.1 Kt
-2 Kt
8 Kt
0 Kt
?
!
!
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Final Glides
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The Final Climb
4 Kt
?
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When to Begin?

• Set McCready to 4 Kts
• How much more height do I need to arrive home at
  my chosen safety margin?
• Remember the wind
• Keep updating as the climb rate changes
• When no more height is needed then go!

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On Glide (or not)

• If you're getting above glide then increase the
  McCready setting
• If you're getting below glide then reduce it
  and/or take another climb

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That Safety Margin

• How far is it?
• What are conditions like on track?
• What is the performance of the glider?
• What is the McCready setting?

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Having Finished

• Do remember to...
• Put the wheel down
• Dump any ballast
• Attempt some sort of reasonable landing
• Not crash

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