1. ESRM 468 Forest Operations
Skyline Mechanics

2. Objectives Know the four types of skyline systems.
Know how to conduct graphical analysis.
Know how to conduct weightless line analysis.

3. Cable Profile Terms

4. Skyline Systems
Live
Standing
Running
Multispan

5. Basics Geometry of right triangles and trig functions.
Forces in right triangles fc2 = fa2 + fb2 Pythagorean relation.
Skyline systems are in equilibrium.

6. Basics
Vertical forces
Horizontal forces
Moments
Deflection

7. Basics Carriage is not clamped to skyline.
Lines are static, no acceleration or deceleration.
The haulback does not provide lift.

8. Basics Calculations are simplified if the load is fully suspended.
Both horizontal and vertical forces sum to zero.
The analysis is based on a skyline profile.

9. Graphical and Weightless Line Free Body Diagram
Skyline S1
Skyline S2 a
Mainline M b c
Payload W
Carriage not clamped to the skyline.

10. Graphical and Weightless Line Free Body Diagram
Skyline S1
Skyline S2 a
Mainline M b c
Payload W
Tension in skyline segments S1 and S2 are the same.

11. Graphical and Weightless Line Free Body Diagram
Skyline S1
Skyline S2 a
Mainline M b c
Payload W
Skyline segment S1 and mainline segment M are parallel so angles a and c are the same.

12. Graphical and Weightless Line Free Body Diagram
Skyline S1
Skyline S2 a
Mainline M b c
Payload W
Payload W is the sum of the carriage and load weights.

13. Graphical and Weightless Line Free Body Diagram
Skyline S1
Skyline S2 a
Mainline M b c
Payload W
For the weightless line method, angle a does not necessarily equal angle b..

14. Graphical Method Non-calculation intensive method.
Used to show how forces operate.

15. Graphical Method
Ground Shape
Draw the profile on graph paper.

16. Graphical Method
Headspar A
Tailhold C
Spar
Tailhold
Ground Shape
Mark the top of the headspar and tailspar on the paper.

17. Graphical Method
Headspar A
Tailhold C
Spar
Tailhold
Ground Shape
Identify the critical point on the profile and draw lines. (see Chain & Board)

18. Graphical Method For live, measure skyline SWL along AB and BC.
Headspar A
Carriage B
Skyline SWL 64000
Tailhold C
Spar
Tailhold
Skyline SWL 64000
Ground Shape
For live, measure skyline SWL along AB and BC.

19. Graphical Method
Headspar A
Carriage B
Skyline SWL 64000
Tailhold C
Spar
Load 31000
Tailhold
Skyline SWL 64000
Ground Shape
Draw vertical from SWL on BC to extension of AB. This is load capability.

20. Graphical Method
Headspar A
Carriage B
Skyline SWL 64000
Tailhold C
Spar
Load 31000
Tailhold
Skyline SWL 64000
Ground Shape
Mainline Tension
Mainline tension is the distance on line AB beyond SWL to vertical line from BC.

21. Weightless Line Method
Form of the graphical method where payload is found by resolving force vectors.
Assumption is that lines have no weight.
Less accurate than the rigid link method.

22. Weightless Line Method
TS1
VS1 a
Skyline S1
HS1
Skyline S2 TM a VM
Mainline M b c a HM
Payload W
TS2
VS2 b
HS2
TS1 = TS2 Skyline tensions, known. They are equal because the carriage is not clamped.

23. Weightless Line Method
TS1
VS1 a
Skyline S1
HS1
Skyline S2 TM a VM
Mainline M b c a HM
Payload W
TS2
VS2 b
HS2
TS1 = TS2 = Safe working load of skyline, (1/3) breaking strength. Known.

24. Weightless Line Method
TS1
VS1 a
Skyline S1
HS1
Skyline S2 TM a VM
Mainline M b c a HM
Payload W
TS2
VS2 b
HS2
TM is tension in the mainline, unknown.

25. Weightless Line Method
TS1
VS1 a
Skyline S1
HS1
Skyline S2 TM a VM
Mainline M b c a HM
Payload W
TS2
VS2 b
HS2
VS1, VM, VS2 are vertical forces in the skyline and mainline. Unknown.

26. Weightless Line Method
TS1
VS1 a
Skyline S1
HS1
Skyline S2 TM a VM
Mainline M b c a HM
Payload W
TS2
VS2 b
HS2
HS1, HM, HS2 are horizontal forces in the skyline and mainline. Unknown.

27. Weightless Line Method
TS1
VS1 a
Skyline S1
HS1
Skyline S2 TM a VM
Mainline M b c a HM
Payload W
TS2
VS2 b
HS2
HS1 does not equal HS2. VS1 does not equal VS2.

28. Weightless Line Method
TS1
VS1 a
Skyline S1
HS1
Skyline S2 TM a VM
Mainline M b c a HM
Payload W
TS2
VS2 b
HS2
Angles a, b and c are known.

29. Weightless Line Method
TS1
VS1 a
Skyline S1
HS1
Skyline S2 TM a VM
Mainline M b c a HM
Payload W
TS2
VS2
Find VS1, VS2, HS1, HS2
VS1 = TS1(sin a)
VS2 = TS2(sin b)
HS1 = TS1(cos a)
HS2 = TS2(cos b) b
HS2

30. Weightless Line Method
TS1
VS1 a
Skyline S1
HS1
Skyline S2 TM a VM
Mainline M b c a HM
Payload W
TS2
VS2
When a haulback is not necessary, HM = HS2 – HS1
Vertical mainline force VM = HM(tan a)
Payload W = VM / (sin a) b
HS2