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 + fb²Pythagorean 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 Carriage not clamped to the skyline.
10	Graphical and Weightless Line Free Body Diagram Tension in skyline segments S1 and S2 are the same.
11	Graphical and Weightless Line Free Body Diagram 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 Payload W is the sum of the carriage and load weights.
13	Graphical and Weightless Line Free Body Diagram 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 Draw the profile on graph paper.
16	Graphical Method Mark the top of the headspar and tailspar on the paper.
17	Graphical Method 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.
19	Graphical Method Draw vertical from SWL on BC to extension of AB. This is load capability.
20	Graphical Method 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 = TS2 Skyline tensions, known. They are equal because the carriage is not clamped.
23	Weightless Line Method TS1 = TS2 = Safe working load of skyline, (1/3) breaking strength. Known.
24	Weightless Line Method TM is tension in the mainline, unknown.
25	Weightless Line Method VS1, VM, VS2 are vertical forces in the skyline and mainline. Unknown.
26	Weightless Line Method HS1, HM, HS2 are horizontal forces in the skyline and mainline. Unknown.
27	Weightless Line Method HS1 does not equal HS2. VS1 does not equal VS2.
28	Weightless Line Method Angles a, b and c are known.
29	Weightless Line Method Find VS1, VS2, HS1, HS2 VS1 = TS1(sin a) VS2 = TS2(sin b) HS1 = TS1(cos a) HS2 = TS2(cos b)
30	Weightless Line Method When a haulback is not necessary, HM = HS2 – HS1 Vertical mainline force VM = HM(tan a) Payload W = VM / (sin a)