04-For-B7 Transportation of Forest Products · May 2013
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
EGBC National Exam — Forest Engineering, 04-For-B7 Transportation of Forest Products, May 2013. Closed book; approved Casio/Sharp calculator only. 3 hours. Six question groups in two parts: Part A (Questions 1–4, choose 3 of 4, 60 points) and Part B (Questions 5–6, both compulsory, 60 points).
Reference texts: Heinimann, Forest Operations Engineering (forest transportation systems, vehicle/road interaction); Sessions, Forest Road Engineering Guidebook (road geometric design, stopping sight distance, road-surface traction); FPInnovations/FERIC reports (log-hauling vehicle configurations, tire-inflation systems, machine/vehicle productivity); Transportation Association of Canada (TAC), Geometric Design Guide for Canadian Roads (stopping sight distance formula, Canadian design practice); the exam's own “Required Propulsion Formulae” page (standard Davis-type railway tractive-effort and train-resistance equations, consistent with general railway/traction engineering practice, e.g. Hay, Railroad Engineering).
Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.
The transmission matches the engine's narrow band of efficient operating speed to the wide range of tractive-force and road-speed conditions a logging truck actually encounters. A diesel engine develops useful torque and reasonable fuel efficiency only over a limited RPM band, but the truck must deliver very high tractive force at low speed (moving a fully loaded rig off a soft landing, or climbing a steep haul-road grade) and comparatively low tractive force at high speed (cruising the paved highway to the mill). The transmission's set of gear ratios provides this mechanical-advantage range: a low gear multiplies engine torque at the wheels (at the cost of road speed) for starting and climbing, and a high gear lets the engine turn at its efficient cruising RPM while the truck moves at highway speed. It also allows the engine to idle disconnected from the drivetrain (via the clutch or torque converter) when the truck is stopped, and provides reverse for backing under a loader at the landing.
The demand on the engine changes systematically over the haul. Near the landing, the fully loaded truck must overcome the largest static and grade resistance from a standing start on the roughest, steepest, and often softest section of road -- this is a high-torque, low-speed regime, met by selecting the lowest usable gears so the transmission multiplies engine torque at the drive wheels. As the truck moves onto the maintained mainline haul road and picks up speed, torque demand per gear falls (resistance still includes grade and rolling resistance but road speed is climbing), and the engine is worked increasingly toward its power output (power = torque × angular speed; equivalently, tractive force × road speed) rather than peak torque. On the final paved-highway segment into the mill, the truck cruises at a comparatively constant, higher speed with modest grade change, so the dominant requirement becomes sustained power near the engine's rated output at a fuel-efficient cruising RPM, with torque demand at its lowest point of the trip (highest gear). The engine and drivetrain must therefore be specified for the worst-case torque condition (fully loaded, steepest grade, lowest speed near the landing) while the transmission's gear spread is what lets the same engine also deliver efficient sustained power at highway speed -- a single fixed-ratio drivetrain could not do both.
