Subtopic: Functional requirements, principles of working, construction and operation of manual, animal, tractor and renewable energy operated equipment for tillage, sowing, planting, fertilizer application, inter-cultivation, spraying, mowing, chaff cutting, harvesting and threshing
Question Statement:
Which of the following operational and kinematic characteristics distinguish rotary disc mowers from traditional reciprocating cutter bar mowers?
Options:
(A) Rotary disc mowers rely on high-velocity impact cutting ($70\text{--}85\text{ m/s}$ tip speed) without requiring a ledger plate counter-shear edge
(B) Rotary mowers have absence of unbalanced reciprocating inertial forces, allowing higher operating speeds of $12\text{--}16\text{ km/h}$
(C) Rotary disc mowers have significantly lower power consumption per unit cut width compared to reciprocating cutter bars
(D) Rotary mower knives are typically free-swinging to swing back into the disc upon hitting stones or rigid obstacles
Answer Key:
A, B, D
Step-by-Step Solution & Explanation
- **Statement A is correct:** Reciprocating mowers require shearing between the knife and ledger plate, whereas disc mowers rely purely on high kinetic energy impact cutting ($70\text{--}85\text{ m/s}$ knife speed).
- **Statement B is correct:** Rotating discs eliminate reciprocating accelerations, allowing smooth high-speed field operations.
- **Statement C is incorrect:** Rotary disc mowers consume substantially MORE power ($2\text{--}4\times$ higher per meter width) than reciprocating mowers due to aerodynamic air drag and continuous acceleration of crop residue.
- **Statement D is correct:** Knives are pivot-mounted on shoulder bolts to fold back during obstacle impacts, preventing catastrophic blade or gear failure.