A tractor drawn rotavator with a rotor radius 300 mm has 6 flanges having 3 blades in each flange acting in one plane. It is operated at a rotor speed of 180 rpm and a forward speed of 3 km·h⁻¹. Increasing the forward speed as well as the rotor speed by 15% each, the change in length of soil slice, in mm, is __________. (Answer in integer)
Official Answer Key:
0 to 0
Step-by-Step Solution & Explanation
The length of soil slice (bite length) cut by a rotary tiller is:
L = v / (n · z)
where v = forward speed, n = rotor speed (rev per unit time), z = number of blades acting in one plane per revolution.
Original bite length:
v = 3 km·h⁻¹ = 0.8333 m·s⁻¹ ; n = 180/60 = 3 rev·s⁻¹ ; z = 3 blades in the plane
L₁ = 0.8333/(3 × 3) = 0.0926 m = 92.6 mm
After the change: both v and n are multiplied by 1.15, while z is unchanged:
L₂ = (1.15 v)/((1.15 n) · z) = v/(n · z) = L₁
The factor 1.15 cancels exactly between numerator and denominator.
Change in length of soil slice = 0 mm
Insight: bite length depends only on the ratio of forward speed to rotor speed. Raising both by the same percentage leaves the soil slice — and hence the degree of pulverisation — unaltered.
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