Defence & Aerospace: Mobility Systems and Vehicle Performance
BEML's defence and aerospace domain covers heavy mobility vehicles, tracked platforms and aerospace structures/ground support. The paper tests applied mechanical reasoning - driveline configuration, gradeability, tractive effort, hydraulics and platform constraints - rather than pure theory.
What is actually tested
- Vehicle configurations: 4x4, 6x6 and 8x8 Tatra-type chassis; transfer case, differential locks, and how the number of driving axles sets off-road traction and gradeability.
- Mobility parameters: power-to-weight ratio (kW/t), gradeability (%), fording depth, side slope, ground clearance, approach and departure angles.
- Tracked platforms of BMP-II class: hydropneumatic suspension, water propulsion, NBC protection; keep automotive limits separate from amphibious limits.
- Hydraulics: pressure = force/area, flow sets actuator speed; recovery winch and suspension circuits.
- Aerospace interface: ISRO-related structures and ground support - tolerances, NDT and material specifications.
Worked example
An 18,000 kg 6x6 vehicle must climb a 30% grade at steady speed. A 30% grade means tanθ = 0.30, so sinθ ≈ 0.287. Grade resistance = mg sinθ = 18,000 × 9.81 × 0.287 ≈ 50.7 kN. Divide by driveline efficiency 0.85 → 59.6 kN at the wheels. With a 0.55 m wheel radius, total wheel torque = 59.6 × 0.55 ≈ 32.8 kN·m, shared across the driving axles. Use sinθ, not tanθ: a 30% grade is not a 30° angle.
Traps that cost marks
- Treating a percentage grade as an angle in degrees.
- Using kerb mass instead of gross vehicle mass with payload, armour and crew.
- Ignoring transfer-case/driveline losses and engine derating for altitude and ambient temperature.
- Confusing fording depth with the water-speed limit of amphibious platforms.