Chassis Layout and Frames Questions and Answers

Answer: C

Full scale and model wind tunnels with rolling roads reproduce the ground effect that a static floor would misrepresent, and computational fluid dynamics allows many configurations to be assessed before any model is built. The two are complementary, with the computation guiding the tunnel programme and the tunnel validating the computation. Road testing confirms the result but cannot efficiently explore alternatives, and towing tanks are used for marine rather than automotive work.

Answer: D

A stationary floor develops its own boundary layer and misrepresents the flow beneath the vehicle, so a belt moving at the airspeed with rotating wheels is essential for accurate underbody and wheel drag measurement. Wheels contribute a substantial fraction of the total drag. Thermal tunnels for cooling development are a separate facility with different requirements. Framing the question as which quantity the change acts upon makes the answer follow without calculation.

Answer: A

Wheels and wheel arches account for roughly a quarter of the aerodynamic drag of a typical car, which is why aerodynamic wheel designs and partial arch covers appear on efficiency focused models. Rotation changes the flow significantly, which is why the tunnel must reproduce it. The contribution is far too large to neglect.

Answer: B

Air drawn through the radiator loses momentum and contributes cooling drag, which can be a tenth of the total, so active grille shutters close the aperture whenever cooling demand is low. Managing the exit of the air is as important as the entry. The conflict between the two requirements is a standard problem in front end design.

Answer: C

Shutters close the grille aperture when the engine does not need cooling, reducing drag measurably at motorway speed, and open progressively as the demand rises. A bonnet vent to manage the exit flow is a genuine complementary measure used on some designs. Fans address low speed cooling rather than high speed drag.

Answer: D

Vibration from the engine, transmission and suspension travels through the mountings into the body, where panels radiate it as noise, and this structure borne path dominates at low frequencies. Airborne noise from the engine bay, the tyres and the wind dominates at higher frequencies and enters through apertures and panel transmission. Controlling both requires quite different measures, isolation and damping for the one and sealing and mass for the other, which is why refinement work is such a broad discipline.

Answer: A

A constrained layer damping pad converts the vibrational energy of the panel into heat and substantially reduces the sound it radiates. Stiffening moves the resonance rather than removing it and cannot raise it above the audible range. Extensive use of such pads is one reason modern vehicles are so much quieter than their predecessors.

Answer: B

Airborne transmission follows the mass law, so a heavier barrier attenuates more, and any unsealed aperture short circuits the barrier entirely. Bulkhead insulation and careful sealing of grommets and drain holes are therefore the principal measures. Reducing panel mass makes airborne transmission worse rather than better.

Answer: C

Tread pattern impact and air pumping generate noise principally between about 500 and 2000 hertz, which is where the ear is most sensitive. The tyre cavity resonance near 200 hertz is a separate and troublesome tonal component. Wheel rotation frequency is far too low to be heard as sound and appears instead as vibration.

Answer: D

A ring of open cell foam inside the tyre absorbs the standing wave in the air cavity and can reduce the resonant peak by several decibels. Several manufacturers now specify such tyres as original equipment. Wheel resonators tuned to the same frequency are an alternative approach acting on the same phenomenon from the rim side.