Which one of the following is the most appropriate reason for aircraft being equipped with conducting tyres?
- (a)They can transfer the charge accumulated on their surfaces during lightning
- (b)They can transfer the charge accumulated on their surfaces being rubbed by air particles
- (c)They can transfer the charge accumulated on their surfaces due to inflight operation of several gadgets
- (d)For preventing sparks while they land on the ground
Answer
Why
Correct: B, they can transfer the charge accumulated on their surfaces being rubbed by air particles. An aircraft in flight builds static charge by friction with air and precipitation, and conducting tyres let that charge drain to earth at touchdown.
Why the others are wrong
- (a)They can transfer the charge accumulated on their surfaces during lightning: Lightning strikes are conducted through the airframe's bonded skin and static wicks, not through the tyres. Conducting tyres address the slow accumulation of frictional charge, not a strike.
- (c)They can transfer the charge accumulated on their surfaces due to inflight operation of several gadgets: Onboard electronics are grounded to the airframe and do not deposit net charge on the exterior. The charge in question comes from outside.
- (d)For preventing sparks while they land on the ground: This states the consequence rather than the reason, and it is incomplete: preventing sparks matters because of the charge already accumulated in flight, which option (b) names.
Concept
Triboelectric charging: two surfaces in relative motion exchange electrons, so an airframe moving through air, dust and ice picks up a substantial static charge that must be dissipated safely once the aircraft is on the ground.
Aircraft tyres are compounded with carbon black to make them mildly conductive so charge bleeds away on contact with the runway. It matters most during refuelling, where a spark near fuel vapour would be dangerous, which is also why a fuel bowser is bonded to the aircraft before the hose is connected.
Key facts
- Static wicks on wing and tail trailing edges discharge current into the air during flight.
- Tyre conductivity comes from carbon black in the rubber compound.
- Bonding the refuelling truck to the aircraft is a separate, mandatory precaution.
- The charge source is external friction, not internal electronics.
The reason names the source of the charge; the spark is the consequence.
Study next
Common traps
- Choosing the option that names the consequence (sparks) rather than the cause.
- Assuming lightning current passes through the tyres.
Applied-physics items like this reward reading every option for whether it states a cause or an effect.
Related PYQs
No directly related past PYQ was found.
Practice
- practice, not a real PYQ
Static wicks fitted to the trailing edges of an aircraft's wings are intended to
- (a)reduce drag
- (b)discharge static electricity into the air
- (c)improve radio reception
- (d)prevent icing
Answer(b) discharge static electricity into the air, reducing radio interference.