Final answer:
The bellows inside instruments such as aneroid gauges contract when you descend and expand when you climb due to changes in pressure.
Step-by-step explanation:
The instruments you mentioned—ASI (Airspeed Indicator), ALT (Altimeter), and VSI (Vertical Speed Indicator)—are crucial for monitoring an aircraft's performance. In a descent, the bellows inside these instruments react differently than during a climb due to changes in air pressure and airflow.
1. ASI (Airspeed Indicator): The ASI measures the dynamic pressure of air. During a descent, as the aircraft descends into denser air, the bellows inside the ASI expand, indicating an increase in airspeed. Conversely, during a climb, the bellows contract as the aircraft ascends into thinner air, reflecting a decrease in airspeed.
2. ALT (Altimeter): The altimeter relies on static pressure to determine altitude. In a descent, the bellows expand as the atmospheric pressure increases, causing the altimeter to indicate a lower altitude. In a climb, the bellows contract due to decreasing atmospheric pressure, leading to a higher indicated altitude.
3. VSI (Vertical Speed Indicator): The VSI measures the rate of climb or descent. During a descent, the bellows expand, showing a negative vertical speed. In a climb, the bellows contract, indicating a positive vertical speed. The VSI provides real-time information on the aircraft's vertical movement. In summary, the behavior of the bellows in these instruments is a result of changes in air pressure and density associated with changes in altitude and climb or descent. Understanding these indications is crucial for pilots to maintain control and ensure a safe flight.