Question

Due to efficiency considerations related to its bow wake, the supersonic transport aircraft must maintain a cruising speed that is a constant ratio to the speed of sound (a constant Mach number). If the aircraft flies from warm air into colder air, should it increase or decrease its speed? Explain your answer.

a) Increase speed
b) Decrease speed
c) No change in speed
d) Depends on altitude

Answer 1

When a supersonic transport aircraft transitions from warm air to colder air, it must decrease its speed in order to maintain a constant Mach number, since the speed of sound is lower in colder air. Option b is the correct answer.

Step-by-step explanation:

The question concerns the operating efficiency of supersonic transport aircraft and how it relates to changes in air temperature and the speed of sound. Speed of sound is affected by the temperature of the air; it decreases as the air gets colder. Since the Mach number is a ratio of the aircraft's speed to the speed of sound, the aircraft must adjust its speed to maintain a constant Mach number when transitioning from warm to cold air.

As an aircraft flies from warm air into cooler air, the speed of sound decreases because sound travels slower in colder air. To maintain the same Mach number, the aircraft must decrease its speed when entering colder air. This reduction ensures that the ratio of the plane's speed to the decreasing speed of sound remains constant.

Therefore, if a supersonic transport aircraft flies from warm air into colder air, it should decrease its speed. The correct option in the final answer is (b) Decrease speed.