Final answer:
To reduce propeller and engine noise after takeoff, techniques such as noise-canceling technology and sound-absorbing materials can be used.
Step-by-step explanation:
To reduce propeller and engine noise after takeoff, there are several techniques that can be employed. One method is to use noise-canceling technology. This involves using microphones and speakers to detect and counteract the sound waves produced by the propeller and engine.
Another technique is to use sound-absorbing materials in the aircraft's design. These materials can help reduce noise by absorbing and dampening the sound waves.