What are the vertical panels that make up the envelope called?

The vertical panels that constitute the envelope of a lighter-than-air craft, such as a hot air balloon or an airship, are referred to as gores. These panels are designed to maintain the shape of the envelope while allowing for the necessary expansion and contraction due to changes in temperature and pressure. Each gore typically has a trapezoidal shape, which helps to create a streamlined profile that is crucial for the aerodynamics of the craft. The use of multiple gores enables the envelope to achieve the needed volume for lift while ensuring that it remains structurally sound and efficient during flight.

Understanding the role and design of gores is essential in aerospace engineering, as they play a vital part in the overall performance and behavior of lighter-than-air aircraft.