Controlling Cabin and Envelope Air Flows and Pressure Differentials to Prevent Envelope Condensation, Enable Cabin Humidification, Improve Fire Safety, and Decrease Fuel Use

The uncontrolled flow of cabin air into the aircraft envelope caused by indoor-outdoor temperature gradients and associated stack pressure differentials causes cabin air to circulate between the cabin and the envelope, producing condensation on the cold fuselage behind the insulation with a number of adverse consequences. These include an inability to practically maintain cabin humidity at normal levels, a reduction in ventilation effectiveness, microbial growth, metal corrosion and structural failures, insulation performance degradation, thermal discomfort, increased engine noise transmission, additional fuel consumption and electrical failures and fires. This paper explains the origin of these stack pressures and the air flows they create between the cabin and the envelope, and indicates means to control the flows and associated cabin-envelope pressure differentials and thereby minimize condensation and its associated problems, improve thermal comfort and fire safety, and coincidentally decrease fuel use.