Aeronautics and Balloon Systems: Lift, Envelope and Operations
Principles of lift
A balloon flies because the air displaced by the envelope weighs more than the hot air inside it. You must understand the relationship between temperature difference, density and lift, and be able to explain why lift falls as the outside temperature rises or the altitude increases. Know the terms: envelope volume, payload, gross lift, net lift, and the difference between the two. Learn how burner output, ambient temperature, and envelope material limits interact, and why the maximum continuous temperature is a structural limit, not a performance target.
Systems and flight operations
Know the components: envelope and its load tapes and parachute valve, burner and fuel system, cylinders and their fittings, basket, suspension cables, and instruments (altimeter, variometer, envelope temperature gauge, and fuel gauge). Understand pre-flight inspection, the inflation sequence, the controlled ascent, level flight by small burner bursts, and the descent and landing technique including the use of the parachute valve for rapid descent. Learn the emergency actions for a burner failure, a fuel leak, a stuck valve, and a high-wind landing, and the correct use of the rip line after landing.
Traps and a rule of thumb
Questions often test whether you understand that lift depends on the temperature difference, not on absolute temperature, and that an altimeter set to QNH reads field elevation on the ground. Traps include assuming more burner means more lift regardless of ambient conditions, and forgetting that the parachute valve is a control, not an emergency device only. Rule of thumb: plan fuel for the flight plus a reserve of at least 30 minutes, and treat the envelope temperature limit as a hard ceiling.
Worked example
On a hot afternoon the pilot finds the balloon will not climb despite full burner. The correct reasoning is that the temperature difference between inside and outside air has shrunk, reducing lift; the remedy is to wait for cooler air or reduce payload, not to overheat the envelope beyond its limit.