10.3 Lighter-Than-Air: Balloons & Airships
Key Takeaways
- A hot air balloon burner sends liquid propane through a heat exchange coil, where burner heat vaporizes the fuel before the pilot light ignites it (Balloon Flying Handbook).
- Propane in a balloon's fuel tank is at ambient temperature, so tank pressure rises as the temperature rises and falls sharply in cold weather.
- Balloons have the right-of-way over all other aircraft categories under 14 CFR 91.113(d), and private balloon pilots need no medical certificate.
- A commercial balloon pilot carrying persons or property for compensation or hire must hold at least a second-class medical certificate, except when giving flight training (14 CFR 61.23).
- When the density altitude is beyond what a balloon's performance chart covers, the pilot should not take off until conditions allow the calculation to be completed.
Lighter-Than-Air: Balloons & Airships
The lighter-than-air category includes free balloons (hot air and gas) and airships. The commercial pilot knowledge areas even name "procedures for flight and ground training for lighter-than-air ratings" (61.125(b)(16)), and the FAA's AGI sample questions ask about propane tank pressure, the burner's heat exchange coil, envelope damage, balloon payload, and density-altitude performance. The main reference is the Balloon Flying Handbook (FAA-H-8083-11B).
How a Hot Air Balloon Flies
A hot air balloon rises because the heated air inside the envelope is less dense than the surrounding air. The pilot controls altitude, not direction: heating the air produces a climb, and letting it cool (or venting hot air through the top) produces a descent. Direction comes from the wind, which often changes with altitude, so the pilot steers by choosing altitudes with favorable winds.
| Component | Function |
|---|---|
| Envelope | Coated nylon or polyester fabric with load tapes; the temperature flag or sensor warns of overheating near the crown |
| Parachute top or deflation port | Opened with its control line to release hot air for descent and to deflate the envelope on landing |
| Maneuvering vents | Side vents on some balloons that rotate the balloon |
| Burner | Pilot light, blast valve, and a heat exchange (vaporizer) coil; a secondary system (often a liquid-fire or "cow" valve) provides redundancy |
| Fuel cylinders | Liquid propane drawn from the bottom through a dip tube; separate vapor valves feed the pilot lights |
| Basket | Wicker or composite gondola carrying occupants and fuel |
The Propane System
- Propane in the tank is at the same temperature as the ambient air. The Balloon Flying Handbook corrects the popular misconception that stored propane is always at -44°F; it turns cold only when it vaporizes.
- Tank pressure depends on temperature: as the ambient temperature rises, propane vapor pressure rises; in cold weather, pressure can fall too low for good burner performance, so some operators pressurize tanks with nitrogen or warm them.
- The heat exchange coil: Opening the blast valve sends liquid propane through a coil in the burner flame, where it is completely or partially vaporized before it exits the jets and is ignited by the pilot light. If no fuel flows through a coil while the burner runs, the coil can overheat.
Preflight, Inflation & Flight
- Preflight: Inspect the envelope fabric, load tapes, and top closure. Small holes are compared with the damage limits in the balloon's flight manual, which define what size and location of damage is acceptable; anything outside the limits must be repaired before flight. Small fabric repairs to envelopes, done per the manufacturer's instructions, are listed preventive maintenance (Part 43, Appendix A).
- Inflation: A fan cold-inflates the envelope, then the burner heats the air until the balloon stands up. Crew hold the crown line to control the envelope.
- Performance: Use the flight manual's load or performance chart for the expected temperature and altitude. If the density altitude is beyond the chart's capability, do not interpolate or extrapolate; do not take off until conditions allow the calculation.
- Payload and weight: The chart gives the maximum gross weight for the conditions; subtracting the balloon system's weight leaves the load available for occupants and equipment, and hot days and high elevations reduce it.
- False lift: Wind shear or a wind gradient near the ground can create temporary aerodynamic lift as the balloon rises into moving air; when the balloon matches the wind speed, the lift disappears and the balloon may descend.
- Hazards: Power lines are a leading cause of serious balloon accidents; landings in strong wind drag the basket; and thermals and convective weather make control difficult.
Balloon Regulations & Certification
- Right-of-way: A balloon has the right-of-way over any other category of aircraft (91.113(d)(1)).
- Medical: A private balloon pilot needs no medical certificate (61.23(b)(4)). A commercial balloon pilot exercising privileges for compensation or hire must hold at least a second-class medical certificate, except when giving flight training (61.23(a)(2)(iii) and (b)(5)).
- Student pilots: a student seeking balloon privileges may be 14 years old (61.83).
- Operations: Sightseeing flights in hot air balloons are among the Part 119 exceptions (119.1(e)(5)), so they are conducted under Part 91 by commercial balloon pilots.
Gas Balloons
Gas balloons use hydrogen or helium sealed in the envelope. The pilot drops ballast (usually sand) to climb and valves gas to descend, so every altitude change uses up a finite resource.
Airships
An airship is a powered, steerable lighter-than-air aircraft. Its envelope is filled with helium, and internal air bags called ballonets are inflated or deflated to maintain envelope pressure as the helium expands and contracts with altitude and temperature, and to adjust trim. Airships are usually flown slightly heavy, using engine thrust and dynamic lift from the envelope to take off and to hold altitude. Their large surface area makes them very sensitive to wind on the ground, where a mast and ground crew are used.
What effect does ambient temperature have on propane tank pressure in a hot air balloon?
What is the purpose of the heat exchange coil in a hot air balloon burner?
Under 14 CFR 61.23, which balloon pilot must hold at least a second-class medical certificate?
A balloon pilot finds that the day's density altitude is beyond the range covered by the balloon's performance chart. What should the pilot do?