by Alan Sanderson
In some areas of the world, the onset of winter means that the balloon systems will be put in storage until spring. In other areas, winter can provide some periods of either stable or long jump weather patterns. If the balloon system is going into storage, be sure that the envelope bag is kept off the floor so air can circulate around it, and it can be kept dry. The basket and other equipment should be cleaned up and stored in an area protected from bad weather and vermin.
Cold weather provides additional challenges to the balloonist. The pilot and crew will bring the winter clothes and gloves that are required to keep them warm. The equipment does not have the same kind of protection from the cold.
Commercial propane is provided as a liquid that is normally between 85 and 100 percent propane (C3H8), with the possibility of 0 to 15 percent propylene (propene - C3H6), with up to 2.5 percent butane or heavier compounds. The mixture depends a lot on what the oil refinery is producing at the time. The propylene has slightly lower energy content than the propane, but it increases the pressure slightly.
| Temperature | Approximate Pressure PSIG |
| Degrees F | Propane |
| -40 | 1.3 |
| -30 | 5.5 |
| -20 | 10.7 |
| -10 | 16.7 |
| 0 | 23.5 |
| 10 | 31.3 |
| 20 | 40.8 |
| 30 | 51.6 |
| 40 | 63.3 |
| 50 | 77.1 |
| 60 | 92.5 |
| 70 | 109.3 |
| 80 | 128.1 |
| 90 | 149.3 |
| 100 | 172.3 |
| 110 | 197.3 |
I have provided a table of propane pressures at various temperatures. During cold weather, the fuel cylinders will chill to the outside air temperature during storage. During flight, as propane is used, the evaporation of the liquid propane inside the fuel cylinder chills it, reducing the fuel pressure even more. During warm weather, the fuel cylinder base and top ring absorb heat from the outside air that warms the propane and maintains fuel pressure. In cold weather, these same exposed parts cool the fuel, reducing fuel pressure.
Know Your Burner
Each balloon manufacturer has a range of pressures under which the burner has been tested. They measure fuel flow, output, efficiency, and general operating characteristics under a range of pressures. They take the results of the testing and determine reasonable operating limitations, such as the minimum pressure that may be safely used in flight. This minimum operating pressure is normally provided in the aircraft flight manual. Other useful data may include fuel flow and heat output at different pressures. In most cases, the burner will continue to put out more heat as the fuel pressure increases. However, there is normally a point where the fuel consumption increases much faster than the heat output. Above this pressure, much of the additional fuel is wasted. More pressure isn't always betterlearn the operating characteristics of your burner.
Keep It Warm
Once you know your system's requirements, and the projected outside air temperature, you have several options. You may determine that you will have adequate fuel pressure by storing the system in a sheltered area or an enclosed trailer. A light bulb hanging inside the trailer may provide adequate heat to maintain fuel pressure. Possibly just a good airtight basket cover will keep the temperature from dropping too much.
You may also use electric heat tapes. If you use them, make sure they are either the self-regulating tapes that reduce output as they warm up, or that you have a timer that will turn them off after a proper interval. Before you use the tapes, carefully inspect them for any cracks or abrasions that may expose any wire. If you find any exposed wire, replace the tapes.
If you either protect the system from the cold, or heat the cylinders, they still have large exposed collars and bases that can lose a lot of heat. Carefully wrap the exposed areas with insulation, such as foam, blankets, or other covering.
Gas It
If you do not heat the cylinders, or you are camping away from a source of power, you can pressurize the cylinders with an inert gas or methane. In areas that provide compressed natural gas (methane - CH4) as motor vehicle fuel, some pilots use it to pressurize their fuel systems. Methane has a much greater pressure than propane, so a high pressure gas cylinder and a 2-stage pressure regulator are required to use it. It can be used in systems with vapor pilot lights.
Inert gases such as nitrogen, argon, helium, and carbon dioxide have all been used for pressurizing fuel systems. High pressure gases need a 2-stage pressure regulator to properly reduce the pressure. Carbon dioxide can be handled with a single stage regulator. Be careful that you do not pressurize a cylinder that is providing propane vapor to a pilot light with inert gas. It will dilute the propane vapor, and could interfere with proper pilot light operation.
If you are using a gas to pressurize your fuel system, do not pressurize until you are certain you will fly. Once you are certain you will fly, do not pressurize the system over 150 psi. If you do not fly after pressurizing the system, the fuel could heat up and cause the pressure relief valves to open. Be sure to release the excess pressure through the 80% (spit) valves if you don't fly, or if you don't use a cylinder after pressurizing it.
If you have no experience in pressurizing a system with gas, work with a pilot who is experienced with gas pressurization systems and techniques. Learn the proper procedures, the potential hazards, and emergency procedures in case anything goes wrong.
Great Balls of Fire
After you have pressurized the fuel system with gas, you are operating with high pressure, cold liquid propane. Watch closely for any signs of a leak around the blast valve stem. Some systems will leak into the pilot light plumbing, so an extra high pilot light can also indicate a blast valve problem. If you have any indication of such a leak, take the burner into a repair station for repair. Blast valve stem seals harden and shrink in the cold, allowing leaks.
When you are ready for your hot inflation, be very careful with the first few burns. Make them extremely short, as an initial long burn with cold fuel has caused a fireball as the cold fuel hits the cold coils.
Stay warm, keep your fuel pressure up, and enjoy your winter flights.