Metering valve.  A valve on a balloon heater that can be set to allow propane to pass through at a specific rate. 

Methanol.  A type of alcohol, usually fermented from wood, required by most balloon manufacturers to be introduced into propane tanks annually to adsorb, and thus eliminate, small quantities of water from the fuel. 

Mildew.  A gray or white parasite fungus which, under warm, moist conditions, can live on organic dirt found on balloon envelopes. The fungus waste materials attack the coating on the fabric. 

Mooring. Operation of an unmanned balloon secured to the ground by lines or controlled by anything touching the ground. See Title 14 of the Code of Federal Regulations, part 101. 

Mouth.  The bottom, open end of a hot air balloon envelope. Also called the “throat.” 

MSL.  Mean sea level. 

Neutral buoyancy. A condition wherein a balloon is weightless and is neither ascending nor descending. 

Nitrogen charging.  A technique of adding nitrogen gas to propane tanks to increase fuel pressure. Used in place of temperature to control propane pressure in hot air balloons during cold weather. 

Nomogram. Technically, a calculating chart with scales that contain values of three or more mathematical variables, widely used in engineering. In ballooning, a balloon’s performance chart is a nomogram. 

Nonporous.  The state of having no pores or openings which will not allow gas to pass through. New hot air balloon fabric is nearly nonporous. 

Notice to Airmen (NOTAM). A notice containing information concerning facilities, services, or procedures, the timely knowledge of which is essential to personnel concerned with flight operations. 

Nylon.  The registered name for a polymeric fabric. Most balloon envelopes are made of nylon. 

OODA Loop. An aeronautical decision-making model particularly suited to ballooning. Originally devised by Col. John Boyd for use by Air Force combat pilots, it has come to be widely utilized in the business community. See the discussion in chapter 1 of this handbook. 

O-Ring.  A doughnut-shaped packing, usually rubber, used between two moving parts to act as a seal. Balloon heater and tank valves usually have O-rings between the valve stem and valve bonnet. 

Orographic.  A term pertaining to mountains or anything caused by mountains, as in orographic wind (wind formed by mountains) and orographic cloud (a cloud whose existence is caused by disturbed flow of air over and around a mountain barrier). 

Overtemp ( or over temperature).  The act of heating the air inside a hot air balloon envelope beyond the manufacturer’s maximum temperature. 

Oxygen starvation.  The condition inside a balloon envelope where all available oxygen has been consumed by the heater flame and additional burning is impossible since propane must have oxygen to burn. In extreme cases, the blast flame and pilot light flame will extinguish after a long burn or series of burns and may not relight until the envelope has “breathed” additional air. 

Parachute top. A deflation system wherein the deflation port is sealed with a disc of balloon fabric shaped like a parachute. Lines attached to the edge of the parachute disc gather into a single line that may be pulled down by the pilot in the basket. 

Pibal.  Pilot balloon; a small helium-filled balloon sent aloft to help determine wind direction, velocity, and stability. 

Pilot in Command (PIC). The pilot responsible for the operation and safety of an aircraft during flight. 

Piezo. (Pronounced pee-ate' zo). A piezoelectric spark generator that is built into many modern balloon heaters to ignite the pilot light. 

Pilot light. A small, continuously burning flame used to ignite the main “blast” flame of a balloon heater. 

Pilotage.  Navigation by visual reference to landmarks. 

Pinhole.  Any small hole in a balloon envelope smaller than the maximum dimensions allowed for airworthiness. 

Porosity.  A condition of the envelope fabric that allows hot air to escape. Excessive porosity requires increased fuel use and results in higher envelope temperatures. 

