A partially opened valve is producing a fraction of the heat  available, but there is no way of knowing what the fraction  is.  [Figure 7-2] Level flight, or equilibrium, is probably the most important  of all flight maneuvers, as it serves as a baseline from which  all other maneuvers are derived. A good pilot maintains level  flight with a series of standard burns.  Level flight is achieved when lift exactly matches weight  and the balloon neither ascends nor descends, but remains  at one altitude. For every altitude, there is an equilibrium  temperature. If a pilot is flying at 500 feet mean sea level  (MSL) and wants to climb to 1,000 feet MSL, the balloon  temperature must be increased. This is not only to attain  equilibrium at the new (higher) altitude, but some excess  temperature must also be created to overcome inertia and  get the balloon moving.  Theoretically, if a pilot were to hold a hot air balloon at a  constant temperature, the balloon would float at a constant  altitude. However, there is no practical way to hold the  envelope air temperature constant. Each time the pilot burns,  the balloon tends to climb. The air in the envelope is always  cooling and the balloon tends to descend. If the subsequent  burns are perfectly timed, the balloon flies in a series of very  shallow sine waves.  [Figure 7-3, Line A] Of course, any  variable changes the balloon flight. A heavier basket load,  higher ambient temperature, or sunny day all require more  fuel (by shortening the interval between burns) to maintain  level flight.  In discussions of level flight, the terms “flying light” and  “flying heavy” are sometimes used and bear explanation.  A balloon is said to be “flying light” when the sine wave  being described in the air is predominately on the high side  of the desired altitude  [Figure 7-3, Line B] . Many new or  inexperienced pilots tend to fly light, and use the vent line  in order to return to the desired altitude; this may create a  situation where the pilot gets into a constant overcontrolling  exercise and is best avoided. “Flying heavy” can be described  as a scenario where the sine wave is predominately on the  low side of the desired altitude  [Figure 7-3, Line C] ; if the  balloon is left alone, it tends to fall. Flying heavy can be  hazardous when contour flying. A balloon pilot must use all  visual cues available and exercise a “finesse” type of control  when contour flying (described later in this chapter). Another advantage of briskly opening and closing the valve  is to minimize the presence of a yellow, soft flame. During  inflation, for instance, a strong, narrow, pointed flame that  goes into the mouth opening without overheating the mouth  fabric or crew is desirable. A partial-throttle flame is wide  and short and subject to distortion by wind or the inflation  fan. If less than a full burn is desired, shorten the time the  valve is open and not the amount the valve is open. Due to  burner design (and the inefficiency of a partially opened  valve), four 1-second burns do not produce as much heat as  one 4-second burn. Through experimentation, standards can be established that  may be used as a basis for all flights. With practice and using  the second hand of a wristwatch, a new pilot can fly almost  level. The exercise of learning the pattern of burns (each day  and hour is different) is an interesting training exercise, but  not a practical real-life technique. The ability to hold a hot air  balloon at a given altitude for any length of time is a skill that  If the mechanical aspects of flying can be learned, the  systematic cadence can be converted into a rhythm that is  smooth and polished. With practice, the rhythm becomes  second nature and pilots fly with precision, without thinking  about it. Using the standard burn, pilots can better predict the  effect of each burn, minimize the potential danger of a burn  to the envelope, and have a better flame pattern. The standard  burn is referred to when discussing specific maneuvers. 7-3 $_{Figure 7-2.}$  Activated burner. Straight and Level Flight