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—Mark West and Martin Harns, Aerostar International, Inc.
Figure 7-1. Burner ratings and calculations.
The Standard Burn
To fly with precision, the balloon pilot needs to know how much heat is going into the envelope at any given time and how that heat affects the balloon’s performance. Balloon pilots have few outside sources, instruments, or gauges to help them fly. When a balloon pilot uses the burner, there is no direct way of knowing exactly how much lift is increased. Because there are few mechanical aids to help balloon pilots fly, some methodology must be devised to standardize a pilot’s input action, so the outcomes of those actions are predictable and the balloon is controllable. The standard burn is one way to gauge in advance the balloon’s reaction to the use of the burner. [Figure 7-1]
The standard burn is an attempt to calibrate the amount of heat being used, and is defined as a burn of four seconds. If each burn can be made identical, the balloon pilot can think and plan, in terms of number of burns, rather than just using random, variable amounts of heat with an unknown effect. The standard burn is based on using the blast valve or trigger valve found on most balloon burners. Some brands use a valve that requires only a fraction of an inch of movement between closed and open, and some require moving the blast valve handle 90°. While the amount of motion required to change the valve from fully closed to fully open varies, the principle remains the same—make each burn identical to another.
The inexperienced pilot should begin with the premise that the average balloon requires one standard burn of four seconds every 25 to 40 seconds in order to maintain level flight. Experience determines the exact length of time between burn intervals, and how other variables such as weight and ambient air temperature affect those intervals. The primary goal is to determine the rhythm of burns necessary to maintain level flight. All other maneuvers, then, become a departure from this point. The burn begins with the brisk, complete opening of the blast valve and ends with the brisk, complete closing of the valve at the end of the burn. During their training, some pilots count “one, one thousand; two, one thousand; three, one thousand; four, one thousand” to develop the timing.
The standard burn does not mean a burn that is standard between pilots, but rather, it is an attempt for the individual pilot to make all burns exactly the same length. The goal is not only to make each burn exactly the same length, but also to make each burn exactly the same. The pilot must open and close the valve exactly the same way each time. Most balloon burners were designed to operate with the blast valve fully open for short periods of time. When the blast valve is only partially opened, two things happen:
1. The burner does not operate at full efficiency, and
2. The pilot is not sure how much heat is being generated.
7-3
Figure 7-2. Activated burner.
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]
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.
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.Straight and Level Flight
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.
　
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本文鏈接地址：Balloon Flying Handbook(85)