Inflator fan placement is critical to a good, quick and safe inflation. But deciding where to put the fan need not be like trying to solve a nursery school rhyme. In fact, it's really as easy as A, B, C.
by Glen Moyer
If you have ever piloted, worked as crew, or even just observed a variety of hot air balloons taking off, it doesn't take long to discover that there seems to be no rhyme or reason to where some pilots place their inflator fans.
How critical is fan placement? It's fair to say that the success of your entire flight depends on it. Without a fan there is no cold inflation, unless you like flapping. With an inefficient cold inflation you run a greater risk of burning the balloon when hot inflating. And so on.
One of the first things any good instructor teaches is that on every inflation you want to pack the balloon as tightly as possible with cold air before ever using the burner. Pack it so tightly, that all of the wrinkled fabric on the ground has disappearedevidence that the envelope is full of air. Why do we do this? To create as large an opening as possible at the throat, thus minimizing the risk of burning the balloon. How do we do this? By filling the envelope with cold air from the inflator fan.
Unfortunately, that may be where the instruction stops. If you ask why the fan is where it is, you may be greeted with an answer like, "because that's where it works best." Or perhaps, "that's where I was taught to put it."
But how do we know that's where the fan works best? First, let's agree on one theory. We all want to inflate as safely, quickly and efficiently as possible. In order to do that we need to place our fan so that is performs at optimum efficiency in filling the balloon while exposing pilot and crew to as little danger as possible in an emergency. To determine that position we need really answer only two questions. 1) Does the fan go to the left or right of the basket, and 2) How far from the mouth of the envelope should the fan be?
Left or right is an easy decision. Look at your fan and find on which side of the engine the exhaust pipe or muffler is located. Your fan should always be placed so that the exhaust is blowing away from the basket. Why? The exhaust from a fan is no different from that of any other internal combustion engine. Breathing it is unhealthy, even for a short duration. Also the heat put out by the exhaust can pose a problem, especially for the pilot during inflation. Always remember that the key to safety is minimizing risks. There's no reason to expose yourself to those exhaust fumes or heat if you don't have to. So, put the fan on whichever side of the basket results in the exhaust fumes blowing away from you.
How far from the envelope do you place the fan is the question that draws a variety of answers. Some pilots put the fan at the bottom of the basket, some about the middle. Others will have their fan even with the uprights and still others will say line up the fan with the base of the burner. To determine which is correct, let's examine the workings of the fan.
Just how does a fan fill a balloon? Obviously it pushes a column of air into the opening at the mouth of the balloon. As more air is blown into the balloon, it begins to fill. The quicker you can get this air into the balloon then the quicker the balloon will fill. Clearly then, the object is to place the fan where the maximum amount of air blows into the balloon.
To determine where that spot is you must begin by understanding that the width of the column of air blown by your fan is equal to the size of your propeller. Much like the beam of light from a flashlight is equal to the size of its lense. However, while the diameter of the column of air pushed by the fan is constant when measured at the propeller, it will widen as it travels over distance. (Actually the force of the propeller moving the air lessens over distance, thus the diameter of the column of air increases as its strength begins to dissipate.)
Plus we know that the maximum opening at the mouth of our balloon is constant. That is to say the skirt of your balloon is only so many feet in diameter at full inflation.
So, in order to get maximum inflation efficiency we need for the diameter of the column of air pushed by the fan to equal the diameter of the opening in the balloon. To do this we must utilize distance, either by moving the balloon or the fan. Obviously, it's much easier to move the fan. So where do we move it to?
Bill Bussey is a veteran balloon pilot. He is a consistent Top 10 finisher at the U.S. Nationals. At a safety seminar he revealed his litmus test for proper fan placement.
"What you want to do is create a forward moving wall of air that is about as round as the throat of your balloon. If you get the fan too close, that won't happen. You'll have air blowing in and air blowing back out," says Bussey.
"Likewise if the fan is too far away, the column of air moving forward is too wide and some of it is spilling off around the outside of the balloon, and that's no good either. Think of it like an old slide projector, before they had telephoto lenses. You set up your screen (the balloon) and then set up the projector (the fan). You put in a slide and turn on the projector. And what did you do if the slide did not fill the screenyou moved either the projector or the screen back until the projected image filled the screen. If the image was larger than the screen, you moved one or the other forward. The same theory applies to fan placement."
Bussey suggests you try this test the next time you have a good calm day. "Take 6 or 8 little ribbons that are about 12 to 15 inches long. Pin these to the inside of your skirt, all the way around. Then crank your fan and look at the results. You may find some that are blowing straight in and others may be moving back at you."
"With the ribbons attached, experiment with your fan placement until you get all of the ribbons blowing into the balloon. That's when you'll know that you've achieved maximum inflation efficiency and your best fan placement. And although that position will vary from one balloon to another, I've found that as a general rule of thumb, the best position is about one foot in front of the bottom of the basket," says, adding, "I don't remember exactly who taught me this, but I know it works. And a good inflation is critical, especially in close quarters with other balloons or in marginal weather conditions. Once you've made the decision to fly, you want to get the balloon up in the air as soon as possible. There's no reason to leave it banging around on the ground."
A final note on fan placement. Always place a crew person on the fan. Far too many pilots, especially if they're short of crew, will crank the fan themselves, perhaps weighing it down, and then let it run while they continue with the inflation. If a fan emergency arises, the pilot's safest place is crouched in the basket since much of the debris will be blown forward in the direction the fan is pointing. No one in front of the fan will be able to safely reach it to shut it down without risking injury to themselves. However, a crew member standing behind the fan can easily hit the "kill" switch at the first sign of an emergency.
