Ever wondered how some people can tell how far away a hot air balloon is just by looking at it? Some people seem to be able to give an accurate altitude and location given only a cursory glance at the balloon! How do they do it? Does it take years of practice and skill?
Well, I have the answer for you. It’s really quite simple! All you need is a pencil or a pen. Here’s what you do: Hold a pencil or pen up from your hand with your arm outstretched in the direction of the balloon (looks very similar to "thumbing a ride"). Compare the apparent width of the balloon to the apparent width of the pencil, pen or thumb. If that the balloon is an AX-7, 8 or 9, if the balloon’s apparent width is about the same as the width of the pencil or pen, then it is a bit under 1 mile away (or about 1500 meters).
Hmmmm, I now have an easy way to measure the distance to the balloon if it happens to be a mile away, but what about other distances? What you have to do is approximate the fraction of the apparent width of the balloon as compared to the apparent width of the pencil or pen. Let say that I find that the balloon appears to be about 1/3 of the width of my pen, then multiply 1 mile (or 1500 meters) by 3 to get the actual distance, and thus, get 3 miles (or 4500 meters). Using a pen or pencil makes these calculations quite easy since I always start with 1 mile as my distance. All you have to do is inverse the fraction (1/3 x pen-width = 3 miles, or 2 x pen-width =1/2 mile, and so on).
Now that you know the basics, here’s why it all works: First you have to know the diameter of the balloon.
typical volume (1000 ft3) 54 77 90 105 135 175 200 balloon diameter (feet) 50 55 57.5 60 65 70 75 (meters) 15 17 17.5 18 20 21.5 23The majority of commercial ride balloons in the Southeastern US are 90s, so your balloon diameter will be around 57.5 feet or 17.5 meters (varies by manufacturer, but not by much).
Next, you need a small object of known width. It is best to consider objects that will be readily available to you while crewing.
balloon diameter (feet) 50 55 57.5 60 65 70 75 pen/pencil (5/16") 1920 2112 2208 2304 2496 2688 2880 thumb (7/8") 686 754 789 823 891 960 1029 soft drink can (2 1/2") 240 264 276 288 312 336 360When you hold an object in your hand, but at arm’s length, how far is that object from your eyes? Well, in my case, it is 2.25 feet (27 inches or 69 cm). To estimate the distance to your balloon, you need to know this as well.
Now let’s assume that when we hold out a pencil at arm’s length the balloon appears to be about as wide as the pencil. Knowing the information above allows us to compute the distance. For me, it would be 2.25 feet times 2208, or 4968 feet (about a mile). Metric: .69m times 2208 is 1524 meters.
Another example: I hold out my thumb and the balloon appears to be about twice the width of my thumb. This adds an additional computation: 2.25 times 789 divided by 2 (or 888 feet or about 1/6 of a mile). Metric: (.69m x 789)/2 = 272 meters.
You won’t have to make all of these calculations every time you need to know how far away the balloon is. For example, I already know that when a balloon appears to be the width of the pencil is one mile away; the width of my thumb, 1/3 mile away. If the balloon appears to be twice as wide as these objects, then it is half as far away as it would be if it were the same apparent width (1/2 the width, twice the distance, and so forth).
Well, with all of those calculations, you should be able to figure balloon distances with relative ease! Now, of course, with what I’ve given you so far, you only know the distance to the balloon. To figure out the balloon’s altitude and ground distance, you need to gauge the angle between the ground and the balloon. If your arm is about 1/4 of the way up from the ground, then the balloon’s ground distance is about 90% of the distance, and the altitude is about 40% of the distance. At half way up, each measurement is 70% of the distance. At 3/4 of the way up, it’s just the opposite of 1/4 of the way. You can guess in between.
Whew! Now you can dazzle your fellow crew members with your balloon tracking abilities. Good luck and be safe!
Eric Goodson is the 1995 President of the Triangle Area Balloon Society (Raleigh, NC). He has been crewing for several years recently became a Student Pilot.