These past two days the Albuquerque Aerostat Ascension Association held their annual “Friends and Lovers” February ballooning event. On neither day was the weather good enough to fly so I thought it would be appropriate to post a blog about the weather and the conditions that generally prevent balloonists from flying.
“Weather” to Fly or Not – That is the Question?
The Conditions that Will Keep us on the Ground
Wind words to look for in a forecast: gusty, breezy, windy, blustery, small craft warnings, high wind warnings
Wind is the most critical factor in safe ballooning; it effects every phase of a flight. More balloon flights are cancelled due to wind than for any other reason. Balloons fly best in light and stable winds of 4-6 miles per hour. Maximum winds are 8-10 mph. Here are the reasons wind is such an issue:
During inflation the balloon is filled with cold air using a fan. The balloon fabric is just a giant sail, and winds approaching 10 mph make it almost impossible to fill the balloon. The wind will cave the side of the balloon in and the resulting sail effect places tremendous loads on both the fabric and the basket. These forces can be 3-10 tons depending on the size of the balloon. The balloon will roll around, sometimes violently. It is tied off to keep even a gentle breeze from causing it to drag downwind, but we have seen a gust cause the balloon to drag the trailer and van it was tied to across the grass! Pretty impressive to watch – not much fun!
Strong winds in flight can take the balloon farther than the pilot has room to fly. Since a balloons flight path and the distance it will travel is dictated solely by the wind’s speed and direction, this can be an issue if high winds carry the balloon into areas that are unsuitable for a landing. Such areas include: metropolitan areas, large expanses of forest, restricted airspace, and large bodies of water. All of these are factors in our immediate flying area.
Lastly, there is the landing. A balloon’s speed across the ground will be the speed of the wind it is flying in. High wind speeds mean that the pilot needs a larger area to land in. A balloon relies on the friction of the basket dragging along the ground to come to a stop. In a high wind landing, you are trying to stop 3-10 tons, depending upon the size of the balloon, without brakes – the basket will skip, drag and bounce along the ground. It will eventually layover on its side while continuing to drag along the ground. Again, impressive just not much fun.
The winds on the surface are just one of our concerns. We have to think three dimensionally and consider what the wind is doing at altitude as well. This is perhaps the most confusing aspect for our passengers. There is not even a hint of a breeze and your flight has just been cancelled due to wind, how come? We look at winds at the surface (the wind you can feel) and the winds at 1 to 9,000 feet. We are not going to go to 9,000 feet, but it tells us if we might encounter issues such as wind shear, turbulence, or strong surface winds later on. Even if there are no winds to speak of at the surface, the winds aloft may drive our decision not to fly. Winds aloft of 18-20 knots or 20 miles per hour can be sufficient to reschedule a flight.
Poor Visibility words to look for in a forecast: foggy, hazy, misty
How far can we see? Our aircraft are designated by the Federal Aviation Administration (FAA) as Visual Flight Rules (VFR) certified. That means we must have a certain amount of visibility to legally fly. The visibility must be 1 to 3 miles, depending on where we are flying. If we don’t have it, we can’t fly!
Rain & Storms words to look for in a forecast: thunderstorms, rain, chance of showers or storms
The decision not to fly in rain or storms seems a simple one – of course we don’t! What isn’t so simple is why your flight may be cancelled when no storm or rain actually happens in the area. We must often make our decision based on a forecast. Despite the many advances in weather prediction, forecasting remains an imprecise science. We often refer to forecasts as “horoscopes with numbers.” Our idea of long range forecasting is 4 hours and we don’t place a great deal of faith in them! Forecasts for our flying area are limited to the Double Eagle Airport and the Albuquerque International Airport (Sunport) . We are practically equal distance between the two and what happens in our flying area may be very different from the forecast – both good and bad!
Storms can be significant events to any type of aircraft, but a balloon is perhaps the most weather sensitive aircraft there is. An airplane can turn and run from a storm whereas a balloon is drawn into a storm. The winds will accelerate and head toward a building storm and flow out of a decaying storm. These gust fronts can occur 75 to 100 miles away from the actual storm and create winds that are dangerous to a balloon. Once again, it’s the wind! If storms are forecast or there are storms within 100 miles we will reschedule flights.
Since hot air balloons fly by changing the temperature inside the balloon with heat, it stands to reason that outside air temperature is going to affect balloon flights, and it does! When the air in the balloon is heated, it becomes hotter and thus less dense than the surrounding outside air. This hotter air is “lighter” and the balloon will float upward. The more heat, the higher up you go. A balloon will fly when its temperature is around 140 degrees above the outside air temperature (generally). So, the colder it is outside, the less heat it takes to fly and conversely, the hotter it is outside, the more heat it will take to fly. Can’t wrap your head around this? Here is an example:
Outside Air Temperature + Heat it Takes to Fly (140 F) = Temperature Inside the Balloon
Cold day of 30 degrees F + 140 F = 170 degrees inside the balloon
Hot day of 95 degrees F + 140 F = 235 degrees inside the balloon (more heat if it’s hot out)
This is of particular concern to companies operating smaller balloons. The smaller the balloon, the less lift capacity it will have and the hotter it must be inside the balloon for it to fly. The maximum continuous operating temperature for most hot air balloons is 250 degrees Fahrenheit. That leaves little margin for safety and for maneuvering on a very hot day.